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JUNIOR COMPUTER KIT ESE plus E1 p & pAll Junior Computer Extens,on Boards availableJUNIOR COMPUTER BOOK: 1 E4 2.3 & 1 E4.50 ea IP & p book 70p)TV Games Extension boards availableELEKTERMINAL KIT MO (plus Et p & p)TELETEXT DECODER KIT £85 (plus Et p & pl(Decoding Board and Ke, 5 card £195707. Nov_ 811Reprint of Teletext 373.7'e0 El 28 iplus large SAE/

PROGRAMMED EPROMSJunior Computer 2 2716 Intetekt Chess ea £82708 Basic E8 2716TV Games £82716 Tape Management a 71301 Elelaerminai £7

2716 Prog_ Management E8 2716 Disco Lights £892S23 Interface E5 82S23 Freq CaunterlIC 3C4 I ea 02716 Housekeeper £8 2716 Talkmg 13,ce £8

PCBs for most Elektor Projects availableSEE OUR FULL PAGE ADVERT IN THIS ISSUE FOR DETAILS ON

BBC COMPUTER PRINTERS etc.

PLEASE A DI) 341p p&p & Lionvvr' (Export: so VAT, p&p at Cost)

Orders from Government Depts. & Colleges etc. welcome.

13.1 0012110C! Price Last on request.Stock items arc normally by return 01 post. Atka.

elektor june 1984

selektorLasers: light sources with a future.

portable distress signalWherever you may be in trouble, on the road, at sea, in the hills, thisunit may bring help quickly.

6-18

6-20

ZX extensions 6-24Dedicated to the ZX computers, this article shows how you can carry outa number of extensions yourself and at low cost.

disco drum 6-32The drummer need no longer feel left out of the modern electronic groupwith our presentation of the 'user-friendly' electronic drum.

daisywheel typewriter printer interfaceThis interface connects an electronic typewriter to a computer's Cen-tronics output port to provide an inexpensive, high -quality printer.

maximum and minimum memorySuitable for storing positive and negative analogue voltages, this memorycan be used in a variety of applications.

missing link

PC board pages

lead -acid battery chargerNow lead -acid batteries are coming back into vogue, we present a designfor fast charging such batteries without reducing their life.

wireless microphoneProfessional radio microphones are not cheap and we have thereforedesigned one which though inexpensive to build still meets the standardsrequired by the Department of Trade and Industry.

merging BASIC programsA single BASIC program can quite easily be formed by combining twoexisting files as this article shows. Software is also included to enable theJC to use the OS disk 2 routines.

echo sounderThe season is almost upon us again when there are almost daily reports ofyachts having run aground: many such unfortunate accidents may beprevented by this echo sounder.

versatile audio peak meterA peak meter with LED display that may be used with any sound systemthat has a power output between 400 mW and 250 W!

market

switchboard

appointments

reader's services

advertisers index

6-34

6-39

6-41

6-42

6-45

Our front cover this monthsuggests two of the projectsin this issue. The 'halo' is, ofcourse, a daisywheel similarto that found in many high -quality computer printers.High -quality in this casegenerally also means highcost, but another, lessexpensive, daisywheel 'user',namely a certain type ofelectronic typewriter, canbe used as a computerprinter with very fewmodifications. We havedesigned a Centronics

6-48 interface for a specifictypewriter, the SmithCorona EC1100, which re-quires no actual hardwarechanges. The interface is,however, versatile enoughfor it to be relatively easilymodified for other type-writers.

In front of the daisywheel isthe portable distress signaldescribed on page 6-20. Thishandy unit may bring helpwherever you may needthis: stranded on somecountry road in your car,

6-63 in trouble while ramblingin the hills, or off -shorewith the rudder of youryacht broken, and in manyother situations we hopeyou'll never get into.

6-54

6-56

6-67

6-71

6-78

6-80

6-82

Next month is ourdouble issue: 'SummerCircuits 1984'. As in pre-vious years, we will offeryou more than 100 practicalelectronics projects for awide variety of applications.It will be on sale fromFriday 15 June. Don't missit!

6-03

Elektor Publishers Ltd., Elektor House,10 Longport, Canterbury CT1 1PE, Kent, U.K.Tel.: Canterbury (0227) 54430. Telex: 965504.Office hours: 8.30 1230 and 13.30 - 16.30.

Editor: P.V. HolmesAssistant editor: E.J.A. KrempelsauerUK editorial staff: R.E. Day, G.P. McLoughlin, L. SeymourOverseas editorial staff: P.H.M. Baggen, A. Dahmen, I. Gombos,

P.E.L. Kersemakers, R.P. Krings,P. v.d. Linden, D.R.S. Meyer,G.C.P. Raedersdorf, J.F. van Rooij,G.O.H. Scheil, M.J. Wijffels

Editorial secretariat: C.H. Smeets, G.W.P. WijnenHead of design: K.S.M. WalravenDesign staff: J. Barendrecht, G.H.K. Dam, K. Diedrich,

G.H. Nachbar, A. Nachtmann, P.I.A. TheunissenPublishing manager: A.J. BrialeyAdvertising manager: S. BrooksBankers: Midland Bank plc, Canterbury. Kent, sorting code

40-16-11, a/c 11014587Giro a/c no. 315-4254

Elektor Electronics is published on the third Friday of themonth preceding cover date with a special 'Summer Circuits'issue for JulyiAugust.

National advertising rates for the English -language edition ofElektor Electronics and international rates for advertising in theDutch, French, and German issues are available on request.

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The circuits are for domestic use only. The submission of designsor articles to Elektor implies permission to the publishers to alterand translate the text and design, and to use the contents in otherElektor publications and activities. The publishers cannot guaran-tee to return any material submitted to them. All drawings,photographs. printed circuit boards and articles published inElektor Electronics are copyright and may not be reproduced ortransmitted in any form or by any means, including photo-copying and recording, in whole or in part without prior writtenpermission of the publishers. Such written permission must alsobe obtained before any part of these publications is stored in aretrieval system of any nature.

Patent protection may exist in respect of circuits, devices, com-ponents etc. described in this magazine. The publishers do notaccept responsibility for failing to identify such patent or otherprotection.

Elektor Electronics is also published in Dutch, French, German,Greek, Italian. Spanish, and Turkish.

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Elektuur B.V.,6190 AB Beek (L), the Netherlands.Elektor Sarl, Le Seau, 59270 Bailleul, France.Elektor Verlag GmbH,5133 Gangelt, W -Germany.Elektor, Karaiskaki 14, Voula, Athens.Elektor Electronics PVT Ltd., 3 Chunam Lane,Bombay 400 007.Elektor, 20092 Cinisello B., Italy.Elektor, Av. Alfonso XIII, 141, Madrid 16.Elektor A.S., Refik Saydam cad. 89, AsianHan kat 4, Sishane Istanbul.

Distribution in U.K.:Seymour Press Ltd.. 334 Brixton Road, London SW9 7AG.

Copyright 01984 Elektor Publishers Ltd., Canterbury.

Printed in the Netherlands. ABC

Volume 10 - Number 6

What is 10 n?What is the EPS service?What is the TQ service?What is a missing link?

Semiconductor typesA large number of equivalentsemiconductors and ICs existswith different type numbers.For this reason, 'universal'type numbers are used inElektor wherever possible:for instance, '741' stands forpA741, LM 741, MC741,MIC741, RM 741, SN 72741.and so on.

Type numbers 'BC 107B','BC 237B', 'BC 547B' allrefer to the same 'family'of almost identical good -quality silicon transistors.In general, all membersof the same family can beinterchanged.

BC 107 (-8, -9) families (NPN):BC 107 (-8, -9),BC 147 (-8, -9).BC 207 (-8, -91,BC 237 I-8. -9),BC 317 (-8, -9),BC 347 (-8, -9),BC 547 1.8, -9),BC 171 (-2, -3),BC 182 I.3, -4),BC 382 (-3, -4),BC 437 1-8, -9),BC 414

BC 177 (-8, -9) families (PNP):BC 177 (-8, -9),BC 157 (-8, -9),BC 204 (-5, -6), BC 307 1-8, -9),BC 320 (-1, -2).BC 350 (-1, -2),BC 557 (-8, -9),BC 251 (-2, -3),BC 212 (-3, -4),BC 512 (-3, -4),BC 261 (-2, -3),BC 416.

Resistance and capacitancevaluesDecimal points and largenumbers of zeros are avoidedin values of resistors andcapacitors wherever possible.Instead, the following prefixesare used:p (pica-) = 10"3n (nano-) = 10-9At (micro-) = 10-6m (milli-) = 10-3k (kilo-) = 103M (mega-) = 106G (gigs-) = 109

A few examples of resistancevalues:2k7 = 2700 .11; 3M3 =3,300,000 n; 820 = 820 siResistors used are''/. watt,5% carbon types, unlessotherwise stated.

A few examples of capaci-tance values:4p7 = 4.7 pF=0.000 000 000 004 7 F;10 n = 0.01 = 10-3 F=10,000 pF

elektor june 1984

ISSN 0308-308X

The DC working voltage ofcapacitors (other than elec-trolytic or tantalum types)is normally assumed to be atleast 60 V. As a rule of thumb,a safe value is usually ap-proximately twice the DCsupply voltage.

Test voltagesDC test voltages shown aremeasured with a 20 ki?./V in-strument, unless otherwisespecified.

U, not VNormally, the internationalletter symbol 'U' instead ofthe ambiguous 'V' is usedfor voltage. 'V' is reservedas an abbreviation for 'volts'.For instance, Ub = 10 V,not Vb = 10 V

Mains voltageMains (power line) voltages arenot given on Elektor circuitsas it is assumed that ourreaders know what voltageis standard in their part ofthe world!Readers living in areas whichuse 60 Hz supplies should notethat Elektor circuits aredesigned for operation from50 Hz supplies. This will nor-mally not be a problem, butin cases where the mains fre-quency is used for synchron-isation, some modification tothe circuit may be required.

Missing linksAny important modificationsto, additions to, improve-ments to, or corrections in.Elektor circuits are generallypublished under 'MissingLink' at the earliest oppor-tunity.

Services to readers.Technical queries serviceSoftware serviceFront panel serviceBack number serviceCopy servicePrinted circuit serviceBook service

Details of all these can befound on pages 80 and 81.

6-04

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6-17

lasers: light sources with a future

The range of applications for laserscontinues to widen. The interactionsbetween laser research and the recentsurge of growth in modern communi-cations, data -storage and consumersystems are producing exciting re-sults, in which 'custom-built' lasersare playing a central part.In optical -fibre communications thelong -wave laser is indispensable. Theopto-electronic data -storage systemwith DOR discs (DOR stands fordigital optical recording) requires alaser of somewhat shorter wavelengthand relatively high power capable ofburning the information into the discin the form of small pits, as well as alaser of lower power for reading outthe information. New consumerequipment, such as the Compact Discsystem and the Laser Vision video -discsystem require inexpensive and rela-tively short-wave lasers.Lasers are going from strength tostrength, not just in professionalapplications but very definitely inconsumer electronics as well. What ismore, every application demands itsown type of laser. Philips Researchactivities extend throughout therange of laser applications. Researchtopics include custom-built lasers,analysis of the properties of promis-ing materials for laser manufacture,optimization of lasers, laser life andthe development of appropriatetechnologies. Some notes on semi-conductor diode lasers follow.

Monochromatic and coherent

The intense and extremely finebeams of light required for theapplications mentioned above can beproduced by lasers. The light from alaser has a very special quality: it isnot only monochromatic (i.e. it has

1

a12

jThsbe./-\

Figure 1. Schematic representation ofwaves of different wavelength and phase.a) Different wavelengths 11, and 12,different phase.b) Same wavelength I, different phase;monochromatic.c) Same wavelength I, same phase; mono-chromatic and coherent.

only one colour, one wavelength) butit is also coherent This means thatall light quanta emitted (photons)are in step with each other: theyhave the same phase. This is illus-trated schematically in fig. 1.Coherence is an essential requirementfor some laser applications, forexample in some optical -fibre com-munication systems. In other opticalcommunication systems it is betterto have less coherence, which meansthat after travelling a short distancethe photons get out of step. To readout a Compact Disc, for example,coherent light is not absolutelynecessary; what is required is light ofone particular wavelength, in a beamthat can be focused to form a verysmall spot.

