April 1988

Radio communications of the future

Digital optical transmitter

Active loudspeaker system

MIDI code generator UK £1.50IR £2.20

(incl. VAT)

EE

April 1988

BBC Micro Computer System88C MASTER SERIES:AM815 88C MASTER 128K E346ADC06 Turbo 1650102) Card E95ADC08 512 Processor £185ADF14 Rom Cartridge E13ADF10 Econet Card £40ADJ22 Ref_ Manual) E14ADJ23 Ref. Manual Part U E14ADJ24 Adv Ref Manual £18

(a)(dl(0)loll(dl(cllc)fcl

B8C ARCHIMEDESPlease enquire about availability anddetails of the s stem.

WORD PROCESSOR ROMs:VIEW 2.1 £35 (d) VIEW 3.0 .. £48 (c)Spealrnaster £49 (dl VIEW INDEX £12 (dlWORDWISE E24 (dl WORDWISE+ E38 (d)

SPELLCHECK IIIliVYSIW1G + £21 fdl £31 (d)INTERWORD £46 (dl EDWORD II E43 (a)LANGUAGE ROMS:Micro Prolog E62 (el fitcrotext £52 (c)ISO PASCAL £51 (c) LOGOTRON E55 (c)LOGO E46 (c1 MACROM £33 (d)USP £39 COMAL .... £43 (d)

UPGRADE KITS: Oxford Pascal £36 (c)1.2 OS ROM E15 (dl COMMUNICATIONS ROMS:DNFS ROM £19 (d) TERMULATOR £25 (dlBASIC II ROM (BBC B) . E22.50 (dl MASTER TERMULATOR £34.75 (d)ADES ROM £26 (dl COMMSTAR 11 £28 (dl1770 DES Kit £43.50 (d) MODEM MASTER £11 (dlEconet Kit OMB+) E55 Id) COMMAND E34 (d)ACORN ADD-ON PRODUCTS:Torch ZEP 100 E229 (a)512 2nd Processor £249 (b)IEEE Interface £265 (b)Teletext Adapter £95 (b)

Ask for full details on our fun range of software

UTILITY ROMs:DOTPR(NT PLUS for FXJRX compatiblesDOTPR(NT DUAL for MX rangeAcorn Graphics Extension Rom ... £28 (dlMedal with 57 disc utEty commands100 page manual £37.50 (el

MULTIFORM Z80 2nd Processor for the BBCThis unique Z80 2nd Processor running OS(M wri avow use of dmost any standard CP:M soft-ware on the BBC micro. It is suppled with a number of afferent CP/M formats and includes aditty to configure it to read other formats. This is particularly useful in environments where com-puters with different CPI/.1 formats are used and the data cannot be easily exchanged betweenthem. Man -is powered imdudes Pocket Wordstar & MS(DOS FIN, utility) (249 lb)fiiSiDOS Read/Write U, ' £49 (c)

META Version 3 ASSEMBLERAssembles 17 of the popular processors. Over 70RC long program on two rocas and a disc andprovides complete Editing and Assembly facilities. It uses appropriate mnemonics for afferentprocessors. Fully nestable macros. nestable conditional assembly OF/ELSE/MOIR modularsource code. true local and global Lth.lq, 32 bit labels and arithmetic. 30 ways to send objectcode and 50 directives.A powerful editor with many features. Send for d,I. .r.:t1 leaflet. £145 (b)

BBC DISC DRIVES5.25" Single Drive:1 x 400K 40/130T DS: TS400 _ _ E90 c( PS400 wan psu £104 lb)5.25" Dual Drive:2 x 400K 40/80T OS: TD800 E170 (a) PD800 with psu E190 la)2 x 400K 40!80T DS with psu and built in monitor stand PD800P E209 (a)3.5" Drives:1 x 400K BOT OS TS35 1 E67 (b( PS35 1 with psu E85 lb)1 400K 80T DS with psu TD35 2 (126 (b( PD35 2 with psu E149 (b)

Combo drives (5.25" & 3.5"):P0853 with integral PSU £165 (al P0853P with integral PSU E179 la)

3M FLOPPY DISCSIndustry standard floppy discs with a life time guarantee. Discs in packs of 10:

5% DISCS 3% DISCS40T SS DD £8.20 (d) 40T DS DD £10.00 (d) 80T SS DO £15.00 (d)80T SS DDE1 2.25 (d) 80T DS DD. £13.00 (dl 80T DS DO £19.50 (dl

DISC ACCESSORIESE6 (dl Dual Disc Cable £8.50 (dl

E1.80 (c) 30 Disc Storage Box E6 (c1(8.50 (c) 100 Disc Lockable Box E13 Id

Fiappiciene buveread Cleaning Kit with 20 'sy n..,hta cleaning kits 51i" E14.50 (d); 31)" El6 Id)

BT APPROVED MODEMSMIRACLE TECHNOLOGY WS Range

WS4000 V21123.(Hayes Compatible. Intelligent. Auto Mat/Auto Answer) E135 lb)WS3000 V21123 ProfessionalAs W54000 and with BELL standards andbattery back up for muuxxy E244 Oa)W53000 V22 ProfessionalAs WS3000 V21/23 but with 1200 baud fuRduplex £409 (a)

WS3000 V22 his ProfessionalAs V22 and 2400 baud fug duplex £537 la)WS3000/138C Data Lead E7 (diWS2000 V21N23Manual Modern E92 (b)WS 2000 Auto Dial Card E27 (d)WS 2000 Auto Answer £27 (d)WS 2000 SKI Kit (5 (d)WS 2000 User Pori Lead £5 (d)(Offer knifed w current stocks)

SPECIAL OFFEREPROMs/RAMS

2764-25 £2.80 (d)27256 £5.00 (d)27512 £9.90 (dl6264LP-15 £2.60 (d)27128-25 (12.5 Vpp) £3.40 (d)27128-25 (21.0 Vpp) £4.80 (d)

PROJECTS:Junior Computer Kit £86 lb)Housekeeper kit £58 (b)Elekterminal Kit (1980) . £50 (b)ASCII Keyboard kit £75 Ib)J C Books 1, 2, 3, & 4E6.90 (c) eaUniversal Terminal (6502) Kit £75 (b)Elekterminal Kit (1983) £70 (b)

PRINTERSEPSONLX800 E189 (a) TAXAN KF'815 (80 col) £269 fa)FX800 £295 (a) KP915 (158 col) E369 (a)FX1000 E405 (a) BROTHER HR20 E349 (a)1E(300 E395 fa) STAR LC10 E209 (alEX1000 £539 la) JUKI 6100 (Daisy Wheel) .... E295 (a)GO 3500 (laser) £1,350 *ITEMS( (Colour) E519 (a)L0500 E349 (a) NAT PANASONIC KX P 1081. £149 (a)L0850 (80 col) £439 (a) NAT PANASONIC KX P 3131_ £249 (a)LQ1050 (136 col) £529 la) NAT PANASONIC KX P1082 _ £175 )a(We hotel in stock a large varkty of printer attachments, interfaces and consumables.Crease mite or phone for details.

ACCESSORIESBUFFALO 32K Buffer foe Epson printers £75 (dl; FXI30 plus sheet feeder £129 (B):EPSON Serial Interface: 8143 £30 (13); 8148 with 2K buffer £65 (b).EPSON Paper Roll Holder E17 lb); FX801130+/85 Tractor Attach E37 lb); RX/FXSCDust Cover £4.50 (dl; LX80 Tractor Unit E20 (c): L0800 Tractor Feed E47 (b).EPSON Ribbons: MX/RX,FX80 £5; MXFLX/FX100 EIO (d): LX80 £4.50 (dl;JUKI: Serial Interface £65 (dl; Tractor Attach. £149 (a); Sheet Feeder £219 (a);Ribbon £2.50 fa); Spate Daisy Wheel £14 (dl.BROTHER HR20: Sheet Feed £229; Mtairies - Carbon or Nylon £3; Tractor Feed£116 (al; 2000 Sheets Fanfold with extra Fine pert'. 9.5" - £13.50; 15" (17.50 lb).BBC Parallel Lead £6; Serial Lead E6 18..1 Paree3 Lead )2m) £12 Id:.

MONITORSMICROVITEC 14" RGB1431 Standard Resolution ... £179 la)1451 Medium Resolution £225 la)1441 Hi Res E365 (a)MICROVITEC 14" RGLIMAL & Audio1431 AP Standard Resolution £199 la)1451 AP Medium Resolution £259 la)MICROVITEC 20" RGELTAL/Aurto2030 CS std Res £380 (al2040 CS ft Res £675 la)hirtsubishi 14" RG8 Med Res 188C1111M1

E219 (al

TAXAN Supervision 620.... E269 la)TAXAN Supervision 625_ _ E319 (a)TAXAN Supervision 770+

(with swivel stand) £499 (a)

12" MONOCHROME MONITORS:

PHILIPS:

7502 Green Screen E 69 (a)7522 Amber Screen E 75 Id

NI Philos Monitors supplied with swivelstand

BOOKSNo VAT on books; Carriage (c)

View 3.0 User Guide E9.00LANGUAGES: Viewstore £9.006502 Assy Lang Prog £19.95 Viewsheet £9.008086 Book £23.95 Wordwise Plus E9.95Acorn BCPL User Guide E15.00Acorn FORTH £7.50 SOUND & GRAPHICS:Acorn USP (7.50 Mastering Music £6.95Acorn ISO Pascal Ref Manual .. £10.00Intro to COMAL E10.00Intro to LOGO £7.50Micro Prolog Ref Manual £10.00Introduction to Turbo Pascal . £14.95Prog the Micro with Pascal .... (8.50

Book £7.50Unix User Guide £19.95Understanding Unix £18.45BBC MICRO GUIDE BOOKSBBC User Guide Acorn £15.00BBC Plus User Guide £15.00Drawing your Own 88C ProgramsE6.95Inside Information £8.95Math Prog in 813C Basic E7.95Toolbox 2 £10.95VIA 6522 Book 4 50

DISC DRIVE SYSTEMS:Advanced Disc User Guide_ . _ .E14.95Disc Book £3.50Disc Programming Techniques E7.95Disc Systems E6.95Re Hang:Wing on the 88C E6.95

APPLICATIONS:Interfacing Proj for BBC1313C and Small fkrsiness

£6.95£5.75

PROFESSIONAL SOFTWAREWordstar made easy £16.95Introduction to Wordstar E17.95Words -tar Handbook £11.95dflase-11 for the first time user E16.95Understanding dBase-III E22.95Multiplan Made Easy £18.95

PROGRAMMINGIUTIUTY Mu(timate Complete Guide .... £16.95Advanced Sideways RantUser ABC of LOTUS 123

(9.95 1-2-3 for Bu £16.95sineSs

£17.45

Advanced User Guide 1880) ... £12.50Guide

Actv Tech in d8ase 11.111 £22.95Applied AssAang on the BBC ..E9_95 Mastering CM £17.95BBC Micro Sideways ROM's RAIrsE9.95 CP1M Bible £16.50Guide to the BBC ROM £9.95 Introducing CP/PA on BBC & 280 £9.95Beginners G....de to W.P .. £7.95 MS PC DOS Prompt £10.95

PROGRAMMED ROMS FOR ELEKTORPROJECTS

50341Jnr. Computer Monitor c -g Dice 2716 E 7.302708 E 4.80 521 CnarGen & Video Routine for DOS

Junior. 2732 + 2716 £16.40522 CharGen & video; Routine for ex-tended junior 2732 + 2 x 2716 E24.00523 Char. Generator .. 2732 E 9.00524 Quantisizer 2732 E 9.00525 Universal Term 2732 f 9.00526 Wird Di Ind 2716E 7.30527 (labyrinth 2716E 7.30530 Daisywheel !face 2 x 2716 E11.00

504 Disco fights505 Chess Intelekt . 2x2716 £14.60506 J C Tape Monitor . 2716 E 7.30507-N J C Printer Mon & PME

2716E 7.30508 J C Bus Control 82523. £ 4.80510 150 MHz Freq Meter 2 x82523

E 9.60514 Dark ROOM Computer 2716 £ 7.30

ALL PRICESEXCLUDE VAT.Please add carriage 50p unless

indicated as follows:

tali 8 l6112.50 lc1f1.501169£1.00

TECHNOLINEVIEWDATA SYSTEM

Tel. 01-450 9764Using 'Prester type motocols.

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P:ded CONTENTSApril 1988Volume 14Number 155

Fuzz unit for guitarsp. 33

42 READERSHIP SURVEY RESULTS 111=Editorial

13 The standard of software

Components

AEI

14 A new multilayer process for integratedpassive devicesby Dr Gordon R. Love

Compute17 Computer management systems take over

by James Lock19 Second generation programmable logic

by E. Baum

24 PROJECT: Stereo sound generator

28 DESIGN IDEA: Computer -controlled musicgeneratorby Dr B. Koyuncu

33 PROJECT: Fuzz unit for guitars36 PROJECT: MIDI code generator

39 Dual trace oscilloscopes: a review - Part 5by Julian Nolan

r Audio & Hi-fi44 PROJECT: Active loudspeaker system

MIDI code generatorp. 36

Radio communications for thefuturep. 54

Radio & Television50 PROJECT: Tuneable preamplifiers for VHF

and UHF TV54 Radio communications for the future

by Dr Chris Gibbins

General Interest60 PROJECT: Computer -controlled slide fader

(2)

66 Superconductivity: further outlook warmerby George Short

68 The efficient alternative to large powerstationsby Dave Andrews

Information

16-23-41-49-64-65 News; 43 Events; 58 Newliterature; 59 People; 70 Readers services;72 Terms of business

Guide lines

75 Classified advertisements 75 Switchboard;76 Buyers guide; 78 Index of advertisers

In next month'sissue:The main theme willbe Artificial Intelli-gence; other articleswill include: Plotter Digital optical

transmitter* VLF convertor Signal processing

and electronic en-cryption

Microcontroller-driven PSU

We regret that ow-ing to lack of spacethis article could notbe included in theApril issue asoriginally planned.

Litar 4C-IO"

fleeam.

Front coverExperimental set-upof four slide projec-tors driven by thecomputer -controlledslide fader de-scribed in our Marchand .April 1988 issues

4 EE

April 1988

Are we about to create a race of Supermen?

Brainwave1111 BETA -Concentration, In ALPHA - Relaxation, El THETA - Imagination, monitorproblem solving, active pleasure, tranquility, creativity hynagogic

thought positive feelings. imagery.

_r _a

BRAINireAvEAtOtityn,

PAONLyRys er^

irC4443cre.

£36. 90

SILVER SOLUTIONThs powerful sher platng compound must be the greatest remlutgon ineiectronics snore the IC! Just wipe on attn a doth to pale PCB traOts.correctors. sore. component leads, etc_ Votth a tam of pure s=lain!EsserEal for RF awaits Top MOS IiFIL'.13io-etectronic arcuals and etanctodesLARGE BOTTLE (150m1) SILVER SOLUTION £11.20 ...VAT.rn Tre ea 13.3 0 tree :33. -Or, 31: ar rot ere, 3,3 atere

THE ALPHA PLANCan icu rear y trap ya s bran to nrit more enect-eayCan you rea4 acne.* pea., performance at tnngs you re re good litCan you mac./ overcome feat shyness. uncertanly?

And can you do .1 al en hoed r«-.1! rpm,Or Eland Le** s famous AAsha Pan has at the a . well recem.,/rn.estorad by a OED krieiS.Cort Lgoarnertary (Ache - Hogg to &cooed...edcut Rea. Tryng) And the concerSCV17 It %gongs.Dr Lewis's lax*. 'The Alpha Plan' is yours for only £2.50 (no VAT)Your future Is waiting.

Tne ETI Brainwave Monitor must be the most astonishing project ever to appear in thepages of an electronics magazine. It will allow you to hear your brairrwaves arid Judgethe relative levels of venous types. It will also help you to control your mind moreeffectively, to be at peak performance in all situations.

Doesn't my mind work perfectly well when left to its own devices?If you've ever been confused, unsure of yourself, shy, unable to pass exams or to

impress people at interviews. you know perfectly well that It doesn't_ Your mind (andeverybody else's) is full of bad habits, inappropriate responses, feelings of inadequacy ...

all pulling you down_ Why should you put up with it?

Mind training sounds like hard work!It can be. If you want to do it the hard way, go and study under a Zen master for fifty yearsor so. You'll get there in the end! With the brairnvave monitor it takes no effort at all. Justthe opposite in fact - trying is the one 'thing you mustn't do!

How do I start?At fast you use the monitor's internal inthcator to exercise your mind. In direct mode youimprove the time percentage: in integrate you concentrate on the amplitude. After thatthe choice of direction is yours. With the Alpha Plan you can reach the core of yourpersonality to root out the weakness and replace it with inner strength Otherwise youcan lust enioy the feelings of rifiv. ire and dear headectness that alpha training brings. orthe creativity and imagery of the theta state.

A friend told me I can use brain power to control lights and things. I can't believe it!As a matter of fact, you can do more than that! The interface sockets on the monitor allowyou to turn lights on and off, control toys and elic,cthl gadgets. play computer games _all with your wind! Are we about to create a race of Supermen? Only time will tea.

The Etrainwave Monitor is featured in the September October and November 1987 issuesof ETL The approved parts set contains: two PCBs, all components including three PM)precision amplifiers. shielded box for screening the bioarnplifiec attractive instrumentcase with tiling feet, controls, switches, knobs. plugs and sockets, leads and materials forelectrodes, full instructions for assembly and use.

Pans we avarie separately We also hem a range et -n-es potsone eearodes boobs. et:Pease send a stamped. sed.acor tale] reNt.iop e d you ?....11 ware tie Isis Othe-roMe. an SAE £.2 grittree you Ws, corstn,cor. detats and father hformaten

Complete Parts Sets for Top ProjectsFEATURED IN ETIMARCH 1988

JUMPIN' JACKFLASHis a Lgghtog *turd - brings

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Voice switch arid Sound tO actioncontroller with endless applications

The parts set consists at a high qualityPCB and all components_ ICs. opto wrialortriac. heat sulk_ pots etc to budd the arcistboard. What you do next is up to you.The Ell article. supplied free with everyset. shows haw to make the most of J F scapablues

JUMPING JACK FLASH £6.90 + VAT

KNIGHT RAIDERFEATURED IN Ell. JULY 1987

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KNIGHT RAIDER CONTROL BOX ONLY£6.90 VAT!KNIGHT RAIDER SEQUENCE BOARD ONLY£13.90 ,VAT,

MATCHBOXAMPLIFIERFEATURED IN En,APRIL 19861,a3 order, amplaters.crewWWIairtry0 -5137.5 tr:10reworg....... Oa reCbtan.C.5133 MC,weekleSinn,:313Creese. We COW awscard pa.s angles and-.Mae, rya:ere are the arpressere .cpatee. reee ree re-CraKra orESairte cusk'y

Toe Weirder real. wee Oneree WW1 a3334 enre oolte-ki LIMC Tre sr)* el aerrerea2DVA331..... =ewe,

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POWERFUL AIRIONISERFEATURED IN ETIJULY 1986

knsrene ac-...aCedVINVirle 01 er

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The DIK-CT Ca: crear cased a gees ow+ ,rreg.a.g,en. enrn acomren wo a cessW.e.a. prztee.01 A. WI was co,ceratae weeMader ran') .121.1711Wr-ai tY1.-CM..13 93oosonde ard UV Apart Irs. straus xpicrorrs.some of re st..snr.ace age...Ws sera d-rraged-s,

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DIRECT ION PARTS SET Imbue:tonsWITH BLACK CASE 111.50 g- WiT areWITH WHITE CASE £11.80 4.1,93" rctuiecl

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397$41 mnamc DAL £1 .ID ,Pa.tat352. Sent, co:se tr. moo %0TClass r to, rggur ci co lidLIA333 Cud comparaar C 3 sat MOO vuUCnCSS Dig 14a -rd 3 Or 1.00 - 5.9J

Al IC. a4Clad .er, EPEE DATA.Prces axe, cre, mole slips last

LM2917EXPERIMENTER SETCongests el Lare9i7 IC. %gloat owed aro-n cord anddalailadeldnairseriti data and ora.r3 la aarralma prcjsaslba1 Can be used Ee eaprrnertstn to erases al Tv Wed Greg life C Sesare(ETI. Datenter tale)

LM2917 Experimenter Set £5.80 VAT

Prices shown are exclusive of VAT, so pleaseadd 15% to the order total. UK postage is 70pan any order. Carriage and insurance foroverseas orders E4.o0. Please allow up to14 days for delivery.

RUGGEDPLASTIC CASEsur.Pe to mars cdreircrerad mars ozrvpler

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LEDsGreen malamute/ LEDskg bal^araPh 64:424S50 ke £3_50 500 her £25Ma for Efi 1003 Ice £45

MGM AND AUDIO EQUIPMENT LEDsAssorted Srrrn LEDs red. green. yeedge andorange 25 el each (103 LEDs) to £6.80

LIMITED

SALES DEPTROOM 110FOUNDERS HOUSEREDBROOKMONMOUTHGWENT

EE

April 1988

A Wolters Kluwer CompanyManaging Editor: Len SeymourPersonal Assistant: L. VousdenTechnical Editor: J BuitingAdvertisement executive:Pauline O'Rourke

Editorial offices:1 Harlequin AvenueBRENTFORD TW8 9EWEnglandTelephone: 01-847 2618 (National)or +44 1847 2618 (international)Advertising: 01-847 2619Telex: 917490 (elektr g)Fax: 01-847 2610

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Elektor sariRoute Nationale; Le Seau; B.P. 5359270 Beilieu! - FranceEditors: D R S Meyer;G C P Raedersdorf

Elektor Verlag GmbHSiisterfeld-Stralle 255100 Aachen - West GermanyEditor: E J A KrempelsauerElektor EPEKaraiskaki 1416673 Voula - Athens - GreeceEditor: E Xanthoulis

Elektor Electronics PVT Ltd.Chhotani Building52 C. Proctor Road, Grant Road (ElBombay 400 007 - IndiaEditor: Surendra lyer

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Typeset & composed in theNetherlands by GBS, Beek (11.Printed in the Netherlands byNDB, Zoeterwoude.Copyright 1988 Elektuur B.V.

ABC

THE STANDARD OFSOFTWARESoftware is a 'written' instruction used by people to tell computers what todo. In principle, the creation of such an instruction, or program, is fairlysimple. None the less, even today, after nearly 40 years of programminghistory, nobody can write programs that are free of bugs. Worse, there is, asyet, no easy way of determining the likelihood of software failure before itis taken into use.

Yet, the way to reliable software was pointed out almost twenty years agoby a number of computer scientists of international repute who had be-come seriously concerned about the quality of software. Then, as now,most programs were produced empirically, and consequently they werenot normally correct the first time they were used in practice. All the pro-grammers could do was to add more instruction -a patch - and hope forthe best. This method of programming has changed remarkably little in theintervening years, particularly when viewed in the light of the other tremen-dous changes in computer engineering that have taken place in thoseyears.

Those scientists in the late 1960s suggested a new approach to program-ming and called it software engineering. This approach is aimed at puttingsoftware design and production on similar theoretical foundations andpractical disciplines as, for instance, electrical and electronic engineering.Unfortunately, the mathematics on which computer programs are based isdifficult. Whereas electrical/electronic engineering uses analytical math-ematics, software engineering uses logic. Logic is a rigid discipline: whereasanalytical methods allow a certain measure of flexibility, logic does not.This means that even a tiny error in a logic argument can upset the whole.

Furthermore, the testing of a long program by logic is beyond even mostmathematicians. This gives programmers, who, in the main, are not trainedin mathematics, let alone logic, not much of a chance. The unfortunateresult for the customer is that programs are tested to only a limited degree.

By the proper use of software engineering, it has become possible to writemuch more reliable - but not yet completely error -free - programs. One ofthe ways this is done is by the use of a formal specification language,which results from rigorous academic work. Researchers in Europe and theUSA have invented several of these. The improvement in quality of theresulting software on both sides of the Atlantic has been encouraging.

All of this, coupled with the efforts of the big software houses to design andproduce integrated software, implies, of course, that programmers have tobecome more disciplined and trained in the rigorous demands of softwareengineering. No doubt, the majority of the estimated 60,000 or so pro-fessional programmers in the western world will be loath to admit, let aloneaccept, this.

Yet, it is clear that software buyers have a right, like any other buyer ofgoods or services, to demand that the expensive programs they are get-ting work properly. Not surprisingly, much software is sold with a disclaimerof warranty. Why do we go on accepting this? Only when we, thecustomers, in the knowledge that the quality of software can be improvedto a significant degree, demand guarantees as to the quality of the soft-ware we buy, will software houses be prompted into the proper use of soft-ware engineering or run the risk of costly litigation.

IA Val or rHew.r...t1 OF C2F,OAAOCKS

EEApr I 1988

A NEW MULTILAYER PROCESSFOR INTEGRATED PASSIVE

DEVICESby Dr. Gordon R. Love

This article describes a new process, derived from techniquesused to produce multilayer ceramic capacitors, which is the key

to a technique, known as Multilythicsz, allowing complexintegrated multi -functional passive circuits to be produced.

IntroductionThere are two fundamentally differentbuild-up processes for multilayer cer-amic devices or assemblies. Each beginswith a slip of finely divided ceramic par-ticles dispersed and suspended in a com-plex organic system. In the more com-monly used process, this slip is cast inthin sheets of controlled thickness anddried; patterns are then printed on it bythick -film silk-screen processing, andthe array of finished devices is assembledby stacking and laminating these singlesheets. This process is generally knownas dry stack or 'tape' manufacturing.The alternative process involves castingthe slip onto an inert carrier, drying it,printing the patterns by thick film pro-cessing, and then casting the next con-trolled thickness layer in situ. This build-up process is then repeated as manytimes as is necessary. This technique isknown as wet stack or 'paint' process-ing.These two manufacturing processes can-not easily be compared, as each has itsown strengths and weaknesses. Forexample, single sheets can be inspectedand discarded if found defective in thetape process, whereas in paint processingthis is virtually impossible. On the otherhand, tape processing requires high pre-cision at two distinct processing steps(printing and stacking), whereas paintprocessing requires high precision onlyat the printing stage.

Process differencesFor both manufacturing processes, aminimum amount of organic binder isrequired both to encourage device for-mation and to facilitate the eventualbinder removal. Binders free of metalliccontaminants are preferred because theyare less likely for contaminate the cer-amic formulation, and they should beremovable completely and easily becausethey must not distort the ceramic or

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leave refractory residues which might in-terfere with the sintering process.These binders and the associatedsolvents should be cheap, non-toxic, andeasy to dry without film formation orcracking; moreover, the binder for theceramic powders must be compatiblewith the (usually different) binder selec-ted for the metal powders.For a tape -based system, the organicsmust have excellent strength because thetape is handled as a self-supporting sheetfor at least part of the process. In ad-dition, many variations on the tape pro-cess involve locating the tape for printingor laminating (or both) by mechanicallycontacting the tape itself. Hence, refer-ence holes must be both well defined anddimensionally stable.In what appears to be a relatively fun-damental conflict with these require-ments, the tape has to be sufficientlyplastic to permit very -high -qualitylamination; otherwise, the sintered bodycan become vulnerable to internal len-ticular voids or `delaminationst Thetape binder should be relatively insen-sitive to variations in ambient tempera-ture and humidity, in order to maintainthe dimensional stability required be-tween the multiple precision steps in theprocess.For a paint -based system, dimensionalstability and reproducibility are deter-mined largely by the carrier plate, and allstrength requirements are essentially metby the carrier. In addition, since thestructure is assembled in situ with eachlayer being solvent bonded to itspredecessors, plastic deformation is notrequired, and this source of `delami-nations' does not exist.On the other hand, since visual inspec-tion for pinholes and other casting/dry-ing defects becomes impracticable, itbecomes essential for high -quality layersto be obtained every time. High-speeddrying is more important in this processbecause paint drying cannot easily beisolated from the rest of the build-upprocess, and so can limit productionrates and overall productivity.

Quantum improvementsWet -build processing has been suc-cessfully employed in the capacitor in-dustry for over 25 years, and a combi-nation of organic chemistry expertiseand mechanical engineering skills has re-cently introduced quantum im-provements to the basic process.The latest generation of processdevelopments has resulted in a tech-nology that is specifically optimized forboth printing and print location accu-racy, as well as for uniform high pro-ductivity for both large and smallmanufacturing runs. The new techniqueis sufficiently different to warrant itsown name: P-4 (for Precision Paint &Print Process) manufacturing.

Fig. 2. Typical Multilythic devices.

This new process is crucial to a newmanufacturing technology, known asMultilythics, which combines the diver-sity of materials used in the thick filmindustry with the economics of manu-facturing and the complexity of finisheddevices inherently available from multi -layer ceramic capacitor manufacturingprocesses.The Multilythic technique allows manydifferent passive functions to be inte-grated into the device 'substrate', so thatthe exterior surface of the device needonly support active devices, special com-ponents like crystal oscillators, anddevices requiring precision trimming. Asa result, the size of assembled circuitscan be significantly reduced, and thissize reduction also offers major im-provements in high -frequency perform-ance.Another benefit of this technologyresults from the incorporation of mul-tiple components into the device, andhence a reduced number of interconnec-tions which, in turn, improves the devicereliability through assembly and in ser-vice. In addition, the small size, coupledwith economies of manufacturing scale,should make the technology cost effec-tive.A typical Multilythics device (Figs. 1and 2) incorporates low -K dielectriccover layers, high -K dielectric capacitorlayers, low -K capacitor conductor layers,thick film conductor and resistancelayers, and semiconductor components.The proprietary materials used in theprocess can be sintered to very high den-sities, and their electrical performancecan be established very accurately andconsistently. The large number of layersused in a typical device can be stackedwith excellent precision in the 'green' orunfired state, and then fired a single timewith uniform shrinkage.

Process benefitsThe high dimensional stability and highyields produced by the P-4 process are

EE

April 1988

A

absolutely essential to the Multilythicsconcept. Because a Multilythic device isan array of components rather than adiscrete device, the whole array must bediscarded if a single component in thearray is defective. Hence, if array yieldsare to be acceptable, single componentyields must be very high.By way of illustration, if the componentyields are 95%, an array of 100 compo-nents would have a yield of 0.59%; a99% component yield would improvethe array yield to 36.6% etc. The P-4process has been found to lead tosatisfactory yields.Another benefit of P-4 assembly ismodularity. Historically, a major limi-tation of wet -build processes has beentheir relative inflexibility. Where unitvolumes allow the assembly process tobe run at its optimum throughput, it canbe extremely productive, and efficient inboth labour and capital investment.However, small runs can be made onlyby 'idling' major components of themanufacturing line for significantlengths of processing time.By re -configuring the assembly equip-ment into smaller process modules, theP-4 process allows manufacturing totake place at constant labour and capitalproductivity over at least a 4:1 ratio ofbatch sizes. This is a particularly import-ant change in the context of the marketfor which Multilythics is intended, sincea contributory factor to the relativelyhigh costs of hybrid thick film manufac-turing has been the difficulty in achiev-ing meaningful automation for smallmanufacturing runs.The P-4 assembly process has beentightly integrated with a computer aideddesign facility so that customers candesign their own devices and obtain amanufactured product in a relativelyshort time.Dr. G.R. Love is Vice President of Tech-nology, Sprague Electric.