Pump action

The operation of a solid-state diodelaser is very closely associated withthe properties of semiconductors, inparticular of two types. The first isthe N -type semiconductor, in whichthe electrical conduction is providedby electrons (negative charge). Theother is the P -type semiconductor,in which there is a deficit of elec-trons. The places that could beocupied by an electron are called'holes'; these are positively charged.Like electrons, the holes can move,and in the P -type material the con-duction is primarily due to themovement of holes.The energy state of the electrons andholes is very important here, and wefind that there are two kinds ofenergy band: the conduction bandwith relatively high energy and thevalence band with relatively lowenergy (see figure 2). The electronsresponsible for conduction in theN -type material are situated at thebottom of the conduction band.When an electron falls into a hole (orrather, when an electron and a holerecombine), a photon can be pro-duced. The energy of the photon,and hence the wavelength of the light,depends on the energy difference

2

I

° 00 02

Figure 2. Energy -level diagram in a semi-conductor. Here 1) is the conduction bandwith freely moving electrons, and 2) is thevalence band with holes, which are alsomobile.

elektor june 1984

between the conduction and thevalence band.Having said all this, we still have nolaser light. Laser is an acronym forLight Amplification by StimulatedEmission of Radiation. Stimulatedemission occurs because the presenceof photons with a particular energycauses the recombination of electron -hole pairs that have a correspondingenergy difference. The object is toretain inside the structure as manyof these stimulating photons aspossible. To keep this stimulatedemission going it is necessary toensure that enough electrons are'pumped' into the conduction bandand holes into the valence bands.In the semiconductor laser thispumping is achieved quite simply bysending an electric current throughan appropriate semiconductor diode.

PN junction

When a layer of P -type material isapplied on top of a layer of N -typematerial (figure 3) a PN junction isformed. Holes will now penetrate

3

P

//%

2

Figure 3. Schematic representation of aPN junction. 1) Holes in the P -type region,2) electrons in the N -type region, 3) thetransitional region, called the junction.From both sides, electrons and holespenetrate into the junction until a poten-tial difference is built up that preventsany further movement of charge carriers.

from the P -type material into theN -type material and electrons willpenetrate from the N -type materialinto the P -type material. As a resultthe P -type material becomes slightlynegative in the neighbourhood of thejunction. A state of equilibriumarises, because more electrons arerepelled by the negative side andmore holes by the positive side.However, if an electric current ispassed through this junction, in thedirection indicated in figure 4,additional electrons will be injectedinto the P -type layer and additionalholes into the N -type layer. On oneside of the junction there will nowbe extra electrons and on the otherside extra holes. In these areas, inthe right circumstances, light amplifi-cation by stimulated emission cannow occur.

6-18

elektor June 1984

4I

1

//../ r 3

N 2

Figure 4. Schematic representation of aPN junction through which a currentpasses.1) Injection of holes and 2) injection ofelectrons into the junction 3). 4) electriccurrent.

SandwichAs we have said, enough stimulatingphotons have to be kept trappedinside the structure. Furthermore, ina practical laser it is necessary tomake sure that electrons and holesdo not leak away from the structure,since it is their recombination thatproduces the photons. To meet theserequirements the double-heterojunc-tion injection laser was designed. Itoriginated at Philips Research Labora-tories in Eindhoven (the Netherlands),which patented a heterostructuresemiconductor laser in the latesixties. ('Heterojunction' means thatthere is a junction between materialsof different composition.) The basicconstruction of such a laser is a sand-wich structure. The active layer (inwhich laser action can occur) iscoated on both sides with layers ofmaterial of a slightly differentcomposition. The composition issuch that the refractive index of thecoating is lower than that of theactive layer. Laser light generated inthe active layer is then totallyinternally reflected by the twocoating layers.In addition, the differing com-position ensures that electrons andholes do not escape from the activelayer. The result is that sufficientoptical amplification takes place inthe active layer. Measures nowremain to be taken to keep part ofthe generated photons functioningas stimulating photons within thestructure, while another part leavesthe structure in the form of laserlight.Cleavage planes of the crystal inwhich the active layer is situated canfunction as partially reflecting mir-rors. A typical double heterojunctioninjection laser structure is shownschematically in figure 5.

Materials usedDepending on the required wave -

5

300pm

GaAs (P)

AlGa As (Pl-GaAs IP)

Al Ga As (N)

GaAs I P1

80pm

z250pm

Figure 5. Typical structure of a double heterojunction injection laser with GaAs asthe active layer. The dimensions are approximately 250 x 300 x 80 pm. The laserlight leaves the laser from the front and back through the partially reflecting mirror.The light emitted at the back (not drawn) can be used as a signal for a feedback circuitthat regulates the current through the laser in such a way as to obtain a constant levelof luminous intensity.I is the current through the laser. 1) substrate, 2) active layer, 3) partially reflectingmirror, 4) stripe for current passage, 5) laser light.

length of the laser light, the materialsused for such lasers are galliumarsenide (GaAs), aluminium galliumarsenide (AlGaAs) and indiumgallium arsenic phosphide (InGaAsP).The multilayer structure is usuallyproduced by the technology knownas liquid -phase epitaxy (LPE). In thistechnology a substrate (a crystalwafer on which the layers are grown)is brought into contact with a hotsaturated solution. As the solutioncools the dissolved substance crystal-lises on the substrate. The substrateused for lasers of relatively shortwavelength (780.900 nm; a nano -metre is one -thousand -millionth of ametre) is gallium arsenide. Epitaxialgrowth of the multilayer structure(active layer plus sandwiching layers)then takes place from a solution inwhich gallium is the solvent andaluminium and arsenic are thesolutes.The AIGaAs lasers producted in thisway have an important application inthe playback of the Compact Disc.For longer wavelengths (1300 nmand 1550 nm) InGaAsP lasers aregenerally used. Their active layerconsists of InGaAsP and the sand-wiching layers of InP. Their primary

application is in optical -fibre com-munications.Many modifications can be made tothe layer structure to optimize thelaser for a particular application, sothat 'custom-built' lasers can beproduced. Lasers for the CompactDisc, for example, should emitphotons that become slightly out ofphase after travelling a couple ofcentimetres; a laser beam reflectedfrom the surface of the disc will notthen show interference with theincoming laser signal. In telecom-munication applications, on theother hand, lasers are often used inwhich the photons keep in phasewith each other over grater distances.

LifeWhen a laser diode, as described here,is run continuously, some of itscharacteristics slowly change. Eventu-ally the laser has to be replaced. Nocomplete explanation can yet begiven for this ageing effect, butinfrared and electron microscopygive some idea of the kind of changesin crystal structure that can occur.

Philips press release

6-19

portable distress signalelektor june 1984

Photo 1. The plastic caseshould be kept as smallas possible in the in-terests of making the cir-cuit portable. If it is to beused in the car it mightnot be a bad idea to adda suitable length of cablefitted with a plug for thecar's cigar lighter socketor crocodile clips for con-nection directly to thebattery.

portable distress signal

a portable'Mayday flare'for the motoristwith engineproblems, thepleasure sailorin trouble, orthe strandedmountaineer

Who, on a clear summer night, has never been surprised to see avery bright star winking in the distance? Generally it is not a star atall (no, it's not a UFO either) but rather the high -power flashing lightindicating the presence of an airliner 20 or 30 miles away. In the fieldof aeronautics it is taken for granted that the lights should be visibleat such distances but there is no reason why the same principlecannot be applied to other applications.

The flash light tube, which is also used instroboscopes, is capable of producingvery intense light, surpassed only by thelaser. Unlike the laser, however, it hasquite a low energy consumption because,although the flashes are high intensity,they are of very short duration. This factled to the idea of using it as the basis fora portable 'distress signal' that could beused to attract the attention of anybodywho might be in the area.

General layoutThe different functional sub -assemblies ofthe circuit are clearly visible in the blockdiagram of figure 1. Two different types ofsupply can be used: either a 12 V lead -

acid car (or boat) battery or four 1.5 V drycells connected in series. The voltagechosen is applied to a converter giving anoutput of 220 V. This consists basically ofan astable power multivibrator and atransformer with a centre -tapped primarywinding. This primary is, of course, fedthe low voltage and causes 220 V to beoutput from the secondary. Note the pos-itioning of the transformer which is typicalof this sort of application.The next step is the voltage doubler, towhich the output of the transformer is fed.The output of the doubler is fitted with apreset that is used to vary the frequencyof the flashes. The other side of the presetis connected to a pair of diacs in series

6-20

that limit the voltage threshold. A diac re-mains switched off in the range from -30to +30 volts and conducts as soon as thevoltage exceeds either the positive ornegative threshold. This produces a cur-rent peak that triggers the thyristor in thenext block. When the thyristor is trig-gered the high -voltage transformer con-nected to it fires the strobe light. Furtherinformation about how a strobe lightoperates can be found in the article en-titled 'strobe light control' published inEleIctor no. 82, February 1982.

The circuitThe circuit diagram of figure 2 is almostas simple as the block diagram we havejust been looking at. The voltage supplied

by the battery or the four dry cells is ap-plied to the points Ub and 0. Themultivibrator consisting of Ti and T2 con-tains two RC networks, R7/C4 and R8/C5,that determine its operating frequencywhich, in this case, is about 80 Hz. Theoutput of the MMV feeds two symmetricalbranches.The transformer (Tr2) cannot, of course, bedriven by Ti and T2 directly because theircollector currents are much too small, atonly a few milliamps. This explains thepresence of the power stages in the emit-ter lines of T1 and T2. One stage is basedon T3 whose base current remains smalleven when the transistor is conducting,whereas its collector current is large.There is a corresponding power stage, T4,on the other side and the collector of

1

45

1.5 Vdry cell

6 V or 12 Vto 220 Vconverter

S4066 - 1

triggerransformer

triggercircuit

voltage threshold

portable distress signalelektor June 1984

Figure 1. As the blockdiagram here shows thiscircuit can be poweredeither from a car batteryor by four dry cells. Twotransformers are used,one is a triggertransformer for the xenontube and the other is a220 V one with a second-ary winding of either 12or 6 V. In this case,however, the low voltagewinding becomes theprimary so that 220 V isavailable at the output ofthe transformer.

6.21

portable distress signalelektor june 1984

Figure 2. Virtually anyxenon tube will work inthis circuit provided it isaccompanied by the cor-rect firing transformer.Naturally, the higher thepower rating of thestrobe light the brighterwill be the flash.

each power switching transistor feeds halfof the primary winding of transformer Tr2.The main purpose of resistor R5 is to limitthe base current of T3 to a reasonablelevel while the transistor is conductingand R9 permits this transistor to bequickly switched off by Tl. As we will seelater, the power transistors do not need aheat sink as they are unlikely to becomevery warm.Moving on to Tr2 now we see that the in-ductance consisting of the primary win-ding of this transformer is charged whenT3 conducts. This energy remains storedwhen the transistor switches off but cur-rent spikes are generated which would besufficient to destroy T3 were it not for thepresence of D5. While one half of theprimary winding of Tr2 is being chargedthe other half transmits the energy it hasstored so that a square wave is inducedon the secondary winding.This voltage is rectified by diodes Dl andD2. The resistors in series with the diodes(R2 and R3) prevent them from beingdestroyed by an overdose of amps whenCl and C2 are discharged. The combina-tion of these two diodes and twocapacitors forms a voltage doubler withthe result that there is a potential dif-ference of about 620 V between thepositive of Cl and the negative of C2.The same voltage is present across flashtube Lal and roughly half this value isavailable at the Cl/C2/R1/R4 junction. Thecharge on capacitor C3 is controlled bypreset PI and these two components forma sort of time -base. A pair of diacs con-nected in series after P1 present a veryhigh impedance when they are not con-ducting. The charging time of C3depends on the position of Pl. As soon asthe diacs' threshold level is reached(ti 60 V for the pair) the thyristor is trig-gered by the pulse arriving at its gate.Capacitor C3 discharges abruptly via Thlwhich causes a short pulse to be

generated at the primary of transformerTrl. This pulse appears at the secondaryof the transformer as a very high voltage,more than 1 kV, which is sufficient tocause the xenon tube to flash.The gate current of thyristor Thl is limitedby resistor RI. By adjusting PI the flashingfrequency can be varied between 1 and15 flashes per second. This frequency isalso, to a certain extent, dependent uponthe voltage supplied by the batteries.