16 EE

April 1988

COMPONENT NEWS

New Fresnel lensesQuantelec has introduced a range ofFresnel lenses for use in intruder detec-tion and security applications. Designedfor use with Quantelec's ranges of dual-element pyroelectric IR detectors, thereare four different types of lens.

The first lenses to be announced are thePolyfen 24A/3 for use in curved formatand the Polyfren 24B for use in flat for-mat. These lenses yield multiple zones(24 in total) including nine main, eightintermediate, five short, and two creepzones. Angular coverage is about 90° forthe main zones, 8 m for the intermediatezones, 4 m for short range zones, and 1to 2 m for creep zones.Quantelec Ltd 46 Market Square WITNEY OX8 6AL Telephone (0993)76488.

New component catalogueA new 282 -page catalogue, giving detailsof the company's extensive range of elec-tromechanical, interconnection, and dis-play products, has been produced byHighland Electronics. Apart from prod-uct news, the brochure includes com-prehensive selection data and appli-cations information.Highland Electronics Ltd AlbertDrive Burgess Hill BURGESSHILL RH15 9TN Telephone (0799)26699.

SEMI optimistic for 1988Semiconductor Equipment andMaterials International (SEMI), thetrade association for the semiconductorequipment and materials industry, haspredicted a much improved 1988 for itsmembers. .

SEMI's data collection programme rep-resents input from more than 200members around the world. Figuresshow an escalating backlog, as orderssteadily rise and drive a positive book-to -bill that reached 1.18 in the 3rdquarter of 1987, up from 0.91 in the 4thquarter of 1986.This optimistic attitude was initiated bystrong worldwide semiconductor deviceshipments, reported by the Semiconduc-

tor Industry Association (SIA), whichtopped $3 billion in September last year,up from $2.5 billion for the same monthin 1986.SEMI European Secretariat CCLHouse 59 Fleet Street LONDONEC4Y 1JU Telephone 01-353 8807.

Cells and batteriesAn 8 -page full -colour brochure out-lining the widest selection of cells andbatteries offered by any electronicsdistributor in the UK has been producedby STC Electronic Services. Products areavailable from such leading manufac-turers as Varta, Duracell, UCAR, Saft,Sonnenschein, Ever/Ready, and Vidor.The brochure is available free of chargefromThe Battery Group STC ElectronicServices Edinburgh WayHARLOW CM20 2DF Telephone(0279) 626777.

High -voltage resistorsA precision high -voltage resistor seriesthat withstands 50 kV DC continuouslyin air and up to 11 kV when immersed inoil is the latest innovation from theSpecial Products Devision of WelwynResistors, a part of Crystalate Elec-tronics.

The series, coded T40, comprises threetypes with resistance values in the ranges1 kohm to 4 Gohm, 15 Gohm, and45 Gohm. Tolerances of plus or minusfive, two, and one per cent, and tempera-ture coefficients of plus or minus 100,50, or 25 ppm/° C are available.Welwyn Resistors BEDLINGTONNE22 7AA Telephone (0670) 822181.

Capacitor catalogueAUDIOKITS have announced the mostcomprehensive catalogue of audio qual-ity capacitors for constructors, serviceengineers, and audio equipment manu-facturers.AUDIOKITS' Component Note ACN12includes detailed specifications, physicaldimensions, and prices of many well-known capacitor types, including JARWonder Caps, Siderealkaps, and BHCALS20A reservoir capacitors. Also in-cluded are ranges with hard:to-findvalues and high -voltage ratings.ACN12 is available to audio constructors

at £4.00 incl. postage. A special version,incorporating trade prices of mostranges, is available free of charge tobona fide audio equipment manufac-turers and service engineers.AUDIOKITS Precision Components 6 Mill Close BORROWASH DE73GU Telephone (0332) 674929.

Additional component rangefor DatelIn addition to its present line of data ac-quisition components, Datel has an-nounced the availability of a completerange of resistor and voltage tuneablefilters, digital programmable filters,logic controlled networks, resistor

i,N,

c\ 010:1/41°-

tuneable oscillators, and oscillator adap-tors. The thirty-seven new products aredesigned to provide front-end filteringand peripheral conditioning for data ac-quisition systems.Datel Intec 2 Business Park WadeRoad BASINGSTOKE RG24 ONE Telephone (0256) 469085.

Linear IC Data bookNow available from the House of Poweris the Unitrode Linear Integrated Cir-cuits Data Book for 1987-88, a com-prehensive guide to the functions andapplications of the Unitrode ranges ofpower, control and interface circuits.Products covered in the book includepower -supply circuits, motion -controlcircuits, power -driver, and interface cir-cuits.House of Power Electron House Cray Avenue ORPINGTON BR53AN Telephone (0689) 71531.

8096 proliferation productfrom IntelIntel has introduced an 8 -bit external busversion of the company's 16 -bit 8096 forreal-time control applications. The 8098has the same 16 -bit CPU and on -boardperipherals as its 8096 counterparts, butwith a price of around £3.40, dependingon order quantities, the 8098 is half thecost of typical 16 -bit devices.Further information fromIntel Corporation (UK) Ltd Pipers Wa) SWINDON SN3 1RJ.

COMPUTER MANAGEMENTSYSTEMS TAKE OVER

by James Lock

The second half of the 1980s is witnessing the full flowering offourth generation interactive computer systems, the integration ofbatch with continuous control, and a trend towards the location

of intelligence close to plant of equipment under control.

Several companies in the UnitedKingdom are investigating the appli-cation of expert systems to process con-trol, and software systems such asAuditor from Energy EfficiencySystems(') are emerging by which plantdata can be transferred, via a company'smainframe computer, into accounts andcosting systems or into sales forecastingand business planning software.An important new control system, in-troduced this year by Ferranti ComputerSystems(2), is the PMS 100. Ferrantidescribes it as an integrated, fullydistributed process control and infor-mation system for supervisory and directcontrol, for continuous, sequence andbatch control, and for high availabilityconfigurations.It is a far cry from the process plantcomputer control system installed byFerranti in 1962 for control of a soda ashplant at ICI's site in Fleetwood. Believedto be the first in the world, that had aprogram of only 1200 words.Computing cards of various perform-ance, all based on the Ferranti Argus 700family of processors, are now used atvarious locations. Computing powervaries from 700 000 inputs per second tomore than two million inputs, dependingon the configuration.PMS 100 is a natural development of thefirst PMS - process managementsystem - installed for the Bayercompany at Leverkusen, FederalGermany, in 1975. Over the years, Fer-ranti technology has been applied inareas ranging from steelworks to radioastronomy.

Making modificationsThe data highway, Systembus SBIO, is anopen system based on internationalcommunication standards able to con-nect to other manufacturers' equipment.In a dual configuration, System SBIOdata highways are treated identically.There is no master and no standby,messages are simply transmitted down afree data highway with the advantage ofallowing twice the bandwidth in normal

operation. A combination of SystemSB10 and Ferranti's wide area networkX.25/F-NET provides a communicationcapability for any size of PMS 100 net-work.PMS 110 is a dedicated process con-troller that incorporates mixed sequenceand continuous control facilities. Nor-mally mounted close to the plant undercontrol, it can be interfaced directly to itor through loop controllers and pro-grammable controllers.A process engineer can modify and de-velop new control schemes from either aterminal at the process management in-formation system or on a portable Ac-cessway 110 programmer located, say, inthe engineer's office.The PMS 105 device gateway allows anymake of process control or operatordevice to be integrated into PMS 110,permitting any make of programmablelogic controller (PLC) or single loopcontroller to be specified.

Familiar engineering termsBatch control in PMS 110 is provided byPMS unit operations, which provides acomplete batch control environment forsingle product, single stream and multi-product multi -stream batch processes.Typical is its use by the Pfizer companyfor batch processing a range of phar-maceutical processes. A number ofbatches can be in progress simul-taneously through different process stepsusing the same train of equipment.The production- supervisor can redefineproduction routes and resources on-line,allowing multi -product manufacturewith a minimum of downtime. Auto-matic batch scheduling permits a cam-paign to be set up in advance so that pro-duction is initiated immediately theplant becomes available and it is alsopossible to change the order of batches.Part of the PMS operations softwarepackage is Constructor (IPC) whichenables the engineer quickly and simplyto build up colour graphic processdiagrams, graphs and logs. The PMSsystem's on-line development facility

uses a high level programming languagewhich has terms familiar to the engineerand requires no specialist programmingexpertise.The trend to put the intelligence of acomputer control system in close prox-imity to the sensors and actuators of aplant rather than relying on a single, cen-tral computer is reflected in NewmarkTechnology's(3) Omnibus range. Thisstems from the Janus Project, con-ceived by Professor John Brignell atSouthampton University for the appli-cation of advanced microprocessor tech-nology to measurement and control.Omnibus measurement and controlsystems compriSe one or more Omni -point computers acting as masterstation/operator interface and a numberof Multipoint measurement and controlcomputers distributed over an Omnibusnetwork. The Multipoint units have beendeveloped jointly by Newmark andJeball, a company formed by ProfessorBrignell, while the Omnipoint com-puters are IBM PC or compatible com-puters in standard or industrial packag-ing.

Collaborative projectAt the heart of the Omnibus concept isa powerful dual processor that im-plements the synchronous data linkcommunications (SDLC) protocol. Toachieve this, Newmark took the IntelBitbus and enhanced it to handle up to250 stations over a range of 5 km, fromsystems that can start with control of asingle loop.Although a personal computer (PC) isan integral part of the systems loop, theessential difference is that this computeris used simply as a central programmerand data manager rather than as a de-cision manager.The majority of decisions made by thesystem take place at the outstations,removing the problems associated with afailure of the main computer or its com-munication systems. The use of a plug-incard allows control of the Omnibus net-work without loading the PC. The

18 EE

April 1988

Multipoint units form the remote outsta-tions, each one designed for use in a par-ticular application or environment -the MP100, MP200, MP300, MP400 andnow the MP500.Omnibus communications ensure thecompatibility of all Omnipoint andMultipoint units to communicate via afast multi -drop serial data highway, aswelll as Omnibus products from othersuppliers. Since Omnibus is Intel Bitbuscompatible it is a widely supportedfieldbus. Moreover, gateways into themanufacturing automation protocol(MAP), direct from the host PC or via astandard interface on the instrumen-tation computer board, enable the Om-nibus range to communicate throughstandard protocols in both process andmanufacturing industry.The need to combine the skills of soft-ware and process experts has formed thebasis of an on -going collaboration be-tween Biotechnology Computer Systems(BCS)(4) and the Department ofChemical and Biochemical Engineer-ing(5) at University College London(UCL) in the development of a com-prehensive fermentation managementsystem. BCS is a member of the PortonInternational group of biotechnologycompanies that operate worldwide. UCLis one of the British Government'sScience and Engineering ResearchCouncil (SERC) designated centres forbiotechnology. Some 50 staff and resear-chers are involved and there is col-laborative work with some 14 otherorganizations besides academic institu-tions and other departments in UCL onvarious aspects of control.

Digital controllersThe first two products are the softwarepackages BIO-i and BIO-pc. BIO-i is apowerful fermentation process manage-ment- system, BIO-pc is a single userbioprocess management system for up tofour reactors with associated on-lineequipment.The design objectives for BIO-i were toproduce a single fermentation manage-ment system that would satisfy the dif-fering needs of the fermentation plantprocess engineer and worker, and theresearch scientist. So BIO-i has beenconfigured as a supervisory system inwhich distributed digital controllers as-sociated with each fermenter are linkedto the 'process computer. Designed foruse with the Digital Systems Equipmentrange of computers, the packageemploys well proven programminglanguages and real time process plantdatabases. Mass spectrometer data isused in the monitoring of off -gases.The distributed nature of the system andthe ease with which it can be configruedmeans that new fermenters, sensors andanalytical equipment are simply incor-porated when they become available.

The new Ferranti PMS 100.

Fresh results of the collaborative pro-gramme, such as the current work onadaptive control, can be added to thepackage. This has been thoroughlytested on the sophisticated range oftermenters and reactors in the UCL pilotplant.BIO-pc is configured on an IBM -AT orcompatible computer, with monitorsand other peripherals, and uses the stan-dard MS-DOS 3.1 software packageoperating system. Its software elementsinclude a complete professional Smartapplications package, a feature of whichis a spreadsheet with graphics that canbe used while the computer is datamonitoring and logging the plant.

Short payback timeKent Process Control Systems(6) hasdeveloped integrated configurations ofits originally centralised K90 computerprocess control system, the P4000 -ICS.This interesting development, instead ofthe single or hierarchical configurationof the K90, permits a number of units tobe linked via the peripheral highway intoone integrated system.Each peripheral highway, of which theremay be more than one per system, has amaximum of eight units, up to four ofwhich may be operator control panelsand the rest control processors. The ar-rangement allows a system to handle dif-ferent sized process control applications,besides offering a low cost entry to ICSsystems. The first two ICS systems havealready been supplied to 9. phar-maceutical company and a major steelproducer.

Kent has also introduced an expertsystem, based on LISP and using aPicon shell, as an option with the P4000distributed control system. The expertsystem is designed to simplify interpreta-tion of the volume of data from the pro-cess variables being monitored on amedium -to -large system. The volume ofincoming data is particularly high dur-ing plant changes such as start-up andshut -down procedures.Several companies are examining the ap-plication of expert systems to processcontrol. The first publicised success inthe United Kingdom has beenLINKman. The Blue Circle cementcompany, in conjunction with SIRA(7),formerly the Scientific InstrumentResearch Association, set it up on aKPCS P4000 distributed control system.LINKman succeeded where attempts atmore conventional computer processcontrol failed. SIRA has made an agree-ment with Blue Circle to market thesystem to other cement producers. BlueCircle has also ordered five completesystems and is anticipating a paybacktime of six to nine months. This quickreturn is largely due to energy savings.

Higher level informationIn 1984, the Alvey Commission set up anumber of expert system demonstrationclubs in various industrial sectors. Thefirst of these was in control instrumen-tation - the Real Time Expert SystemsClub of Users (RESCU). The study ofan expert system as an adviser on qualitycontrol at an ICI company ethoxylatesplant for batch production of detergents

has recently been completed.Systems Designers(8), the contractor forthe RESCU club of some 22 members,has now initiated a further club, theCognitive Systems Club (COGSYS), toconvert the results of RESCU into atruly commercial, fully supported prod-uct. It is expected to appeal to chemical,food, pharmaceutical and other processindustries, the utilities and energy sec-tors, and the parts manufacture and as-sembly industries. Members of theCOGSYS club will benefit from sales ofthe completed product and membershipis still open to companies and academicinstitutions.At the end of 1986, ICI launchedAuditor, its plant performance monitor-ing package, with the support ofBritain's Department of Energy and theChemical Industries Association (CIA).The system, the result of new thinkingabout the quality of management infor-mation in the production sector in thelight of reduced fortunes following theoil crises, is now used in more than 60ICI plants and is being sold to other

companies in the chemical and other in-dustrial sectors through IndustrialEnergy Systems.Auditor technology is simply a higherlayer of production information and ituses existing monitoring devices and in-formation. Linked to the company'smainframe computer systein it cantransfer data into the accounts andcosting system or into sales forecastingand business planning software.The package also interfaces with twohigher level systems developed by ICI.Co-Audinator is designed to monitorand optimise the running of a whole sitewith several interacting plants, andEnergy Management System is used forsite or company -wide energy monitoringto allow comparisons of differentperiods of production with differentmixes of product.Auditor systems installed at ICI havehad an average payback time of sixmonths. A standard Auditor packageconsists of a DEC MicroIl computerwith a winchester disk, twin floppydisks, one or two display units (normally

EE

April 1988in colour), and a printer.

I. Energy Efficiency Systems Ltd, Midland House,202 Linthorpe Road, Middlesbrough,Cleveland, United Kingdom.

2. Ferranti Computer Systems Ltd, WythenshaweDivision, Simonsway, Wythenshawe, Man-chester, United Kingdom, M22 5LA.

3. Newmark Technology Ltd, Heathrow Causeway,152/176 Great South West Road, Hounslow,United Kingdom, TW4 6JS.

4. Biotechnology Computer Systems, ClevelandHouse, Church Path, Alton Green, Chiswick,London, United Kingdom, W4 5HR.

5. Department of Chemical and BiochemicalEngineering, University College London, GowerStreet, London, United Kingdom, WCIE 613T.

6. Kent Process Control Systems, Biscot Road,Luton, United Kingdom, LU3 1AL.

7. SIRA Ltd, South Hill, Chislehurst, Kent, UnitedKingdom, BR7 5EH.

8. Systems Designers PLC, Centrum House,101/103 Fleet Road, Fleet, Hampshire, UnitedKingdom, GUI3 8PD.

SECOND GENERATIONPROGRAMMABLE LOGIC

by E Baum

The direct interface system on amicrocontroller is, in principle, verysimilar to that on a microprocessor. Infact, there are slight differences betweenthe individual processor manufacturers,but the applications, i.e. connection ofdynamic RAMs, demultiplexing of pro-cessor buses or mailbox functions, ap-pear to be very similar. That is why allsemiconductor manufacturers offer arange of standard chips which can beconnected directly to their own pro-cessors. However, there remain manymore applications, where these interfacemodules, or even logics, i.e. latches orother TTL logics, must be added. Forthis, discrete logics in the 74xxx seriesare often relied upon. PLAs and EPLDs(erasable programmable logic devices)are also frequently used.It is now possible to imagine integratingthe processor interface and the interfaceto the controller or processor in a singleEPLD. The density of this module of upto 1800 gate equivalents is thereforequite sufficient. However, thanks to thevery simple and regular structure of thebus interface, many of these gates re-main unused on the chip. This essen-tially has two disadvantages. Firstly, the

chip could be even cheaper if thesuperfluous gates were totally dispensedwith. Secondly, EPLDs and PLAs withlarge numbers of gates are slower, sincethe internal capacities are greater andthe signal propogation speeds are slower.In some circumstances therefore it isnecessary to rely on several smallmodules.The new member of the EPLD familyfrom Intel, the 5CBIC (bus interfacecontroller), fills this gap perfectly. Asthe name implies, this chip offers ahighly integrated solution for all designswhich contain bus transfer lines orgenerate control signals. Even the driver,which in some cases still has to be pro-vided in a bus interface, can more oftenthan not be dispensed with when the5CBIC is implemented. The maximumcurrent on the bus side can be 32 mA.The 5CBIC thus offers all the advan-tages of high integration such as lowspace requirement, low current require-ment, low system and manufacturingcosts, and so on.Figure 1 shows the basic 5CBIC design.The 8 -bit wide A port on the busmanagement unit, BMU, lies directly onthe processor or controller bus. On the

"user side" there are two further 8 -bitports, B and C As will be seen later,these three buses are bidirectional andcan be combined randomly, evendynamically, with each other. The sec-ond largest block is the programmablelogic unit, PLU, which contains an 8macrocell EPLD unit. The PLU has 8dedicated inputs and 8 bidirectionalpins. Both blocks can be supported viathe control unit.

Bus Management UnitThe bus management unit links ports A,B and C together and controls andmonitors the data flow over their lines.At the same time, the user can choosewhether the data flowing into these portsis to be latched or not. For this a latchenable signal can be generated in thePLU or supplied directly via a pin.Various EPROM cells, or dynamicallymodifiable signals generated by thePLU, control the data flow. Each portcan also be connected with any other.Depending on the requirements or thesubsequent hardware, the signal can begiven out on One of the outputs invertedor directly. Three signals generated in the

20 EE

April 1988

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PLU can be sent by the output buffer tothe ports in the high resistance state, inorder that data may then be receivedthere. A multiplexer can make the signalsfrom a port, latched or not, available tothe PLU AND/OR array. The connec-tions between the three ports on theBMU itself, are programmed viaEPROM cells (Figure 2).

Fig. 2. The data flow can also be configureddynamically.

Consider the connection of the 5CBICto, for example, an Intel controller in theMCS 51 family. Then, using the BMU, itis possible to demultiplex the addressand data bus and make the rest of thecircuit available separately on ports B

and C. The driver current of 32 mA perpin should be sufficient for most appli-cations. The working frequency of theexternal logic can be up to 12.5 MHz.Internally, the 5CBIC can work with upto 20 MHz. The PLU can now "ob-serve" the data or address flow andchipselects, generate other controlsignals or simulate an additional parallelport.

Programmable Logic UnitThe second large block on the 5CBICchip is the programmable logic unit,PLU. This essentially has a 5C060 EPLDsuperset. Eight macrocells can, with thehelp of EPROM cells, be adapted to the

application (Figure 3). Eight dedicatedinput pins and 8 bidirectional pins canbe connected to the macrocells. Con-sidering that data from ports A, B or Ccan also be obtained via the internalfeedback bus, the user has up to 24 in-puts, and up to 8 outputs available perproduct term.As has already been seen with theEPLDs and PLAs logic operations, se-quences are firstly converted into anAND/OR structure, which is usuallygenerated and optimized by the develop-ment system, IPLDSII (Intel Program-mable Logic Development System, ver-sion 2). This structure can then be veryeasily implemented in the AND/OR ar-ray on the input of a macrocell as a so -

Fig. 3. The 5CBIC macrocells - I/O latches and high driver currents - make the use of theprocessor bus an optimal application.

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9.0070-13

Fig. 4. The IPLDSII allows the use of TTL,

called sum of products. Each macrocellalways has available the 8 dedicated in-put signals, the 8 macrocell feedbackloops, the 8 signals on the bidirectionalpins, and the signals on one of the BMUports. Since all signals are dealt withdirectly and inverted on the AND/ORarray, any combination can be pro-grammed by setting the correspondingEPROM cells. As opposed to the 5C060,each input signal can be individuallylatched. The only exception are the 8 bitswhich come from the BMU. These mayonly be latched together, or not at all.The latch enable signal for each inputlatch can either be generated individu-ally with the help of a product term orby a common control signal.Behind the OR gate, which can compriseeight product terms, there is an inverterwhose optimum algorithm (EspressoMinimizer) makes life a little easier,since it allows DeMorgan's theorem tobe reproduced in the hardware. Theconsequent I/O section of the macrocellis therefore very like that of the 5C060(Figure 3). Combinatorial or registerlogics can be created here. With registerlogics there is a choice of four registers.Depending on what is most suitable forthe application, either a D-, toggle-, JK-or RS-flipflop is used. Whereas whenusing a D- or toggle-flipflop all eightproduct terms are connected to one in-put, with the RS- and JK-flipflops theproduct terms are shared arbitrarily be-tween both inputs. Each register in theI/O part of a macrocell has a set and aclear input which are controlled via oneof its own macrocells.The clock signal, the latch -enable andthe output -enable signals can be in-dividually selected for control betweeneither the control bus (synchronous) or aproduct term (asynchronous). This also

gate array, and user -defined symbol libraries.

gives greater flexibility in comparisonwith the macrocells of, for example, the5C060.The output of a macrocell can be fedback into the AND/OR array via eitherthe control- or feedback bus. This signalis picked off before the tristate buffer inthe cell's output. Behind the buffer, andthus physically linked with the I/O pin,there is a second pick -off. If, therefore,the variable generated by the macrocell isonly needed internally, it can be furtherused as input if the buffer has to beswitched to high resistance. Using thisdual feedback option, it is very simple togenerate the so-called buried registers.The development system keeps thesefunctions transparent for the user.

EE 111April 1988

IPLDSII: expansion of thedevelopment system supportsthe 5CBICOn many points, the developmentsystems of the EPLDs have been im-proved with the IPLDSII (Intel Pro-grammable Logic Development System,Version II - Figure 4). The new hard-ware is now based on the Intel Program-mer IUP-PC. Apart from EPLDs, allother EPROM -based modules, EPROMmicrocontrollers, etc. can also be pro-grammed.More important though for daily work-ing with EPLDs are the changes in thesoftware. So a new algorithm for op-timization (Espresso Minimizer) was im-plemented. For large EPLDs in par-ticular, important improvements weremade in the design density. The fitter,and thus the program part, whichassigns a design for optimization of themacrocells in the selected EPLD, hasalso been improved.Working with the IPLDSH has also beensimplified considerably and made morecomfortable. Although previously it waspossible to use modular design methodsand link together several source files,now it is possible to go even further backto the design macros. The macro -librarycomprises three blocks:

TTL macro -libraryIntel Gate Array Library

User -defined library

The TTL library comprises a collectionof the most -used modules in the 74series. The user enters the modules withthe corresponding connections to the re-mainder of the logic. The macro -expander then converts this informationinto EPLD primitives which are reunited

5

P LeA0

T

fJ OeA1,-B

OeB

P

0

A

oil r -c 0

T

LeC C-Port inputs to C are registeredL

BECO70-14

Fig. 5. With the aid of the IPLDSII, the 5CBIC bus management unit can be configured veryeasily.

EE

April 1988in the minimizer. The expander alsorecognizes if a chip is not being fullyutilized and erases the remaining gates.So, for example, if with the 7400 only 2of the 4 gates are used, only 2 will be im-plemented in the EPLD.Sometimes it is possible to use EPLDs asprototypes or backups for a gate arraydesign. In order to make this as simple aspossible, Intel has grouped the gate -array macros in a further library, whichcan be implemented in an EPLD.Of great interest, of course, is the possi-bility, with the help of a few utilities, forthe user to -create a library himself, theelements of which can also be made upof those of the other two, i.e., the TTLlibrary.As with the old version of the IPLDS,for documentation an advanced designfile (Netlist File), a logic equation filewith the actually implemented and op-timized functions, and a report file withthe utilization and pin assignment of theEPLD is generated. If during compilingerrors are found, the messages are "col-lected" in an error file.In the software output, a JEDEC-compatible file is generated which servesas input variable for one of the program-ming units, from Intel or another, whichsupport the EPLDs.The basic version of the IPLDSII sup-ports the circuit input with the help ofan editor. It is however simpler to use thelogic builder which allows interactivegraphically -supported conversion of acircuit diagram into a netlist. The logicbuilder also makes configuring the5CBIC bus management unit verysimple. A BMU block diagram comes upon the screen (Figure 5). Using the cur-sor, it is possible to "go into" the desiredblock, i.e. the block for port C. Bysimply pressing the "RETURN" key, itis now possible to select from all the con-figuration possibilities. The respectivefunctionality is entered on the circuitdiagram on the screen as are the connec-tions to the other ports. Later the outputenable (Oex), latch enable (Lex) or select(SeLx) signals are connected. The signalscan be connected directly to pins or con-trolled from one of the macrocells. Thecompiler takes care of the allocation.In order to simplify input, various soft-ware packages expand the IPLDSII.ISTATE for example allows input ofstate diagrams and truth tables. Furtherlibrary and conversion packages allowcircuit diagram input using PCAD orDASH.

Since the middle of 1987, Intel has alsobeen offering an IPLDS-compatiblesoftware package for circuit diagram in-put, which is reasonably priced.SCHEMA II, as the package is called, isproduced by OMATION and sold by,amongst others, Intel. In addition totheir own schematic capture software,some libraries contain EPLD primitivesand 74xxx symbols, which can be sup-

01ATA(07.1gri>

CONTROLS >

PORT 8

PORT ASCRIC

SYNCHRONIZERARBITERCONTROL

PORT C

0

LATCH

LJ

PORT 8

PORT ASCILUC

7- BIT COUNTER

PORT C

*COUNTEROUTPUTS

CONTROLS

47NEYORT

EVEN ADDRESS I 000 ADDRESS

0 PROCESSOR 2

LOWER ADDRESS

UPPER ADDRESSLATCH

880070-15

Fig. 6. Two 5CBICs in a 16 -bit, twin -processor system carry out the control of the dual -portedRAM.

ported by the IPLDSII. The circuitdiagram can now be input and advan-tage taken of the SCHEMA software, i.e.by plotting on simple EPSON printers orHP LASERJET, and even on plottersworking with larger than A4 format.The circuit, which may, of course, con-tain TTL symbols, is converted into anadvanced design file, which then serves

to the IPLDS compiler. Thedesign is minimised and then fitted into

the EPLD selected. In addition to theplot files, the same output files aregenerated for documentation as whenthe logic builder is used. In additionSCHEMA II offers a range of otheraids. Thus, it is possible for the user toautomatically create parts lists, carry outa design rule check, check routing, andprint out various data formats, pinlists,netlists, and so on.

Fig. 7. Photograph of the experimental set-up of Fig. 1.

EE

April 198816 Bit dual port memoryA popular way of making computersfaster is to have several processors work-ing in parallel on a single task. Here, theprocessors must from time to time ex-change data for synchronization andmanagement from shared memories.This exchange takes place more oftenthan not via a dual -ported RAM. The

logic, which is necessary for managingsuch a RAM, can now very easily becreated with the help of two EPLDs ofthe 5CBIC type (Figure 6). Here, two16 -bit processors are accepted which canaccess a joint memory bank. Each5CBIC can work with an 8 -bit width.Two are therefore required. The firstmodule manages the upper 8 bits of the

databus. It also takes care of arbitration.The second manages the lower 8 bits. Inthe PLU, a 8 -bit counter is implementedwhich is required in other parts of theapplication. Further information isavailable from Intel in the form of appli-cations leaflets.Eckart Baum is with Intel, Munich.

COMPUTER NEWS

DATAMAN S3Dataman's new Intelligent PROM Pro-grammer and Universal DevelopmentSystem, DATAMAN S3, is the next linkin the evolutionary chain of tools formicrosystem designers, radically differ-ent from the big benchtop PROM Pro-grammers.

S3 looks more like a rechargeablecalculator than a Prommer. Indeed it isrechargeable, by three hour boost orovernight trickle, and will burn up to1000 PROMS from its extensive libraryof EPROMS and EEPROMS withoutrecharging. It's an EMULator too, andwill stand in for PROMS up to 27512size with 100ns access - all 25, 27 28series in fact, and many others. It isn'tjust a ROM EMULator: it's a RAMEMULator as well, with a Flying WriteLead to grab the microprocessor's Writeline. Variables and Stack can be kept inS3's memory - and inspected andedited there just like the rest of theprogram. What's more everything isstored in continuous memory and re-tained even when S3 is turned off.S3 can be used without touching thekeyboard - by two-way RS232 interfacewith a remote computer via the standardDB25 socket on the back. All thekeyboard functions work on the bigscreen. Assembled code can bedownloaded in one of the standard for-mats at 9600 baud.The missionary work of introducing S3has already begun and product isavailable for immediate delivery. It costs

£495, plus VAT. Right now there's a treeinspection, 30 day money -backguarantee operating.Contact DATAMAN, Lombard House,DORCHESTER, Dorset DTI 1RX orphone 0305 68066

Free VMEbus catalogueA new catalogue detailing MicroSys'range of VMEbus CPUs, memory andI/O modules is available exclusively inthe UK from Dage. Free on request toengineers, the 28 -page colour brochureprovides shortform details on over 50VMEbus boards and modules, as well asmany other items from cables to boxedsystems.Dage (GB) Ltd Rabans LaneAYLESBURY HP19 3RG Telephone(0296) 393200.