Constructional detailsThis circuit can be constructed on theprinted circuit board shown in figure 3.The various connection points fortransformer Tr2 are also clearly marked onthe component overlay. If the circuit ispowered by means of four 1.5 V dry cellsa 2 x 6 V/800 mA transformer is needed.The 'automotive' version uses a 2 x 12 V/400 mA transformer. Points X and Y areconnected to the secondary of Tr2 asthese are two 220 V points. The + and 0points connect to the battery pack or thepoles of the car battery. Make sure whenfitting the strobe tube that its polarity iscorrect; the anode is usually indicated bya dot.The great advantage of this circuit is that itis very small and can be fitted into asuitable small plastic case (plasticbecause of the high voltage present!) andis then truly portable. With the flash tubemounted inside the case a hole will haveto be made to enable the light to shinethrough (strangely enough). Thephotograph at the start of this articleshows the end result. If the range of thelamp must be increased this can be doneby the simple expedient of fitting a reflec-tor behind it.

ApplicationsThe operating life of this circuit is one ofits most important characteristics. If it is

2Tr2

DI

1N4007

R2

$4065 - 2

6-22

3 portable distress signalelektor june 1984

powered by a car battery this should beno cause for concern as some proverbialknight is bound to fly to your assistancelong before the battery begins to suffer(we hope!). If, on the other hand, four1.5 V dry cells are connected in series acontinuous operation of four hours can beexpected. Adding an on/off switch im-proves this considerably, of course. Thenthe signal need only be started whenthere is a chance that someone may seeit.The applications for this circuit are manyand varied. Mountaineers or cavers couldinclude it in their pack under the motto ofbeing prepared. Another obvious use is inthe car especially as the flashes producedare very bright but not ria771ing. Pleasuresailors could likewise be glad to have thecircuit flashing an indication of their pos-ition in the event of distress.There is one important point to note aboutthe circuit, namely that there is a veryhigh voltage present, especially acrosscapacitors Cl and C2. On no account

should you start working on the circuitwhile this voltage is present. Thecapacitors must be first allowed todischarge fully or they may be dischargedby shorting the two terminals with a verywell insulated piece of wire.Everybody knows, of course, that there isno possible reason for needing this cir-cuit; 'My car is properly maintained andnever breaks down' you say, or 'I never gomountaineering just before the weatherunexpectedly deteriorates', or (this one isasking for trouble) 'Murphy doesn't exist!'.The trouble is that Murphy does exist andis always just around the corner with somenew catastrophe. This circuit may just tipthe balance in your favour for a change. N

Parts list

Resistors:R1 = 470 9/10 WR2,R3 = 12 QR4 = 150 kR5,R6 = 820 4 if Ub =6 V or 1k8 if Ub = 12 V

R7,R8 = 47 k for Ub = 6 Vor 100 k for Ub = 12 V

R9,R10 = 1k8R11 = 330 QP1 = 1 M preset

Capacitors:

C1,C2 = 8 ...10W350 Velectrolytic

C3 = 1p/100 VC4,C5 = 100 n

Semiconductors:

D1,D2,D5,D6 = 1N4007D3,D4 = BR 100 diacT1,T2 = BC 5471373,T4 = BD 139Thl = TIC 106D

Miscellaneous:

La1 = xenon tube flashlamp

Tr1 = trigger transformerfor La1

Tr2 = mains transformer,2 x 6 V, 800 mA, forUb -- 6 V or 2 x 12 V,400 mA for Ub = 12 V

Figure 3. The flash tubemay be mounted on theprinted circuit boardshown here or it may bemounted separatelydepending on the type ofcase chosen. To avoidconfusion when fittingthe components it is im-portant to remember thatthe diacs do not have apolarity.

6-23

ZX extensionselektor june 1984

ZXmore bytes,more inputs,moreoutputs, . . .

SCART = Syndicat desConstructeurs d'ApparedsRadiorecepteurs etTeleviseurs = (French)Association of radio andtelevision receivermanufacturers. Thisassociation decided sometime ago to terminatevarious inputs to, andoutputs from, TV receiversinto a 20 -pin socket. This isbecoming a Europeanstandard.

One of the great attractions of the ZX computer (ZX-81, ZX-spectrum)is its low price. However, if you want to extend it, things do not lookso good any more: ready-made extension modules are not exactlycheap. This is, of course, not only the case with Sinclair computers.At the same time, it is not necessary to spend a great deal of moneyon more facilities: you can do a lot yourself and save money. Thisarticle describes a number of extensions which you can carry outyourself: memory extension, disk drive' inputs and outputs, videooutput for improving the picture quality, and two joy -sticks for theSpectrum.

extensionsBefore discussing the extensions in detail,let us first see what we have to work with.The data, address, and control buses arenot buffered at the edge connector of theZX 81. One of the first requirements in anextension scheme is therefore a bufferstage. It connects the computer via a con-trol circuit and some interface logic to anElektor bus board, into which most otherextensions can then be connected (seefigure 1). The buffer cannot be used withthe ZX-Spectrum, as the memory extensioncan be provided internally in this com-puter, and the other extensions do notreally need a buffer.

1

ag pc hoard83014

Figure 1. Block schematicof the ZX81 extension.The bus buffer board pro-vides connection to theElektor bus board.

ZX81

e.g. pc board83082

51054 1

A TV interface in the ZX computer pro-vides a suitable signal that is madeavailable at the video outputs. These out-puts enable a monitor or TV receiver withSCART or A/V output sockets to be con-nected to the computer and so ensurethat a high -quality picture is produced.Apart from the buffer circuit, we have notdesigned any printed -circuit boards forthe extensions described. The reasons forthis are that the circuits are small and un-complicated enough to be wired conven-tionally and that many of you may not wishto use all the driver stages. The circuit forthe video output may be small enough tofit into the case of the computer.The ZX 81 may, at least as far as hardwareis concerned, be connected to the VDUcard described in our September 1983issue via the buffer stage and in that waybe provided with a high -quality video out-put: 24 lines of 80 characters each. Youwill have to write the necessary softwareyourself. A further point before we cometo the details: we have not tested whetherthe operational program of the ZX ROMallows corresponding jumps but think itprobably will. To be able to tackle this ex-tension. you need to know your wayaround the ZX 81 ROM handbook andElektor's own Paperware 3 as the softwaremay prove quite challenging.

Buffer stageBy far the larger part of this circuit (seefigure 2) is self-evident. The address bus isbuffered by ICI and IC2, and most controllines by ICS. These three ICs are type74LS244 three -state line drivers. Theenable inputs, GI and G2 (Pins 1 and 19),of the ICs are permanently connected toearth so that the drivers are always active.Pull-up resistor RI ensures that the BUSRQinput of the computer (a CPU input) islogic high unless taken low by some ex-ternal circuit.The data bus is buffered by a 74LS245 two-way, three -state driver IC. The change ofdirection is controlled by the RD signal ofthe Z80 microprocessor in the ZX 81: thissignal is applied to the DIR input (pin 1) of

6-24

IC4 from the output (pin 3) of the controlbus buffer IC5. When the G (enable) inputof IC4 is logic high, all inputs and outputsof the buffer become high impedance(the 'third state') and the data bus isdisabled. NAND gate N34 and IC3 form adecoder for the lower 8 Kbyte block ofthe ZX 81. This block contains the ZXROM. When the memory is accessed(MREQ logic low), IC3 is enabled. If at thesame time the three highest address linesare logic 0 (= ROM range), the output(pin 15) of IC3 becomes low, the output ofN34 goes high, and the data bus buffer isdisabled. In all other cases, pin 15 islogic I, when the external RAM or the I/Oat address $ 2000 may be accessed. Apartfrom these, about 250 I/O addresses areaccessible via A0 ... A7 and IORQ as wewill see later.All this is true, provided switch SI isclosed, which ensures that the internalRAM of the ZX 81 is disabled. This isnecessary because the internal RAIvICSsignal of the ZX is held logic high. If youwant to work with the internal RAM,switch S1 should be opened. When exter-nal equipment is then connected to theZX, problems may arise during writing ofdata owing to the incomplete internaldecoding of the ZX 81. This must be bornein mind when the addresses for the driveconnections are being fixed, so that thecomputer can be used as a drive com-puter without the RAM extension.Also because of the internal constructionof the ZX 81 - in this case relating to thevideo monitor - it is essential to combineCPU signal M1 with the address line Al5(the Ml signal in the ZX 81 has beenmisused for monitor control). This has thedisadvantage that only data may be loadedinto the upper 32 Kbyte range, but nocommands.Where the printed -circuit board shown infigure 3 is used, construction of the bufferstage should present no problems. Thepin connections of the extension plug areshown in figure 4. The board and plug arebest connected by a length of flat ribboncable. The connection to the bus board(for instance, that described in ourDecember 1983 issue) may also be madewith flat ribbon cable. It is, however,simpler and better, though also more ex-pensive, to fit a 64 -way female and maleconnector to the buffer and bus boardsrespectively: this enables the two cards tobe plugged into one another.

Power supplyAlthough the stabilized +5 V as well asthe unregulated +9 V supply in the ZXcomputer may be used for the extensioncircuits, there is a limit to the additionalload that can be placed upon the internalpower supply. It may be best, particularlyif further extensions are to be added at alater date, to build a new (additional)mains power supply, for instance, thatdescribed in our January 1983 issue. Theforthcoming 'Summer Circuits' issue of

2

5 V

0 V 0

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mon

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ZX extensionselektor june 1984

00000

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410 0411 0Al2 0413 0A140A150

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17

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15

613

11

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IC274LS244

16

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7

12

9

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254

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25a

244

24a234234

22

22a

16 21

5 21

140

204

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Elektor Electronics is also planned to con-tain a new mains power supply for com-puters. If, however, you plan to incor-porate only some of the extensions, thepower supply shown in figure 5 will suf-fice: this can provide a constant current ofup to 1 A. Capacitor Cl is a single 2200 IAelectrolytic or two 1000 1.1 ones in parallel.

Memory extension for the ZX 81This is probably the most needed exten-sion for the ZX 81. It is based on the

32a184

113

R1[1

05V

0

0

3

0OOO

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0v

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411

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84054-2

Figure 2. The circuit ofthe bus buffer consistsbasically of four busdrivers.

6-25

ZX extensionselektor june 1984

Figure 3. The pc board ofthe bus buffer makes anuncomplicated and cleanconstruction possible. Itmay be plugged into theElektor bus board.

Parts list(only for buffer circuit)

Resistors:

R1 = 1 k

Capacitors:

Cl,C2 = 100 n

Semiconductors:

1C1,1C2,IC5 = 74LS244IC3 = 74LS138IC4 = 74LS245IC6 = 74LS00

Miscellaneous:

PC Board 84054Flat ribbon cablePlug and socket connector

for ZX81S1 = microswitch (optional)64-iway female connector

(optional)

Table 1. The addressrange in which theuniversal memory cardfitted with eight6116 RAMs is decoded bythe DIL switch on theboard. Other positionsare, of course possible,but the ones shown arethe most important forthe ZX81. RAMTOP isonly a theoretical valuehere (see text).

WRROORF -0-2H10-04413

IVI

sus -a -R[3AD 0Al 0A2A3 0COA4OAB./GAB0A7

°AlOA13

1 0

3 20°443

04:11' 00 0

0000000 0002. 0000000

0 0000000?

+ 50 0 0

ra

-6-

O0

OOO

0

OOOOOOOOOOO000OOO0OOO0OO0O0

'universal memory card' published in ourMarch 1983 issue. Cards with a smallercapacity do not make sense, as the oneused may be completed piecemeal as re-quired. The '16 K dynamic RAM card'(Elektor April 1982), or the '64 K dynamicRAM card' (Elektor September 1983) mayalso be used, but you will have to modifythem yourself. The 'universal memorycard' has two real advantages: first, in con-trast to dynamic RAM cards, it solvestiming problems of static RAMs, and, se-cond, it may be fitted with a mixture ofRAMs and EPROMs. The latter makes itpossible therefore to store games, controlprograms, or even the software for theVDU card. To enable EPROMs to be pro-grammed, the 'Z80 EPROM programmer'as published in our January 1984 issue maybe fitted directly onto the universalmemory card. As the card can be pro-vided with 28 -way connectors, the5564/5565 8 Kbyte memory (static RAM) orthe 2764 EPROM, or both, may also beused. The relatively high price of theformer ICs will no doubt be coming downover the next 6 ... 12 months. It istherefore seen that the card can provide amemory capacity of up to 64 Kbyte whichis more than the ZX 81 can address.

Table 1

Address range DIL switch RAMTOP8 4 2 1 (see text)

8 K . . 24 K 1 1 0 1 24 57616 K . 32 K 1 0 1 1 32 76832 K 48 K 0 1 1 1 49 15248 K _ . 64 K 0 0 1 1 65 536

We have no doubt that most of you willstart by using eight 6116 ICs to give a16 Kbyte RAM. Only the second contact ofthe DIL switch (2) on the address decoderof the memory card is then closed. Thecard is addressed from 8 ... 24 K($ 2000... 5FFF). The ROM lies in therange below that. This gives 8 Kbyte ofBASIC memory and 8 Kbyte of machinecode and data memory.If you want to reserve an address rangefor I/O ports, for instance, for the switchoutputs which are described below, putthe card in the range 4000...7FFF. Thiswill make the range 2000...3FFF availablefor these ports when DIL switch '4' isclosed. A general remark about thedecoding of the memory card: beause ofthe twos complement arrangement, thefour highest address bits must be inverted,as shown in table 1.The memory extension is tested byreading the system -variable RAMTOP asdescribed in chapter 26 of the BASICmanual of the ZX 81. Be careful, however,because with extensions above 32 Kbyte(ROM range), RAMTOP does not change.Evidently, Sinclair have not foreseen thepossibility of such an extension to theiroperating system, and there is thereforeno facility for testing the RAMTOP fromdecimal 32767 downwards. This meansthat with this extension the RAMTOP hasto be set every time after switch -on. If, forinstance, you have extended the memoryto 48 Kbyte (8 Kbyte ROM, 8 Kbyte re-served for I/O, and 2 x 16 Kbyte RAM),you have to write:111 POKE 16389.192MI NEWFor other extensions these instructions will

6-26

have to be recalculated with the help ofchapters 26, 27, and 28 of the BASIChandbook.

Memory extension for the ZXSpectrumAn external extension of the Spectrummemory is not necessary as the mainboard has already been prepared for this(and in the 48 K Spectrum it has beencompleted during manufacture). Apartfrom the eight TI 4532 or 3732 memory ICs(IC15 ... IC22), it is necessary to insertfour ICs: IC23 (74LS32), IC24 (74LS00),and IC25 and IC26 (both 74LS157 - NOTNational Semiconductor).There is a point to note in respect of thememory ICs mentioned: these are not,strictly speaking, 32 Kbit memories, but64 Kbit stores of which it has been foundduring the final test in manufacture thatone of the 32 Kbit sections is defect. Anaddition to the type number indicateswhich of the two sections is usable so thatyou must bear this in mind during the ad-dressing. The Spectrum board has a wirebridge close to the Z80 which must beconnected to +5 V or earth, dependingupon which section can be used. This iscertainly of great economical advantage toSinclair, because these ICs are verycheap indeed, particularly when they arepurchased in bulk. The individual Spec-trum user does not have this advantage,because these reject ICs are practicallynot available in the retail trade. Fortunately,there is another possibility: using the 4564(= 2164. 3764, 4164, 4864, 8264, dependingupon the manufacturer) in its 200 ns ver-sion. These ICs are of course readilyavailable and probably at prices not muchhigher than those of 32 Kbit ICs. Wherethe bridge is connected to in this casedoes not matter as both sections may beaddressed.There is no need to worry about having todo without the other 32 Kbytes, becausewe have designed a small circuit, 'softswitch: which allows the Spectrum to useeither half.The soft switch circuit is shown infigure 6. Gates N3 and N4 form a NORlatch whose inputs are enabled by gatesNi and N2 when address $ 0001 (= deci-mal 1) is selected on the address bus andthe IORQ signal is active. The decoderforms a wired OR connection.With the instructionIN 1the address, the IORQ signal, and an RDare generated and output 0 goes logiclow.With the instructionOUT 1, n (n is any number between 0 and256)the address, the IORQ signal, and the WRsignal are generated and output Q goeslogic high.Point A in figure 6 is the centre of the wirebridge near the Z80 mentioned above. The10 k resistor may be soldered on theSpectrum board instead of the relevantsection of the wire bridge.

4a

rt

2r, I FralCS RFSH

Al 411

As RESET46 HUSRO

A7IIVAITAS

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410 RD

All 1080412 MREQ

A13 HALT414 NMI

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ZX extensionselektor June 1984

1

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RFSHMI

12 V

12 VWAIT

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IOREOMEMREQHALTNMIINT

04

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07413A15

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As the bistable is biased by Cl, output Qis logic 0 immediately after switch -on. Youtherefore leave the normal memory rangewith instruction OUT and reenter it withinstruction IN.The extra 32 Kbytes may be used formachine language programmes orsubroutines. There is at all times onerestriction: the system variable RAMTOPmust be located below the switchablerange (how is described in the BASIChandbook of the Spectrum). If youtherefore want to make use of the full2 x 32 Kbyte, you have only 16 Kbyteavailable for the BASIC program. If youlocate RAMTOP so that 32 Kbyte remainavailable for the BASIC program,2 x 16 Kbyte are retained in the switchablerange. As you may locate RAMTOP moreor less where you please (but, of course,not in the ROM range), it is possible tochoose the most beneficial memory divis-ion for the particular program.

Drive computerIf you want to actuate just one relay, ortwo relays alternately, the small extensionshown in figure 7 may be used with theZX81. With the Spectrum, the address

5

)11, tCI Cl.

9 MW =MIsaaci000 !22°°-

_J

Figure 4a. Pinout of theedge connector of theZX81..

Figure 4b. .. and of theZX Spectrum.

Figure 5. This simplemains power supply, pro-viding 5 V at 1 A, sufficesto power all extensions.

C21th C3:

16V

5v

Apo8400$ S

7805

1

6-27

ZX extensionselektor june 1984

Figure 6. The soft switchcircuit for the ZX Spec-trum gives access to32 Kbyte additional RAMmemory.

IOREO

A15

A14

Table 2. This small pro-gram enables operationof the circuit of figure 7.

decoding has to be supplemented, for in-stance as shown in figure 6. Only addressline Al must then be inverted by the freeinverter. The principle remains the same,however when the address decoderrecognizes a valid address (the gatesbelow N6 in figure 7, together with R4,form a wired OR connection), the softwarecauses a write or read pulse to begenerated (RD or WR goes logic low), and

6

N1 ... N4 = 74LSO2N5 ...N10 = 74LS05N11 ... N14 = 74LS33N15 ...N19=74LSO5

84054.6

Table 2

10 REM switch control20 POKE 16515,21930 POKE 16516,040 POKE 16517,20150 POKE 16518,21160 POKE 16519,070 POKE 16520,20180 PRINT "IN (11 or OUT 12)"90 INPUT X

100 IF X = 0 THEN GOTO 130110 IF X = 1 THEN GOTO 150120 GOTO /30130 LET Y = USR 16518140 GOTO 80150 LET Y = USR 16515160 GOTO 80

this sets or resets the NOR latch formedby N3 and N4. Basically, this is the samecircuit as for the soft switch. The driverstages switch the relays on or off underthe control of the latch. The drivers con-sist of a bias resistor, a Darlington tran-sistor, and a free -wheeling diode. If onlyresistive loads are switched by the tran-sistor. the free -wheeling diode is, ofcourse, not necessary. The currentthrough the transistor may be 500 mAmaximum and the relays must thereforebe chosen accordingly.Table 2 shows a small program for theZX81, which is self-evident from lines 80and 90. If you want to include this pro-gram in a larger one, the jump addressesfor the GOTO instructions must bechanged accordingly. The first line of thecomposite program must contain a REM,because the POKE instruction in thisrange are for writing only.The wired OR connection is retained evenafter the supplementary address decodinghas been added. The program for theSpectrum is reduced to a simple, singlelineOUT 3, YorIN 3where Y may be any decimal number be-tween 0 and 256.It is important that in the Spectrum theIORQ signal is used and not, as in theZX81, the MREQ signal.Figure 8 shows a further control circuitwhich not only makes eight switched out-puts, but also eight inputs on request,available. The driver stages are similar tothose in figure 7, but here they are con-trolled by latches (74LS374) instead of abistable. The level at the output of IC4 isheld until the 'computer writes a newword onto data lines (DO ... D7).The data can (also) be set by switchesSi ... S8 the levels of which (switch closed= 0!) are sensed by IC5. Pull-up resistorsR9 ... R16 ensure an unambiguous inputlevel into IC5. The actual function of theeight switches depends on which of thesections is controlled and on the program.Output port IC4 is enabled by the output(pin 11) of address decoder N11 and theWR signal: both these signals are appliedto AND gate N12 (note that although thisis, strictly speaking, an OR gate, it func-tions as an AND gate because all signalsare active when low). The memory driveraccepts the data word from the bus at theleading edge of the pulse at pin 11 of IC4.The input port is likewise enabled by theaddress decoder, but in this case in con-junction with the RD signal. The AND gateis here formed by N13. The addressdecoder is again constructed as a wiredOR gate and decodes hex addresses 3FE0and 3FE1. These are used instead of themore obvious FFFF to prevent problemswith incomplete decoding in the ZX81when the internal ZX RAM is used. This is,of course, only so during reading whenboth the input port and the internal RAMare scanned: a typical case of double ad -

6 -28

7 ZX extensionselektor june 1984

ZX .37

WR

ATI

IOREO

AT

A;5

AS

A4

SV

OV

OS

0

5V0

R3

2

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O

Fif13

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I: 5 EV

A4

00

0 8IC1 IC2

cr)

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1N4148

71 72 L2RI R2

IBC 517dos

N I . N4 = ICI = 74LSO2N6 N1I = IC2= 74LSO5

34052..7

dressing. The addresses chosen can alsobe decoded fairly simply and are locatedbelow the RAM range in an unused inter-nal section of the ZX81. This is, of course,only so if the internal RAM is used. Whena memory extension is added, make surethat these addresses remain available forI/O operation: the extension must there-fore be located in the range starting atS 4000. The conversion of the addressesfrom hexadecimal to decimal is describedfully in the handbook, so that you canreadily access the addresses mentionedwith PEEK and POKE instructions.

Joy -sticks for the SpectrumThe new ZX interface II offers thepossibility of connecting two joy -sticks tothe Spectrum and read ROM modules(with games). However, at almost £30.00 (atleast in the UK; prices are higheroverseas) this is not exactly a cheap addit-ion. If you want to be able to read ROMmodules, this can be done without theSinclair interface. and at the same timeyou can connect the two joy -sticksdirectly.Figure 9 shows a cross-section of theSpectrum board. The connections for thekeyboard are located directly under, andsomewhat to the right of, the ASTECmodulator. Chapter 23 of the SpectrumBASIC handbook gives some very import-ant information about addressing thekeyboard.The cursor keys (arrow keys 5 ... 8) may

Table 3

IN KEY S = 5IN KEY S = 6IN KEY $ = 7IN KEY $ = 8

IN 61486IN 61438IN 61438IN 61438

If the indicated bit is '0', theindicated key is pressed.

data bit 4 : -data bit 4 :data bit 3 :data bit 2 :

Table 4

IN KEY $ = 1 IN 61486 data bit 0 - (1)IN KEY S = 2 IN 61486 data bit 1 (1)IN KEY $ = 3 IN 61486 data bit 2 1 (1)IN KEY $ = 4 IN 61486 data bit 3 I (11IN KEY S = 5 IN 61486 data bit 4 trig- (1)

gerIN KEY $ = 6 IN 61438 data bit 4 - 12)IN KEY $ = 7 IN 61438 data bit 3 - (2)IN KEY S = 8 IN 62438 data bit 2 1 (2)IN KEY S = 9 IN 61438 data bit 1 1 (2)IN KEY S = 0 IN 61438 data bit 0 trig- (2)

ger

be scanned with the instructions given intable 3. This can be tested with the pro-gram in table 5 which enables the writingof horizontal OR vertical lines on thescreen. Interface II uses the number keysfor the joy -sticks (see table 4). The IN in-struction has a great advantage in thatvarious directions may be scannedsimultaneously. From a comparison of thetwo tables it becomes clear how the cur-sor may be controlled with a joy -stick and

Figure 7. This small con-trol output enables theZX81 or the ZX Spectrumto switch two relaysalternately.

Table 3. During scanningof the cursor keys on theIN instruction, the ZX81uses two memory cells:61486 and 61438. Becauseof this, it is not possiblewithout some furtherwork to control the cur-sor with the joy -stick.