Fibre optic transceiverFiberdata AB of Stockholm have de-signed a fibre optic transceiver that pro-vides noise -free data transfer betweenIBM S30 -series computers and theirperipherals.The transceiver, which provides com-munication over distances of up to fourkilometres, converts electrical data into

optical signals and vice versa, so that thedata can be transmitted via fibre opticcables.Tekelec Ltd Cumberland House Baxter Avenue SOUTHEND-ON-SEA SS2 6FA Telephone (0702)337337.

DRIVE HEAD CLEANING KITNational Computer Supplies has ex-tended its range of micro maintenanceproducts with the introduction of thefirst automatic 1/4 inch data cartridgehead cleaning kit. Manufactured by

Dusan and costing £29 retail, it cleansdirty drive heads in half a minute. Con-tactNational Computer Supplies FourLanes End Horsley Woodhouse DERBY DE7 6AY Telephone (0332)883333.

First all-CMOS STEbusprocessorThe first all-CMOS processor board forthe STEbus has been announced byBritish Telecom MicroprocessorSystems. Based on Intel's 8031 CPUwith CMOS memory and I/O, theboard's very low power consumptionand inherent noise immunity make itideally suited to the implementation ofcomputer systems for battery -poweredor harsh -environment applications.British Telecom Microprocessor Systems

Martlesham Heath IPSWICHIP5 7RE Telephone (0473) 643101.

24

'Epr§aILREO SOUND GENERATOR

A high -quality stereo sound effects board for the Universal I/O bus,based on Valvo's Type SAA1099 advanced single -chip complexwaveform generator. Applications include enlivening computergames and operation as a programmable test generator for

simulation of composite AF waveforms.

Here is yet another simple to build exten-sion board for the Elektor ElectronicsUniversal I/O bus (I). It answers thepopular demand for an advanced soundgenerator that can be programmed toproduce an astoundingly wide variety ofcomplex sounds in stereo, simply byhaving the computer send the appro-priate commands and datawords foreach channel via the Universal I/O bus.The main specifications of the soundgenerator board described here areshown in the shaded box below.

Digital soundThe block diagram of the Type SAA1099programmable sound generator chipfrom Valvo (Philips/Mullard) is shownin Fig. 1. The interfacing logic is shownto the left and at the top of the drawing.To the computer, the chip appears as aWOM (write only memory). Reading ofthe chip status is, however, possible if theprocessor writes copies of the com-mands and data into a RAM table forretrieval at a later stage. Input line AO ofthe sound generator chip is made highfor loading register address bytes, andlogic low for databytes. The interfacelogic on board the SAA1099 latches theregister address, obviating the need torepeat this when writing new data to thelast selected register. The process ofsound generation in the SAA1099 iscompletely digital, and based on pulse -width modulation.Table I gives an overview of the functionassigned to each bit in a particularregister. The required octave is pro -

STEREO SOUND GENERATORBOARD

Features:

II six frequency generators2048 tones in 8 octaves

two noise generatorsIII six tone/noise mixersIII six stereo amplitude controllersII two stereo envelope generators stereo six -channel output mixer on -board 2 x 200 mW AF ampli-

fier

grammed separately for each tone gener-ator by writing a 3 -bit number inregisters 10H, 11H and 12H. The fre-quency range covered within each octaveis given in Table 2. The frequency pro-duced, A, is determined by the contentsof registers 08H...0DH incl., and can becalculated from

8 x1062117-0. (I -F2/25511

(consult Table 2 for O,, and Ft).The contents of registers 14H and 15H

determine which signals are passed bythe six on -chip mixers. There are fourpossibilities: (1) all signals are blocked;(2) only the tone is passed; (3) only noiseis passed; (4) both the tone and noise arepassed. The noise generator clockrate-hence the noise colour -is in-dividually programmable on the left andright channel by writing the appropriatedata to register 16H.

[Hz]

Six amplitude controllers can be pro-grammed to set the volume of thegenerated sound on the stereo outputchannels. This is effected by writing datato registers 00H...05H incl. (left: LSnibble; right: MS nibble).The last programmable section to be dis-cussed is the envelope generator, whoseoperation is best explained with refer-ence to Table 2 and Fig. 2. In the draw-ing:(1) indicates that the output amplitude is

determined only by the amplitudecontroller when the envelope generator isdisabled;(2) indicates that the maximum ampli-

tude is 15/16th of the value set by theamplitude controller when the envelopegenerator has been enabled;(3) indicates the moment when a new

envelope waveform can be started byreloading EO and/or El.

1

VA CS

11 IAd aria

IS

.00tsv 'SS'ea'

DEFER II 1 TOM

crtA:zOPEANTLA

Edema Pea mW Ota,, NOSE

ONEROOR 0

f r fr ...an Og......COUCTINWS

H 11"133TATALOOP

TOEONEIONot 0 -I mpuTme

CORTFOLTER

47t I <

TOEGOTT IATCE H COETROOR

00b0Oteit-N_

7.1TONE

GENTANTOR 7..m.-nie4

OTTETROLLOMETOPE

GENERATOR*1- Da ---e0, 1._1__.

H.Fs-- tOS '4 IN

07GENERATOR i SAAI099

TOGGENERATOR]

Ampur_ccCONTELLOP

'U. ft'or r .41

l'E'r <TOPEGENTAATTE a CCETRO-TER =2=, banal 12CS

W.,AT T, 7E1RO

TOEGEORATIOStom'

AMMOCOPTERGELER

,,OPERATOR t

.1.71Pc - 1

Fig. 1. Internal structure of the Type SAA1099 programmable sound generator.

Table 1.

EE

April 1988

2

INTERNAL REGISTER MAP

register; dataT2 ITD1ITIT Functionaddres 1 D7 D6 I D5 i D4 IT33

00 ARO ALO Amplitude 0, right/left

Amplitude 1, right/left

Amplitude 2, right/left

Amplitude 3. right/left

Amplitude 4, right/left

Amplitude 5, rightileft

Frequency 0

Frequency 1

Frequency 2

Frequency 3

Frequency 4

Frequency 5

Octave 1: Octave 0

Octave 3: Octave 2

Octave 5: Octave 4

Frequency Enable

Noise Enable

Noise generator 1:Noise generator 0

Envelope aenerator 0

Envelope generator 1

Sound Enable

01 AR1 ALI

02 AR2 AL2

03 AR3 AL3

04 AR4 A 4

05 AR5 AL5

06i

00

07 I 00

08 FO

09 i Fl

OA F2

OB F3

OC F4

OD F5

OE 00

OF 1 00

10 I 0 01 I 0 00

11 0 03 0 02

12 0 05 Ii 0 04

13 00

14 ' 0 0 IFE5 FE4 IFE3 FE2 FE1 FE0I

15 0I

0 NE5 ,NE4 NE3 NE2 NE1 NE0

16 Ni I NO

17 00

18 E0

19 I E 1

1A 00

lB 00

IC.; 00 0

'SE

10 00

1E'I

1 00

1 F 00

The letters in brackets to the right of theenvelope waveforms in Fig. 2 refer to thebit combinations in Table 2 (E0 -El; bit 1,2, 3).When the envelope mode is selected fora channel, the amplitude of the associ-ated amplitude -controller is roundeddown to the nearest even value (the LSbit is considered low). If, for example,the volume was set to value 1, it isrounded down to 0. An envelope gener-ator can also function as a tone gener-ator. If the controlled frequency channelis inactive (tone & noise generatorturned off), the programmed envelopewavevorm will appear at the output. Inthis way, the sound generator board canfunction as a programmable waveformgenerator with a maximum output fre-quency of about 1 kHz. Faster envelopewaveforms can be achieved by reducingthe resolution of the envelope from 4 to3 bits (bit 5 of byte E0 or El). The speed

of the envelope is determined by fre-quency generator 1 (or 4), or by the com-puter repeatedly writing to the addresslatch, clocking the envelope generatorwith the WRITE signal (\VS). Theperiod of the envelope, t; is calculatedfrom

te= 8/fclock

in the 4 -bit mode, or

te=4/fc1ock

in the 3 -bit mode.

Bit SE (sound enable) can be used forturning the sound generator on and off.The programming of sounds is largely amatter of trial and error establishing ofthe required bit patterns, writing 'data tothe chip, listening to the resultant sound,debugging the data and register selec-

ba t.:17=11 21217=

3 2 1

3

Vrn

/A .d/ .,/ ..ad4,,"//I it/2 -2

Fig. 2. Programmable envelope waveformshapes.

tions, and making the requiredmodifications.

Circuit description andconstructionThe sound generator board is composedof relatively few parts-see the circuitdiagram of Fig. 3. The WR signal forthe SAA1099 is made by combiningR/W and 4)2 in gates NI and N2. Thecrystal -controlled oscillator built aroundTi and T2 provides the 8 MHz clocksignal for the sound generator chip.The pulse -width modulated outputsignals of the SAA1099 are converted toanalogue in R -C filters composed ofR4. lb incl. and C3. ..Cs incl. Inte-grated stereo output power amplifierICI can provide about 2 x 200 mW tothe loudspeakers.Construction of the board is straight-forward, and requires no further detail-ing. Supply power for the sound gener-ator board may be obtained from thecomputer. Due attention should be paidto adequate decoupling, however: insome cases, interference on the supplylines from the computer will necessitatefeeding the board from a separate,regulated, 5 V supply (cut off pins 1 and2 at the board side of edge connectorK1).

Control softwareControl programs for the sound gener-ator board should be written with easeof register operations in mind. A simple,yet effective, way of achieving access tothe registers and their contents is to

26 EE

April 1988

00 IC0102 SAA

1099

04

05

06

07

L&1

LS2

H1. -J114 = IC 3 = 74110100T1, T2 =13F494

67142-3

Fig. 3. Circuit diagram sound generator board.

5startREM initializationDIM register (31)FOR N=0 TO 31

POKE addres-latch, NPOKE data -latch, 0register(N) : =0

NEXT N

REM initialization completeREM start experimenting

loop

clear screenREM print register contentsFOR N=0 TO 31

PRINT N;registertN)

ii NEXT N

INPUT "addres",addresINPUT "data",dataregistertaddres) :=dataPOKE addres-latch, addresPOKE data -latch, data

go to loop

make use of a register selectionsubroutine, in conjunction with datastatements and arrays. Also, do notforget to copy data written to theregisters in reserved memory areas of thecomputer.The program structure shown in Fig. 5 isintended as a guide for writing one'sown control programs for the sound gen-erator board. The program starts bydimensioning array variable "register".

This array is set up to enable the com-puter to keep track of the data written tothe registers in the interface. Next, allregisters in the SAA1099, and array"register", are reset to nought in a FOR -NEXT loop. The program then enters ainfinite loop for fetching register selec-tion codes and data from the keyboard,and transferring these to the SAA1099via the Universal I/O bus. First, theregister contents are displayed on screen,so that the status of all registers is knownat any time. Consecutive INPUTstatements then prompt the user to enterthe register address, and associated data.The program then updates the contentsof array "register", and, of course, thatof the addressed register. It then returnsto the loop entry point.

Finally, here are two examples of soundsthat can be generated by the sound ef-fects board:Steam locomotive: set AR2 and AL2 toan arbitrary value greater than 1. SetNE2=1; N0=0; E0=4. Bits and bytesnot mentioned are set to nought, except,of course, the sound enable bit.Bell: set the volume as required (AR2and AL2). Set F2=FFu, 02=7; FE1=1;FE2=1; E0=4 and SE=1. Bits and bytesnot mentioned are set to nought. St

Reference:in Universal I/O bus. Elektor Elec-tronics May 1985, p. 35 ff.

Fig. 5. Suggested structure of a controlprogram for the sound generator board. Completed prototype of the stereo sound effects generator for the Universal I/O bus.

EE

April 1988

Table 2.

REGISTER DESCRIPTION

ARx, ALx 4 bits for amplitude control of generator x, left and rightchannel.

Fx 8 bits for frequency control of generator x in designatedoctave.

Ox 3 bits for octave control of generator x.000 lowest octave 30...60 Hz001 50...122 Hz010 122...244 Hz011 244...488 Hz100 489...977 Hz101 978...1950 Hz110 1.95...3.90 kHz111 highest octave 3.91...7.81 kHz

FEx 1 bit FEx = 0 indicates that generator x is off.FEx = 1 indicates that aenerator x is on.

NEx 1 bit NEx = 0 indicates that mixer x does not add noise.NEx = i indicates that mixer x adds noise.

N1, N2

i

1-----

2 bits for noise generator control. These bits select the clockrate of the noise aenerator.

00 31.3 kHz01 15.6 kHz10 7.6 kHz11 51 Hz to 15.6 kHz (frequency generator 0.'3)

I Et:), El

'

7 bits for envelope control.bit 0 0 = left and right component have the same

envelope.I = right component has inverse envelope of thatapplied to left component.

bit 1,2,3 000 zero amplitude la)001 maximum amplitude (b)010 single decay (c)011 repetitive decay (d) waveforms are100 single triangular le) illustrated in Fia. 2.101 repetitive decay (f)110 single attack (g)111 repetitive attack (hi

bit 4 '0 = 4 bits for envelope control Una* =977 Hz).1 = 3 bits for envelope control (fmax = 1.95 kHz).

bit 5 0 = internal envelope clock (frequency generator 1or 41.

1 = external envelope clock (address vaite pulse).bit 6 must be 0.bit 7 0 = reset (no envelope control).

1 = envelope control enabled.

SE 0 = all channels disabled.1 = all channels enabled.

4

T1

Parts list

Resistors

R) -10KR2... R5 incljts;Rti=11<0Re;)ThRto=47KR9= 18K

Capacitors:

CI;C4;C7;C3o=100nC3:C6= 100C2;C:1;CIO:Cti =100m; 6 VC5:C8;CI6=In0C12:C14=470m; 6 VC13;Cie=150nC17:C18=470pC19=33p

Semiconductors:

TI;1-2=BF494 (Crickiewooci Electronics)ICI =SAA1099 ICSI Electronics)IC2=U24328 (AEG-Telefunken; Cirkit)IC3=74HCT0O

Miscellaneous:

X1= quartz crystal 8 MHz.Kr= 21 -way right-angled plug to D1N41617(stock no. 471-418: Electromail 05362045551.

LS1;LS2= miniature loudspeaker: 8 0;250 mVI.

PCB Type 87142 ((see Readers Services page).

T2

I

C20000OO0

8CsI I C192

;.C5 C1 rikg:Ild

C11 C9

017 010 C2

C14C130

:11

Fig. 4. Printed circuit board for building the stereo sound generator.

28 EE

April 1988

DESIGN IDEASThe contents of this column are based solely on information supplied by the author

and do not imply practical experience by Elektor Electronics,

CCOIVPUTER C NTROLLEDMILS C GENERATOR

by Dr B. Koyuncu, Department of Physics, Kuwait University

The design of a generator is described, which is operated via acomputer to control NOTE, OCTAVE, and VOLUME. It simulates a14 -key piano with the computer keyboard acting as that of thepiano. BASIC programming is used for operation and storing the

music for playing at a later stage.

The musical piece is coded in binaryform with the aid of a BBC personalcomputer. The information on the datalines is fed into the circuit through thecomputer's user port. There are threecontrols: VOLUME, OCTAVE, andNOTE. The system is shown diagram-matically in Fig. 1.The system generates the whole tones(white notes=naturals on the piano) ofthe first two octaves above middle C.Fourteen notes are thus available span-ning a frequency range of 263 Hz to992 Hz. Music is generated eithermanually by manipulating the keyboardor automatically from the computermemory.

System descriptionSix computer data lines are used fromthe output port. Since seven notes areavailable in each octave (doh, my, me,fah, soh, lah, te), three lines are allo-cated for note control. These lines repre-sent the binary variations 001-111: eachcode represents a note.Two octaves (the first and second abovemiddle C) are available and one data lineis used for their control. A 1 on the dataline represents the first octave, and a 0,the second octave, above middle C.The last two lines are used to control thevolume. Since there are four possiblestates (00-11), four volume levels are

available in the circuit. Each data line isinput to a one -bit register. A 6 -bitparallel -in register is used to transferdata from the computer.A 3 -to -8 decoder decodes the relevantregister outputs to generate the fre-quencies corresponding to the sevenwhite notes. No decoder is necessary forthe two octave control. Since fourvolume levels are available, a 2 -to -4decoder is allocated to provide thesefrom the two data lines.

6 Bit Register

VolumeControl

2 bits

OctaveControl

bit

NoteControl3 bits

2/4 decoder 3/8 decoder

Digital A temiator

Power Amplifier

Oscillator

Loud Speaker

Ftg. 1. Block diagram of the circuit.

Decoder outputs for note control andthe single octave control signal (high orlow) are fed into a Wien bridge oscil-lator. Volume control is introduced onthe oscillator output via an attenuator:2 -to -4 decoder outputs are used as relaycontrol lines to include discrete attenu-ation levels to the oscillator output.One of the important effects associatedwith the musical notes and octaves is thegeneration of sine waves at different fre-quencies and amplitudes. These sinewaves are generated by the oscillatorwhen the relevant computer keys arepressed: the sound is obtained from aloudspeaker via a power amplifier.Each octave contains 12 notes: 7 whiteand 5 black (at least on the piano). Ona piano, the white notes are:

C; D; E; F; G; A; B

while the black notes are:

C#; D#; F#; G#; A#

The standard musical note is A and itsfrequency is 440 Hz. In the diatonicscale, the ratios between whole notes are:C:D = 9:8D:E=10:9E:F =16:1517:G= 9:8G:A =10:9A:B =9:8

EE

April 198829

Since standard A=440 Hz, the C belowit (middle C)=

9/10 x 8/9x15/16 x 9/10x 8/9 x440=264 Hz.

Since in the diatonic scale the ratio be-tween different successive notes varies, itis difficult to tune a keyed instrument tothe diatonic scale.This difficulty is obviated by using thechromatic scale, in which the ratio be-tween the frequencies of successiveascending notes is a constant (2' '2=1.059463). The ratio for descending suc-cessive notes is 0.943874. The ratio be-tween similar notes in successive ascend-ing octaves is 2; in successive ascendingoctaves 1/2: these ratios are the same asin the diatonic scale.In the present design, the lowestgenerated frequency is taken as themiddle C, i.e., 261.63 Hz. The other 13frequencies are: 293.66; 329.63 . .. 880;987.77 Hz (these can also be ascertainedfrom Table 1).Each of these frequencies is generated bya separate Wien bridge oscillator,diagrammatically shown in Fig. 2. In thecoupling network associated with thistype of oscillator, it is convenient, butnot essential, to make the resistances andcapacitances equal. The ratio We(=gain) is given by

V/e=R/(3R +jcoCR 2 - loCOC) [I]

For zero phase shift, co2C2R2=1. Sincethe frequency, f -1/2nRC, the value ofV/e becomes 3. Thus, in its simplestform, this type of oscillator has a gain of3 and the phase shift is zero. Oscillationwill be maintained at a frequency whichgives zero phase shift between the signalsat points A and B in Fig. 2.

2

e

IcT _TL-c

TAMPLIFIER

Fig. 2. Simplest form of oscillator.

The practical circuit must be modified toallow for amplitude stability, and this isprovided by thermistor Rm. The resist-ance of this component decreases whenthe power dissipation rises. The averageoutput voltage available from the oscil-lator is 1 V.. The optimum value ofthe thermistor is about 1 k4. This meansthat only 1 mW of power is dissipated: Fig. 6.

consequently, the variation in resistanceis very small. So, the circuit has to beable to produce a relatively large changein voltage for a small variation of resist-ance. Therefore, the thermistor andWien network are combined into abridge circuit as shown in Fig. 3. Oscil-lations are maintained by increasing thegain of the amplifier to a level which isjust sufficient to overcome the attennu-ation of the network. If, for any reason,the output voltage increases, the resist-ance of Rm decreases, the total attenu-ation will approach 3, and this will re-duce the voltage fed to the amplifier.Ideally, while the total phase shift mustremain zero, the amplification must behigh so that points A and A' in Fig. 3have approximately equal potentials.

Fig. 3. Simple oscillator with bridge network.

Design procedureD -type, positive -edge triggered, flip-flops are used to store the on-line datacoming from the computer. In addition,data coming from the output section ofthe user port is already stored in theserial register of this port.The relevant output lines are connectedto the circuit via three -state buffers.When the control line of a buffer is ac-tive, the input to the buffer is passed toits output; otherwise, the input isisolated and the output will be high im-pedance.Two sets of buffers are used to switch be-tween computer and manual operation.The inputs for one set are coming fromthe user port, while those for the otherset are coming from the manualswitches. One set of buffers has an activelow control line, whereas that for theother set is active high. The levels on

4 ControlSwitch

Manual/Auto

Dam)from

Computer

Datafrom

ManualSwitches

74 L5 244 wzz-v

Outputto theCircuit

Fig. 4. Computer/manual operation by twosets of three -state buffers.

these lines are controlled by mechanicalswitches. The switching arrangement isshown in Fig. 4.Information stored temporarily in theregister is decoded by the 3 -to -8 and 2 -to -4 decoders. The 3 -to -8 decoder hasthree inputs which give seven outputcodes, 001 -Ill. Any particular 3 -bit inputcode produces a low level at the relevantdecoder output and a high level at all theother outputs. Each decoder output cor-responds to a particular oscillator signal

upsmsommnomommintalmnsiisinagszitunimutiont11 11 11 11 11 II II 74LS 08

(0001 1111

00 0, 02 03 0. 0, 06 07

Fig. 5. 3 -to -8 logic decoder.

and is used to actuate a magnetic relay.The 2 -to -4 decoder is similar to the 3 -to -8 circuit, but has only four outputs.Each output represents a volume level.This is effected by the output actuatinga magnetic relay that introduces a givenattenuation onto the oscillator output.The decoders are constructed from ANDgates and inverters as shown in Fig. 5 (il-lustrated is the 3 -to -8 decoder).

6

Oscillator9.8K

2.2 SK

R3.1 98 K

R4.1_55 K

R,.0 21 K

2/4Decoder

PowerAmplifier

Manual/AutoData lines via0 Flip Flops

LoudSpeaker

Digital attenuator.

30 EE

April 1988

Table 1.

Frequencies in Hz of the chromatic scale over eight consecutive octaves.

toneoctaves

C C# D D# E F F# G G# A A# B

+4 4186.00 4434.91 4698.62 4978.02 5274.05 5587.64 5919.90 6271.91 6644.86 7039.99 7458.60 7902.12+3 2093.00 2217.46 2349.31 2489.01 2637.00 2793.80 2959.93 3136.00 3322.48 3520.00 3729.31 3951.10-2 1046.50 1108.73 1174.70 1244.55 1318.50 1396.90 1479.96 1568.00 1661.24 1760.00 1864.66 1975.50-1 523.25 554.36 587.33 622.25 659.26 698.46 740.00 784.00 830.61 880.00 932.33 987.770 261.63 277.19 293.66 311.12 329.63 349.23 370.00 392.00 415.31 440.00 466.16 493.88-1 130.81 138.59 146.83 155.56 164.81 174.61 185.00 196.00 207.65 220.00 233.08 246.94-2 65.41 69.30 73.42 77.79 82.41 87.31 92.50 98.00 103.83 110.00 116.54 123.47-3 32.70 34.64 36.71 38.89 41.20 43.65 46.25 49.00 51.91 55.00 58.27 61.74

7

BASS VIOL

TROMBONE

E TT E-...DRUM

fa

FLUTE

4 VIOLIN

OBOE

4 CLARINET

PICCOLO

TRUMPET

FRENCH HORN

BASS CLARINET

BASSOON

BASS TUBA

-41

CELLO

VIOLA

to -

HUMAN VOICES

1,,B4C3C3E3,3C3,3,3C202E2F2G2A2,2c,

1 1 111 q !!I !Ill cloy F1G1A1alc2DZE2F2G11112c3D1311383c431.

A32.70

A65.41

A130.81

A261.63

A523.25

A1046.50

A2093.00 4186.00

Fig. 7. Correlation between piano keys, notes, octaves, and frequencies.

The oscillator output is connected to the2 -to -4 decoder and power amplifier via aswitched attenuator network as shown inFig. 6. When a particular volume levelhas been selected, the corresponding 2 -bit code is fed to the decoder. The appro-priate decoder output becomes activeand closes a specific magnetic relay.Consequently, the oscillator output issubjected to a measure of attenuationbefore it is applied to the power ampli-fier.The Wien bridge oscillator contains R -Ccombinations that determine the notesand octaves. Each note -octave combi-nation represents a frequency and this isvaried by changing the value of thecapacitance (octaves) or that of theresistors (notes).For instance, frequency fi of the octaveabove middle C (treble stave) isf =1/2nR 1C1, while frequency h of thesame octave is h = 1 /21tR 2C-1. So,fl/f2=R2/R (and also =1/2'122).Therefore, R2=R1/2' 12, R3=R 1/22 12,

.R 7=R 1/26 '2. If Ri is given a value

of, say, 20 kg, the others can becalculated from the above equations.Capacitance C-1 for the octave abovemiddle C is calculated as 0.03 /iF forft =middle C=261.63 Hz and Ri=20 kg. For notes in the 2nd octave abovemiddle C, the value of the capacitance ishalved, so that C2=0.015 pF.The various resistors and capacitors areconnected to the relevant relays as shownin Fig. 8. The control lines of the relays

connecting each pair of equal resistorsare joined together to the outputs of thenote control decoder. The same tech-nique is used for the capacitors.The relays connect two resistors and twocapacitors simultaneously into the bidgecircuit to activate the oscillator. Theresult is one of the 14 available notes atthe output. A general layout of this ar-raneement is eiven in Fie. 9.Manual operation is provided by means

8

Output ofDecoder forNote control

1 13IX

IOctave ControlLine.

EV.4272 - 17

Fig. 8. Connections hetween coupling network and relays.

-4-5

V

Man

ual

Aut

oS

witc

h

10K

10K

10K M

anua

l

Aut

o

3904

Dat

a lin

esF

rom

Com

pute

r0.

030.

015

7

3.3K

Ra

4.1K

R4

15.1

3K

R3

6.8K

0,03

1.1F

0 01

5k/ F

R2

178K

Man

ual S

witc

hes

+5V

t1

ti5

oQ0

3904

CK

07

A

R4

20K

355

OP

-A

m

1.2K

500Q

100

S2

I. 55

K

Th

(4K

)0.

21 K

RI:

9.8K

Re.

-2.

9K

3:1.

98K

06 0

504

03 0

204

000

0402

03

3/8

Dec

oder

2/4

Dec

oder

1213

74 7

,1

CK

D

-<>

CK

C,K

1415

L_L_

0

-0 C

K

Q

CK Ext

erna

lC

lock

Gen

erat

or

LM 380

4 70

j..1

F

2 7K

4000

pF

Loud

Spe

c:ka

t.

8800

72-1

9C

O m

00 M

EE

April 1988

Table 2.

KEYS :

CODE :

NOTE :

space

32

A

65

C

S

83

D

For frequencies of notes, see Table 1.

D

68

E

F

70

F

G

71

G

H

72

A

J

B

74

space

32

z

90

Cl

X

88

DI

C

67

E'

V

86

F'

D

66

G1

N

78

Al

Al

77

B'

of simple transistor circuits and mechan-ical switches. Each transistor is driveninto saturation or switched off by themechanical switch in its base circuit. Thecollector potential will then be 5 V orzero respectively. This potential is ap-plied to the relay control lines in the os-cillator and in the attenuator networkvia D -type bistables and decoders. Thecircuit diagram of the music generator isgiven in Fig. 9.

Computer softwareThe flow chart (including the algorithm)of the program is given in Fig. 10, andthe actual program in Fig. 11. Theprogram is written in BASIC and storedon a floppy disk.

Create 3 arrays

N1161 : note signals

V(4) :volume signals1(11ox.): for storing

Note index of Asot Note +VII)

fraga-zs

Fig. 10. Flory diagram.

As the user plays the music by pressingthe relevant keys on the computer (seeTable 2), the computer stores the notesin a one-dimensional array. When hefinishes playing, the computer will askwhether playback is required. If theanswer is YES, the computer stores thearray in a file. The size of the array inwhich music is stored is 2,500 lines. Thislow number is due to the limitations ofthe computer memory. The array allowsthe playing of music for about 10minutes.

Further possibilitiesThe hardware design may be interfacedto any type of PC with the appropriateA/D converters to their user ports.The software can be modified to allowthe user to play music on the keyboard

of other PCs. Since the BBC micro hasan 8 -bit user port register, it can send28=256 signals. It can, therefore, beused to generate 256 different notes.These notes are fundamentals, not har-monics. A volume range of 30 dB is used

11

10 REM (GENERATION OF MUSIC BY USING HARDWARE AND RUC INTERFACE86 - JAN 87 ) =A

20 REM THIS PROGRAM IS AN INTERFACIN FOR.30 REM THE COMPUTER GENERATED MUSIC40 WAIT=8SO HAX=250060 DIH N(16)70 DIM T(MAX)80 DIM V(4)90 CLS100 PRINT -WELCOME TO THE MUSIC PROGRAM -110 PRINT -VOLUME CAN BE OF DEGREE 1.2.3 OR 4 O11LY-120 INPUT -VOLUME IS OF DEGREE ?-VOLUME130 IF VOLUHECI OR VOLUME,4 THEN 110140 PRINT -PLEASE NOTE THE FOLLOWING -ISO PRINT -YOU HAVE TWO OCTAVES -160 PRINT -EACH OCTAVE HAS 7 NOTES -170 PRINT -THE FIRST OCTAVE BEGINS AT KEY .2. AND ENDS AT KEY180 PRINT -THE SECOND BEGINS AT KEY .A. AND ENDS AT KEY .J.-190 PRINT -IF YOU RANT TO EXIT.THEN:200 PRINT -PRESS THE KEY 0-210 V(1)=0220 V(2)=16230 V(3)=32240 V(4)=48250 FOR J=1 TO HAX260 T(J)=0270 NEXT J280 J=1290 INPUT -NOW PRESS THE RETURN KEY TO START300 9AFE62=1.FF310 .FXI1,15320 REPEAT330 A=INKEY(WAIT)340 DATA 32.65.83.68.70.71.72.74.32.90.88.67.86.66.78.77350 IF A=48 THEN GOTO 470360 RESTORE370 SOT=O380 FOR I=1 TO 16390 READ N(I)400 IF A=N(I) THEN SOT=I-1410 NEXT I420 ?&FE60=SOT+V(VOLUME)430 X=?&FE60440 T(J)=X450 J=J+1460 UNTIL (J)HAX)470 ?&FE60=0480 PRINT -YOU CAN NOT PLAY MUSIC ANY MORE -490 IF J(MAX THEN T(J)=-1500 INPUT -DO YOU RANT TO STORE MUSIC?,

RN -.YS510 IF YS= -N- THEN GOTO 580520 6 = OPENOUT (-MUSIC-)530 FOR J=1 TO MAX540 PRINTEB.T(J)550 NEXT J560 PRINT -YOUR MUSIC IS STORED NOW -570 CLOSES580 INPUT - DO YOU WANT TO LISTEN TO STORED MUSIC? N=NO ,FOR YES

.SS590 IF S9= -N- THEN GOTO 700600 C=OPENIN (-MUSIC-)610 J=1620 REPEAT630 INPUTEC X640 TIME =0650 IF TIME<= 7 TRES 650660 ?&FE60=X670 J=J*1680 UNTIL (J>MAX) OR (TWO))690 CLOSES C700 sFX12,0710 ?&FE60=0720 PRINT -YOU HAVE EXIT FROM THE MUSIC PROGRAM -730 END

PLAYING MUSIC -TS

NRPT

11=110 .FOR YES PRESS RETU

PRESS RETURN -

880072 -21

Fig. 11. Listing of the BASIC control program.

EE

April 1988

Output of 3/8 Decoder" Note Control Lines"

Fig. 12. General layout of the wien bridge oscillator.

at the oscillator output. The frequencyof the notes may vary ±2 Hz around theexact values, but this is not noticeable byear.The thermistor, which protects the relaysfrom over -heating, takes a finite time towarm up. This time and the time delays

in relay operation cause the outputsound from the speaker to have a smallpeak before becoming steady. This effectis considered to be perfectly acceptable,since in a piano the sound also peaksfirst before attaining a steady statesomewhat below this peak value.

FinallyAn instrumentation amplifier is used forthe oscillator. Any frequency driftcaused by temperature variations is mini-mized by the drift -compensation net-work.The circuits are best placed in a metalbox and all wiring kept as short as poss-ible to keep any interference at bay.

References:1. Electronic Engineering 27:330, 350

and 410, July to September 1955.2. Journal of the AES 14, No. 1:21,

1966.3. Journal of the AES 17, No. 258, 1969.4. Third Int. Congress on Acoustics

1959-Elsevier Publications Co.,Amsterdam.

5. Computers and Automation, 13 No.8:16, 1964

6. Microelectronic Circuits by Adel S.SEDRA, 1982.

7. Electronic Principles by A.MALVINO, 1982.

8. BBC User Guide Book, BBC, 1982.

Acknowledgments:The assistance of Rowida Mustafa andAkram Farhat of Kuwait University isgreatly appreciated. The project wasfinanced by an SP023 university grant.

FUZZ UNIT FOR GUITARSPlayers of the lead or rhythm guitar will appreciate the wide

range of sounds produced by this low-cost fuzz unit.

The fuzz unit described here is simple tobuild from commonly available parts,yet gives excellent results with almost anycombination of lead or rhythm guitarand guitar amplifier (valve or transis-tor). It has three controls that guaranteea wide range of available effects, and isrelatively simple to align.

Circuit descriptionWith reference to the circuit diagram ofFig. 1, the fuzz unit is powered viaswitch Si, which is automatically closedwhen a jack plug is inserted in socketIC2. The output of the circuit remainsshort-circuited to ground, however, untila plug is inserted in Ki. This arrange-ment effectively prevents clicks andnoises in the guitar amplifier when theeffects unit is being connected. Theguitar signal is applied to electronic

switches IC3A and IC313 via coupling ca-pacitor C19. The configuration of theelectronic switches is controlled by footswitch S3 and inverter/LED driver Ti.When the foot switch is open, i.e., notactuated, R20 takes the control input ofIC3i3 to the positive supply level, so thatthe guitar signal is passed from K to IC2with a series resistance of about 90 Q,formed by the closed electronic switch.When the foot switch is closed, T3 con-ducts, LED D9 lights, IC313 is opened,and IC3A and IC3D are closed. Theguitar signal is fed to the distortion cir-cuit via IC3A and Ci, and is returned tothe amplifier via C16 and IC3D.The circuit around opamp ICI, FET Ti,T2 and rectifier Di is a peak limiter(clipper) whose onset -level is defined byPi. The distortion effect is, however, notcomplete as yet. Coupling capacitor C5feeds the signal to a passive filter net-

work. High -frequency components inthe signal are boosted or attenuatedwhen BRIGHT switch S2 is set to positionA or B, respectively. When S2 is set toposition C, the filter is largely ineffec-tive. The filter characteristics may bedefined to individual taste by redimen-sioning of Clo: the roll -off frequency ofthe network decreases with increasingcapacitance.Preset P2 serves to set the optimumsignal amplitude for the distortion stageset up around IC2. The feedback net-work of this opamp includes R17 andanti -parallel diodes Di -D4, which in-troduce the required distortion. The dis-tortion level can be set with P3. Thesignal is then fed through an R -C low-pass, a diode limiter and a volume ad-justment, before it is applied to the elec-tronic switch configuration discussedabove.

Ci DF256C

334

Construction and adjustmentConstruction of the fuzz unit is a routinejob: simply fit all the parts in accordancewith the PCB overlay (see Fig. 3) and theparts list. Be sure to observe the polarityof the diodes and the radial electrolyticcapacitors.The completed circuit board is best fit-ted in a sturdy diecast enclosure, asshown in Fig. 2. The foot switch, LED,and COMPRESSION and DISTORTION con-trols are fitted onto the bottom plate ofthe enclosure. Sufficient room should beleft inside to accomodate the 9 V PP3battery, which is preferably secured withdouble -sided adhesive tape.The circuit is, of course, best set up withthe aid of a sinewave generator and anoscilloscope, but a rather simpler align-ment procedure is set out below for con-structors not in possession of these in-struments. Connect the fuzz unit to theelectric guitar and the power amplifier,and verify that it is being powered by thebattery. Actuate the foot switch, set P3to the minimal resistance position, andswitch off the BRIGHT filter (set S2 toposition C). Play an h note on the guitar

l kHz), and set Pi for minimumaudible distortion. Adjust P2 and actu-ate the foot switch a few times until the

02

in,4001

R16

BTI 9V

7

D3, D4= 1N4148D1, D5-08 = AA1191C1 ,1C2 = TL0711C3=4066 effect Cf

* see text

53UL

R18

R191 R20

0 09

13

2

2

VIXUNE

50k652-

CIO1Rim

25225V

3

4

019

Di2p225V

C20

8C547

10313

;1'iR22 R23

2.2251

R25

fi

4:400

87255 -1

Fig. 1. Circuit diagram of the fuzz unit for electric guitars.

EE

April 1988signal from the effects unit and the"dry" guitar signal are of equal ampli-tude (this also depends on the positionof VOLUME control P4).Adjust the circuit as follows if thepreviously mentioned test equipment isto hand. Apply a 1 kHz sinewave of150 mV amplitude to the input of thefuzz unit. Set the BRIGHT switch to pos-ition C (off). Connect the scope to junc-tion S2 -P2, and adjust Pi for maximumamplification without running intonoticeable distortion. Increase the signalamplitude to 300 mV, and reduce the dis-tortion observed on the oscilloscope asfar as possible by carefully re -adjustingPI. Replace Ti with a another BF256Cif the distortion can not be reduced to anacceptable level: these FETs aremanufactured to a relatively wide toler-ance in respect of dynamiccharacteristics. Set the volume of the ef-fects unit as outlined above.

The fuzz unit has a moderate currentconsumption, so that an alkaline PP3battery should last for about 300 hours.This is reduced to about 40 hours, how-ever, if D9 is fitted. Much of the batterycapacitance can be saved by using ahigh -efficiency LED, mid increasing thevalue of the series resistor, R19. DiodeD2 protects the fuzz unit against reversevoltage when the battery is connectedwith the wrong polarity.

Fig. 2. Internal view of the prototype. The input and output sockets are types with a built-inswitch contact.

Fig. 3. The printed circuit board for building the fuzz unit.

Parts list

Resistors (± 5%):

R1;R2;(112;R13;R21 . R24 incl. =1 MOR3= 100RR4;Re;Ri 1= 2M2118;R7;R2o=100KRe=1K5Rs=4K7Rio=27KRi4;R17= 10K1115;1116=1K0

1118=22K1119=2K7R25 = 330KPi =50K linear potentiometerP2 = 50K preset HP3= 100K linear potentiometer

P4 = 50K logarithmic potentiometer

Capacitors:

Ci;Cii= 33nC2=1 09; 25 V; radialC3;C17;Cle= 1001Ca = 10011; 25 V; radialC8;Ce;C7;C14 =1110; 25 V; radialCe = 22nCs=10nClo=ln0C12;C16;C1s;C2o=2p2; 25 V; radialC13 = 100pCI8=10n

Semiconductors:

DI;D5...D8 incl.=AA119D2= 1N4001

D3;D4= 1N4148Ds= LED (red)Ti =8F256CT2=BC5478T3 = BC 547

IC1;IC2=TL0711C3=4066

Miscellaneous:

K1;K2= headphone socket for 6.3 mm plug(with built-in switch).

Si = SPST switch in socket (normally open).S2 = 3 -way, single -pole, rotary switch.S3= foot switch.S4= SPST switch in socket (normally closed).PCB Type 87255 Esee Readers Services page).

36 EE

MID3ril9 CODE - GEN -1,RAP3R

In line with this month's theme,electrophonics, we present a

handy, versatile and inexpensive tobuild tool that helps tracing down

and resolving incompatibilityproblems encountered in setting uprelatively complex configurations of

MIDI instruments.

by R. Degen

The acronym MIDI (mustcm. INSTRU-MENT DIGITAL INTERFACE) is nowadaysknown to virtually every user of elec-tronic instruments and associated equip-ment. Since its introduction in 1983, theMIDI standard has gained wide accept-ance, and has proved relatively simple toimplement thanks to the use of a serialtransmission standard for data exchangebetween compatible instruments in anetwork. Experienced users of MIDIequipment are, however, also aware ofthe system's limitations. One of the bestknown problems associated with theMIDI standard is that it becomes moredifficult to manage with increasing com-plexity of the equipment configuration:the more instruments, the moreinstrument -specific codes, and thegreater the risk of addressing equipmentwith incorrect or non -recognized codes.

TroubleshootingAny electronic musical instrument fittedwith a serial asynchronous interface tothe MIDI standard (31.25 Kbit/s; ±1%)has a receiver and/or transmitter circuit.Transmission of an 8 -bit dataword com-mences with one start bit, and is ter-minated with one stop bit. The 10 -bitpulse train has a duration of 320 ps. Theinterface is essentially a 15 mA currentloop built around an opto-coupler. Eachoutput preferably drives only one input,and received signals are, therefore,reshaped and fed to a MIDI THRU output.The MIDI communications protocoldistinguishes between status bytes(>127), followed by one or moredatabytes (<128), real time messages,and exclusive messages.The code generator proposed here is aMIDI compatible accessory device that

enables sending any 8 -bit hexadecimalcode (0... 25510 or 00.. .FFHEx) to aninstrument fitted with a MIDI input.But why bother to generate single com-mands at typing speed when the MIDIinterface is geared to high-speed com-munication? The answer has alreadybeen hinted at in the above introduction.The need for developing the MIDI codegenerator arose from difficulties en-countered in working with incompatibleMIDI instruments of different type andmake. It often happens that a relativelycomplex set-up of instruments and otherdevices connected via MIDI links simplydoes not work as required. Finding thecause of the malfunction is not easy, es-pecially in relatively complex instrumentset-ups. The speed at which data is car-ried between instruments is so high as tomake code analysis without relativelycomplex equipment virtually impossible.A simple test device as described hereallows sending MIDI datawords sequen-tially to an individual instrument bypressing 2 keys on a keypad. In this way,even the most complex MIDI controlstrings can be generated to enable check-ing the instrument's response. This wayof testing may be compared to using anAF test generator plus oscilloscope to

trace down a fault in an amplifier.Most MIDI instruments are suppliedwith a manual that gives more or less de-tailed tables listing the MIDI codes thatare recognized or transmitted by the in-strument. These 2 -character codes(MIDI datawords) can be supplied by thecircuit described here: the code isgenerated and transmitted by sequen-tially pressing the 2 appropriate keys ona hexadecimal keyboard. LEDs indicatethe transmission of the first and secondcharacter in the MIDI dataword.The code generator is essentially com-posed of the following functionalblocks: keyboard encoder, parallel -to -serial converter, central clock, and adriver for the status indication LEDs.The unit operates autonomously from aregulated power supply.

Circuit descriptionEssentially, the circuit fetches two hexa-decimal characters from the 16 -keykeypad, combines them into a singledataword, and transmits this in thepreviously discussed MIDI format.There is no parity bit, and the serialdataline is logic "1" in the non -activatedstate.

EE

April 1988Figure 1 shows the circuit diagram of theMIDI code generator. The circuit is com-posed entirely of conventional HCMOSintegrated circuits, and is, therefore, in-expensive to build.Oscillator Ni-Ni feeds the central clocksignal via N3 and N7 to binary counterIC6, whose 4 -bit output QA ...QD sup-plies the binary equivalents of numbers0...15 incl. to keyboard encoder ICJ,latch ICz and shift register IC5. Theclock signal for counter IC6 is inhibitedin N7 by the "keyboard activity" signalobtained via Schmitt -trigger Nio and in-verter N6.When power is applied to the circuit,bistable FF1 is reset by network R3 -C2.Output Q of FF1 is logic low, so that Nsprovides a logic high level to LED driverTi. Di lights to indicate that the codegenerator awaits the first, most signifi-cant, hexadecimal character (MSnibble).

Assuming that none of the keys ispressed, N7 passes the clock pulses tocounter IC6. The keyboard encoder, ICI,is a 4 -to -16 demultiplexer that translatesthe 4 -bit binary code at its inputs A... Dinto a low pulse at the relevant output.Each demultiplexer output is connectedto a key, Si ...S16. If, for example, keySii is pressed (nibble AH), the clocksignal is inhibited the instant ICI ac-tivates output 10. This means that thebinary equivalent of "10" is latched inIC2, becauses the rising edge of thepulse supplied by Nio causes FF1 totoggle and clock ICz via output Q.Latch IC2 supplies the 4 -bit binary codecorresponding to the MS nibble of theMIDI dataword to the parallel load in-puts of shift registers IC4 (inputs G andH) and IC5 (inputs A and B). InverterNs supplies a logic low level to Ti, Di isturned off, and D2 lights to prompt theuser to enter the LS nibble on thekeypad. Releasing the key restores theclock signal for IC6, and restarts thekeyboard scan activity. When the secondcharacter is typed in, the correspondingbinary code of the LS nibble is presenton inputs C...F of ICs. Output Q ofFF1 goes logic high, and N9 activatesthe SHIFT / LOAD inputs of theshift registers, IC4 and ICs. These loadthe 8 -bit datawords at their inputsA... H, and are switched to the SHIFTmode when the output of N9 goes high,which happens when the key is released.The MIDI dataword is converted toserial format, and shifted out via in-verter N4. Simultaneously, FF1 receivesa new clock pulse, and output Q revertsto logic low. Counter IC6 is clockedagain, and LED Di indicates that a newMS nibble may be entered via thekeyboard.The start and stop bit required in theMIDI dataword are obtained by connect-ing output QH of IC4 to input SER ofIC5. It is seen that SER on IC4 is madepermanently logic high, together with

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inputs A ...F incl. (these are the 6 non-used bits of the 16 -bit shift registerformed by IC4-IC5). The shifting out ofbits applied to the parallel inputs is fol-lowed by that of the bit applied to SER,so that IC4 supplies a series of logichigh pulses after the 4 databits. After afew clock pulses, these bits are also pres-ent on the serial output of IC.. Togetherwith input bit H of ICs (a permanentlogic "1"), these form a series of stopbits. The start bit is loaded into ICI asthe logic low level permanently appliedto input G. The complete MIDI com-mand is, therefore, defined by the paral-lel data received via inputs G, F...A(IC5), G, H, F... A and SER (IC4) inthat order.Finally, preset Pi enables accurately set-ting the serial bit rate on the Inoi ourline to 31.250 Kbit/s.

Construction and use inpracticeA prototype of the MIDI code generatorwas constructed on a piece of veroboardas shown in the accompanying photo-graph. The wiring was made in thin en-amelled copper wire, fitted at the rearside of the board. The DIN socket andthe 16 Digitast keys are convenientlymounted direct onto the component sideof the board. The circuit is best fitted ina sturdy enclosure if portable operation

Parts list

Resistors (±5%):Rulis;Rs=220RR2=3K3R3= 180K114=4K7R7=18KPi =25K or 22K preset

Capacitors:

Ci =1n0C2 = 470nC3= 220nC4=100p; 16 VC5 . .Ca incl=100n

Semiconductors:DO2= LED03= 1N4148ICI =74HCT154IC2=74HCT173IC3 = 74HCT74IC4;1Cs=74HCT165ICs = 74HCT93IC7=74HCT132ICa=74HCTO4Ti =BC547

Miscellaneous:

Ki = 5 -way DIN socket for PCB mounting.Si ...Ste Digitast key (ITT Schadow).Veroboard as required.Note: it regretted that a ready-made PCB for

this project is not available.

38 EE

April 1988

MIDI - frequently used codes System Messages

Note: all codes are given in hexadecimal notation

Channel Voice Messages

STATUS DATA DATA

80...8F 00...7F 00...7F NOTE OFF I+ channel number) + note number+ VELOCITY

90. . . 9F 00...7F 00.. .7F NOTE ON (+ channel number) + note number+ VELOCITY

AO...AF 00...7F 00...7F POLYPHONIC KEY PRESSURE/AFTER TOUCH

(+ channel number) + note number +PRESSURE VALUE

80...8F 00...79 00...7F CONTROL CHANGE I+ channel number) +CONTROL + VALUE

CO...CF 00...7F PROGRAM CHANGE I+ channel number) +PROGRAM

DO...DF 00...7F CHANNEL PRESSURE/AFTER TOUCH I+

channel number) + VALUEE0...EF 00...7F 00...7F PITCH WHEEL CHANGE I+ channel number)

+ CHANGE LS8 + CHANGE MSB

In each message, the four least significant bits designate the channel number(1...16 incl.; 0=channel 1; F =channel 16). Example: 97=NOTE ON forchannel 8. The status words given below are always followed by one ortwo databytes (<80) as required.

Note numbers:6C 1108):60 (96) :

45 (69) :

3C (60) :

24 136) :

18 (24) :

15 (211 :

DOH high (88 keys)DOH high (61 or 73 keys)LAH 440 HzDOH from keyboard centreDOH low (61 keys)DOH low 173 keys)LAH low (88 keys)

VELOCITY:0 : NOTE OFF (do not use 0 as default value)1 : ppp (pianissimo)40: mpmf (mezzo -forte); default value7F: fff (fortissimo)

FO SYSTEM EXCLUSIVE (consult documentation supplied withequipment)

Fl ...F7FlF2

F3F4... F5F6

F7

SYSTEM COMMONnot definedPOSITION POINTER I+ 2 databytes)SONG SELECT 1+ 1 databytelnot definedTUNE REQUEST

EOX (marks the end of message SYSTEM EXCLUSIVE)

F8... FF REAL TIME

F8F9

FAFB

FC

FD

FE

FF

TIMING CLOCKnot definedSTARTCONTINUESTOP

not definedACTIVE SENSINGSYSTEM RESET

Channel Mode Messages

BO. _BF 7A...7F 0...7F CHANNEL MODE I+ channel number) +MODE + MODE

130...8F 7A 0 CHANNEL MODE (+ channel number) +LOCAL CONTROL OFF

80...BF 7A 7F CHANNEL MODE 1+ channel number) +LOCAL CONTROL ON

90...BF 7B 0 CHANNEL MODE I+ channel number) + ALLNOTES OFF

80...8F 7C 0 CHANNEL MODE I+ channel number) + OMNIMODE OFF (ALL NOTES OFF)

80.. BF 7D 0 CHANNEL MODE I+ channel number) + OMNIMODE ON (ALL NOTES OFF)

130...8F 7E 0...F CHANNEL MODE I+ channel number) +MONO MODE ON (POLY MODE OFF) (ALL

NOTES OFF) - NUMBER OF CHANNELS(0=all receiver channels)

80...8F 7F 0 CHANNEL MODE I- channel number) + POLYMODE ON (MONO MODE OFF) (ALL NOTES

OFF)

is envisaged. The supply voltage for thecircuit is obtained from a NiCd batteryor a suitable mains adapter.Set Pt to the centre of its travel, and thecode generator is ready for testing in aMIDI environment. The MIDI outputon the generator corresponds to a stan-dard arm! OUT connection, and can beused for feeding otherwise unavailablecodes to certain equipment. Similarly,the code generator can be used in con-junction with an expander for realizingMIDI functions not supported by a stan-dard MIDI keyboard.

Use a standard MIDI cable for connect-ing the code generator to an instrumentthat is known to respond to, say, theNOTE ON/NOTE OFF command.Program this instrument to listen toMIDI channel 1, and send the followingcode sequence:

90 3C 40.The function of these three bytes is asfollows (also consult the accompanyingoverview of frequently used MIDIcodes):

90 selects the NOTE ON mode on chan-nel 1;3C is the note number ("doh" from thecentre of the keyboard);40 is a commonly used velocity code.Carefully adjust the oscillator clock fre-quency if this does not work. Ifnecessary, use a frequency meter connec-ted to the output of N3 to set the clockoscillator to 31,250 Hz.End the played note by typing:

80 3C 40.

Some useful articles on MIDI:

Fantasia on a MIDI theme. Elektor Elec-tronics November 1985, p. 52 ff.MIDI expander from Bohm. ElektorElectronics March 1986, p. 21 ff.MIDI split control. Elektor ElectronicsMarch 1987, p. 31 ff.MIDI signal redistribution unit. ElektorElectronics May 1987, p. 20 ff.

EE

April 198839

TEST & MEASURING EQUIPMENT

Part 1: dual -trace oscilloscopes (E)

The final article in Julian Nolan's review of dual trace oscilloscopesdeals with the Hung Chang OS -635.

The Korean company of Hung Chang is,perhaps, better known for its range ofDMMs, frequency sources, andcounters, some of which are sold undera variety of retail trade names.The Hung Chang OS -635 is a 35 MHzdelayed sweep oscilloscope with a 6 kVCRT retailing at £399 (excl. VAT), whichis only about £80 more than one wouldexpect to pay for a 'basic' 20 MHzmodel.The delayed sweep is of the 'coarse' var-iety; the instrument is also fitted withtrigger hold -off and single sweep modes.The OS -635 is fitted with a standard IECmains socket. The line voltage is exter-nally adjustable to 100, 120, 220, or240 VAC.The instrument is not fitted with a swivelstand, but the single position stand pro-vided instead allows easy stacking of theunit.The OS -635 is of average depth andwidth: 352 mm and 294 mm respect-ively, but its height of 162 mm is perhapsrather more than might be expected.Two high -quality probes (1.4 ns rise timewhen in 10:1 attenuation mode) are sup-plied as are accessories for use withthem, including a BNC adaptor andspring -loaded clip.

Front panel. The front panel is probablyone of the OS -635's most distinguishingfeatures, with colour -coded sectionssuch as triggering and Y -amplifier func-tions. Although the colour coding addsto the ease of operation, the panel is not,as common, anodised, but the markingshave been printed on. This, togetherwith the exposed potentiometer bushesof some controls, gives the instrument arather rough and ready appearance.However, this certainly does not meanthat it is of low quality.

Y -amplifiers. The attenuation coef-ficient of both Y -amplifiers is variableover a range of 10 V/div to 5 mV/div. Inaddition to this, a x 5 magnification fa-cility is also available, enabling maxi-mum sensitivities of 1 mV/div to beachieved.Undoubtedly, one of the main featuresof the OS -635 is its 35 MHz bandwidth.

This is maintained down to 5 mV(-3 dB). The 1 mV/div sensitivity bringswith it the restriction of a 10 MHz band-width (rise time 35 ns).Both Y -amplifiers have a continuouslyvariable attenuation control, which in-creases the maximum attenuation coef-ficient to 30 V/div. Only one channel canbe inverted.The performance of the Y -amplifiers isreasonable in terms of frequencyresponse and bandwidth, given theirrelatively high frequency range. But,despite these mediocre characteristics,they are still undoubtedly better than theaverage 20 MHz Y -amplifier at this pricelevel.Despite being specified at 3%, overshootis particularly evident on some ranges,although it remains within the quotedlimit.The dynamic range is somewhat limitedat about 41/2 divisions at 35 MHz, butshould, none the less, be acceptable formost purposes.A minor point is that the x5 magnifierhas the effect of magnifying the traceoffset, which is set by the Y positioncontrol, with the result that some repo-sitioning of the trace is required whenthe x 5 magnifier is actuated.Since the x 5 switches are incorporatedin the Y position controls, it happensthat when these controls are accidentally

turned when they are pulled out to actu-ate the x5 magnifier, the trace shifts. Ifthis has already been centred, an un-necessary adjustment is required to re -centre it.Chopped (200 kHz) or alternate sweep isselected automatically by the time basespeed setting.

Triggering. Triggering on the OS -635 iscomprehensive, including LF and HFfiltering, alternate channel sourcing andTV synchronization. In addition to this,unusually for a scope in this price range,an external +10 facility is also provided.The auto/normal and triggeringthreshold controls are combined intoone in a similar manner to the x5 at-tenuation coefficient magnifier. Here,the problems brought about by this arenot so acute, but still noticeable; theauto position is selected with the levelcontrol fully out. All other triggering.controls (of the slider type) are, however,relatively easy to operate.TV triggering is particularly notable, be-ing selectable from positive or negativesynchronization and, with the inclusionof automatic line and frame switching,incorporated into the timebase coef-ficient selector. Triggering sensitivity isalso good: typically 0.2 div to 10 MHz,increasing to 1 div at 35 MHz and 3 div

40 EE

April 1988

Table 17.

ELECTRICAL CHARACTERISTICSline voltage: - 100, 120, 220, 240 VAC

± 10%, externally adjustable. Powerconsumption: 30 Watts

Line frequency: 50-60 Hz

MECHANICAL CONSTRUCTIONDimensions: - W 294 mm, H 162 mm,

D 352 mmHousing steel sheetWeight: approx. 7.5 kg

Y AMPLIFIER ETC.Operating modes: -CH1 alone, CH2 alone.Inversion capability on CH2 only.Any combination of CH1, CH2 (alternateor chopped (250 kHz))

CH1 CH2Frequency response 0...35 MHz(-3 dB).

Risetime < 10 nsec, (35 nsec x 5 Mag.)Deflection factor 10 steps:5 mV/div...5 V/div ± 3%.

x 5 magnifier extends range to 1 mV/div,MHz bandwidth.

Input coupling: AC, DC or Gnd.Input impedance: 1 MQ/25 pF; max inputvoltage 300 (DC + peak AC)

X -Y MODECH1 X-axis and CH2 Y-axis. Less than 3°phase shift at 50 kHz

Bandwidth DC to 1 MHz (-3 dB).

SWEEPOperating modes - normal: timebase Adisplayed (no delay); intensified:timebase A intensified by trig delay overmagnification area; delayed: A sweepstarts after delay time.

A sweep time 100 ns/div to 0.5 s/div±3% in 21 ranges; 1-2-5 sequence;vernier control slows sweep down by uptp 2.5:1.

Delay time - 10 ms to 1 ps in 5 steps,1:1 sequence; variable control for fineadjustment.

Sweep magnification - x 5 ± 10% totalerror.

Hold off - variable up to 10:1.Delay modes - continuous delay.Delay jitter - 1/5000.Single sweep facility.

TRIGGERINGTrigger modes - auto and normal.Trigger coupling - AC; DC; HF reject; LF

reject; TV frame and line (auto).Trigger sources - Ch; Ch2; alternate;line; ext.; ext/10.

Triggering sensitivity - internal: 1 div at35 MHz; external: 0.2 Vpp at 35 MHz.

MISCELLANEOUSCRT - measuring area 80 x 100 mm;accelerating voltage 6 kV; metal backed;PDA.

Compensation signal for divider probe -amplitude approx. 0.5 Vpp ±3%; fre-quency 1 kHz.

Z modulation sensitivity - 3 V (completeblanking).

Warranty - 1 year.

at 60 MHz, which is the maximumreliable trigger frequency. External trig-ger sensitivity is also good at 100 mV to10 MHz and 0.2 V to 35 MHz. This can,however, be increased by means of the+10 control to eliminate false triggering,caused, for example, by noise. An alter-nate channel, or composite mode, is alsoincorporated for observation of twounrelated (in terms of frequency) signalsources. Triggering symmetry (rising orfalling slope) proved to be out by ap-proximately 1 division over a total ver-tical deflection of 8 divisions. The HFand LF facilities provided are effective inobtaining a stable trace even in cases ofwaveforms with a very high modulationcontent, and are a further useful ad-dition to the OS -635's trigger functions.Both trigger and 'ready' LEDs are alsoincorporated, lighting when the scope isstably triggered or reset respectively.Trigger holdoff is also a feature of theOS -635, which makes the triggeringfacilities provided by this scope amongstthe best in its class.

Timebase. The OS -635 is equipped witha single timebase and an uncalibratedvernier delay time control. This has theconsequence that in the vast majority ofsituations only uncalibrated delayedsweep measurements can be made ofwaveforms which exceed the maximumhorizontal deflection limit of 10 div-isions. In most cases this limitation doesnot affect the measurement of waveformrise times.The main timebase itself ranges from arespectable 0.5 s/div to 100 ns/div,although, obviously to limit the cost ofthe deflection circuitry, only a xhorizontal magnification system hasbeen incorporated, increasing the maxi-mum deflection speed to 20 ns/div. Thetrigger delay time coefficient can beselected from one of 5 (the front panel ismarked for 6) covering the range from1 sec to 100 msec in a 1:1 sequence. Thisdeparture from the standard 1-2-5 se-quence is false economy since, althoughit reduces the number of switch positions

to 5 instead of 15, highly accurate ad-justment of the vernier control is re-quired at higher magnification levels. Italso has the effect of reducing the easeof use of the delayed sweep facilitysignificantly in my opinion, largely dueto the accurate vernier adjustmentswhich have to be made. Rise timemeasurements would have been greatlyhelped by the provision of a triggereddelay facility in addition to the normalcontinuous mode, as well as a delay line.Looking at the situation in perspectivehowever these facilities can hardly be ex-pected for £399, but effective operationof the delayed sweep facility withoutthem may in many applications prove ex-tremely difficult. The delayed sweep dis-play modes of normal, intensified ordelayed should be adequate for mostpurposes.Timebase accuracy is inside the specified±3% (and the rather high ±10% whenusing the x 5 magnifier). Linearity isalso within the quoted ±3% over mostof the range, although it is noticeable atthe start of the trace over the first 11/2small divisions on the maximumtimebase speed that the deflectioncharacteristics were, to say the least,non-linear.