Table 4. This is how thetwo joy -sticks may besensed with IN instruc-tions. As the five databits are detectedsimultaneously, it ispossible to realize graphicfunctions relativelyquickly.

6-29

ZX extensionselektor june 1984

Figure 8. The largest ofthe extensions for theZX81 and ZX Spectrummakes eight freely pro-grammable output portsand eight input portsavailable.

Table 5. This simple pro-gram enables the drawingof vertical or horizontallines on the screens withthe cursors. With smallmodifications it may alsobe used for trying out ortesting the joy -sticks (seetext).

8 Els..

2E3

25, A2

25a A3

24c A4

24a AS

734 4623. A7

22e AB

22a 6321c A10.

1

21a A111,

20c 4121Ms 4131

1

19e 4141

1

19a 4151

31s WI

30e '09 80

27c MRECI

7c

7a

Es

10c

12.

0001D2

03Da

05D607

'1141 Ro

SPECTRUMZX-s1

I

Al

a

5V

2X-51

aa-

3

5V

3 .z1 2_4 5

68 IC4 9

13 74L5374 12

14 IS

17 16

18 19

OE .....tC l0

18

5V

5 ... 30 V++

0fti

01 DB1N4148

TI 78

e2

B3

Bs

BS

e6

57

El9

151-7420

16

14

12

9

N1... N6 = IC1 = 74LS05N7 . N9 = IC2 = 74LS15N10 ... N13 = IC3 = 74LS32

IC574LS244

94054

2

6

8 I

5...30 V

500 mA

R9 9169

OFTIEEL

11

13

15

10I 4 4 41117

SI se

also why Sinclair has not provided thisfacility: the joy -sticks use the addresses61486 and 61438. Most current joy -stickshave only one (common) earth connectionwhich must be used for selection. You cansee from figure 9 that cursor control is

Table 5

10 LET Z = 8620 LET X = 12730 IF IN KEY $-40 IF IN KEYS=

-50 IF IN KEY $ =

Z +160 IF IN KEY S =

X +70 PLOT X, Z80 GOTO 30

5 AND X > 0 LET X =

6 AND Z >0 LET Z =

7 AND S < 174 LET Z =

8 AND X < 254 LET X =

therefore not possible this way because atall times only one of the common lines (1,2, 3, 4, 5 or 6, 7, 8, 9, 0) may be used: theycannot be used simultaneously. At thesame time, the figure shows how you canconnect two joy -sticks to the Spectrumwithout using interface H. All you need toknow is the plug pinout of the joy -stick.Figure 10 shows the standard pinout, inthis case of the Atari joy -stick as used withthe Sinclair interface II. If you use othertypes, check the pinout with an ohm-meter. Otherwise, the connections may bemade as shown in figure 11 with, for in-stance, flat ribbon cable. The program oftable 5 may still be used by changing thekey numbers accordingly.

Video outputNormally, the ZX computer is connected

6-30

to the aerial input of a TV receiver. Thecomputer contains a UHF modulatorwhich converts the video signal into aUHF signal similar to the one receivedfrom the TV transmitter. The UHF signal isdemodulated in the TV receiver into avideo signal. For normal TV broadcaststhis is perfectly all right, but with a com-puter so close to the TV receiver this is,from a technical point of view, a bad solut-ion, if only for the simple reason thatbecause of the double conversion there isbound to be loss of quality.Nowadays, single -colour data monitors(green or amber) are available at attractiveprices, although normal colour versionsremain pricey. Many modern colour TVreceivers are provided with a SCARTsocket or DIN A/V socket for connectinga video recorder (the problem of someloss of quality also arises with the videorecorder). However, these sockets make itpossible to connect the video signal fromthe computer directly to the video inputof a monitor or TV receiver. With bothcomputers this is readily done by meansof a small interface. The result is far betterdefinition and, in the case of the Spec-trum, better colour reproduction.In the Spectrum the video signal isalready available at the edge connector(terminal 15 at the underside of the board,see also figure 4b). If there is no signalpresent, there is a wire bridge missing onthe board. This is located close to TC1and TC2 and has been drawn in the com-ponent layout of the board. If necessary,this wire bridge should be soldered in.The signal amplitude is 1 Vpp with a d.c.offset of +2 V. The signal must be buf-fered if a colour monitor or TV receiver isused. This may be done, for instance, withthe video amplifier described in ourDecember 1983 issue. This amplifier is ad-justed so that its output signal into 75 Q(video input impedance of the TVreceiver) is also 1 Vpp.Equally good results may be obtainedfrom a simple emitter follower (seefigure 12), in which the d.c. offset comes togood us& This circuit, as well as that ofthe video amplifier, may be used withboth the Spectrum and the ZX81. As theZX81 provides a stronger video signal thanthe Spectrum (about 2 Vpp), it is advisableto connect a 68 ohm resistor in series withthe output signal to give better matchingwith the 75 Q input.The video signal of the ZX81 may be takenfrom pin 16 of ICI, or from a point directlyconnected to this and which is more ac-cessible (for instance, D9 may be un-soldered and its anode connection used).With a bit of luck it may be possible to fitthe interface in the computer case. In theSpectrum you can then take the videosignal directly from the input of theASTEC modulator at the edge of the com-puter board. The connecting point issituated in the centre of one of the shortersides of the modulator and is in easyreach.Although the video signal is always buf-

9 gr. 123 4 5 61890ZX extensionselektor june 1984

) 0000_1 1_0 0 0 0. 0 0 0- - - -

:0fr

:j2ra 7

:eci

:p.

10 01 -CI-O 2

O3 CI 0 30 0 02:4

0 0 049 8 7 6

.)06v-92.

o not cornscted 08cornmm

84054 10

11 joystick

5 34 1

02 0 0 0

_9 7 6I

joystick2

84054-9

Figure 9. The keyboardconnections on the Spec-trum board are locatedunderneath and to theright of the ASTECmodulator. They are usedfor connecting thejoy -sticks.

Figure 10. Commonpinout of a joy -stick.

50 40 30 21

9 89 6 61'

a not conrocted

amocclicimbosrd X

ZX SPECTRUM

84060 11

0

0

0 0 0 0 0

r.4

12

Video

2X 81

/SPECTRUM

9v

2N2219

160n

SPECTRUM

2X 81

Video

VDP75

100P1SV

84054-12

fered, make sure that a terminatingresistor which may have been provided inthe input of the buffer stage MUST beremoved. In the video amplifier fromElektor No. 104 (December 1983) this is RI.Furthermore, in this and other amplifiers,but not in the emitter follower, it is ad-visable to add a coupling capacitor (toprovide d.c. decoupling). In the Elektoramplifier it is also beneficial, but notnecessary, to change over the polarity ofC2 because of the 2 V d.c. offset. $

Figure 11. Wiring layoutof the joy -stick connec-tions to the Spectrum. Becareful when removingthe ribbon cable: thismust not be bent!

Figure 12. This simpleemitter follower makes itpossible to connect thevideo signal of the ZXcomputer to the video in-put of a monitor or TVreceiver.

6.31

disco drumelektor june 1984

a choice ofrasta, funky, ordisco beats . . .

or would youreally prefer themonotonous'boom -boom' ofother drumsynthesizers?

Figure 1. The circuit ofthe disco drum consistsmainly of an envelopegenerator, triggered eitherby calibrated pulses pro-vided by another circuit(such as a metronome) orby the variable amplitudepulse output from the'drum' of figure 2, and afrequency and amplitudemodulated sinusoidaloscillator.

CLK

0

Contemporary music is quickly reaching the stage where it is the rulerather than the exception to use computers, or at least synthesizers,as 'instruments'. Many people see this as unnecessary but would likea small degree of electronicization in their music. Guitarists have longbeen familiar with phasers, flangers, echos, and so on but anotheressential member of any group, the drummer, seems quite happywith strictly mechanical drum sticks. Now, to throw the cat in amongthe pigeons, we have designed an electronic drum for the drummerto play with.

disco drumNobody could say that we neglect elec-tronic music at Elektor. Admittedly, it hasbeen dormant for quite a while now butwe felt this was necessary to give readerswho are so inclined the time to come togrips with our last major work, the presetunit for the polyphonic synthesizer. Theproject proposed here is a more modestdesign; sort of a drum 'synthesizer'.The drum sound is relatively easy to ob-tain as it is simply a matter of generating asinusoidal audio signal and modulatingthis with an envelope having a very steepattack and an exponential decay. Thisgives the effect of an apparent amplitudemodulation due to the fact that lower fre-quencies have a greater 'impact' on theear than higher frequencies of the sameamplitude.

The 2206 again .

The circuit diagram of figure 1 shows adesign with two inputs and at least threemerits: it works well, it is easy to make,and it doesn't costs a lot. The two inputscould also be considered as a furthermerit as they expand the range of -poss-ible applications.

The heart of this circuit is the XR 2206function generator (IC3) which providesthe sinusoidal signal. The frequency ofthe signal output at pin 2 is proportional tothe current flowing between pin 7 andground. This current is controlled by tran-sistor T1 as a function of the voltage ap-plied to its base. We will see later howthis control voltage is derived. A 15 Vpositive pulse applied to the CLK inputcharges Cl almost instantaneously ..ria Dl.The discharging time across D2, whichbegins immediately after the falling edgeof the pulse, is determined by the positionof the wiper of Pl.Impedance matcher IC2 is needed to pre-vent the amplitude of the envelope curve,derived from the charging and discharg-ing of Cl, from being proportional to therepetition frequency of the input pulses.The envelope signal is fed to the voltageto current converter, T1, (via R3, P2, andR5) for the frequency modulation and topin 1 of IC3 for the amplitude modulation.We were not satisfied with just the illusionof amplitude modulation so even with notrigger input the frequency of oscillatorIC3 is within the audible range. If thiswere not the case envelopes with a small

1

DI3

1N414802

1N4148

2

C7

-1I-477.

a

C23130

'3Cc

BC 547

7

Cr

oo'1 5 IC32206

Ca C=Ir 73

R53

C6

cal

15V

O

63 V

DI 00

= 30,-63 V

075056 1

6-32

2

amplitude would not even be able to trig-ger the oscillator, or, strictly speaking, tomake it rise above the sub -audio range.The lowest frequency is set by biasing thebase of T1 with P3, the minimum ampli-tude is decided by tuning preset P4 sothat no output signal is seen from IC3after the envelope has decayed com-pletely.

The two inputsSo far we have avoided mentioning thesource of the trigger pulses that are ap-plied to the input. This could be a se-quencer, a rhythm box, a synthesizerkeyboard, ... or any one of a long list ofequipment capable of providing the(0 ... 15 V) positive pulse required by thecircuit. The pulse provided by the '0' or'S' outputs of the metronome published inthe November 1983 issue of Elektor isanother suitable possibility. If this is usedthe values of C2 and C3 in the metronomemust be increased to about 470 n to en-sure that the pulses are long enough tocharge CI (in the disco drum) completely.A drum would not be a drum without hav-ing something to hit. With this in mind ourdemon drum designer came up with thepiezo-percussion instrument shown infigure 2. This consists of a disc ofplywood about 20 cm in diameter, a thicksheet of rubber to cushion the blows, anda piezo electric buzzer which in this caseacts as a pressure sensor. The buzzer sup-plies pulses to ICI with an amplitude pro-portional to the intensity of the blow. Thissignal should only be used when a fre-

3

quency modulation proportional to the in-tensity of the blow is desired, as indicatedby the different envelopes in figure 3. A3130 was chosen for IC1 because, at rest,the output of the amplifier must return tozero to enable Cl to discharge. In thesame vein the leakage current of Cl isquite important; the smaller it is the better.For this reason a pair of 2 IF non -electrolytic capacitors in parallel are to befavoured over a single 4.7 pF electrolytic.When we finished our electronic drum wedecided that the best way to test it was toask some famous drummer to try it out.No expense was spared (!) and we eventu-ally managed to get hold of the residentgroup at the Muppet Theater, DoctorTeeth and his Electric Mayhem Orchestra.The drummer. Animal, sat in front of thedrum and then it seemed as if all Hellbroke loose. A couple of hours later Doc-tor Teeth came to talk to us. 'Hey, man, I'msorry about your drum but Animal says itnot only sounds good, it tastes good as

14

disco drumelektor june 1984

Figure 2. A 'drum pad'can be made using apiezo electric buzzer as apressure sensor (CI, anordinary sheet ofplywood (13). and a sheetof thick rubber (Al. Inspite of its simplicity this'instrument' is quite sen-sitive to changes in theintensity of the blow.