CRT. The 6 kV tube enables both goodintensity and brightness to be main-tained over the whole range of sweepspeeds. The CRT itself is of the metalbacked PDA variety and gives a goodperformance, especially in terms offocusing, which is certainly of a highstandard. The tube is slightly curvedacross its face, howevei, and while this isnot to a great degree, and should not af-fect measurements, it is still worthnoting. Tube geometry is reasonable,with some barrelling and pincushioningpresent. The tube's good performance ishindered by the lack of an automaticfocusing circuit, with the consequencethat any major alterations in tubebrightness can cause considerabledefocusing of the trace, making someform of focus adjustment essential for

Table 18.

CATEGORYUnsatis-factory

Satis-factory Good

VeryGood Excellent

TRIGGER FACILITIESTRIGGER PERFORMANCEDEL'D SWEEP FACILITIESDEL'D SWEEP PERFORMANCECRT BRIGHTNESSCRT FOCUSINGY AMP ATTENUATION RANGEINTERNAL CONSTRUCTIONEXTERNAL CONSTRUCTIONOVERALL SPECIFICATIONOVERALL PERFORMANCEEASE OF USEMANUAL

x

xx

x

xx

x

xx

x

x

x

x

accurate measurements.

Construction. Construction of the OS -635 is poor. While mostly not of lowquality, the OS -635 is in places poorlyfinished, with a number of sharp edgesevident on the enclosure both internallyand externally. Internally, masking tapeand small pieces of dowelling are used toseparate some of the wire interconnec-tions, which, while perhaps not impair-ing the reliability of the instrument, arereally unacceptable in a modern instru-ment.External construction is based on a steelchassis, with two sheet steel panelsenclosing the top, sides and underneathof the scope. These appear to have hadlittle done to them in terms of machiningsince being originally pressed and foldedsince they still contain one or two sharpedges. The front panel surround is con-structed from four separate pieces ofaluminium with the consequence thatthey are joinded at each corner.Internal construction is of a higher stan-dard, with the high voltage and EHTsupplies enclosed, and the Y -amplifierspartially screened. The scope is basedaround four PCBs, connections fromwhich are all made by connectors foreasier servicing and while this leads to alarge number of interconnections, itshould not affect reliability. As well asbeing used to separate some of the inter-connections, masking tape is also usedaround the CRT.Overall construction both internally andexternally appeared to be average in its

class, and whether this will effect the re-liability remains to be seen. The qualityof components used is generally goodand this may be worth taking into ac-count.

Manual. The 30 page manual includes afull circuit and PCB layout diagrams. Afull circuit description and initial set upinformation is also given, along withcalibration and preventative mainten-ance sections.

Conclusion. Looking at the specificationalone, the OS -635 appears to represent aextremely good price/performance ratio,with a 35 MHz (-3 dB) bandwidth,6 kV PDA tube and delayed sweep fa-cility. In reality, some of these facilitiesare limited in their performance, whichis especially true of the delayed sweep fa-cility, which in some situations offerslittle more than can be achieved with ascope that possesses a good trigger per-formance. Having said this, both thetriggering performance and facilities of-fered by the OS -635 are good for a scopein its class and should not be ignored.An automatic focusing circuit is not fit-ted, which is unfortunate since the 6 kVPDA is capable of producing a trace ofboth excellent intensity and sharpness,but to maintain this without the pro-vision of an automatic focusing circuitrequires an adjustment in the focusingpotential for a significant change intrace intensity. Both the internal and ex-ternal construction have the appearanceof a preproduction prototype rather than

EE

April 1988a production model, but despite thisthere is not apparent reason why the OS-635 should not be reasonably rugged ina variety of environments. To sum up,for its specification the Hung Changrepresents a very good price/perform-ance ratio, its particular strengths lyingin its 6 kV CRT and 35 MHz bandwidth.The OS -635 may well be worth consider-ing for a large number of applicationswhere a bandwidth of 35 MHz and highbrightness tube are required on a limitedbudget, or as a cost effective alternativeto a 20 MHz scope.

The Hung Chang OS -635 was suppliedby Black Star Ltd. 4 Harding Way St. Ives HUNTINGDON PE17 4WR Telephone (0480) 62440

Other oscilloscopes available in theHung Chang range.OS -615S - dual trace 15 MHz portable;rechargeable battery operated; weight4.5 kg; sensitivity 2 mV; maximumdeflection speed 100 ns/div; 1.5 kV CRT;up to 2 hours operation from fullycharged batteries; £399 excl. VAT.

OS -620 - dual trace 20 MHz; sensi-tivity 5 mV; maximum deflection speed40 ns/div; 2 kV CRT; component tester;power consumption 19 W; £295 excl.VAT.

OS -650 - dual trace 50 MHz; sensi-tivity 1 mV; n1aximum deflection speed40 ns/div; 17 kV CRT; delayed sweep100 ms to 1 Ns; £579 excl. VAT.

INSTRUMENT NEWSProgrammable synthesizer/function generatorCrystal -controlled long-term stabilityand reproducibility are two of the majorbenefits offered by the Philips PM5191proarammable synthesizer/function gen-erator now available from ElectronicBrokers Dorcan House MeadfieldRoad LANGLEY SL3 8AL Tele-phone (0753) 44878.

IEEE488 (GPIB) Bus Analyserfrom ThuribyThe Kenwood LA -1910 GPIB Bus Ana-lyser is available from Thurlby Elec-tronics Ltd New Road St. Ives HUNTINGDON PE17 4BG Tele-phone (0480) 63570.

Data Line MonitorThe Comtest DLM 100 Data Line Moni-tor, a time and trouble saving tool formonitoring RS232 communications, isavailable from M -Trade (UK) Ltd P.O.Box 35 LONDON SW1W 8TX Telephone 01-730 0681.

Sine -wave invertersAbulon have launched a new range ofportable, low-cost, high -quality staticsine -wave inverters for operation frommains or 12/24 V DC supplies. Detailsfrom Abulon Electronic Systems Unit233 Stratford Workshops BurfordRoad LONDON E15 2SP Tele-phone 01-47- 9644.

AF Power Meter from CrotechA new AF power meter, Type 2018, canmeasure outputs of up to 150 W into 4,8, or 16 ohms loads and is available fromCrotech Instruments Ltd StephensonRoad St. Ives HUNTINGDONPE17 4WJ Telephone (0480) 301818.

New storage unit forSchlumberger Data LoggerIn response to market demand,Schlumberger Instruments has upgradedits industry -standard Solartron Orionseries data loggers, introduced a newdata storage medium to improve loggingspeed and transportability of results.Schlumberger-Solartron 'VictoriaRoad FARNBOROUGH GU14 7PW Telephone (0252) 544433.

Dual -channel signal analyserfrom Bruel & KjaerBy bringing new flexibility and ease ofuse to fast Fourier analysis, the 2034dual -channel signal analyser makes thisfast and precise technique useful inmany more sound and vibrationmeasurement applications.Bruel 8 Kjaer (UK) Ltd HarrowWeald Lodge 92 Uxbridge Road HARROW HA3 6BZ Telephone 01-954 2366.

Single function instrumentsfrom ITTNew from ITT Instruments is the MXseries of single function instrumentswhich are suitable for a wide range ofprofessional and laboratory appli-cations. The range comprises the MX029voltmeter, the M039 ammeter, and theMX038 centre zero ammeter. ITT In-struments 346 Edinburgh Avenue SLOUGH SL1 4TU Telephone (0753)824131.

42 EE

READERSHIP SURVEY RESULTS

As already reported in last February'sissue, the response to the ReadershipSurvey has been very good. Now that thereplies from many overseas readers havealso been analysed, it is possible to ex-pand on the early results published inFebruary. The general trends then indi-cated have, in the main, been confirmed.Once again, we would like to express ourthanks to all those readers who took thetrouble to complete the questionnaire.

Your likes and dislikesApart from electrophonics, the interestsof readers are fairly evenly dividedamong the other nine areas listed. Thetop three "likes" are, however, Test &Measurements (1); Computers (2); .andAudio & Hi-fi (3).

How interesting do you findthe following features?

Editorial. The vast majority of readersthink this a worthwhile feature. To manyit is a must, but about 7% find it a wasteof paper.News. More than half the readers thinknews coverage is just about right.Another 9% consider it a must; yetanother 20% want more; but to 6% it isa waste of paper.Book reviews. About half the readersfind this column just about right, butanother 35% want more space given toit. Six per cent think the feature is awaste of paper.New products. More than half thereaders think coverage is just aboutright; to 10% the column is a must.Another 33% want increased coverage,but nearly 3% find it a waste of paper.Letters. Interest in this column is dividedbetween those who think coverage isabout right (48%) and those who wantmore letters (30%). Around 4% think ita waste of paper.Reviews. Some 40% of readers find thereviews useful, but another 24% wantmore and yet another 24% want fewerreviews.Projects. Nearly all readers think thatconstructional projects are a must, andabout 25% of hem want to see more.Informative articles on:(a) electronics - to a large number ofreaders, these articles are a must (39%),and many others (49%) want to see morespace dedicated to it. Not surprisingly,only 1.2% want less coverage, and nonethinks these articles a waste of paper;(b) telecommunications - more than16% of readers find this type of article

a must; 40% feel that coverage is aboutright; another 30% want increasedcoverage, but 10% want less spacededicated to it;(c) computing science - more than athird of readers feel that coverage isabout right; nearly another third wantmore. To over 17% of readers the col-umn is a must, but 12% want to see lesscoverage.(d) physics - over 41% of readers thinkarticles on this subject are fine; over 13%consider them a must; 29% want in-creased coverage; 9% want less spacegiven to it; and 7% find it a waste ofpaper.(e) general science - some 39% ofreaders like the coverage of this subject;to another 13% it is a must and yetanother 25% want increased coverage.Almost 11% want to see reduced spacegiven to it, and 9% think it a waste ofpaper.

Buying habitsVirtually all readers (95%) look in theadvertisements for components; 33%for measuring equipment; 39% for com-puter hardware and software; 26% forother commercial equipment; 36% forbooks; and 29% for tools.

Reading habitsTwenty-two per cent of readers read allarticles; 62% read most of them; and16% read a few of them.

Nearly 25% of readers read through allthe adverts; over 48% read most ofthem; and 26% a number of them.Twenty-seven per cent of readers obtainthe magazine by subscription; 63e/o buyit from a newsagent; nearly 5% buy itfrom a specialist electronics shop; andover 4% borrow it from their college oruniversity library.Once a subscriber always a subscriber?Perhaps, for 43% of subscribers havebeen for over 5 years, and another 33%for 3-5 years.Many readers are magnanimous people:almost 40% lend their copy of the maga-zine to one or more friends.

Readership profileOver half the readers are professionallyengaged in electronics, and about 20%of them list electronics also as one oftheir hobbies. Thirty-seven per cent ofreaders are hobbyists, and 12% arestudents.

Fifty-five per cent of readers are quali-fied electronics engineers or technicians(28.2% and 26.8% respectively).Another 7.6% are corporate engineers,but 37.5% have no formal qualification.Almost 28% of readers have a universitydegree, and a further 12% have an HNDor HNC. Another 15% are still studyingfor a qualification in electrical/elec-tronics engineering.

These are the cold facts of the survey,but much more information comes, ofcourse, from the comments most readershave added. More of these in a moment.As to the results shown, if we comparethe survey with a general election, wehave been given a clear mandate by ourreaders to continue publishing the maga-zine as it has been developed over thepast few years. That is not to say thatthere is no room for improvement. In-deed, we will keep the findings of thesurvey before us for a long time to cometo help us in our endeavour to give ourreaders what they want in the most ap-propriate and beneficial manner.Many readers have asked why we cannotpersuade retailers to stock kits of partsfor our projects.',We have tried, but didnot meet with much success or en-thusiasm. The UK, in contrast to manycontinental countries, has very few elec-tronics retailers operating at local level.Instead, we are served by many good orvery good mail order firms. Unfortu-nately, these are, in the main, not in-clined to stock kits; they are, of course,always prepared to make up a kit to in-dividual requirements.Other readers would like to see us hanga price tag on our projects. Regrettably,in the past that has not proved practical,in view of the widely varying prices fromarea to area and, indeed, from countryto country. None the less, this matter wilbe looked at again as differences may beless marked now.

The many suggestions for future projectswill all be looked at by our technicalassessment committee; no doubt a num-ber of them will come to fruition in duecourse.

Quite a few readers have asked for thereturn of our infocards. This is alreadyunder consideration, and the infor-mation will probably be restarted in theSeptember issue: this will, however, forcommercial reasons, not be on card, butcontained as a normal page in the maga-zine.

A good number of requests have come in

for more advanced test equipment proj-ects, while others are asking for somesimpler projects. Somehow, we will seehow we can satisfy these two opposingrequirements.

Some readers have complained about thecontents of the magazine being toomixed up. They are right, and we havealready started to do something aboutthat as a glance at the contents pages ofour February and March 1988 issues willshow.

We have been criticized for omitting in-formation on PCBs for projects thatwere published more than a year beforethe current issue. We sympathize withthose who feel inconvenienced by this,but would point out to them that asimple telephone call or postcard willnot only tell them whether a particularPCB is still available, but will also enablethe board to be reserved, if still availableand if so required.

Still on the subject of PCBs, other com-plaints are that we no longer publish`PCB pages'. Again, we sympathize withthose who miss these pages, but wouldadvise them that ever since we discon-tinued those pages, we have been offer-ing to send the relevant drawing (onpaper) free of charge. A number ofreaders have asked whether the drawingscould be made available on film: yes,they can, but in view of the cost in-volved, we will have to make a smallcharge for them.

A few readers deplore the demise of theso-called Summer Circuits, but far morewelcome the new format of our com-bined July/August issue. The latter feelthey now have the best of two worlds: a`normal' magazine, with all thebackground that is so necessary for agood understanding of electronics, and asupplement crammed with practical cir-cuits. To the many inquirers who haveasked for twelve monthly issues per yearwith a quarterly supplement containingreviews, a number of practical circuits,and so on, we say: "Patience, this matteris under active consideration in our com-mercial department". Regrettably, in thepublishing world, for all sorts ofreasons, such changes cannot take placeovernight: we are looking at next year, oreven the one after that.

Many of our overseas readers have askedfor a more international tinge to be givento component information and infor-mative articles in general. Readers in thiscountry may wonder why? The answer isthat we have almost as many readers inContinental Europe (often ex-patriates)as in the UK (that is, for the Englishissue: nothing to do with our sistermagazines published in most Europeancountries in their own language. This is,

of course, because English is the com-mon language of electronics).

Some readers feel that the magazine isgetting too technical and suitable for aselect few only. We do not see it thatway: after all, electronics, in all its facets(audio; radio & TV; telecommuni-cations, computer technology; etc) isgrowing at an unbelievable pace, and allthose who are working in it, and eventhose who are merely interested in it,have no option but to grow with it orleave the field altogether. To be engagedin practical electronics, be it as a pro-fessional or as an amateur, requires agood and thorough understanding of itstheory and continuous updating of itsbackground. There is no other way.

Those readers who feel that the letterswe publish are of no interest shouldknow that we only print those that wefeel will be of general interest. Such let-ters form only a small part of those wereceive regularly.

It is comforting to read from manyreaders' comments that there are nolonger the difficulties with obtainingcomponents there once were. Somereaders are still experiencing problemsfrom time to time, however, but wewould assure them that we will continueto try and improve the information givenwith the projects.

A great many readers have asked forsome information on Elektor Elec-tronics, and this is, therefore, perhaps agood opportunity to tell you a littleabout .ourselves.Elektor Electronics is not only the nameof the magazine, but also of thecompany responsible for the manaee-ment, production, and publishing of themagazine. Its editorial offices arelocated in Brentford, Middlesex(management, publishing) and Beek inthe southern Netherlands (production).The company is one of four whoseholding company is Elektuur By, itself acompany within the Wolters KluwerGroup. This group owns a number ofpublishing companies in theNetherlands, Germany, France, the UK,and the United States. Apart from ourthree sister companies operating inFederal Germany, France, and theNetherlands, we have associates inAustralia, Brazil, Finland, Greece, In-dia, Italy, Portugal, Spain, and Sweden.Each of the thirteen magazines deter-mines its own editorial policy, which isthe responsibility of the relevant editor.Most of the contents of the magazine arethe result of a busy international designand development department in Beek.There, a team of ten qualified engineersand technicians is responsible Tor themajority of the constructional projectsthat appear regularly in the magazines.

EE

April 1988

These original articles are written inDutch, English, French, or German, andtranslated by professional translatorsinto the other languages. The writers areinvariably native speakers of thelanguage in which they write. A notableexception is our technical editor, JanBuiting, who has a degree in Englishhowever and is bilingual. The remainderof the editorial staff of Elektor Elec-tronics is English.Apart from the original projects de-signed in Beek, and in line with thefreedom of editorial policy, themagazines are free to buy appropriateconstructional projects or descriptive,informative, or educational articles fromfree lance authors. Elektor Electronicsmakes more use of this opportunity thanits sister magazines. Few major intern-ally generated projects are not publishedhowever.Interests of the editorial staff vary wide-ly and range from amateur radio & TV(including satellite TV reception),robotics, computer chess, and elec-trophonics, to simpler things like music,stamp collecting, history, and ecology,not forgetting squash, swimming, andpot -holing. Many of the staff are avowedelectronics enthusiasts who spend mostof their time with a soldering iron orcalculator in their hands or in front of acomputer monitor.

It is, of course, impossible to deal withmore than the most frequently en-countered comments. However, we willtry and deal on an individual basis withthe comments so many people took thetrouble of passing on to us.

EVENTS

12-14 April Scottish Computer Showat the Scottish Exhibition and

Conference Centre, Glasgow. DetailsfromCahners Exhibitions LtdChatsworth House59 London RoadTWICKENHAM TW1 3SZTelephone 01-891 5051

26-28 April British Electronics Week(incorporating the All Elec-

tronics Show; Electronic Product De-sign; Fibre Optics; Circuit Technolo-gy; Automatic Test Equipment; andPower Sources and Supplies) atOlympia, London. Details fromEvan Steadman (Services) LtdThe Hub9 Emson CloseSAFFRON WALDEN CBIO 1HLTelephone (0799) 26699

o.ACTIVE LOUDSPEAKER SYSTEM

The loudspeaker system published last month is ideal for beingcombined with the active phase linear network published last

year and Sanyo's new series of output amplifier modules.

The closed box design for the UniphaseLoudspeaker System (" is ideal for anactive three-way system based on theAc-tire Phase -linear Cross -over Networkand Sanyo's Type STK-4036XI 50 -wattoutput amplifier module. The position-ing of the drive units in this box is suchthat the phase differences at the cross-over points of the three units is virtuallyzero. This further accentuates the ex-cellent phase behaviour of the phase-linear network.Many output amplifier modules havenot been well received by some audiodesigners in the past. Much depended,of course, on the type and manufacturerof these devices. However, the manufac-turers have not been idle, and nowadaysthere are a number of excellent moduleson the market. For a number of reasons,the choice for the present design hasfallen on Sanyo's STK-4036X1.The design also incorporates a sophisti-cated protection circuit that wasoriginally published in 198931.

The STK-4036X1Most output amplifier modules arehybrid circuits and the STK-4036XI is noexception. In essence, a hybrid module isnothing but a small board onto which anumber of chips and passive compo-nents have been mounted, after whichthe whole has been encapsulated.The new Sanyo series of output ampli-fier modules is identified by the lettersXI following the type number. The seriesconsists of 7 models, STK-4036XI toSTK-4048X1, which provide outputsfrom 50 W to 150 W, all into 8 ohms. Asurvey of the entire series is given inTable 1. A noteworthy characteristic inthe table is the very low harmonic distor-tion of the modules.Compared with the previous models, theXI series has been extended internally asshown in Fig. I, which illustrates thetypes 4036XI to 4042X1.The input stage consists of a differentialamplifier, Tr3 and Tr4, which is loaded bycurrent mirror Tri:Tr2. The signal at thecollector of Tr3 is applied to cascodeamplifier Trs-Tr2. The DC setting of theinput and cascode stages is effected bytwo constant -current sources, Trs andRS.

The output stages consist- of transistorsTrio -Tr -13. In the XI series, in contrast tothe previous models, complementarytransistor pairs are used, which is a goodstep forward.Darlington Trs provides the quiescentcurrent setting. Not, perhaps, anoriginal idea, but it is reliable and gener-ally gives good results.The additional material required isshown in Fig. 2. It consists mainly of thepower supply (2b) and a number of highwattage resistors, electrolytic capacitorsand frequency compensation compo-nents. The latter are omitted from themodule deliberately by the manufacturerto give designers the freedom to deter-mine the bandwidth of the amplifier.When reading through the description ofFig. 2, it is advisable also to glance atFig. 1 from time to time to see what isconnected inside the module to thevarious pins.The symmetrical supply for the moduleis applied to pins 12 and 14. The pre-amplifier stages are powered by a voltagederived from the main supply via pins 5and 15. Networks 122-C9 and Rs-C11re-duce the effect to the preamplifier stages

of voltage variations in the main supply.A feedback circuit, including active DCcorrection provided by integrator IC2, isinserted between the output (pin 13) andthe inverting input (pin 2). The amplifi-cation of the module is determined bythe ratio It3:1Z4. With the values of thesecomponents as stated, the gain amountsto just under 27 dB.The output signal from the module isalso applied to low-pass filter R14-C1sand then compared in IC2 with the Qpoint of the amplifier. Any deviationsare fed to the inverting input of themodule (pin 2) via R13. This arrange-ment obviates the need for an electro-lytic capacitor in the feedback loop,which is distinctly noticeable in the qual-ity of the reproduced sound").Capacitors in the input circuit are MKTor MKH types to avoid the use of elec-trolytic ones in the signal path. NetworkRI -C-1 limits the bandwidth of the inputsignal to minimize the likelihood of in-termodulation distortion in the ampli-fier.Network Rs -Cs between pins 8 and 11limit the bandwidth of the differentialinput amplifier. Capacitors Cs, Cs, and

1

80

TR

15

7 R2

11 0-

1 0

206 0

40

Pv1123 TR1.

Ri

30 TRS.9

TR7 RIO

R3R7

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SUB 05

1R9

R9

R11

09 10

0 14

TR 13

TRI2

0 13

012

880030-1

Fit!. 1. Circuit diagram of the Sanyo STK series output amplifier module.

EE

April 1988Table 1.

Max.values

Recommendedvalues

THD forPoirnao = 50 W

No. of Us into Gain Potmaxi THD Nam*Type pins Us Ts RL = into f = 20 Hz...20 kHz into 4 Q

8 AY 8 Q Av = 26 dB Av = 40 dB f = 1 kHz

V °C V dB W % % WSTK 4036X1 ± 53.5 125 ±37.0 26-45 50 0.003 0.008 55STK 4038X1 ±58.0 125 ±40.0 26-45 60 0.003 0.008 60STK 4040X1 15 ± 63.0 125 ±43.5 26-45 70 0.003 0.008 70STK 4042X1 ±67.0 125 ±46.5 26-45 80 0.003 0.008 80STK 4044X1 ±74.0 125 ±51.0 26-45 100 0.003 0.008 100STK 4046X1 ±80.0 125 ±55.0 26-45 ' 120 0.003 0.008 120STK 4048X1 18 ± 87.0 125 ±60.0 26-45 150 0.003 0.008 150

2a

b

RI

635

15

C2 202

CI R2

OMB470p

R7

ECM

cal 136

100p

11

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STK4036 XI

145C11

9

c7 CIO

1000 10163V *see feel

7

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MIN1° R11*

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CS C6

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100563V

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Fig. 2. Circuit diagram of the complete output amplifier.

C7 further limit the frequency responseof the module.Resistor Ril forms a common emitter re-sistance for the output transistors. Nor-mally, each of the push-pull halves hasits own emitter resistance, but Sanyo haschosen a different approach.Inductor Li, wound on resistor R9,prevents excessive currents withcapacitive loads. Boucherot networkRio -Cu ensures that the output stagesremain properly loaded at high fre-quencies, since the loudspeaker im-pedance then rises sharply.The power supply is of conventionaldesign which needs no further expla-nation.Tests on a couple of prototypes gave ex-cellent results as can be seen from Table2.The design uses three identical circuitsbased on a 50 -watt module, fed from acommon power supply. It is, of course,possible to use lower rated modules forthe mid- and high -frequency outputstages, but these would then need aseparate power supply, which makes thedesign more expensive.

Cross -over networkThe cross -over filter is identical to thatin Ref. 2, but its circuit diagram isreproduced here for convenience's sake.It should be noted that the values of thecomponents give change -over points at370 Hz and 3200 Hz.

Protection circuitThe protection circuit is very nearlyidentical to that in Ref. 3, but its circuitdiagram is reproduced here for con-venience's sake. Compared with theoriginal circuit, two components havebeen added: a resistor and a diode inseries between the junction of R16 -S,and pin 13 of IC3 (N9). These additionalcomponents ensure that the circuitoperates immediately after a reset (theoriginal circuit delayed this until a newaudio signal had been input).Furthermore, the temperature monitor,

46 EE

April 1988

Al2, Ala=lC2=TQ72AM/ADA-CS rTS7372AI = ICS= 11071A.S. AS =1CSc 71.072AA Al =lei=T072A3, Al = iC7=TLOTSAZ AG =CA =T072

Fig. 3. Circuit diagram of the phase -linear cross -over network.

IC11, of the original circuit has beenomitted, since the modules have such alarge heat sink that overheating is for allpractical purposes impossible.Otherwise, the monitoring circuits con-trol virtually everything in the amplifier:as soon as a signal appears at the input,the supply is connected to the outputstages. In the absence of a signal formore than five minutes, the supply isswitched off again. Also, during normaloperation, the DC setting of each outputstage is monitored separately.

Combining the circuitsFirst, of course, all printed circuitboards should be populated. The boardfor the output amplifiers is shown inFig. 5. Inductor Ll consists of 3 layersof 10 turns each wound onto Re from1 mm diameter enamelled copper wire.Where higher wattage modules 4046X1or 4048X1 are used, resistors Rita to Riicshould be added, because these moduleshave parallel connected output tran-sistors. With modules 4036X1 to 4044XI

only resistor Rli is required. Themodules should be mounted last of all:do not shorten their pins.When populating the filter board, takecare to solder all resistors in their correctpositions: I% metal film resistors oftengive problems in this respect. It is ad-visable to check each of these resistorswith an ohmmeter.The addition of the resistor and diodeon the protection board should notcreate any problems.When the five boards have been com-pleted, they should be fitted in a suitableenclosure. That for the prototypes en-abled it to be fitted at the rear of theloudspeaker enclosure. This ensured thatthe connecting wires between loud-speakers and output stages were kept asshort as possible. It is, of course, alsopossible to install all circuits at the bot-tom inside of the loudspeaker enclosure.The wiring diagram for the entire elec-tronic part of the loudspeaker system isshown in Fig. 6. Note that there is onlyone central earthing point: it is import-ant to stick to that to avoid earth loopsbetween the screened cables. The screens

of these cables should be connected toearth at only one side.Good care should be taken, as always, toensure that any mains -carrying parts andwiring should be well insulated.The output modules may be screwed toa large heat sink without insulation, butwith copious use of heat conductingpaste.The input socket should be isolated fromthe box.If, as proposed, the boards of the filterand protection circuits are mountedabove one another, they should beshielded from each other by a suitablemetal plate. This is necessary to preventthe protection circuits causing inter-ference in the filter (this happened in theprototype, and it took a day to find theculprit).Once everything is completed, thesystem should be tested without theloudspeakers. When the mains isswitched on, the reset button of the pro-tection circuits must be pressed to startthese circuits.If everything is found in order (particu-larly, there should, of course, be no DC

4

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n:13

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EE

Aprii 1988

Parts list(for each of the 3 output amplifiers)

Resistors:

Ridie=1k0R2;1:113=33 k

R3=12 kRa= 560 RRs= 10 k117;Ra = 100 R

R.= 10 Ril WR,5 =4R7

Rts=0R22; 5 WRe2;R14 = 1 M

fi1s;Fit6=2k2

Capacitors:

C1=470 pCz=2p2 (MKT)Cs=6p8C4=1/10 (MKT)Cs=1n0Cs;C;;Cs =100 pCs;Co = 100 p; 63 VCio;C12=10p; 63 VCt3= 100 nCit;Cis= 220 nCir;Cir= 100 p; 40 VCiECte= 2 x 10,000 p; 40 V

Semiconductors:

01;02=1N4148DED4=15 V; 1 W; zerterICI=STK-4036X1IC2=LF411B, = BYW64

Miscellaneous:

Mains transformer 2x25 V;4.5 A secondaryRel.Re2= 12 V; 1 make (contact 250 VAC;5 A)

Re3= 12 V; make (Contacts 250 VAC; 6 A)Fuse, 2 A, delayed actionFuse, 0.5 A, delayed actionMains switch, DPSTPCB 880030 (3PCB 85120PCB 87109

000000000000000-,.:

a 1 =11 1 b

' r411c.a

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EE

April 1988Table 2.

Prototype measurements

Power output OIL = 8 QISignal-to-noise ratioBandwidth 01'0=1 WITHD (P0=1 WI

Input sensitivityOutput impedance

: 50 W:> 110d8

3 Hz...150 kHz ( -3 dB): < 0.005% (1 kHz)

< 0.03% (20 Hz...20 kHz): 1 VMS

< 0.02 4 (20 Hz...20 kHz)

on the output terminals), the outputamplifiers may be connected to the out-put terminals (but not yet to theloudspeakers).The operating sensitivity of the protec-tion circuits is set by Pi.All potentiometers on the filter boardare then set for minimum attenuation.Note that Pi and P3 should be turned inthe opposite direction from P2 and P4.Next, the output signal at the BP ter-

minal should be set for an attenuation of1 dB by P3, and that at the HP terminalfor an attenuation of 2 dB by P4. This ismost conveniently done with the aid ofan audio generator and AC voltmeter,but it may also be done with the aid ofan ohmmeter: set the wiper of P3 to 0.9of the total resistance, and that of 134 to0.8 of the total resistance. These ohm-meter aided settings should, of course,be carried out with the mains switched

off.Finally, the loudspeakers may be con-nected: they should all be in phase.The reproduction from the active systemwas noticeably better than that of thepassive version of last month. This isparticularly so at the lower and thehigher frequencies.

References:1. Uniphase Loudspeaker System,

Elektor Electronics, March 1988,p. 36.

2. Active Phase -linear Cross-over Net-work, Elektor Electronics, September1987, p. 61

3. Audio -controlled Loudspeaker Moni-tor, Elektor Electronics, December1985, p. 55.

4. Top -of -the -Range Preamplifier, Part3, Table 4, Elektor Electronics,January 1987, p. 35.

AUDIO & HI -Fl NEWSVoice CoilReaders interested in loudspeaker manu-facture and design are advised that sincelast November there is a new Newsletterfor the Loudspeaker Industry, calledVOICE COIL .

Aimed primarily at the loudspeaker in-dustry, the newsletter is designed to be auseful information resource of currentand important data of interest tomembers of the manufacturing com-munity. Voice Coil will contain infor-mation on new products, literature,research papers, computer software,patents, marketing research, as well as afree classified section.Voice Coil is published monthly byAudio Amateur PublicationsP.O. Box 576PeterboroughNew Hampshire 03458-0176U.S.A.

Titanium -dome tweeter kitMetal dome tweeters are becoming in-creasingly popular and Wilslow Audionow offer a titanium -dome tweeterupgrade kit which suits most speakersthat were originally fitted with one -inchsoft -dome units. The kit is suitable forreplacing tweeters that have a sensitivityof up to 91 dB (normal: 89 to 90 dB).A cleaner, crisper response is claimed,and the increased power handlingresulting from the ferrofluid cooling ofthe voice coil makes this a usefulupgrade for pre -CD speakers now beingused with a CD -based system.The kit includes a constant -impedancelevel control with a flush mountingescutcheon which fits neatly into thebaffle board. The existing cross -over net-work needs no modification.

The kit, for a pair of speakers, is pricedat £41.90, incl. VAT, plus £2.50 p&p, andis available fromWilmslow Audio Limited 35-39Church Street WILMSLOWSK9 lAS Telephone (0625) 529599.

Portable sound intensityanalyserBruel & Kjaer's new Type 4433 SoundIntensity Analyser is a portable andsimple -to -use solution to many differentnoise measurement problems. It allowsaccurate on -site operation without in-convenient cables.

The 4433 measures the net acousticenergy flow by the two -microphonepressure gradient technique. It is able tolocate and discriminate between soundsources, giving a complete acoustic pic-ture even in conditions of high-levelbackground noise. This makes it poss-ible to make measurements in situ thatpreviously required an anechoic room.Bruel & Kjaer (UK) Ltd HarrowWeald Lodge 92 Uxbridge RoadHARROW HA3 6BZ Telephone01-954 2366.

AR introduces EnvironmentalPartnersFollowing on from the success of AR'sdesign -award -winning Powered Partners

and styled by the same internationaldesign house to match the AR elec-tronics range, the new AR Environmen-tal Partner packs a lot of speaker into asmall package.The Environmental Partner is a full-

range loudspeaker system with a four -inch polypropylene -coned woofer and a1.25 -inch liquid -cooled tweeter in asleek, wedge-shaped cast aluminiumcase, finished in smart scratch -resistantblack.Teledyne Acoustic Research HighStreet Houghton RegisDUNSTABLE LU5 5QJ Telephone(0582) 867777.

The Real Hi-fi StoryWritten by hi-fi and music writer PeterHerring, this booklet demystifies thewhole business of buying hi -ft equip-ment. If has been produced by theBritish Audio Dealers Association(BADA), the Federation of BritishAudio, and a selection of importers ofquality hi-fi (known as 'The Friends').Any readers interested in buying hi-fican obtain a free copy of the booklet(normally priced at £2.50) by writing to:The Sound Advice Centre40/41 Great Castle StreetLONDON WIN 7AF

50 EE

TUNEABLE PREAMPLIFIERS FORVHF AND UHF TV

The second, final, article on remote -tuned, masthead mounted, RFpreamplifiers deals with high-performance aerial boosters for the

VHF and UHF TV bands. These circuits give a considerableimprovement in reception compared to run-of-the-mill widebandaerial boosters. Connected to a good directional aerial, they areideal for picking up signals that are normally noisy, or impaired by

cross -modulation from strong nearby transmitters. But TV DXersneed not be told . . .

The preamplifiers described can be builtby anyone with reasonable experienceconstructing electronic circuits. Specialcare has been taken in the designs tominimize the necessary work on induc-tors, while alignment is straightforward,because in most cases it only entails set-ting a direct current. The amplifiers arebuilt on high -quality printed circuitboards available through our Readers'Services, and are tuned and poweredfrom the master tuning/supply unit de-scribed last month.

VHF preamplifier: circuitdescriptionWhat is commonly referred to as theVHF TV band is roughly the frequencyrange between 45 and 68 MHz (Band 1),but also that between 175 and 225 MHz(Band 3). Band 2 is the FM radio broad-cast band. It is important to note herethat the above band limits are given asguidance only, because they are set dif-ferently in many countries and regions inthe world. This also goes for the TVsystem used (PAL, SECAM, NTSC,positive/negative video, horizontal/ver-tical polarization, number of lines,channel assignment, frequency of thesound subcarrier, etc.). In the UnitedKingdom, Band 1 is currently allocatedto military communications; the formerTV services in that band have been trans-ferred to UHF in 1983.

The circuit diagram of the VHF pre-amplifier is given in Fig. I. Unbalanced(50..75 Q) or balanced (200...300 Q)cables are connected to input inductorL.1.1. The aerial signal is coupled induc-tively to the base of low -noise RF tran-sistor Ti via LIB and CI, which is con-nected on a tap for impedance matching.The input inductor, Li, is tuned to therelevant TV channel by the seriescapacitance formed by varactors D3 -D4.The voltage at the junction of these vari-able capacitance diodes is the voltage onthe downlead cable minus 8.2 V. The

junction capacitance of a varactordecreases with the reverse voltage on it,so that the lowest value of the downleadvoltage, 9 V, causes the input inductor,Li, to resonate at the lowest frequency,i.e., the preamplifier is tuned to thelowest TV channel.The amplifier can be set up for oper-ation in TV Band 1 or Band 3 simply byfitting the appropriate inductor in pos-ition Li (this will be reverted to underConstruction).Choke L3 forms a high impedance forthe amplified RF signal on the downleadcoax cable, and feeds the tuning/supplyvoltage to series regulator T2 and zener-diode DI. The function of these compo-

nents is similar to IC' and D3 in theFM -band preamplifier described lastmonth. The forward drop across LEDDi is fairly constant, and provides thereference voltage at the base of regulatorT2. Preset Pi makes it possible to set theoptimum collector current for the RFamplifier transistor, Ti. RF signals atthe base and collector of the BFG65 areblocked from the bias voltages by chokesL2 and L4, respectively. Gain of the pre-amplifier is fairly constant at about18 dB, both in Band 1 and Band 3. Thenoise figure was not measured, butshould be of the order of 1...2 dB, i.e.,considerably lower than almost any con-ventional wideband aerial booster.

Fig. 1. Circuit diagram of the low -noise, remote -tuned, preamplifier for VHF TV Band 1 or 3

EE

April 1988VHF preamplifier: construc-tionCommence the construction with mak-ing Li as required for the relevant fre-quency range (note that this may extendbeyond the indicated band limits). Donot skip the constructional hints in thefollowing paragraphs if you intend tobuild the Band 1 version of the pre-amplifier.

Band 3 (175-225 MHz):1. Close -wind LIB as 4 turns 01 mm

(SWG19) enamelled copper wirearound a 06 mm plastic former. Use aminiature screwdriver to spread the turnsevenly at about 1 mm. Study the pos-ition of the inductor on the board, andbent' the wire ends towards the holesprovided. Use a scalpel or sharp hobbyknife to remove the enamel coating onthe wire ends over a length of about3 mm. Pretin the connections, scratchoff residual solder resin, and pretin oncemore. Check for a smooth, tinned, sur-face.

Fig. 2. Close-up photographs shim Mg induc-tor Li in the VHF Band 3 preamplifier.Fig. 2a: seen from the side of LIB: Fig. 2b:seen from the side of LIA (note the tap madein twisted wire).

3

fir

/1"ZT 078 es:a

0 4003 67 z0 O

ig. 3. The printed circuit board for the VHF Band 1 or 3 preamplifier.

Parts list

VHF PREAMPLIFIER. CIRCUIT DIAGRAM:FIG. 1.

Resistors ( z

R = 100KR2 = 1008R3= 680RR4=3K3R5=22RR6= 10KPI =100R preset H

Capacitors:

Semiconductors:

Dr = red LEDD2 = zenerdiode 8V2; 400 rnW03:D4= BB405Tt = BFG65T2 = BC160

Inductors:

Winding data and materials are stated in thetext.

Cl;C2=1n0 miniature ceramic plate: pitch: Miscellaneous:5 mm.

C3=47n; 35 V; axial PCB Type 880045 Isee Readers Services page).

EEApril 1988

2. Locate the position of the tap on LIBat 1 turn from the ground connection.

Carefully scratch off the enamel locally,pretin the small copper area, and con-nect a short length of 00.5 mm(SWG25) enamelled copper wire. Placethe plastic former plus inductor onto thePCB, and bend the tap wire towards therelevant hole. Do not solder any connec-tion as yet. Make sure that the tap doesnot create a short-circuit between theturns of Lis.3. The input coupling inductor, LIA, is

wound as 2 turns 00.5 mm (SWG25)enamelled copper wire, with a tap at thecentre. Wind this inductor in betweenthe turns of LIB to assure the necessaryinductive coupling. Insert the wire belowthe turn of LIB that has the tap on it.Wind the wire upwards into the freespace between the turns of LIB, until itis opposite the connections of Liu.Draw out about 4 cm of the wire, fold itback again towards the former, and windthe last turn upwards into LIB.4. Use precision pliers to twist the. 2 cm

long wire pair that forms the tap onLiA. Hold the end of the wires in thepliers, and carefully revolve these in yourhand until the wires cross practically atthe body of the plastic former.5. Place the former with the inductors

on it onto the PCB, and revolve bothLIA and LIB until all six wires can be in-serted in the respective holes. Scratch offthe enamel coating from the tap and theends of LIA, pretin, clean again byscratching, and ensure a smoothsoldering surface. Press LIB together tolock up the turns of LIA. The final ap-pearance of the completed inductor isshown in the photographs of Fig. 2.Drill and file the hole that receives theplastic former. Fit the wires of Li intothe respective holes, and verify correctcontinuity. Do not use a core in Li.

Band 1 (45-68 MHz):For the lower frequency range, Lt iswound on a Type T50-12 ferrite core(012 mm) from Micrometals.1. Wind LIA as 8 turns 00.5 mm

(SWG25) enamelled copper wire, witha twisted centre tap created as discussedabove.2. Wind LIB as 20 turns of 00.5 mm

(SWG25) enamelled copper wire, witha twisted tap at 4 turns from the groundconnection.3. Fi) the complete inductor onto the

PCB, making sure that the windingsremain secure on the ferrite ring.

Chokes L2, L3 and L4 are identical forboth versions of the VHF preamplifier.They are wound as 4 turns 00.2 mm(SWG36) enamelled copper wire throughsmall ferrite beads (length: approx.3 mm).The printed circuit board for the VHFpreamplifier is shown in Fig. 3 (note thatthe component overlay is relevant to the

version for Band 1). Completion of thepreamplifier should not present prob-lems. Grounded component wires andterminals are soldered at both sides ofthe board. Coupling capacitors CI andC2 are miniature, plate or disc, ceramictypes with a lead spacing of 5 mm.Mount these as close as possible to thePCB surface. Conversely, mount T2 in amanner that rules out any likelihood ofa short-circuit between the TO5 case(which is at collector potential) and thePCB ground surface. Finally, fit a15 mm high brass or tin metal sheetacross Ti as indicated by the dashed lineon the component overlay.

The UHF preamplifier:circuit_ description.The circuit diagram of the low -noise,remote -tuned, UHF preamplifier formasthead mounting is shown in Fig. 4.Like the VHF booster, this amplifier isbased on the Type BFG65 RF transistorfrom Valvo (Philips/Mullard), but inthis application has tuned input and out-put circuits. The tuning voltage forvaractor pairs Di -D2 and D3 -D4 is ob-tained as in the FM -band and VHF pre-amplifiers, namely by subtracting thefixed drop across a zenerdiode from the

voltage carried on the downlead coaxconnected to the master tuning/supplycontrol. The tuning range of the ampli-fier covers the entire UHF TV band(470-860 MHz). The shaded rec-tangular blocks in the circuit diagramare straight lengths of silver-plated wirethat function as inductors (Li; L2).Balanced aerials or feeder systems with atermination impedance of 200...300 Qare connected to LIB. This coupling in-ductor is omitted when the input signalis unbalanced (50...75 Q). In this case,the centre core of the coax cable is con-nected direct to a matching tap close tothe ground connection (cold end) ofLIA. Regulator ICI ensures that T, is fedwith a constant supply of 8 V, while Piis used for setting the optimum collectorcurrent (this can be read on a microam-meter connected to test points TPI andTP2).The UHF amplifier has a typical gain of12 dB and, like the VHF version,achieves a noise figure that beats the vastmajority of wideband aerial boosters.

The UHF preamplifier:constructionThe UHF TV band preamplifier is con-structed on the PC board shown in

4

.11

LIB

LIA

D1

02

- TP1 TP2

RI

CI

n

R3

R2

P1

C3

BFiG65

100k

r,

L2

IC 1

78 LOS

C5

7VC6

L31p 40V 4.=

C2

BFG65

C4

Inim R6in

133

R4 =Ns

(NM

D4!

100k

100k

1)1...D4 = 882058

C

05

C7( R5

4775V

MI5

*see text

8V2

4- (DC)

0

8E0045-3

RF

Fig. 4. Circuit diagram of the preamplifier for UHF TV reception.

EE

April 1988

0-4

00 0

®`0E PS. 8E30044

0TP1

C5M C3x

IC1

Fig. 5. Track layout and component mount-ing plan of the PCB for the UHF preampli-fier.

Fig. 5. Study the component overlay,and bend LIA (if required), Lie and L2to size from 01 mm silver plated copperwire (CuAg). Do not solder these induc-tors in place, however, until they runstraight over the full length, and are pos-itioned so that the top of the wire isalways exactly 3 mm above the PCB sur-face. Fit leadless disc or rectangulardecoupling capacitor C3 in the slot pro-vided in the PCB. This (brittle!) capaci-tor is soldered once at the track side(connection to L2), and twice at thecomponent side (ground and, again,L2). Now position the RE transistor, Ti,in between the wire inductors, and solderthe 2 emitter terminals direct to theground surface. Carefully bend the col-lector terminal upwards, cut it to length,and solder it to the tap on L2. One ter-minal of coupling capacitor C2 is alsoconnected direct to this junction, whilethe other terminal is secured in a PCBhole-see the photograph of Fig. 6.Bend the base terminal of Ti upwards,and carefully cut this to a length ofabout 2 mm. Solder a 1nF SMD capaci-tor, CI, in between the tap on LIA andthe base terminal. RI is also soldereddirect to the base junction. Fit a 15 mmhigh screen across Ti as indicated onthe component overlay.Wind choke L3 as 6 turns 00.2 mm(SWG25) through a small (3 mm long)ferrite bead. The fitting of the remainderof the components is straightforward,

Parts list

UHF PREAMPLIFIER. CIRCUIT DIAGRAM: FIG. 3.

Resistors (±5%):

RI =22K112= 100R

R3;134;Rs=100KRs = 10KPt =1K0 preset H

Capacitors:

Ci;C4= 1n0 SMD.C2 =1n0 miniature plate ceramic.C3= 1n0 leadless ceramic (disc or rectangular).Cs=1/10; 16 V; axialCs =14; 40 V; axialC7=479; 35 V; axial

Semiconductors:

Di ...Da incl. =BB205BDs= zenerdiode 8V2; 400 mWIC i = 78L08Ti =BFG65

Inductors:

Winding data and materials are given in the text.

Miscellaneous:

PCB Type 880044 (see Readers Services page).

Fig. 6. Top view of the line inductors in thepreamplifier for UHF TV.

and should not present problems. Besure, however, to observe the polarity ofthe 3 electrolytic capacitors and the 5diodes!Figure 7 shows completed prototypes ofthe VHF and the UHF aerial boosters.

Setting upThe setting up of the preamplifiers mere-ly entails adjusting the collector currentof the RF transistor, and finding outwhich value of the tuning voltage cor-responds to a particular TV channel.

VHF preamplifier:Insert an ammeter between the collectorof T2 and L4. Connect the powersupply/tuning unit described last month,and set the output voltage to 20 V. Ad-just Pi for a reading of 5 mA, thenverify the presence of about + 11 V onthe varactor junction. Vary the tuningvoltage, and verify that the collector cur-rent of Ti remains constant. The LEDwill light dimly.Connect the preamplifier to the aerialand the supply/tuning unit. Also con-nect the TV set, and set up a tuning scaleby marking the channel numbers as afunction of the tuning voltage. In thecase of the Band 3 preamplifier, the tun-ing range can be corrected by carefullycompressing or stretching the turns ofLie.The collector current of Ti is optimizedby tuning to a weak transmission, andsetting Pi for minimum noise. This set-ting is typically found at collector cur-rents between 3 and 10 mA.

UHF preamplifier:Connect a millivolt meter to TP1 andTP2 as shown hi the circuit diagram. SetPi for a reading of 500 mV. Make notesof the tuning voltage required for anumber of TV channels in the UHF

54 EE

April 1988band, and provide a UHF tuning scaleon the master supply/tuning unit.

General considerationsThe values stated for the operating cur-rent of Ti are given as a compomise be-tween a low noise figure (low collectorcurrent), and high amplification in com-bination with good intermodulationcharacteristics (high collector current).The collector current may, therefore, beset to different values to suit the appli-cation in question.

As stated in last month's article, there islittle point in installing the remote -tunedpreamplifiers in any place other than asnear as possible to the relevant aerial.This is the only way to prevent the at-tenuation introduced by the downleadcoax cable degrading the system noisefigure. The preamplifiers described havesufficient gain to bring the system noisefigure down to practically the preampli-fier noise figure, but only if they areproperly aligned and installed. B

Readers interested in TV-DXing are ad-vised to contact the British AmateurTelevision Club Mr Dave LawtonGOANO "Grenehurst" PinewoodRoad High Wycombe BucksT-TPI2 4DD.

Fig. 7. Prototypes of the V H I preamplifier deft: Band 3 version). and Ole UHF preamplifier(right).

RADIO COMMUNICATIONSFOR THE FUTURE

by Dr. Chris Gibbins, Rutherford Appleton Laboratory

Overcrowding of the radio spectrum is severely restricting the re-liability and information -carrying capacity of existing communi-

cations systems. But moving to higher frequencies, where there ismore room, brings a different set of problems to do with theatmosphere and weather. Research at the UK Science and

Engineering Research Council's Rutherford Appleton Laboratory iscompiling valuable data for the design of systems for the future,

exploiting frequency bands that are so far little used but for whichthe necessary technology is already available.

A massive expansion in radio communi-cations over recent years has generatedan ever-increasing demand for morechannels, and those channels are havingto carry more and more information, beit voice, television or other kinds of data.The net result is that the radio spectrum,a restricted resource, is fast becomingovercrowded. This creates problems ofinterference between adjacent channels

(as anyone who listens to short-waveradio, especially at night, will know well)with reduced reliability. There is anadditional side -effect of such over-crowding: the bandwidth available toeach channel, which determines theamount of information that can betransmitted, is severely limited. 'That initself restricts both the capacity and thereliability of communications systems.

Millimetre wavesA remedy for these problems is to befound in exploiting higher and higherfrequencies, made possible through thedevelopment and availability of newtechnologies. Communications now ex-tend well into the microwave region ofthe electromagnetic spectrum (fre-quencies up to 30 GHz) and even beyond

rAF0-19,C.Die

'Attenuation of microwave and millimetre-wave radio signals by the Earth's atmosphereat sea level. Molecular attenuation is presentall the time and is produced by water vapour(H20) at 22 and 183 GHz and by oxygen (02)at 60 and 119 GHz; there are many more ofthese 'absorption lines', mainly from watervapour, at even higher frequencies. The rangeof the highly variable attenuation caused byrain is shown by three representative curvesfor light drizzle, typical rain and intensethunderstorms. The arrows at the bottom in-dicate the frequencies at which the Ruther-ford Appleton Laboratory is makingmeasurements.

into the millimetre -wavelength region(frequencies from 30 to 300 GHz). Theseregions of the spectrum are still rela-tively uncrowded, particularly at thehigher frequencies, and the bandwidthsavailable are so large that they open upthe possibility of new communicationschannels with a capacity for carryinghuge amounts of information.But use of the microwave and millimetrewave regions of the spectrum for com-munications brings an additional set ofproblenS not met with at lower fre-quencies. The Earth's atmosphere startsto interact with the radio waves, resultingin attenuation of the signals which mustbe taken into account in the design ofsystems. There are two distinct and quitedifferent effects, which are shown in thefirst diagram. First, the molecules of ox-ygen and water vapour in the atmos-phere absorb radiowaves at certaincharacteristic frequencies. This is knownas resonant absorption. They re -radiatethem isotropically, that is, equally in alldirections, a fraction of a second later;this means that the signal is attenuatedthrough the loss of directivity andcoherency. The second effect is that rain-drops, hail and snow scatter the signals,thereby attenuating it still more. This ef-fect is non -resonant and increases withincreasing frequency, as the wavelengthdecreases and becomes comparable withthe sizes of raindrops; at that point thescattering process is most efficient andsignal attenuation is greatest. The firsteffect, molecular absorption, is presentall the time, and changes only slowly

with varying temperature, pressure andhumidity. A great deal of research hasbeen undertaken into this phenomenonand the effects of molecular absorptioncan now be predicted fairly accurately.So the designer of communicationssystems can take reasonably accurate ac-count of attenuation by oxygen andwater vapour when assessing the overallperformance of microwave andmillimetre -wave links.

Fade marginSignal attenuation by rain and otherforms of precipitation, however, presentsa quite different problem. Precipitationis a highly variable phenomenon, chang-ing both in time, space (that is,geographic location) and intensity. Thismakes it much more difficult to take ac-count of rain attenuation in designingsystems. The problem is generallytreated statistically instead of by the sortof exact calculation that can be used formolecular attenuation. The systemsdesigner specifies a level of reliability fora particular communications link: forexample, the link might be required toprovide acceptable voice communicationfor 99.9 per cent of the time, or accept-able television transmission for 95 percent. That means the users can toleratethe service being unavailable for 0.1 percent or 5 per cent of the time respect-ively. The designer then needs to knowwhat level of signal attenuation will beexceeded on the link for these smallpercentages of time. This is known as the'fade margin' which the link must beable to overcome when providing an ac-ceptable signal-to-noise ratio, to achievethe specified level of reliability. This, inturn, has an impact on the transmitterpower, receiver sensitivity and the size ofthe antennas, which in the end affectsthe overall cost of the system. It istherefore of paramount importance that

EE

April 1988the systems designer should haveavailable the most accurate informationfrom which to derive the necessary fademargins, to achieve the most reliable andcost-effective design.Fade margins are not easily calculableand in general tend to be empirically de-rived from transmission measurementscarried out over long periods. A greatdeal of work has already been done atfrequencies up to about 40 GHz, andthere are extensive data banks fromwhich the necessary statistical infor-mation and service predictions can bederived. For example, the InternationalRadio Consultative Committee (CCIR)at Geneva collates, distils and publishesinformation of this kind. At higher fre-quencies, however, there is a markedpaucity of data.

Foundation for systemsTo provide the necessary information onterrestrial radiowave propagation, theRutherford Appleton Laboratory has setup an experimental transmission rangeat its Chilbolton Observatory near An-dover, in southern England. This facility,represented schematically in the seconddiagram, works on a number of linkstransmitting over a distance of 0.5 km atfrequencies of 37, 57, 97, 37 and210 GHz in the millimetre -wavelengthregion of the electromagnetic spectrumand at wavelengths of 10.6 pm in theinfra -red and 0.63 pm in the visibleregion. Frequencies of 37, 97, 137 and210 GHz were chosen as representativeof those parts of the spectrum where at-mospheric attenuations due to oxygenand water vapour are low; such parts areknown as atmospheric 'windows' andhold out the opportunity for cost-effective, widebandwidth communi-cations. The 37 GHz channel can alsoprovide the means for comparing theresults from the 500 m range with exten-

To datacoon

f.

PTOCESS

cc.trorer

A

Rece.ers

37 tat

57GHt

97Citz

137 G342

113 pm

-1oz..0 -Ate,

pr!ract'

Teroperatzte

930mTrarornmeA3,

37 GM:

57GHz

97 GHz

137 Wiz

Matz

10 pm

Op pro PIAUI

HALISNOw RAs FALL FLUE

Schematic diagram of the 500 m experimental range at Chilbolton.

56 EEApril 1988

sive measurements made at this andlower frequencies at other places and byother workers. The 57 GHz frequency,on the other hand, is near the 60 GHzoxygen absorption band, where veryhigh attenuations of up to 15 dB(decibels) per kilometre occur, whichmeans 97 per cent of the signal is at-tenuated at a distance of one kilometrefrom the transmitter and only three percent remains to be received. Such regionsof the spectrum could be used for securecommunications, for example wheretransmission range should be restricted,or for multiple repeated use of a fre-quency in a dense urban environment,because the atmosphere produces extraisolation between links operating at thesame frequency.In addition to the transmission links, theChilbolton Observatory compiles a com-prehensive set of meteorological data,including measurements of temperatureand humidity at a number of places andheights above the ground. There arethree rapid -response rain gauges, Whichmeasure the rainfall rate at differentpoints along the range at 10 -second in-tervals, while a fourth rain gauge isequipped with heaters to assist themeasurement of snow during the winterand hail in the summer. A distrometermeasures the distribution of the sizes ofraindrops, important in the developmentof theoretical models to describe rain at-

refractometermeasures the refractive index of the at-mosphere, which affects the level of scin-tillation, the name given to small, veryrapid fluctuations in the received signalpower. The meteorological observationsare completed with surface pressure andwind speed and direction.Outputs from all the links and sensorsare coupled via an interconnecting com-puter bus to the main data -collectioncomputer, which records all themeasurements on magnetic tape every 10seconds. Additionally, when attenuationdue to precipitation is detected on therange, the outputs from the transmissionlinks are recorded separately at a rate of100 measurements per second. Thedatacollection computer also initiatesautomatic calibrations of the links every6 hours. All magnetic tapes are sub-sequently .calibrated and verified on amain-frame computer, and the data filesput into an archive for anlysis.The 500 m range, then, is a well in-strumented open-air laboratory designedto study in detail the interaction betweenradio waves and the prevailing weatherconditions, by providing comprehensivepropagation data for a distance overwhich meteorological conditions areessentially constant. The range has beenin operation for about three years and asubstantial data base of propagationdata has now been accumulated. It is be-ing used for a variety of studies aimed ata more detailed understanding of the

The transmitter cabin at Chilbolton. Hoodskeep rain off the windows through which thesignals are transmitted. The transmitters aremounted on benches supported independent-ly from ground, inside the four concretepillars. This prevents vibrations in the cabinaffecting the equipment. The anemometerand vane mounted on top of the cabinmeasure wind velocity.

various phenomena which may affectthe reliability of communicationssystems, and providing the statistical in-formation required by systems designers.

Two main analysesThe data base is being extensivelyanalysed in two different ways. Detailedstudies are being made of individualevents, such as particular rain storms,snow storms, fogs and so on, to learnmore about the way radio waves pro-pagate through such phenomena. Fromsuch studies it will be possible to developmore detailed and accurate theoreticaldescriptions than so far exist of the wayvarious kinds of precipitation and soforth interact with radio waves. Thesetheoretical models, as they are generallyknown, can then be used to predict whatmay happen on proposed new communi-cations links in areas where little, if any,propagation or metereological data ex-ist. The second mode of analysis isaimed at providing the kind of statisticaldata necessary for the most cost-effective design of new communicationssystems, and to provide a statistical database for testing and validating theprediction techniques being developed.Analyses based on individual events areclassified according to the type of event,for example rain, snow, hail, fog or scin-tillation. Extensive studies on rainalready indicate a general overall agree-ment both with similar studies con-ducted elsewhere and the theoreticalmodels which so far exist, such as thoserecommended by the CCIR. Never-theless, certain significant differenceshave been found, which may possibly beattributed to the differences in climatebetween southern England and theplaces where other studies have been

made. Understanding suchclimatalogical differences is very import-ant in being able to develop predictionmodels if they are to be applied to anyplace on Earth. We feel that our workwill help considerably in achieving this.Attenuations produced by rain vary con-siderably, of course, because they de-pend on the features of the rain. Lightdrizzle may attenuate the signals by onlya few per cent over the 500 m range,whereas intense thunderstroms can at-tenuate by more than 30 dB km-' at97 GHz, for example; in other words,only 0.1 per cent of the signal remainsafter a distance of one kilometre. For-tunately, such events are very confined.

Snow and fogOf great interest is the effect that snowstorms have on millimetre communi-cations. There is shortage of such dataand the few results available show widevariations. Snow is generally difficult tocharacterize quantitatively with regardto shape, size and wetness of the flakes.These characteristics vary widely, andwhen snow is carried by the wind itbecomes difficult even to measure effec-tive deposit rates. However, we havedeveloped a rapid response snow gaugewhich is producing very encouragingresults. The effects of wind are kept aslow as possible by surrounding the gaugewith a fence, which reduces wind speedsclose to the gauge and so improves theefficiency of capture. Using this tech-nique, we find good correlations be-tween attenuation and snowfall depositrates. Results so far indicate that whensnow is very dry the attenuations are low,compared with rain, for the sameamount of liquid water deposited; butfor wet snow, attenuations can be con-siderably higher. The attenuation clearlydepends not only on the amount of li-quid water falling, but also on the degreeof wetness of the snow flakes. Con-siderable effort is being devoted to tryingto characterize this in terms of othermeteorological parameters such as airtemperature, so that empirical relation-ships can be developed to help theprediction of attenuation.Fogs, on the other hand, affect themillimetre links very little; thewavelengths are much greater than thesize of the water droplets and the scatter-ing process, which causes the attenua-tion, is not significant. In general, theattenuations found at millimetrewavelengths are only a few per cent atthe 500 m range. At infra -red and opticalwavelengths, however, very severe at-tenuations, of more than 80 dB km-',often occur in the visible range in fog,representing a visibility of only about200 m; only one millionth of one percent of the signal remains at a distanceof one kilometre from the transmitter.