Figure 3. Just as thecalibrated pulses suppliedby a metronome, forexample, provideenvelopes with a constantamplitude, the pulsesgiven by the drum pad infigure 2 result inenvelopes whoseamplitudes are pro-portional to the intensityof the blows.

6-33

daisywheel typewriterprinter interfaceelektor June 1984

an inexpensivehigh qualitycomputerprinter

Sooner or later every serious computer user feels the need for aprinter. A look at the price and a quick check of the bank balancegenerally causes a state of gloom to set in with a lot of programmingtime being spent humming verses of Blaise Pascal's not -so -well-known ode 'Oh, for a little printer'. Now, however, there is a cure forthis condition. Most electronic typewriters have a keyboard laid outas a matrix which is controlled by means of software. All that isneeded, then, is to tap into the output of the matrix and feed in thecodes for the characters to be printed and the machine will recognizethem just as if the same key has been pressed. The best part of all isthat this does not even require any drastic modifications to theexisting circuit.

daisywheel typewriterprinter interface

Table 1. An example ofhow the eight lowest ad-dress lines of EPROM IC1are encoded.

Certain electronic typewriters that haveappeared recently are equipped with aninterface for a computer (such as anRS232C, Centronics, IEC, and so on).These are of no interest to us as they donot need any adapting, provided the inter-face chosen is the right one. There areothers which, although electronic, are notintended to be controlled by a micro com-puter. Many of these, however, have a suf-ficiently good quality to price ratio tomake them a sound proposition formodification to a high -quality printer for acomputer system, even if it already has adot-matrix printer. First, of course, there isthe little matter of an interface, but thatneed no longer be a worry. We havedesigned a Centronics interface for a cer-tain type of electronic typewriter and it isversatile enough so that it could relativelyeasily be modified for other types ofmachines.The machine we chose is the SmithCorona EC1100 portable electronic type-writer, mainly because it is a simple,robust, machine with a good quality toprice ratio and it is quite freely available.It is a daisywheel machine and, as wehave already made clear, it serves as areference here rather than being the only

Table 1

Matrix EPROM

Y7 Y6 Y5 Y4 Y3 Y2 Y1 YO A3 A2 Al AO0 0 0 0 0 0 0 1 1 1 1 1 F

I t 0 I 0 1 0 E

t ° 1 0/

0 1 D0 1 0 0 0 C

0 1 1 B0 0 1 0 A0'0 1'0 0 0 1 90 0 0 0 0 0 0 0 0 0 8

A7 A6 A5 A4 A3 A2 Al AO

typewriter for which this interface can beused.

Simulating the matrix decodingAs figure 1 shows, the keys are arrangedin a matrix of 8 x 9 lines which the pro-cessor in the typewriter (an 8039) willdecode by sweeping it with a 2 mspositive pulse. When a key is pressed thepulse applied to one of the input lines ofthe matrix (columns YO ... Y8) reappearsat one of the output lines (rows AO ... A7)and the cross-reference thus obtained tellsthe processor which key was pressed.Our modification must therefore place thecode corresponding to the character tobe printed on output lines A. To do thisthe ASCII code for the character must becombined with the input code to thematrix (YO ... Y8) generated by the pro-cessor to form an EPROM address con-taining the exact same data that would bepresent on lines AO ... A7 if the key forthe same character were pressed. Thismeans that the keyboard does not have tobe modified at all and can be used nor-mally. An example of this procedure (forthe ASCII character 'P') is given in table 2and we will return to this later.Moving on to the circuit diagram of figure2, we see that only a few ICs are needed.The most essential one is. of course, IC1, a2716 EPROM, whose data outputs are con-nected to the A7 ... AO lines of the matrix.The diodes, Dl ... D8. are included to en-sure that the existing keyboard can still beused when the interface is connected. Ad-dress lines A10 ... A4 receive the seven -bit ASCII code for the character that is tobe printed from the computer via its Cen-tronics output (D6 ... DO). The four re-maining address lines, A3 ... AO, receivethe code generated by IC8 (a 10 to 4 lineBCD encoder). This is the BCD equivalentof the input code to the matrix (Y7 ... YO)

6-34

Table 2 daisywheel typewriterprinter interfaceelektor june 1984

EPROM IC1: addresses EPROM IC1: dataA10A9 A8 Al A6 A5 A4 A3 A2 Al AO

101 1 0 1 0 0 0 0, 1 0 1 0

ASCII code Y2 (OAHex)50Hex (131

D7 D6 D5 D4 D3 D2 D1 DO0 0 0 1 0 0 0 0

line A4 of thematrix is active

that is inverted by N5 ... N12 so that the40147 will accept it. This conversion is in-dicated in table I, the left side of whichcontains the configuration of the matrixlines showing the positive pulse (the '1')sweeping the lines. The right side of thetable is the resultant codes output fromIC8, which are, of course, in negativelogic (so '1' is 0 V and '0' is +5 V). Aspecific example, outputting the code cor-responding to the character `P', is given intable 2. The key for this character isnumber 29 and when pressed it links Y5to A4. The BCD code corresponding tothe matrix configuration when the pro-cessor is scanning line Y5 is AHEx. Thusthe EPROM address containing the datacorresponding to the ASCII character 'P'is constituted by codes 50FiEx (ASCII `P')and AHEx. The data must be programmedsuch that line A4 in the matrix is activated;i.e. with 10HEXThe second EPROM, IC2, is needed for afew specific functions: shift, keyboard II(KBII), and carriage return (CR). The SHIFTA line is activated every time an ASCIIcode output by the micro computer cor-responds to a character in the upper

register of the typewriter keyboard. LineKBII can only be activated by the pro-cessor when line Y8 is active because ofthe presence of N3. This signal gives ac-cess to several special characters, furtherdetails of which can be found in the SmithCorona user's manual.

Timing the signalsFor the CR signal we must move on to thetiming of the signals. We also have to startby taking a step backwards to the momentwhen the data appeared at the Centronicsoutput of the micro computer. When thedata is valid the processor outputs anegative strobe pulse. This pulse triggersmonostable MMVI whose output pulse(set with P1) is about 100 ms. The BUSYline is then activated, via N2, preventingthe micro computer from sending anynew data to the Centronics port. Thisresults in a printing speed of about ninecharacters per second. SimultaneouslyMMV2 produces a pulse of about 50 mswhich delays the enabling (OE) of IC1 sothat the codes for SHIFT, KBII, and CRgiven by IC2 always appear a fraction of a

1

CONE 1

AD tooAl 90A2 80A3 70Aa 6AE 50AS 40A7 305V 20LED I

41)1.85

141:

47°

/111131/41;

5(efel

411

I"(

1419. 8.91:

ere

°SE(

a'Cr.7

OS:83fr

W6lfi3 4 9

62 4.1W4e\'\yREPEAT -

CONE 2

28 112.85:20). 39 '

ef'fa es(3 '431 r 16

fie 14: 4 Ft: T:

0.5:10 (.1112 8 64

46 151.7 44: ,2)7 1/211: 06:

"16. d?1fr 411:3P0 Cele

dfielefila 22 ac25 ff?2. iN 33 AUX

11)11:11(1 atC2f: 17;?: PR: OPP

0000..0 .1 0

840551

Table 2. An example ofhow the EPROM is ad-dressed for a given ASCIIcode (for the character'Pl. The address is 50HExand the data is 10HEx.

Table 3

AO: 01Al : 02A2: 04A3: 08A4: 10A5: 20A6: 40A7: 80

Table 3. These are theonly matrix output codespossible as only one lineat a time can be active.

Figure 1. The keyboardmatrix is connected tothe main printed circuitboard of the SmithCorona EC 1100 by meansof two connectors:CONE 2 where we findthe pulse that sweeps thekeyboard to detect anykey that is pressed, andCONE 1 to which weapply a code simulatingthe pressing of the keycorresponding to thecharacter to be printed.These two connectors areeasily located on thetypewriter's printed cir-cuit board.

6-35

daisywheel typewriterprinter interfaceelektor june 1984

Figure 2. The Centronicsinterface is branchedparallel to the existingkeyboard and simulates akey being pressed by ap-plying the pulse that ap-pears at one of the inputlines (YO WU of thematrix to one of the out-put lines (AO ... A7).Potentiometer P1 shouldbe adjusted to give themaximum possible print-ing speed without thetypewriter failing to printany of the charactersproperly.The interferancethreshold can be greatlyimproved by connectinglines DO... D6 in theCentronics socket toearth via 10 k resistors.The interface is then 'off'when there are no signalspresent.

second before those output by ICI.The CR pulse poses a particular problemas no character may be either received orprinted while the carriage is on the returnjourney - unlike a printer the typewriteris not bidirectional. This is why the CRsignal resulting from the ODHEX code ap-plied to ICI and IC2 controls a thirdmonostable to activate the BUSY line forthe duration of the carriage return.Capacitor C4 in the time base of IC7charges to a certain extent depending onthe time between two CR pulses so thatthe duration of the carriage return is pro-portional to the number of characters inthe line ended by the ODHEx code.The typewriter automatically performs aline feed (OFHEX) after a carriage return.Computers generally follow a ODD (CR)with a OFHEX (LF) which gives two linefeeds instead of one unless the OFHEXcode is suppressed in EPROM ICI, as wehave done. This saves the trouble ofhaving to suppress it in the computer. Aswe did not want to lose the line feed func-tion completely it is assigned the codeOFHEX (CTL-O).The RC network made up of R7 and CIOis used to convert the BUSY signal (activelogic high) to an ACK signal (active on thefalling edge) which some Centronics inter-faces require.

Construction and fittingBuilding this project is greatly simplifiedby using the printed circuit board designshown in figure 3. As usual, it is a goodidea to fit the wire links first to ensure thatthey will not be forgotten. The EPROMsshould be mounted in good qualitysockets, especially if the typewriter usedis not the EC 1100 as these ICs will thenprobably have to be removed severaltimes until the coding is fully correct. Asthe layout of the printed circuit board in-dicates, the mounting point have beenprovided to be compatible with the caseof the typewriter. To connect the interfaceto the typewriter a pair of 10 and 12 pinmale and female connectors will beneeded, as shown in figure 4. These arenot strictly essential, however, as the cablecould simply be soldered at the ap-propriate points on the Smith Corona'sprinted circuit board, marked CONE Iand CONE 2. The type of connectionused for the Centronics input is left toyour own initiative as it must be modifiedto what is needed.The supply voltage for the interface istapped from the typewriter itself (pin 2 ofCONE 1 = +5 V). A ground connectionmust be made between point '0' near C7on the printed circuit board of figure 3

2

CONE 2

4 6 S0_ V70 ; 7 2C

:o "C -0147:0-174.70 .co C

iD

M10., e.CI

.4704

5 V

Pt

470%

40t

2 4.0.8WW1

3-iR

- /T.19 R la_le,

/09V21.990/.-C 0

5v9

-c 1_Ic

5vet III!0 8 0

1C4 ICS ICET''toe (1) OCO

15414813 3

0422

72

7

04

6-

4542act_ 42.09

44.6 77I2.20Desre

IC22716

D.

STE

5(

241

154148

AN_02H

4.3

IT "H I --T-Tra41CO

05 u'1AS

1C1-07 53

2716 Dm LS °S E as

05

:/1 "H 34 .

-452VO-01

O

ti3

5V

®-L

coNE,

S V

IC77555

141.11/1.1.9V2 = IC3 = 4098: 4528NI _ 53=s.IC4 = 4093N4._. 505117412 = ICS = 404957._.510513= IC6 = 4049

6-36

3

and the GND point near CONE 6 (thesupply connector). The current consump-tion of the interface is about 150 mA,which the existing supply can providewithout any problem.When you pick up the EC 1100 to start tomodify it one of the first things you willnote is the lack of any type of screwholding the two halves of the casetogether. As with most such problems,separating the halves of the case to get at

the innards is easy once you know how.The top part of the case is fitted withseveral plastic clips which mate withgrooves in the bottom half so to separatethe two the sides of the top must bepressed and lifted to release the clips.