EE

April 1988

Gas flaresThe 500111 range can easily accom-modate a variety of differentmeasurements or experiments fromother interested groups, especially as allthe instrumentation and the data collec-tion system are based on a universal in-terface standard. As an example of this,an interesting and novel investigationwas carried out into millimetre -wavepropagation through flames, in collab-oration with one of the oil companiesoperating in the North Sea. The problemwas what effect gas flares on the drillingplatforms might have on the communi-cations systems. A large flame wasgenerated, about three metres wide,three metres high and half a metre deepand the signals were transmitted throughit. Little effect was observed at thelowest frequencies, though large attenu-ations occurred in the visible range.There was, however, a general increase inthe level of scintillation of the signals,which might possibly be of concern atthe very high frequencies but of littlesignificance at the frequencies at presentin use for communications systems.The other type of analysis of results isaimed at obtaining the kind of statisticalinformation needed for direct appli-cation to communications systemsdesign, for example finding out whatfade margins should be allowed for givenlevels of operational reliability. This isnecessarily a longterm project, becauseit is important to find an average over ex-tremes of the prevailing meteorology andit can be done reliably only over anumber of years. Statistical data now be-ing accumulated include such infor-mation as the percentages of time thatvarious. levels of attenuation are exceed-ed, from which fade margins can bedirectly derived; probability distribu-tions of the duration of fades to yield in-formation on the length of data`dropouts'; the times between fades,which tell us how often deep fades arelikely to occur; and the rate of change offading, which indicates how rapidlysignals are likely to change, which is par-ticularly important in digital radio com-munications systems. The propagationstatistics are complemented by similarstatistics of meteorological parameters,especially of rainfall rates. Direct com-parison. of these two sets of simul-taneously obtained data then enablespropagation conditions to be predictedsimply from rainfall data, which is rela-tively easy and inexpensive to obtain andis measured routinely by weatherbureaux in most countries of the world.

Future workThe information obtained on the 500 mrange will be of immense value in pro-viding propagation statistics and in

The 97 GHz receiver with its 15 cm diameter antenna and swan -neck waveguide feed. Its solid-state local oscillator is mounted on a heat sink on the right-hand side. A battery -operatedpower supply biases the receiver's Schottky -barrier mixer to its most sensitive operatingregion.

developing propagation models andprediction techniques for planningfuture communications systems. Thedata is being collected over a relativelyshort distance, chosen deliberately to en-sure that the meteorological conditionswould be nearly constant over the range.In general, however, practical communi-cations links operating at millimetrewavelengths will have much greater pathlengths, perhaps up to several tens ofkilometres or more, depending on thefrequency.It is generally found that precipitation,the dominant source of fading in themillimetre region, is characteristicallynot homogeneous or uniformlydistributed horizontally. Widespread(statiform) rain is found to contain im-bedded convective cells with higher rain-fall rates than the surroundingstratiform regions. Such cells tend, onaverage, to be about 12 km apart andfrom two the three kilometres indiameter. As a result, it is not practicablesimply to scale the data obtained on the500 m range to path lengths of morethan about two kilometres.To obtain data over the longer pathswhich would be used in operationalmillimetre -wavelength communicationssystems, an additional link is beingdeveloped to operate in conjunction withthe 500 m range over a path of aboutseven kilometres. This will provide dataon path -length scaling, in which the500 m data are applied to longer, more

practical link lengths; at the same time itwill produce a data base for validatingpractical prediction techniques. The linkwill operate at frequencies of 55 GHz,near the peak of the oxygen absorptionband, and 95 GHz, in an atmospheric`window'. These represent two regions ofthe radio spectrum in which there is con-siderable interest, for reasons alreadymentioned, to do with their applicationto specific types of future communi-cations systems.These two sets of multi -frequency trans-mission links, operated simultaneously,will enable us to build up one of themost comprehensive propagation database for future millimetre -wave ter-restrial communications systems design.The detailed and extensive programmeof data analysis now going on and beingproposed will yield essential informationfor expanding terrestrial radio communi-cations into the millimetre -wavelengthregions of the radio spectrum for theforeseeable future.

58 EE

April 1988

porting information. All circuits canNEW LITERATURE readily be modified or extended by

Antennas Volume 2:Applicationsby S. Drabowitch & C. AnconaISBN 0 946536 17 1320 pages - 234 x 156 mmPrice £35.00 (hardback)This book is the second of a two -volumework intended to provide practisingengineers, as well as students of elec-tronics engineering, with a thorough,concise introduction to the applicationsof antennas. Volume 1, reviewed in theNovember 1987 issue of this magazine,deals with the most important principleson which the theory of antennas isbased.In the second volume, the authors exam-ine the applications of these principles.Beginning with large antennas, they lookat focusing systems and go on to con-sider the antennas a signal -processingcomponent, providing a novel insightinto how the antenna may be treated asa spatial filter.The second section of the book examinessmall antennas and plasma -embeddedantennas. The quasi -static approxi-mation for low -frequency antennas ispresented and followed by a look atdipoles and slots, and frequency -inde-pendent antennas.The final section deals with antennas inlinear plasmas, which is of particularimportance in the study of antennas onspacecraft and breakdown phenomena.S. Drabowitch is a consultant atThomson-CSF, Professor at l'EcoleSuperieure d'Electricite, and a seniormember of the IEEE. The late C. An-cona was Director of Studies at theSociete Technique d'Application etRecherche Electronique, Paris, and Pro-fessor at l'Ecole Superieure d'Electricite.Like the first volume, the present onehas been translated excellently by MegSanders.I thought in November that this workcould well become a standard work onantennas. Now I have been able tosample the second volume, I am sure ofit.North Oxford Academic Publishers Ltd120 Pentonville RoadLONDON Ni 9JN

Electronic Circuits Handbookby Michael TooleyISBN 0 434919 68 3277 pages - 246x 187 mmPrice £14.95 (soft cover)The title of this book might well havebeen Electronic Circuit Design Hand-book, for that is what it is. A thoroughlypractical work that provides the readerwith a useful collection of working cir-cuits, together with the necessary sup-

readers to meet their own individualneeds.Related circuits have been groupedtogether and cross-referenced in the textand index so that readers are aware ofwhich circuits can be readily connectedtogether to form more complex circuits.Apart from circuit design, the book alsocontains chapters on tools and testequipment required for the design andconstruction of electronic circuits and achapter on the actual construction of acircuit from a 'paper design'. This latterchapter deals with matrix boards,printed circuit boards, soldering tech-niques, and fault finding. The finalchapter is a real gem: it contains ten testequipment projects from a DC powersupply through a transistor tester to apulse generator.The book gives both the American andBritish/IEC standards for logic gates,although Mr. Tooley quite rightly pointsout that (as yet) the American MIL/AN-SI standard is preferred by many equip-ment manufacturers.Some minor criticisms mainly concernterminology, such as the use of 'dutycycle' and 'fall time', for which the morecorrect terms are 'duty factor' and`decay time'. These should, however,only affect students, who will be put onthe right track by their lecturers anyway.Altogether a welcome book for the prac-tising engineer, technician, student, andenthusiast alike.Heinemann Professional Publishing Ltd22 Bedford SquareLONDON WC1B 311H

BASIC & LOGO in Parallelby S.J. WainwrightISBN 0 85934 171 2152 pages - 178x 110 mmPrice £2.95 (paper back)LOGO and BASIC are two quite differ-ent types of computer language. Bothwere originally developed to enable be-ginners to make rapid progress in the useof computers.BASIC is an all-purpose language that isin the same family as FORTRAN,ALGOL, PASCAL, and C.LOGO is a language in the same familyas LISP, and with a philosophy ofprogram development akin to that ofFORTH.It is a common misconception thatLOGO is just a Turtle Graphicslanguage. In fact, LOGO has powerfularithmetic and list -processing capabili-ties, and is one of the languages involvedin artificial intelligence aspects of com-puting. Nevertheless, LOGO's simplebut powerful graphics capabilities havegiven it a place in educational comput-ing as it may help people to experimentand learn by a process of discovery.

This book takes BASIC and LOGOtogether, and examines how things aredone in each of them.A powerful LOGO -Graphics interpreterwritten in BBC BASIC is presented atthe end of the book. This will enable thereader to explore Turtle Graphics aspectsof LOGO before investing in a fullLOGO interpreter.

More Advanced PowerSupply Projectsby R.A. PenfoldISBN 0 85934 166 692 pages - 178x 110 mmPrice £2.95 (paperback)This book is the companion volume toPower Supply Projects by the sameauthor, and should be of interest toanyone who has a reasonable knowledgeof power supply basics and would like tolearn about recent developments andmore advanced designs.The practical and theoretical aspects ofthe cricuits are covered in some detail,and the reader is not assumed to have aprofound knowledge of electronic circuitdesign. However, it is recommended thatanyone who is not familiar with the fun-damentals of power supply design andoperation should consult a copy of thecompanion volume.Topics included in the present book in-clude switched mode power supplies,

trackingregulators and computer -controlled sup-plies.The book should satisfy the vast ma-jority of power supply design needs notcovered in the earlier work.

The two above books are published byBernard Babani (publishing) LtdThe GrampiansShepherds Bush RoadLONDON W6 7NF

Radiowave Propagationby Lucien BoithiasISBN 0 946536 06 6330 pages - 234x 156 mmPrice £35.00 (hardback)Since the beginning of the twentieth cen-tury, dramatic progress has been made inthe area of radiowave propagation: thefirst radiotelegraphic link; the discoveryof the ionosphere; and the developmentof intercontinental telecommunications,radio relay links and satellite communi-cations.Aimed primarily at practising electricaland electronic engineers, the bookpresents a comprehensive, structuredstudy of the propagation phenomena oc-curring between a transmitting and areception antenna, with one or both ofthem located on earth.Using numerous graphs, figures, and

59

charts, the first part of the book dealswith line -of -sight propagation, begin-ning with considerations of propagationin free space and the fundamentalphysical phenomena involved: reflec-tion, refraction, diffraction, and scat-tering. The effects of the ground and thetroposphere on propagation are exam-ined together with a review of knownanomalies in line -of -sight propagation.The second part of the book deals withthe three major mechanisms affectingnon -line -of -sight propagation: knife-edge diffraction, tropospheric scatter,and reflection by the ionosphere, andgoes on to consider phenomena associ-ated with noise, particularly over greatdistances, and to distortions of all kindsaffecting radio communication.Lucien Boithias, a scientist of inter-national repute, is Chief Telecommuni-

cations Engineer at the Centre Nationald'Etudes des Telecommunications(CNET).Its clear and accessible overview makeRadiowave Propagation an essential ref-erence work for all those interested inunderstanding and applying propa-gation phenomena.North Oxford Academic Publishers Ltd120 Pentonville RoadLONDON Ni 9JN

BRITISH STANDARDSBS4061:Part 1:1987BS4061:Part 2:1987Both these new standards deal with theDimensions of pot -cores made of mag-netic oxides and associated parts, butPart 1 deals with the dimensions in ageneral manner, while Part 2 deals

EE

April 1988specifically with pot -cores of Britishorigin.

BS6840:Part 14:1987Part 14 of the Sound system equipmentstandard is a guide for circular and ellip-tical loudspeakers; outer frame diam-eters and mounting dimensions. It ex-cludes cone dimensions of loudspeakersand depth of loudspeakers.

British Standards may be ordered fromThe Sales DepartmentBSILinford WoodMILTON KEYNES MK14 6LE

Readers should also note that eachcounty in the UK has at least one or twolarge Public Libraries where completesets of British Standards are kept forgeneral consultation.

PEOPLEGary Clark, formerly Software Managerof Camberley -based Base Ten SystemLimited, has taken up the newly formedposition of Business Manager of thecompany's Telecommunications Prod-ucts Group.

Ian Summerfield, left, newly appointed byCirkit as product manager, power suppliesand ferrite products, is seen here discussingthe Bulgin power supply range with Tim Roe,Bulgin Power Conversion Division's market-ing manager.

Louise England, 22, has joined WestHyde Developments, the Aylesbury -based enclosures manufacturer, asMarketing and Public Relations Co-ordinator.

Roger Lucas, 16 (second from left) and Paul Dagley-Morris, 16 (third from left), bothmembers of Cheltenham College, gained third place in the 1987 Young Engineers for Britaincompetition, sponsored by the National Engineering Council, for their animal !mums meter(intended for measuring shock in animals). They are seen here with Dr. C.B. Jennings (extremeleft), Head of Mechanical Engineering at South Bank Polytechnic, who travelled toCheltenham to present the awards on behalf of the Council, and Alan Miers (extreme right),Head of Electronics at Cheltenham College, who accepted a cheque for £200 for the Collegeas part of the award.

Ken Manser has joined Base Ten SystemsLimited as Sales Manager of their Tele-communications Products Group atCamberley.

John Sturmey has joined RoxburghElectronics as Product Manager forswitches. He was previously responsiblefor international sales at Arrow Hart,covering the North European, Asian,and African markets.

Mietec, the European ASIC manufac-turer, has appointed Keith Pruden, 28,as UK Sales Manager with responsi-bilities for UK sales and customer sup-port.

John Spring has been appointed ProductManager for Passive Components withHouse of Power, the Orpington -basedelectronic components distributor.

EE60

COMPUTER -CONTROLLED SLIDEFADER (2)

The slide effects unit introduced last month is completed with acontrol program and an optional keypad that together control nofewer than sixteen slide faders. Although written for the MSX seriesof home computers, the BASIC program should not be too difficult

to rewrite for running on almost any other micro equipped withenough parallel I/O lines for driving the slide controller board(s).

The preparation of a smoothly runningslide presentation on four or more pro-jectors is practically impossible withouta design tool that enables the photogra-pher to compile his batches of slides,find attractive combinations as regardscolour and intensity, and decide on theorder, lamp intensity and the time 'a par-ticular slide is shown. Once all this hasbeen decided on, revised, and once moreverified in a trial run of the show, it ispossible to store all the necessary com-mands in the computer for retrieval andautomatic execution at a later stage. Toaid and guide the many enthusiasticphotographers keen on showing theirachievement to a larger audience, wehave written a BASIC programme forMSX computers, and developed aspecial command keypad that connectsto the computer's joystick input.

Overview of functionsA short description of the commandssupported by the slide controllerprogram is given in the Table below.Clearly, the success of the visual effectsdraws on the photographic ingenuity ofthe operator, in casu, the programmer

who creates the file that contains thecommands to be executed sequentially.The artistic aspects of creating a slidepresentation are not dealt with in thisarticle: general considerations and usefulhints can be found in books andmagazines on the subject ofphotography.

When the program is started, it displaysthe menu screen (see Fig. 1). The user isprompted to select automatic or manualoperation by the flashing text:

[A]UTOMANUAL

The capital letters in square bracketsdenote the key to be pressed for the as-sociated function. Typing M makes itpossible to use the keyboard for selectingcontrol commands from a menu. Theselected function is marked with anasterisk (*). The largest possible array ofslide projectors is composed of fourblocks of four projectors, each with itsown address area in the I/O and TimerCartridge for MSX micros. This ar-rangement is equivalent to four I/O car-tridges fitted in parallel in a single I/O

SUMMARY OF EFFECTSFADER

Fade types:hard; snap; cut; flipfast to very slow

Double projection:superimposeflash

partial image

Twinkling and animationFade in

Fade outClearSlide carriage control

ON COMPUTER -CONTROLLED SLIDE

very fast fading (<1 s).1... >10 s.

projects two slides simultaneously.flash -like appearance of a slide onto theprojected image.a number of masked slides are projectedsimultaneously.

fast sequential projection of slides.projector lamp intensity is graduallyincreased.projector lamp intensity is gradually reduced.all slide carriages are returned to position '1.forward, reverse.

slot, and enables controlling 16 projec-tors simultaneously via 4 slide controllerboards (keep an eye on the total currentconsumption). Keys [shift]l...[shift]4select the block number, and keys 1...4the individual projector. Provision hasbeen made for the simultaneous selec-tion of multiple projectors, which neednot be part of the same block. Afterselecting the projector(s), the com-mand(s) can be issued. Options aredisplayed at the top of the menu.

1

EFFECTS FADING RATE SPECIAL

(D)issolve MI fastPluperiopose .[N]ornalfade 1110 ; [Wongfade 10jut . e(x)tra long[T]winkleIFI lash

PROJECTOR IN PROJECTOR BLOCK

[Hcsfe1

I go[C]lear

(II first ]shiftl[ll 1 - 4121 second Ishlft1121 5 - 8131 third [shift113) 9 - 12141 fourth Ishift1(4) 13 - 16

SLIDE CHANGE

[-J forward (clef](.J reverse1/1 no change1,) forward direct(<1 reverse direct

Fig. 1. The start-up menu prompts the userto enter functions and control commands forthe slide fader unit(s).

To begin with, there is, of course, theslide fade effect. This is obtained withthe aid of command "dissolve". Thelamps in all projectors that illuminatethe reflective screen are quenched, andthose in the selected projectors aregradually turned on. Function"superimpose" is similar to "dissolve",but works with half the light intensity.Function "fade in" turns the lamp in aparticular projector on at a certainspeed, without quenching the lamps inthe other projectors. "Fade out" is thecomplementary function. The fadingrate for the above functions is program-mable: fast; normal (5 s), long (15 s) orextra long (30 s).The "twinkle" effect gives a fast, se-quential projection of slides in a numberof projectors (running -light effect),

while "flash" gives a brief, single, pro-jection of one or more slides.Five options are available for slide car-riage control. The first, "forward", isthe default function that results in auto-matic feed -forward of the slide carriagefollowing a fade-out command, i.e., itcan only operate in conjunction with ef-fects "dissolve", "superimpose", and"fade out". Function "reverse" issimilar to "forward", except, of course,for the direction of travel of the slidecarriage. Automatic slide changing isdisabled with function "no change".Functions "forward direct" and "re-verse direct" give instantaneous slidechanging. Selected projectors provide afade out (unless the lamp was alreadyquenched), followed by a slide carriagefeed in the relevant direction.As to the special functions shown in themenu: "go" (space bar or return key)runs the selected function or effect. Theselected function is not carried out, how-ever, before the relevant projectors havecompleted previously received com-mands. Function "home" has two op-tions. Pressing the home key causes theselected projector(s) to revert to the firstslide, but not before the projector(s)lamp(s) is/are quenched. Pressing the[shift] and [home] key simultaneouslycauses all projector lamps to be quench-ed, all slide carriages to be set to the firstposition, and all projectors to bedeselected. Function "clear" ignoreskeyed -in commands, and restores thepreviously selected function.

Command stringsAn example may help at this stage to il-lustrate the programming procedure.The following command string is keyedin:

[shift]41Q12 F3 4 ON1234[return]

Note that the 3 spaces are significant, asthey stand for "go". [shift]4 selects pro-jector block 4 (projector numbers13...16 incl.). I and Q announce a fastfade-in on projectors 1 and 2 of block 4(numbers 13 and 14). The space charac-ter that follows causes the programmedfunction to be carried out. F3 selects aflash on projector 3 in block 4 (number15), and the space brings it into effect.4[space] causes a flash from projector16. Note that it was not necessary at thisstage to type another F, since the flashfunction is still in operation. The nextcommand sequence, ON1234[return]results in a fade-out at normal speed,followed by a carriage feed -forward. Thefade-out is not effected on projectors 15and 16, since these had their lamps fullyquenched already, but the automaticfeed -forward (default) is still effected.Commands and selections are notbrought into effect before "go" is selec-ted; editing of command sequences is,therefore, possible. Selection of otherprojectors is, however, only possibleafter a "clear" command.

Automatic controlIt is, of course, convenient to run thecompiled presentation automatically.The control program supports automaticoperation with or without tapesynchronization.Projector commands can be put inDATA lines from line 8000 onwards (anexample of an automatic presentation isincluded in the programme listing). Thestructure of the lines is similar to thepreviously discussed strings that areentered manually. If available, the diskdrive on the computer may be used forstoring projector commands on floppydisk. Disk or tape storage is not sup-ported by the control program, however,

EE

April 1988so that suitable save and load procedureswill have to be provided by the program-mer.A number of additional program func-tions are available during the automaticexecution of the slide show. Pressing key"M" reselects manual operation, while"A" reverts to the automatic mode, inwhich the computer continues process-ing the data from where it was inter-rupted. If necessary, slide carriages arereturned to the positions they had beforethe automatic mode was interrupted.Function "W" waits for the space bar tobe pressed, or for "M" to select manualoperation. This makes a short pausepossible for exchanging complete slidecarriages. Function "R" (restore) causesthe program to start at the first data line,after returning all projectors to the in-itial settings. Function "E", finally, endsthe show. Programmers should note that"E" and "R", contrary to the otherfunctions, must each be put in a separatedata line. The home key can not be putin a data line in the form of an ASCIIcharacter. This problem has been solvedby the use of letters "h" and "H",which represent [home] and [shift]home,respectively. The other functionsrecognize both capitals and lower caseletters.Synchronization to a tape recording iseffected via the trigger input on thejoystick interface (hardware), and thewait -for -tape routine (software). The(relay) output of the pulse decoder isconnected between trigger input A andGROUND of joystick 1. A simple rec-ord/playback system for taperecorders isshown in Fig. 2. The I kHz tone gener-ator (Fig. 2a) is activated by pressing Si.The tone decoder (Fig. 2b) is connectedto the AF output of the recorder, and en-ergizes the relay contact when the tone isdetected as the tape is being played back.

61

2a

MEMlen

A 1, A 2 = IC 1 = 3240Re 1 = 12 V, max. E0 mA

12V

11'14148 03

Ref

C4MOM

760,

3V9

RIO

T1 BC 547

000

37473

b

0 12V

O

12V

Fig. 2. Circuit diagram of a simple tone generator (2a) and associated decoder (2b) for tape s)nehronization.

62 EEApril 1988

The Record -Playback Amplifier de-scribed in 41) is ideal for use in conjunc-tion with the tone generator anddecoder. To prevent it being overdrivenby the tone generator, it is recommendedto use the resistor -potentiometer con-figuration shown as an option for thecircuit of Fig. 2a. Also, CI is best in-creased to 100nF to lower the tone fre-quency to about 100 Hz. In the tonedecoder, P2 is fitted instead of R9 toenable accurately setting the optimumsensitivity.Programming the slide sequence isfacilitated by the message "press but-ton", displayed following the executionof a command. The user can then ar-range for the next synchronization pulseto be recorded on tape.

Program descriptionThe program listing starts with an over-view of the variables used (lines140...530). This should prove helpfulfor possible extensions at a later. stage,and prevents the programmer losingtrack of declared variables. Manyvariables are declared as arrays, in whicheach element belongs to a particular pro-jector. There are also arrays that containonly two elements. These are notdeclared beforehand, since this is not re-quired in MSX BASIC for arrays of upto 11 elements (0...10 incl.). A numberof variables will be discussed below withan aim to clarify the operation of thecontrol program, and to aid program-mers of non-MSX computers convertingthe software for use on their machine.

Variable X is a counter used within theON INTERVAL routine in lines5500... 5690. This variable may not beused for other purposes after theON INTERVAL initialization, becauseintervals always return X as 16, irrespec-tive of the previously assigned value. Ar-rays T1 ...T6 hold the timing periodsthat are used during the changing of theslides. TI(I) determines the on -time ofthe feed -forward relay that controls thecarriage in projector I. T2(I) indicatesthe wait time before the change is com-plete. T(3)I and T(4)I have similar func-tions for reverse changing. VariablesT(5)I and T(6)I serve as counters duringthe changing period. Their starting valueis copied from T(1)! and T(2)I, or T(3)Iand T(4)1. The values in arrays TI .. .T4depend on the specifications of the pro-jectors used, and may be defined in-dividually for each projector. In prac-tice, it will be found that a single valuefor the arrays enables satisfactory oper-ation of all projectors, even if these dif-fer in respect of type and make.Arrays B1 and B2 indicate activity of anyone projector in the system. B(1)I in-dicates whether or not the lamp intensityfor the relevant projector is beingchanged, while B(2)I signals slide chang-

ing activity. The fade rate is set by thevalues in S(1), S(2), DE(1) and DE(2).S(1) and S(2) indicate the step size usedfor increasing or reducing the lampintensity. DE(1) and DE(2) define thenumber of times the ON INTERVALroutine is skipped before the lamp inten-sity is re -adjusted. The values assignedto these variables depend on the selectedFADING RATE. The (temporary) stepsize and delay information are recordedseparately for each projector with theaid of variables S1(I), DWI and D(2)I.Among the most essential lines in theprogram is number 860. This determinesthe rate at which the command executionsubroutine is called. StatementON INTERVAL -15 causes the mainprogram that arranges the entering ofcommands to be interrupted at15 x 20= 300 ms intervals to write newdata to the slide controller board(s).Command input is thus separated fromcommand output, preventing key actions

disrupting an effect while this is beingexecuted. The interval rate is set to300 ms to allow sufficient time for thecomputer to run the interval routine (line5500...5690). Too short an interval timewould cause the interrupt to begenerated'during the execution of the in-terval routine, making it impossible forthe computer to return to the mainprogram. It was found that 300 ms givesa reasonable time division between themain program and the interval routine.If the interval time is changed, allvariables containing period definitionsmust be changed also (T1. T4, DELDE2, SI and S2).

An optional keypadThe circuit diagram of an external, op-tional, keypad for entering all programfunctions is given in Fig. 3. The keypadis connected to the second joystick in-put, and is essentially an extended ver-

3

01_034= It:4113

03K

13.4,13te

Jee 3ziedikig:

44-0

P4 "

020

&:

-ctrhAi<

a:'oa

P70

0

jy.".0__.

1,271:20

014ifES'20 0--.

-0 0-4

03

04

Or

Fig. 3. Circuit diagram of the auxiliary, optional, keypad connected to the joystick input onthe computer.

EE

April 1988

Fig. 4. Layout of the keypad PCB (not available through the Readers Services).

sion of the circuit described in "1. Fig-ure 4 shows the track layout and compo-nent mounting plan. It should be notedthat this PCB is not available ready-made through the Readers Services. But-tons S-.15 ...SID incl. are dummy switchescovered by 6 double -size keytops.The machine -language routine thatbelongs to this control keypad is linkedto the computer -resident keyboard driver(lines 5800...5990). When writing or

debugging one's own control routines, itis important to remember that thekeyboard routine is loaded only once.This is so arranged because the hookvector that points to the keyboardroutine of the computer is moved and re-placed by the start address of the keypadroutine. Running this procedure twicecauses the computer to lose track of thestarting address of the resident keyboarddriver, so that the slide control program

Parts list9 -way female sub -D connectorDi... D44 incl.= 1N4148St...S3o incl.= PCB mounted data switch;

momentary action. Licon series 61 Alpha Type61-101xx00 (xx is keycap colour code).Keycaps: 6 off double, and 18 off single. 17WSwitches Division of 17W Limited Norway Road Hilsea Industrial Estate Portsmouth P03 511T. Telephone: (0705)694971. Telex: 86374.

Note: it is regretted that the PCB for the auxili-ary keypad is not available ready-made throughthe Readers Services.

64 EEApril 1988

is apparently not working. Data errorsreported during tests invariably requireinstruction POKE &HF975,00 to be runbefore restarting can take place.

The keypad routine can be tested separ-ately with the aid of line

KEY = STICK(X)- (8*STRIG(X))-(16*STRIG(X +2))

where X is the number of the joystickport.Alternatively, use

1 DEFINT A: A =USR0(0): IF A< >0THEN PRINT A: GOTO 1 ELSE 1

Instruction A=USR0(0) fetches thenumber of the actuated key. Its effect issimilar to statement AS=INKEY$. Theroutine has a buffer with a holding ca-pacity of 128 key actions. The buffer is

cleared by pressing keys [shift] and[clear] sequentially, while just [clear]empties the buffer until the last "go"command. The [shift] key must alwaysbe pressed individually to ensure that thekeypad routine assigns a differentnumber to the next key pressed. The keynumbers returned by the routine corre-spond to the numbers of the switches(1...23 incl.; 24 is the [shift] key). Thenumber is increased by 24 when thepreviously pressed key was [shift](25...47 incl.). The keypad routinereturns a nought to indicate that no keywas pressed when it was called.

References:") Record -playback amplifier. ElektorElectronics October 1987, p. 44 ff.'1) 16 -key input for MSX micros. ElektorElectronics July/August 1987, Supple-ment p. 17.

51

17:A

3 F.-761

21A

4

111E1111E1

111 111 111

Go

Ni

X M

A

Fig. 5. Location and lettering of the keys onthe auxiliary keypad.

The listing of the BASIC controlprogram is available free of charge bysending a self-addressed, stamped en-velope to our Brentford office (over-seas readers: please include 2 IRCs).

ELECTRONICS NEWSColour television monitorVistek's high -standard grade 2 colourtelevision monitor has been designed forgeneral-purpose applications in studioand similar environments where grade 1performance is not required. TheGM2716's all-round performance andwide range of facilities are said to makeit ideal for most colour monitoring re-quirements.Vistek Electronics Ltd Unit C WessexRoad BOURNE END Buckingham-shire SL8 5DT.

Optical fibre cleave toolA new tool to facilitate the cleaving ofoptical fibres is being produced underlicence from British Telecom PLC. Itconsistently produces highly accuratesquarely cleaved faces and is ruggedenough for use by technicians at theroadside during optical -fibre instal-lation.The tool is self -calibrating with a widerange of fibre types: 50/125; 62.5/125;85/125; and 100/140 multinode all -silica,and 5/125 and 8/125 monomode fibres.Further information from K.V. Kirk &Sons The Winship Industrial Estate Milton CAMBRIDGE CB4 4BD.

Electronic fingerprintrecognitionAn electronic fingerprint recognitionsystem developed by scientists at Edin-burgh University's electrical engineeringdepartment has received £500,000 back-ing to build a full-scale demonstratorand carry out field trials.The system was invented by the depart-ment's Professor Pete Denyer and aprototype has already been built and

THE ELECTRONICS INDUSTRYThe UK Electronics Industry continues to face a strong international challenge at homeand abroad. The EEA News Bulletin tells how the major UK electronics companies areachieving success in UK and Export markets by selling equipment, systems andsoftware using the most advanced technology.

EXPORTSThe UK Electronics Industry exports half its production of equipment, systems and soft-ware. Total exports have trebled in value between 1980 and 1987, led by exports of dataprocessing equipment, which in 1987 resumed their upward trend. All other sectors alsoincreased their exports, with radio and electronic capital equipment maintaining apositive balance of trade in civil and defence goods. The relatively low level of export ofcommunications products reflects the dosed nature of this market; Government and EECmoves to open international competition in telecommunications are to be encouraged.