Programming the EPROMsWe have purposely left the programmingof the EPROMs until last. This part of the

daisywheel typewriterprinter interfaceelektor june 1984

Parts list

Resistors:

RI = 390kR2 = 470kR3,R7 = 10kR4 = 1M2R5 = 270kR6 = 47kP1 = 470k preset

Capacitors:

CI = 470nC2 = 220nC3,C5 = 10nC4 = 4p7/16 VC6 . C9 = 100nC10 = 22n

Semiconductors:Di ... Dli = 1N4148IC1,1C2 = 27161C3 = 4098. 45281C4 = 4093IC5,1C6 = 4049IC7 = 7555IC8 = 40147

Miscellaneous:Smith Corona EC 1100electronic daisywheeltypewriter

Optional:2.5 mm connectors, one offeach male 10 pin, female10 pin, male 12 pin, female12 pin, such as Molex5267-10a, 5264-10,5267-12a, 5264-12.

Figure 3. The printed cir-cuit board was carefullydesigned so that it can bemounted in the machinebeside the existing board,so it simply has to befixed in position withthree screws. Links toCONE 1 and CONE 2could be made in themanner indicated infigure 4. Don't forget theconnection to ground.

6-37

daisywheel typewriterprinter interfaceelektor june 1984

Figure 4. Connection tothe Centronics interfaceis simplified by using thesame type of connectorsas the machine alreadyuses for CONE 1 andCONE 2. The new con-nectors are mounted on apiece of veroboard towhich the cable for theinterface is also con-nected. The diagram isduplicated once with apair of 10 pin connectorsand once with 12 pinconnectors.

Table 4. The contents ofEPROM Mt

Table 5. This is the datastored in EPROM IC2. Alladdresses not mentionedcontain 01HEx.

4

keyboard

newconnectors

Table 4.key rt-o. addtess 4.343 45

914

1033

31

60

58

1011

123

553057

45

218228Z3F24F256

26F27F25EMa2AF2BE2CE2042887FF3A L.,

4002eeos°a40so014001

200$

20

46

313E1

3CF30E2E83FA5EF40E

7 8084 OF9

009089789

12 3063 31F4 32F5 33f6 34f

7 MF 10

8 36F 209 37F 40

10 33F 8311 39E 01

088 20208 40

31 585 4046 5DE 10

3 7CF 0113 788 8313 708 2032 7E9 01

32 5C9 01

36 Sill 0253 428 02

43C 04

44C 02450 4046C 0147C TO

488 01

499 10445 03464 CC

4CA Da

404 044E13 044F4 01504 10

51D 01

52D 93530 TO

existingconnectors

interface

24 54C26 55C52 56C21 57050 53025 a3C49 EA 0

Table 5.

0000 : 01 0106: 01 D200: 01 D300: 01 D408: 00 D500: 00 0600: 01 0700: 01D010: 01 D110: 01 0210: 00 D310: 01 0410: 00 0510: 00 D610: 01 0710: 010026: 01 D120: 01 0220: 00 0320: 01 0426: 80 0520: 00 0620: 01 0720: 01D630: 01 0130: 01 0230: 02 0330: 01 0438: 00 0530: 00 0630: 01 0730: 01

D040: 01 0146: 01 D240: 00 0346: 01 D440: 00 0540: 00 0640: 01 0740: 010050: 01 0150: 01 0250: 00 0350: 01 0450: 06 0550: 00 04'50: 01 0758-: 01D0_0: 01 0160: 01 0260: 00 0360: 01 0466: 00 0560: 60 0660: 01 0760: 0 i0070: 01 0170: 01 D270: 00 D370: 01 04713: 00 0570: 00 0670: 01 0770: 01DOA@ : 01 D180: 131 D280 : 00 0380: 01 D480: 08 0580: 00 D680: 01 0780 : 0100-7/0 : 01 0190: 01 0290: 00 0390: 01 0490: 00 0590: 08 D690: 01 0790: 0100f:10 : 01 lAt.1 : 01 02P10 : 00 D3A0: 06 04A0: 00 D5A0 : 00 06140 : 01 D7A0 : 01D080: 01 0180: 01 0280: 00 0380: 01 0486: 80 0580: 01 0680: 1 0780 : 00DO C0: 01 D1CO: 01 D2CO: 81 03C0: 02 D4C0 : 00 D5C0 : 01 D6C0 : 81 0700:0000: 0 01013: 01 0200: 61 0300: 01 0400: 00 0500: 01 0600: 1 0700: 01DO E0 : 01 DlEO: 01 D2E0: 01 03E0: 62 04E0: 00 05E0: 00 06E0: 01 D7E0: 0008F6: 01 D1F0: 01 D2FO: 06 D3FO: 00 D4FO: 00 D5FO: 01 06F0: 01 07F6: 01

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Figure 5. The keys havethe normal QWERTYlayout and some havethree functions, whichare dealt with in theuser's manual. Thenumbering of the keyscorresponds to that in thematrix of figure 1.

project may seem somewhat illogical dueto the layout of the keys and their pos-itions in the matrix (as figure 5 shows). InEPROM IC2 only one sixteenth of thememory space is filled as the first four ad-dress lines are not used. The table cor-responding to the contents of EPROM IC1is arranged according to the ASCII codes(which are not indicated). These EPROMs

can be programmed by the user himselfor may be purchased pre-programmedfrom Technomatic Ltd.Finally, a quick recap of the commandsrecognised and executed by the machine:CTL-K (OBHEX) = VT, CTL-H (08HED =BS, DEL (7FHEX) = erase, and CTL-O(OFHEX) = LF instead of the usual CTL-J.

14

6-38

The anemometer featured in our October 1983 issue contains amemory which stores the minimum and maximum windspeedsmeasured in the form of positive analogue voltages. A simpleaddition can make this memory store negative values also. Theresulting maximum and minimum memory is suitable for a number ofapplications. As an example of these we describe an electronicversion of Six's famous thermometer; other possibilities are. left toyour own ingenuity and imagination.

maximum and minimummemoryelektor june 1984

maximum and minimummemoryThe amateur meteorologists among youwere no doubt delighted with the anem-ometer and wind direction indicatorpublished in our October 1983 andJanuary 1984 issues respectively. Yourweather station can now be augmentedwith an electronic maximum and minimumthermometer. Such a thermometer, usingalcohol instead of electronics, was in-vented by the British physicist Six. Itenables the recording of both the highestand the lowest temperatures reachedsince the thermometer was set.

The circuitOnly a synopsis of the circuit is givenhere as a detailed description appeared in

our October 1983 issue.The memory of the anemometer storestwo voltages between 0 V and 1 V, ofwhich one represents the highestrecorded windspeed, and the other thelowest. As these values are continuouslycompared with the current windspeed,they are always up to date. The attractionand usefulness of such circuits is theirfacility for retaining analogue values for along time. The actual storing takes placein digital form in a binary counter. Beforethe content of the store can be comparedwith the current value, it is changed intoan analogue voltage by a digital to analogconverter. Whether the memory is up-dated or not depends on the result of thecomparison.

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Figure 1. The circuit ofthe memory which isalmost identical to that ofthe anemometer. Theearth potential at pins 2of IC9 and 3 of IC4respectively is shifted byA6 which enablesnegative voltages to beprocessed.

6-39

maximum and minimummemoryelektor june 1984

IC2LM335

adj_ I I

2

IC2LM335

Figure 2. The temperaturesensor in which P1 setsthe output voltage at 0 Vfor 0 °C. The adjustmentterminal of the LM335 isnot used.

Figure 3. Only a fewmodifications are necess-ary to the printed -circuitboard: two breaks andthree extra connections.The wire bridge along C9and R16 should beomitted.

RIC1

0 5 V

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84060-25V

The memory must, however, be expandedto make it usable with negative inputvoltages. The temperature sensing unitcan be calibrated to give an outputvoltage of 0 V at an ambient temperatureof 0 °C. Temperatures above 0 °C result inpositive voltages, those below in negativevoltages. In the circuit described, the in-put voltage range can be set between-1V and +1 V.The circuit of the augmented memory isgiven in figure 1, which shows that the ad-ditional stage consists of an operationalamplifier, A6, and associated components.The opamp, which functions as a voltagefollower with unity gain, is powered bythe existing symmetrical ±5 V supply. Thevalues of R18, P3, and R19 are necessary to

3

enable the output voltage of A6 to bepreset somewhere between 0 V and -1 V.The actual value preset by P3 is somewhatmore negative than that representing thelowest expected temperature. The func-tion of A6 is to shift the earth potential ofthe D/A converter IC9, current/voltageconverter A5, and the measuring instru-ment to the preset value.The other addition is, of course, the tem-perature sensor, the circuit of which isshown in figure 2. The sensing unit, IC2,is a type LM335 which converts changesin temperature into voltage variations. Itstemperature/voltage slope is 10 mV/K inthe range -40 °C ... +100 'C. The outputof IC2 is fed to opamp IC1 which arrangesfor the output voltage to be 0 V at an am-bient temperature of 0 °C. Output voltageUt is then related to the ambienttemperature at 10 mV/°C provided that theoutput of A6 can really go down to -1 V.This is guaranteed as long as R4, R5 andR6 are high -stability (1%) metal -filmresistors, and P3 has been adjustedcorrectly.

Construction and calibrationThe printed circuit used is identical to thatof the anemometer (EPS 83103-1), which isconstructed as described in the anemo-meter article, with the exception of thewire bridge alongside C9 and R16. Insteadof this, break the earth connections of pin2 of IC9 and pin 3 of IC4 and wire thesepins, together with junction C9/R5, to theoutput (pin 6) of ICl2. The circuit aroundthis opamp, and, for that matter, the one ofthe temperature sensor, is so small that itis best built on a small piece of wiring(Vero) board.Start the calibration by adjusting P3 so thatthe output of A6 lies between -1 V and0 V as required; normally, this will be-400 mV, corresponding to an ambienttemperature of -40 °C. Then adjust P2 togive +1 V (+100 °C), measured with adigital multimeter, at the junctionR16/R4/C9. It may be necessary toenlarge R16 slightly to achieve this result.The setting of P1 and the value of R17 areboth dependent on the measuring instru-ment and its scale. They have to beset/computed on the assumption that thevoltage at T is 10 mV/°C.It is interesting to connect a digital multi -meter between 'f and earth, because thatinstrument can read negative voltages. Atemperature below 0 °C will therefore beindicated as such. The same can, ofcourse, be achieved with a centre -zerometer which has been calibrated from-40 °C to +40 °C.Finally, adjust PI in the sensing circuit togive a voltage of 0 V at pin 6 of IC1 at anambient temperature of 0 °C. If you wantto avoid working with ice cubes, you mayadjust P1 to give a voltage of 2.730 V at itswiper, measured with a digital voltmeter.

6-40

elektor June 1984

analytical videodisplay(May 1984, page 5.31)We regret that line - 15 hasfallen out of Table 2 onpage 5-35; this line reads:15 10101 150 1 0 1 0 0 0 51 blueAlso, the end of line - 14should read: 50 blue.

6-41

elekior June 1984

The following pages contain themirror images of the track layout ofthe pc boards relating to projectsfeatured in this issue to enable you toetch your ovm boards. To do this, yourequire an aerosol of 'ISOdraft'transparentizer (distributors for theUK: Cannon & Wrin, 68 High St.,Chislehurst, Kent, 01 467 0935, whowill supply the name and address ofyour local stockist on request), a mer-cury vapour lamp, sodium hydroxide(caustic soda), ferric chloride, positivephoto -sensitive board material (whichcan be either bought or home made byapplying a film of photo -copyinglacquer to normal board material). Wet the photo -sensitive (track) side

of the board thoroughly with thetransparent spray. Lay the layout cut from the relevant

page of this magazine with its

CN1

0CO

PC board pagesDANGER! Ultra -violet light is harmful to your eyes, sowhen working with a mercury vapour lamp, wear someform of effective eye protection.

printed side onto the wet board.Remove any air bubbles by carefully'ironing' the cut-out with some tissue.paper. The whole can now be exposed to

ultra -violet light. Use a glass platefor holding the layout in place onlyfor long exposure times, as normallythe spray ensures that the paper sticksto the board. Bear in mind that normalplate glass (but not crystal glass orperspex) absorbs some of the ultra-violet light so that the exposure timehas to be increased slightly. The exposure time is dependent

upon the ultra -violet lamp used.the distance of the lamp from theboard, and the photo -sensitive board.If you use a 300 watt UV lamp at adistance of about 40 cm from theboard and a sheet of perspex, anexposure time of 4 . .. 8 minutes

should normally be sufficient. After exposure. remove the layout

sheet (which can be used again).and rinse the board thoroughly underrunning water. After the photo -sensitive film has

been developed in a sodium hydrox-ide solution (about 9 grammes ofcaustic soda to one litre of water) forno more than 2.2 . . . 3 mins at 20-C,the board can be etched in ferricchloride (500 grammes of FeC13 toone litre of water). Then rinse theboard (and your hands!) thoroughlyunder running water. It is advisable towear rubber or plastic gloves whenworking with caustic soda or ferricchloride solutions. Remove the photo -sensitive film

from the copper tracks with wirewool and drill the holes.