A Data peoctsvIngeciLdFc.nl

B Ccinponmts an -dsub-awe=blles

C Radio andelectron?: capitalequipment

D Ccaurneecalicasequipment

ziro

£ million

EXPORTS OF PRINCIPAL PRODUCTS

--

.---------..:7-.---'------'"---1.-....-._......--..-

------ ------ - ----- ' ----------- .

19N 15N) 1;81 I,52 1%3

Source: The Electronic Engineering AssociationI9S6

A

C

1%7(estimated)

tested. Potential applications for thedevice, which electronically matches apresented fingerprint against a memorystore of "authorized prints, includedoor and computer systems security andpoint of sale machines.Initial development work was supportedby the Quantum Fund, which is backedby the British Linen Bank, the ScottishAmerican Investment Company, and

Edinburgh University to provide venturecapital for commercially exploitablework at the university.Quantum will provide further capital toenable the university team to build a full-scale demonstrator of the device. Thiswill then undergo field trials with De LaRue Company, who will have exclusiverights to the technology.

EE

April 1988

r;i:

CEPT European standardsinstituteIn the wake of the EEC proposal for thedevelopment of a 'real' common marketfor telecommunications equipment andservices (as first reported in ourSeptember 1987 issue), the DirectorsGeneral, Telecommunications, of theConference Europeenne des Admini-strations des Postes et des Telecom-munications-CEPT-have decided toestablish an autonomous European Tele-communications Standards Institute.This decision marks a major step for-ward in the production of EuropeanTelecommunications standards.

767.; :11z)17817.:. 37.1.1

'

s:) 11-11.7..)iii;:ii:170:7) 176:j t-*

r

Rediffusion Radio Systems' LF/MF/HFcommunications system console which thecompany will fit in seven Type 23 frigates andtwo training outfits of the Royal Navy.

Incomtel brochureInternational suppliers of telecommuni-cations and broadcasting services, In-comtel, have increased turnover by 50%through projects in thirty countries.To mark this, the company has pub-lished a new brochure which outlines thefull range of facilities now available.Their services include feasibility studiesand project planning to project com-pletion and on -site training of localstaff. All design work is undertaken inthe UK, but Incomtel's own engineersand technicians always take up residencein the country concerned to superviseprojects.INCOMTEL Ltd 225 GoldhawkRoad LONDON W12 8SB Tele-phone 01-743 5511.

New CTCSS panelA new CTCSS encode only panel, TypeCDS37E, has been announced by Com-munication Development Specialist. The

panel complements the VE CTCSS en-code panel and provides a program-mable encode only facility for most two-way radio applications.CDS Limited P.O. Box 83BASINGSTOKE RG25 2PX Tele-phone (0256) 83528.

New RF amplifier chipNational Semiconductor has introduceda low -noise RF amplifier for use over thefrequency range 500 kHz to 1 GHz. Thedevice has a power gain of 14 dB at500 MHz.The LH4200 is a hybrid IC with agallium -arsenide front end for highspeed, and bipolar 2nd and 3rd stagesfor high -power output. Output im-pedance is 50 ohms.National Semiconductor Corporation 301 Harpur Centre Home Lane BEDFORD MK40 1TR Telephone(0234) 47147.

Revised circuit analysispackageNumber One Systems' PC circuitanalysis package, ANALYSER II, hasbeen thoroughly revised to includeanalysis of Microwave Striplines andTransmission Lines. This is a very rarefacility in low-cost design tools whichwill make a significant contribution toremoving the mystique of HF circuitdesign. The revised package will be dis-cussed further in our July issue. In themean time, further information may beobtained from Number One SystemsLtd Harding Way SomershamRoad St. Ives HUNTINGDONPE17 4WR Telephone (0480)61778.

New PAL coderThe latest addition to Visitek'sVaricomb range of high -quality codingand decoding equipment is an entirelynew PAL coder that provides a 'clean'luminance signal, free from chromamodulation, but without the timing

RADIO & TV NEWS

problems normally associated withcomb -filter designs.Vistek Electronics Ltd Unit CWessex Road Bourne End BucksSL8 5DT Telephone (06285)31221.

Module stores four lines ofvideoBAL Components are offering a newMicrosonics VDM36 series 2H/4Hvideo delay module capable of storingfour lines of video.The VDM36 provides two 128 its videoin/video out delay channels, which canbe cascaded to form a 4H delay with a2H tap, or used independently as 128 psdelays.BAL Components Ltd BermudaRoad NUNEATON CV10 7QF

Control processors for microwave and radarapplications have been developed by RanoMicrowave Instruments Ltd DunmereRoad Bod min Cortina!!. They were de-signed for remote computer control via thegeneral purpose interface bus-GPM-orlocal, manual control via a front panel.

ERA satellite seminarThe rapid growth in satellite communi-cations has led to an increasing need forhigh data -rate links between spacecraftto enhance the capacity, coverage andconnectivity of systems. The impli-cations of adopting such links will bediscussed at ERA's forthcoming seminarInterorbit and Intersatellite Links:Systems and Technology, which will takeplace on 29-30 June, 1988, at the RoyalGarden Hotel, London. Further infor-mation from ERA Technology Ltd Cleeve Road LEATHERHEAD KT227SA Telephone (0372) 374151.

66 EE

April 1988

SUPERCONDUCTIVITY:FURTHER OUTLOOK WARMER

by George Short

London's Science Museum recently acquired a new exhibit. It isnot much to look at: a cylinder of black ceramic material. But thesmall company from the London suburbs which made it is proud

to claim that it is the world's first high -temperaturesuperconducting solenoid. It is just one manifestation of the burstof research activity into a new class of superconductive materials.

Superconductivity is the property of cer-tain materials to lose all electrical resist-ance. The phenomenon was discoveredby the Dutch physicist Heike Kammerl-ingh Onnes, who announced in 1?11 thatmercury becomes superconductiVt whencooled to a very low temperature, aboutfour degrees above absolute zero (4 K).It soon emerged that a number of metalsbecome superconductive when coldenough. In every case the temperature re-quired was only a little above absolutezero, attainable in practice only by im-mersing a specimen in liquid helium,which boils at 4.2 K at atmosphericpressure.Having to reach such a low temperaturewas inconvenient but did not precludewhat seemed at first to be an ideal appli-cation of the discovery, making electricalmotors and generators of high powerand efficiency. A great deal of the energywasted in electromagnetic machines is inheat generated through the resistance oftheir windings by the flow of current.Removing the resistance by making thewindings out of superconductive wireseliminates the loss.Unfortunately, this hope was dashed bythe discovery that superconductivity isdestroyed when the wire is immersed ina strong magnetic field. Because motorsand generators need strong fields tooperate properly, the hoped -for improve-ment seemed unattainable.

Further researchNevertheless, superconductivity was afascinating and unexpected effect. Forthat reason alone it became an import-ant subject for physical research, andmore was discovered.What makes a superconductor lose itsresistance? At first it seemed likely thatat the very low temperatures involved theatomic structure of the material ar-ranged itself in a perfectly ordered form.Electrons could then, it was argued,move through the empty space betweenthe atomic nuclei without colliding with

anything and losing energy. But the ex-planation is far more complex.One interesting aspect is that the elec-trons which mediate superconductivityappear in what are known as Cooperpairs, with opposite spins. Subtle quan-tum effects are involved, too.Loss of electrical resistance is only oneof several changes that take place whena superconductor is cooled below thecritical temperature at which resistancedisappears. There are striking magneticeffects: the permeability of the materialdrops to zero and magnetic flux in thematerial disappears; the thermal con-ductivity increases sharply.The phenomenon of electron tunnelling,whereby electrons are able to penetratebarriers which classical physics oncedeemed impassable, is particularly im-portant. Professor Brian Josephson atCambridge University, who gained aNobel Prize for his work, predicted anddemonstrated that when two supercon-ductors are separated by a very thin in-sulating layer electrons are able to passthrough the insulation even when there isno electromotive force to drive them. Ifa driving voltage is applied, oscillationsare produced at a frequency whichdepends only on the voltage and twowell-known physical constants, Planck'sconstant and the charge on an electron.One implication is that if the frequencyis measured the applied voltage can becalculated. This means that a Josephsonjunction, as it is now known, could pro-vide for the first time an absolutemeasure of the volt.

Niobium tinAbout half a century after superconduc-tivity was discovered another findingsuddenly renewed hopes of putting theeffect to practical use. This was thepossibility of making metallic alloys thatwould stay superconductive in very highmagnetic fields. Alloys of niobium andtin are now used in powerful elec-tromagnets.

An electromagnet of normal construc-tion has the unenviable quality ofmanifesting zero efficiency, for all theenergy in the driving current is dissi-pated in the resistance of the coil wire. Ifthis resistance were reduced to zero byusing superconductive wire, the ends ofthe winding could be connectedtogether, leaving the energising currentto circulate for ever without externalhelp.The idea is so attractive from theengineering point of view that it is worthgoing to the expense of installing liquidhelium refrigeration to keep the coilcold. The energy saved by abolishing coilresistance more than pays for the cost ofrefrigeration. At any rate, that is so inthe applications for which superconduc-ting solenoids are used. These includefield coils for nuclear magneticresonance body scanners, chemicalmicrowave spectrometers and large parti-cle accelerators. The wires used for thewindings are composite: the supercon-ductive alloy parts are bonded to copperconductors. If, as can happen, a smallpart of the superconductor is overloadedand reverts to ordinary conductivity thecopper acts as a temporary low -resist-ance bypass until it cools down. Suitablealloys are being made in the UK by IMI.Superconducting coils have been propos-ed for use in hovertrains. The idea is touse superconductive electromagnets tosuspend the train in the air only a shortdistance below an overhead track. In thisway friction could be minimised and thetrain would glide along smoothly at highspeed.A less futuristic use of magnetic levita-tion is in a superconductive bearing. Oneconsequence of the magnetic propertiesof a superconductor (or, rather, its an-timagnetic properties) is that a magnetbrought near to a piece of superconduc-tor experiences a repulsive force. Given asuitably shaped superconductor, thisrepulsion can keep the magnet floatingin the air. So, if the magnet is an axle, itcan be rotated virtually without friction.On a small scale such a low -friction

bearing could be very useful ingyroscopes for navigational instruments,where frictional drag is a source of error.On a larger scale, a combination ofsuperconductive coils and floating axleswould be useful in electric motors andgenerators.

Electronic applicationsIt is hoped that with the arrival of 'high -temperature' superconductors many ofthe possible low -power applicationsworked out with liquid -helium -cooleddevices will become much more prac-ticable.The new superconductors work at tem-peratures above the boiling point of li-quid nitrogen (77 K or -196 °C). Liquidnitrogen is relatively cheap and safe. Onelitre of liquid helium costs around fourUS dollars, is expensive to store andtricky to handle. Liquid nitrogen inBritain is cheaper than beer and easy tohandle. At a recent demonstration at theRoyal Society in London, researchers onsuperconductivity from BirminghamUniversity, in the English midlands,stored it in ordinary vacuum flasks ofthe kind used at picnics and poured itout for use into throwaway plastic cups.One envisaged application is thecryogenic computer. The technology hasalready been worked out, notably byIBM, but shelved because of the liquidhelium problem. The computer makesuse of the fact that superconductivitycan be destroyed by a magnetic field.This, a nuisance in power applications,is a blessing for computing. It enablesthe resistance of a circuit to be switchedfrom nothing to something small butfinite, which is the basis of gate circuit.If gates can be made, computing circuitsare feasible. The absence of resistance inthe superconducting state makes forhigh speed operation, and speed is aprerequisite for improving conventionalcomputers in which operations are car-ried out in sequence and the duration ofa sequence determines the speed ofworking.

Extremely sensitiveResistance in communications engineer-ing brings with it another penalty: noise.Any resistance in an amplifier generatesnoise, which sets a lower limit to the am-plitude of signal which can be detected.Below that limit the resistance noisedrowns the signal. For satellite and deepspace communications it would be at-tractive to reduce amplifier noise by in-corporating superconductors into theearly stages of receivers. Some liquid-helium -cooled devices are in use now;liquid -nitrogen -cooled amplifiers shouldenable the cost to be reduced and thefield of application widened.One amplifying device already achievedin liquid -nitrogen 'high -temperature'

form, at Strathclyde University,Glasgow, is the superconductive quan-tum interference device, or SQUID. ASQUID is essentially an extremely sensi-tive detector of changes in magnetic fieldstrength. Its uses range from military tomedical. A SQUID can, for instance,detect submarines by monitoring thechanges they produce in the Earth'smagnetic field in their vicinity. It canmonitor blood flow (blood is magnetic)when placed near a blood vessel.In radio, superconductors could be usedto reduce the size of aerials, which areusually made in dimensions that bear asimple relation to the wavelength. Theubiquitous half -wave dipole is anexample.

A piece of yttrium barium copper oxidesuperconductor floats above a strong perma-nent magnet.

Attempts to reduce the size to a verysmall fraction of a wavelength arevitiated by a sharp reduction in theaerial's ability to radiate signals. Thisability is described in engineering termsby saying that an aerial has a certainradiation resistance. A resistance ab-sorbs energy and the radiation resistanceof an aerial is really a fictitious quantitywhich describes the aerial's ability tolaunch energy into the space around it.Aerials much shorter than a wavelengthhave very low radiation resistance. Ashort vertical wire aerial, for example,behaves like a resistance of a tiny frac-tion of an ohm in series with a very highcapacitive reactance. In theory it shouldbe possible to tune out the reactance andallow energy to flow freely to the resist-ance (that is, to radiate). In practice, thelosses of the inductance coil needed totune out the aerial capacitance are sogreat that virtually all the energy is lostin the coil.If the coil could be made superconduc-tive this waste could be avoided. A shortaerial could then, in theory, be as ef-ficient a radiator as a long one. And,because a good transmitting aerial is agood receiving aerial too, a short super-conductive receiving aerial should alsobe efficient. One form of aerial whichseems to hold great promise for fabri-cation in superconductive form. is theloop aerial. It is in effect a form of elec-tromagnet coil and in its normal form isinefficient.

The ceramic nature of the new high -temperature superconductors posesproblems in applying them. Thematerials themselves are quite easy tomake. The current most popular one, yt-trium barium copper oxide (YBa7 Cu307) has been made in school laboratoriesin the USA and Britain. It is, however,brittle. This is the reverse of what isneeded, which is a ductile, easily formedmaterial, capable of being drawn intowires, pressed into sheets and foils andso on. Fortunately, some of thecomputing -type applications call forvery thin layers deposited on insulatingsubstrates. Several standard methods formaking these are available, includingsimple vapour deposition in vacuum anddeposition from an ionised gas. Evenprinting, using inks made of the re-quisite materials, shows promise. If thematerial in powder form can be made tosuperconduct, it should be possible toform 'wire' by first packing the powderinto a metal tube and then reducing thetube diameter by a wiredrawing tech-nique, squeezing down the powder insidein the process. It may well be that suc-cess in applying the new materials willdepend more on the development ofsuitable fabrication techniques than in adeep understanding of how they work atthe crystal structure level.

Even higher,temperatures?Why stop at liquid nitrogen tempera-tures? Why not make room -temperaturesuperconductors and avoid the coolingproblem altogether?A few years ago this seemed impossible.Recently, there have been reports andrumours of apparent superconductivity,if not at room temperatures at least attemperatures far above that of liquidnitrogen. So far the results have provednot to be reproducible. This very -high -temperature superconductivity appearsto have been produced by some for-tunate accident during the manufactureof the new ceramic superconductors.And it has been transient, disappearingwhen the material is heated and cooled anumber of times. This suggests that itmay be a new form of superconductivitywhich is a function of the internal struc-ture of the bulk material and appearsonly when the heat treatment (sinteringof metallic oxides at about 950 °C) usedin its manufacture chances to be right.Once the process is understood it may bepossible to reproduce it to order. Yetanother class of superconductors may beon the way.

088

THE EFFICIENT AL1ERNATIVETO LARGE POWER STATIONS

by Dave Andrews

Decentralizing electricity generation, but maintaining a grid system with a much larger number of smallpower stations, is an idea gaining favour with many engineers. Installations in industrial premises can

generate enough power for local needs and in off-peak periods feed power into the grid system forother users. Moreover, such stations are already developed and on the market, and their efficiency

ratings are impressive.

In most of the industrialized world,generating power on a large scale has fol-lowed a trend away from large numbersof very small power stations to smallnumbers of very large ones. The reasonshave been that coal-fired steam cyclestations showed impressive economies ofscale, for large power stations could bemade more efficient: developments inhigh -voltage transmission meant that thelarge stations could be built out in thecountry, where land was cheap andpollution was not so noticeable.In the UK, generating sets work at up towell over half a thousand megawatts,compared with a few hundred kilowattswhen large-scale generation of electricitybegan. This established model has beenseen as the economical path for develop-ing countries too: diesel generators serv-ing remote villages are giving way tolarge, central power stations, and distri-bution by overhead high -voltage lines.However, this model may have beenturned on its head by the development ofa new kind of mini power station. Evensmaller than the first power stations, it ischeaper, nearly three times as efficientand less polluting than they were. Such astation is so small that it can be tuckedinside existing buildings. Large numbersof them could be installed in an in-dustrialized or a developing country,generating power at low voltage andfeeding any surplus into the publicsupply, to be sent to other load centres.This arrangement would save heavy in-vestment in central power generationand high -voltage transmission lines.There are now about 200 of these smallstations already installed in the UK.

Power outputA mini power station usually consists ofan industrial gas or diesel engine drivinga generator, just as in a conventionalstation but only the fraction of the size.A typical output is about 40 kWe(kilowatts, electrical) compared with atypical conventional station's 2000 MWe(megawatts, electrical). Mini stationsnow range in output from 18 kWe to2.5 MWe. Under development are unitsfor 3 kWe and 8 kWe. One kilowatt of

A typical twin -set mini power station.

output is enough to run a single bar ofan electric fire.The mini station is fitted with equipmentthat enables it to be directly connected toa public supply cable and operate inparallel with it. Its output is used withinthe building or, if it is producing asurplus, the extra energy is sold to bepublic supplier. Modern electronics tech-niques enable systems to be producedthat can start up and connect themselvesto the alternating -current mains supplyentirely automatically, and to stay syn-chronized with the mains frequency andphase. In small stations up to about90 kWe this is achieved by using an asyn-chronous generator, which is used firstas a motor to start the engine, and thenas the generator; this does away with theneed for starter batteries. The asyn-chronous generator has the advantagethat it is always synchronized with thefrequency of the supply to which it isconnected, so no synchronization pro-cedure is needed. In larger systems,where the inrush of starting from themains would be too high, battery startand synchronous motors are used. Witha synchronous generator, automatic syn-chronizers are used to bring the gener-ator into correct phase and synchroniz-ation with the mains before the mainscontactor closes. Automatic devicesmonitor and control all aspects of thesystems's performance, and either indi-cate alarms or shut the units down ifthere is any mechanical or electricaldefect.

Instead of a radiator to dissipate heatfrom the engine, as in a conventionalstandby generator set, heat exchangersare fitted so that this normally wastedheat is profitably used. Places that canbenefit economically, include leisurecentres, hospitals, residential schools,swimming pools, prisons, hotels and fac-tories, where the recovered heat can beused for central heating and hot watersupplies, or perhaps for some industrialprocess. In effect, the fuel is used twice,once for generating power and a secondtime for producing heat.

Warm climatesIn countries with a warm or hot climate,mini power stations still have such appli-cations because a great deal of the heatload is independent of external tempera-ture, and there will be much more scopefor using the engine's waste heat togenerate cooling for air-conditioning orrefrigeration plant. In such places thewaste heat is used to drive an absorptiontype of heat pump. This is particularlysignificant in developing countries,where expensive diesel -generated elec-tricity is often used simply to provide airconditioning at very low efficiencies andhigh cost.Capturing and using this normallywasted heat dramatically increases theefficiency of power generation becauseany generating system, whether based onnuclear or fossil fuel, always has to getrid of about two-thirds of the input fuelsimply as heat, which means very lowoverall efficiencies if that heat cannot beused. Moreover, large power stations areusually sited out in the country, awayfrom any building which could use suchheat, so they have to waste the heatdeliberately in the familiar coolingtowers. A further nine per cent is lost intransmission and distribution, whichbrings overall efficiencies down to about28 to 30 per cent. By capturing thisheat, mini power stations can boast ef-ficiencies over 2.5 times that of a typicallarge system, thereby allowing them toproduce much cheaper power.In the UK and western Europe, wheregas prices are low, the industrial spark

EE

Aprii 1988

Fused isolator. Lockable 4 -core armoured cable

Electricity authority'skilowatt-hour meter

Authority'sincoming supply

Main bus -bars

Plug -and -socketconnection

in Off setting only

Combined heat and power (CHP)unit kilowatt-hour meter

10 -core control 2 -core gasinterconnecting cable supply cable

Circuit breaker

Star/Delta starter

6 -core main connectioncable (plus separate earth wire)

Installation scheme for a 40 kWe station.

is favoured for use inmini stations. It is similar to a carengine, but is much more heavily builtand is designed for extremely long lifecoupled with low costs of running andmaintenance. The engine can run on awide variety of fuels including landfillgas, biogas, natural gas, liquidpetroleum gas, mine drainage gas andlow thermal value gas from wood orcrop residue gasifiers. The latest lean -burn engines have electrical efficienciesof 35 per cent, which is better overallthan the efficiency of central power gen-eration when distribution losses aretaken into account. Depending on localfuel prices, an alternative might be thediesel engine. Dual -fuel engines are ruledout by their high capital cost,maintenance costs and their extra com-plication. The 3 kWe and 8 kWe units Imentioned earlier are based on a rotaryengine. Stirling engines, which offer thepossibility of running on coal, are alsobeing looked at closely.Typical payback times for these appli-cations are two to four years if the equip-ment is installed by a consumer who canavoid the total costs of electricity supply,or perhaps three to five years if the elec-tricity authority installs the system.Paybacks for a nuclear power stationtake an amazing 20 to 40 years.

Housing systemsA forthcoming report from the UK

Open University's Energy ResearchGroup shows that the technology couldbe well adapted to modern low -energyhouses in the UK, with one 40 kWe unitshared between 40 houses linked byburied hot water pipes. Existing houseswould need one 40 kWe unit for 20houses; this would be equivalent toabout 2 kWe of mini power station out-put per house.Another idea being worked on by Ap-plied Energy Systems at Watford is therotary engined mini -power station smallenough to fit into individual houses. Ifsuccessful it will have the advantage thathot water pipes will not be needed to linkhouses and it will avoid the cost of heatmetering.Comparison with the motor car engineshows that any notion of too many minipower stations being needed is wrong:there are many millions of similarly sizedengines fitted in road vehicles today, andproduction easily keeps pace with the de-mand. Furthermore, by spreading theelectrical source among a large numberof sets ensures that the breakdown of asingle station has a negligible effect onthe whole system, which is not alwaystrue of very large central power stations.Put another way, when do all roadvehicles break down simultaneously?And what percentage of cars do we seebroken down on the motorway?Reliability is endorsed by the fact thatindustrial engines to drive mini powerstations have been used in the oil in-

dustry for over 50 years. They are de-signed for very long life and there areexamples that have clocked up theequivalent of 25 years' continuous run-ning.Sometimes it is alleged that mini stationsare economic only because of low fuelprices, which may not last for long. Butthey convert gas into heat as efficientlyas do existing gas boilers, and do notconsume any extra gas for generatingelectricity, so the price of the electricitythey produce is largely independent ofthe gas price. There are, too, mini sta-tions that can run on coal dust if gaswere to become prohibitively expensive.

Dave Andrews was until recently an areamanager with Applied Energy Systems ofWatford and is now a freelance consultant.

EE

April 1988

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aftware is also available fromECHNOMATIC LIMITED (for address,

.ee inside front cover).In Sweden. printed -circuit boardsshould be ordered fromELECTRONIC PRESSBox 63S-182 11 DanderydTelephone: 08-753 03 05

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301 Circuits £6.25302 Circuits E 6. 25303 Circuits E7.95

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Elektor Electronics binder ... E2.95

FRONT PANELS

Indoor unit for satel-

No. Price(El

VAT(El

lite TV reception 86082-F 3.50 0.53Top -of -the -range 86111-F1 5.60 0.84

preamplifier 86111-F2 4.45 0.67Intelligent timestandard 86124-F 15.70 3.71

Digital sine -wavegenerator 87001-F 5.45 0.82

Autoranging DMM 87099-F 2.80 0.42Frequency mete, 27286-F 10.75 1.61

SOFTWARE

Software in IELPROMs

pP-controlled frequency

No. Price VAT(El (El

meter 1 x 2732 531 9.00 1.35X -Y plotter1 x 2732programmable timer

532 9.00 1.35

1 x 2732 535 9.00 1.35GHz pre -scaler1 x 2732automate yourmodel railway

536N 9.00 1.35

1 x 2716marine computer

537 7.30 1.10

1 x 2716 538 7.30 1.10Jumbo clock2 x 2716 539 14.60 2.20Graphics card2 x 82S123printer buffer

543 9.60 1.44

1 x 2716 545 7.30 1.10MSX EPROMmer1 x 27128 552PK 7.30 1.10Intelligent time standard1 a 2764 553 10.00 1.50EPROM emulator1 x 874811 558-A15.00 2.25Stave indication unit

for I.T.S. 559 15.00 2.25

PRINTED CIRCUITS

Readers who wish to maks their ownPCBs Ilor private end persona' use only)may in many, but not ail. case* receivethe reIerent draw irgs Ir-,a of charge byordering these on the order form oppositeend encl.:sing a stamped addressedenve;apre IcrefaraNy 9,6 it, or230,150 mini.

No. Price VATICI (El

MAY 1987Capacitance meter 86042 5.15 0.56

No.

Metal detectorMIDI signal distributionSpot sine wave

generator 87036-1 rot wailer*JUNE 1987Intercom for motorcyclists 87024 6.85 1.03

Spot sine wavegenerator 2 87036.2 rot arailatie

Autoranging DMM 87099 6.55 0.98JULY/AUGUST 1987Men bridge oscillator 87441 2.15 0.32Duty factor analyser 87448 5.85 0.88Digital voltage :current

display 8746832 K pseudo ROM 87500Headphone amplifier 87512Halogen lamp arKner 874527-cbgit code lock 87463SEPTEMBER 1987Surface -mount stereo

FM receiver 87023 3.20 0.4816 Kbyte CMOS RAMfor C64 87082 4.10 0.62

Active phase -linearfilter 87109 15.00 2.25

EPROM emulator 87136 17.50 2.63OCTOBER 1987IEEE interface 87054 Not availableSW adapter 87145 Not available14 -bit D.A convener 87160 9.00 1.35Fleconfingtitaybackamplifier 87486 Not available

Low -noise microphoneamplifier 87058 3.45 0.52

NOVEMBER 1987SSB Receiver for 80 mand 20 m

BASIC computerDimmer for inductive

toads 87181IR Transceiver 87179DECEMBER 1987Digital motor driver for

Flit modelsFrequency meterLCD VU meter

JANUARY 1988DCF77 Receiver andFrequency Standard

Stereo limiterLight.powered

thennorrieler 87188 6.75 1.01Switch -mode PSU 880001 5.00 0.75FEBRUARY 1988Intel.,gent timestandard 86124-2 7_15 1.07

Infra -red headphones 87640 6.10 0.92Presr_aler for frequencymeter 880005 9.25 1.39

MARCH 1988Infra -red detector foralarm systems 87067 4.55 0.68

Slave indication unit 87104-1 10.50 1.58for 1.1.S 87104-2 10.50 1.58

Corriputer-controlledslide fader 87259 15.00 2.40

Low -noise preamplifier 880041 6.50 0.98for FM receivers 880042 5.00 0.75

Signal divider forsmartie TV receivers 880067 5.00 0.75

APRIL 1988Stereo sst.nd generator 87142 7.25 1.09Fuzz 'sr guitars 87255 6.50 0.98

Ode Not availableActive - .:speakssus:a- 880030 7.50 1.13

C

Price VAT(fl ICI

86069 4.25 0.5487012 7.40 1.11

6.50 0.984.00 0.609.00 1.35

rat svaJablerot avalsbae

87051 14.75 2.2187192 20.25 3.04

6.00 0.90Not available

87098 4.5087286-A 12.5087505 6.7587520 6.75

0.681.881.011.01

86124-A 8.70 1.3187105 Not avelatle87168 7.25 1.09

880040-1 5.25P.S00.14 6.25

for VHF & UHF TV =E= -J45 5.50e preamplifiers

0.790.940.83

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January 1988February 1988March 1988Apnl 1988May 1988June 1988July/August 1988September 1988October 1988November 1988December 1988January 1989February 1989March 1989April 1989May 1989

17 Dec. 198714 Jan. 198818 Feb. 198817 Mar. 198814 Apr. 198812 May 198816 June 198818 Aug. 1988IS Sep. 198820 Oct. 198817 Nov. 198815 Dec. 198819 Jan. 198916 Feb. 198916 Mar. 198920 Apr. 1989

9 Nov. 19874 Dec. 1987

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13 May 198815 July 198812 Aug. 198816 Sep. 198814 Oct. 198811 Nov. 19885 Dec. 1988

13 Jan. 198910 Feb. 198917 Mar. 1989

26 Oct. 198720 Nov. 198728 Dec. 198729 Jan. 198826 Feb. 198825 Mar. 198829 Apr. 1988

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2 Sep. 198830 Sep. 198828 Oct. 198821 Nov. 198830 Dec. 198827 Jan. 19893 Mar. 1989

HE & VHF TechniquesTelecommunicationsSensorsElectrophonicsArtificial IntelligenceElectronics & ArtAmateur Radio & TVComputers & MicroprocessorsPower suppliesOptoelectronicsComputer -aided test & measurementAudio & 111.5TV & videoKnowledge -based systemsTelecommunicationsRobotics

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EE

April 198879

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P.O. Box 3, Rayleigh, Essex. Telephone Sales (0702) 554161.Shops at: Birmingham. S. New Rood, 6,1,,,,,Te 021 384 8:11

Bristol. 302 Goxeslee Rood. Te8 0272 23201fLandon -159-161 *ng Street Hccenerwral W6ie 01 748 0926klioncheseer. 8 OskM Rood Tei 061 236 0281Saithomplon. 46-48 Beeta Voky RoceL 1V_ 0703 225831Sovittend-on-Sea. 282-284 tendon Rood Wed&rr-or.-&,d. rase,- Tet 0702 5540C4

fra vp c copy of our 1988 cat.'og.efrom any branch of Wit.SN HIM for iLst

£1.60. Or to receive your copy try past

send £1.60 - 40p p&p to our P.O. Box

oddress if you Eye outside the U.K.

please send £2.75 or 12 bernatiocoal

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