O10

6-42

elektor June 1984

f.m. wireless microphone 84063

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ZX extensions 84054

portable distress signal 84048

daisywheel typewriterprinter interface 84055

6.43

elektor June 1984

PC board pages

6-44

........ r

........ ... -

lead -acid battery chargerelektor june 1984

lead -acid battery chargerThe lead -acid battery has improved so much in recent years that itcan often be a good and less expensive substitute for the popularNiCad battery. A special charger is required, however, as the lead -acid battery must be charged at a constant voltage rather thanconstant current. The charger described in this article uses one oftwo charging voltages automatically selected depending on thecurrent flowing through the battery. In this way we get an optimalcompromise between short charging time and long battery life.

What springs to most people's mindswhen the lead -acid battery is mentioned isthe automotive version. That is a heavybox full of acid providing the energy tostart the car and needing occasionalmaintenance to keep it healthy. Lead -acidbatteries are also used for a multitude ofother applications, such as large torches,small cordless household appliances,models, and, of course, as an emergencysupply for important equipment in case ofmains failure.The modern lead -acid battery is availablein all shapes and sizes. There are evengas -tight versions enabling the lead -acidbattery to be used in many applications asa replacement for the commonly usedNiCad battery.The lead -acid battery has a few importantadvantages over its NiCad counterpart,especially if the current requirement isfairly high. Its energy capacity is muchgreater than the NiCad's, and the samecan be said of its output. The lead -acidbattery's greatest strength is the largenumber of charging and dischargingcycles possible relative to the low pur-chase price (compared to the NiCad).The lead -acid battery must be charged ina completely different way than the NiCad

equivalent. The latter requires a constantcharging current whereas the formerneeds a constant voltage. The battery thencontrols the charging current itself so thatthe minimum of gases are generated. Thedifference between these two methods ofcharging is shown in figure 1.The charging voltage of a lead -acid bat-tery is largely responsible for its lifespan.It should be noted, in passing. that the lifeof a completely discharged lead -acid bat-tery is only a few weeks, so it is a verybad idea to simply leave a batterydischarged. Using a high charging voltagegives a short charging time but also ashort lifespan, while a low chargingvoltage results in a long charge time andlong lifespan. To give you an idea of thevalues we are talking about here, aGeneral Electric gas -tight lead -acid bat-tery has a lifespan of three years with a`high' charging voltage of 2.45 V per cell.It is then charged to 95% of nominalcapacity in eight hours. A 'low' voltagecharge at 2.30 V per cell increases thelifespan to eight years (provided the bat-tery is continuously connected to thecharger) but the time needed to charge isthen fifteen hours (see figure 2). The im-portance of the charging voltage is ap-

a two -stagedesign toenable fastchargingwithoutreducing thebattery'slifespan

6-45

lead -acid battery chargerelektor june 1984

Figure 1. Graph a showsthe curves for thevoltage, internal pressureand temperature of alead -acid battery chargedat constant current. If aconstant voltage chargeis used (characteristic blthe curves for pressureand temperature aremuch better as no over-charging then occurs.

Figure 2. This graph clear-ly shows the effect ofcharging voltage on thebattery's lifespan.

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parent by the fact that the difference bet-ween the two voltages is only 0.15 V.The lead -acid battery charger must makesome sort of compromise between charg-ing time and lifespan. The voltage at thelast part of the charging cycle is es-pecially important for the battery'slifespan. If the current is too large it willcause a deterioration in the lead grid towhich the active pan of the battery isfixed. A lower charging voltage will makethe current correspondingly smaller sothere will be less deterioration. This isparticularly important if the battery isnearly always connected to the charger.The solution for this is a charger thatadapts the voltage to the current flowingthrough the battery. The lead -acid batterycharger described here uses a two -stagesystem in which the charger itselfswitches from high to low voltage whenthe charging current falls below apreviously set value. The circuit is notonly suitable for normal charging but canalso be used for applications where thebattery is generally on stand-by.

The chargerEven though the operation may soundsomewhat complicated the circuit is quitesimple and. as figure 3 shows. only con-tains 16 components. It is based on an

2

T

84010 2

LM 317 voltage regulator (ICI) which en-sures that the voltage at the output is con-stant. This voltage is initially defined byvoltage divider R5/R6 + P2. The lowvoltage that decides the current in thesecond pan of the charging cycle is setwith preset P2.A thyristor and a resistor (and a normallyclosed push button) are connectedpaiallel to R6 and P2. When the thyristorconducts R4 is switched in parallel withR6 + P2 so that the output voltage dropssomewhat (this is the second part of thecharging cycle). The moment that Thl trig-gers depends on the output current. Thisis the reason why resistor R7 is connectedin the zero voltage line. The gate of thethyristor is connected to the outputvoltage of ICI via R2, Rl, and Pl. If thecharging current is fairly large the voltagedrop across R7 keeps the potential dif-ference between gate and cathode toolow to trigger the thyristor (the voltageacross R7 is negative with respect to thatacross RI + P1 so the gate -cathode voltageis URI + P1 - UR7)-After a certain length of time the batteryis charged so far that the current hasfallen to the value set with Pl. Thethyristor is then triggered. R4 is con-nected in parallel with R6 + P2, and theoutput drops to the low voltage. As wehave already seen. the difference betweenhigh and low voltage is quite small atabout 0.15 V per cell. When the outputvoltage is the low value LED D3 will light.In order to prevent the thyristor from be-ing triggered as soon as the circuit ispowered up. but with the battery not yetconnected, a push button, SI. is included.After connecting the mains supply andthe battery. SI is pressed causing the highvoltage to appear at the output and a'large' current to flow through R7. Thepush button is then released and Thl re-mains off as long as the current throughR7 stays high enough.The charging current can be measured byconnecting a meter in parallel with R7.This is indicated with dotted lines infigure 3.

Calibration and useThis circuit is easily constructed on apiece of Veroboard. Some of the com-ponents in the diagram have two values,one of which (marked with an asterisk)should be used for the 12 V version andthe other for a 6 V version of the circuit.The IC must be mounted on a heatsink asit tends to get rather warm. The value ofresistor R7 depends on the capacity of thebatteries that are to be charged. as wewill see shortly.The circuit must be supplied with a rec-tified and smoothed voltage of at least 3 Vmore than the output voltage from theregulator. The supply used must be ableto provide at least 1/10 of the currentcapacity of the battery but this should notbe more than about 1.5 A as this is thevalue at which the LM 317's internal cur-rent limiting comes into action. This cur -

6 -46

rent limiting does depend on the exacttype of regulator used; for the LM 317K orLM 317T it is 1.5 A but for LM 317H orLM 317M the current is limited at 0.5 A.The value of resistor R7 is calculated fromthe formula: R7 = 0.3 Wiswitching Theswitching current (or, the current at whichthe circuit switches from high to lowvoltage charging - which seemed a bitlong to put in a formula) can be set to anyvalue. A good compromise would be acurrent that is 1/10 or 1/20 of the nominalbattery capacity (see figure 4).The circuit must now be calibrated withthe power switched on but without anybattery connected. If everything is work-ing the thyristor will conduct and D3 light.Connect an accurate, preferably digital,meter onto the output and set P2 until themeter reads exactly the number of cellsmultiplied by 2.3 volts. Three cells need6.90 V and six cells give a value of 13.8 V.Press SI and keep it pressed. Nowmeasure the output voltage, which mustbe the number of cells times 2.45 volts(7.35 V for 3 cells and 14.7 V for 6 cells). Ifthe voltage is not close to this value theresistance of R4 may have to be changedand P2 then readjusted. The final adjust-ment is to set the switching point withpreset P1. The most obvious method ofdoing this is to connect a partly dis-charged battery to the charger. Rotate thewiper of PI completely towards RI andthen press SI to start high -voltage charg-ing. Measure the current through the bat-tery (by connecting a voltmeter across R7;I = U/R7) and check from time to time,every half hour or so, whether the currenthas dropped to the desired value. Whenthis point is reached PI must be trimmeduntil the LED just lights. The charger isthen ready for use.Using the circuit is very straightforward:- Connect the supply to the charger and

switch on. The LED should light.- Connect the battery to the output of the

charger.- If fast charging is desired press SI. The

LED is then not lit.- After a certain length of time D3 lights

to indicate that the switching point hasbeen passed and that the charger ischarging at normal speed.Finally, a note about the characteristicsshown in this article. In principle theseonly apply for General Electric lead -acid

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batteries but most similar batteries havethe same sort of characteristics. They areonly included in this article to indicate thetype of curves that can be expected.

1111

Literature: The sealed lead battery hand-book by General Electric

lead -acid battery chargerelektor June 1984

84070-3

Figure 3. The voltage out-put from the charger,whose circuit is shownhere, is automatically setdepending on the currentflowing through the bat-tery that is beingcharged. If M1 is in-cluded the 10 k presetmust be trimmed so thatM1 reads the same valueas an ammeter connectedin either the '0' orline to the battery undercharge.

Figure 4. This gives anidea of the charging cur-rent when a battery ischarged at a constantvoltage. The charger usedhere had current limitingset at 500 mA, which iswhy the characteristicbegins where it does.

6-47

To dispel any misgivings you may have had, we would like to start byemphasizing that the design published here has little in common withthe 'wireless microphones' that are sometimes offered for sale. It is,in fact, a substitute for a real professional wireless microphone. Itsminiature transmitter provides very good quality sound. The receiveris simply a modified version of the 'personal FM' published in Elektorin September 1983.

wirelessmicrophone

a high qualityFM transmitter

A wireless microphone may not seem likea very unusual project for an electronicsmagazine given that there are ready-madeversions fairly freely available. These are,however, nothing more than toys, whenconsidering their stability and harmonicsuppression. Furthermore as they operatein the broadcast FM band they are illegal.Professional wireless microphones are acompletely different story, of course. Theytransmit high quality sound over quite areasonable distance. Frequency stability,harmonic attenuation, bandwidth, and allother specifications are extremely good.In Britain wireless microphones must belicensed and have type approval from theDepartment of Trade and Industry (whoseaddress is at the end of this article).A wireless microphone needs a suitablereceiver and to simplify matters we usedan existing design, the 'personal FM'radio. Admittedly, better receivers couldbe imagined but the personal FM is, atleast. compact and its quality leaves littleto be desired.

The transmitterApart from the receiver, which is a

Specifications:frequency range: 35 . 40 MHzoutput power: 3 ... 10 mW

(E.R.P.: 0.5 . . 1.5 mW)harmonic attenuation: 60 dBspurious RF radiation: < -60 dBfrequency stability: better than 10 kHzfrequency sweep (bandwidth):-<;. 180 kHzmicrophone signal: min. 1 mV, max. 200 mVaudio bandwidth: 40 Hz . . 15 kHz 1 ÷ 2 dB)current consumption: 25 .. 30 mA

Rot LIR = 9 . 18 V)

separate unit, the wireless microphoneconsists of two parts; a microphone cap-sule and a transmitter. The transmitter isoften mounted within the case of a largemicrophone, but an alternative is to mountit in a separate case that fits into an insidepocket. We chose to use this latter option.Either electret or dynamic microphonesmay be used as the microphone amplifieris matched to different impedances bychanging only three resistors (as we willsee later).Strictly speaking an FM transmitter needsonly an AF modulation stage, an oscillator,an amplifier, and an output filter but we

6-48

1wireless microphoneelektor june 1984

XTO X

455

Discriminator

A

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VCO LPFsnatchingcircuit

134.063-1

have added a few extras, as the blockdiagram of figure 1 shows. These arenecessary due to the fact that the fre-quency deviation needed for Hi-Fi is dif-ficult to combine with the high frequencystability demanded - certainly in the caseof a miniature transmitter. A frequencydeviation of 100 or 200 kHz is easy to ar-range with a free -running oscillator butthe stability that can then be achievedleaves a lot to be desired. If a crystaloscillator is used the opposite is the case:the stability is then good but it is not soeasy to obtain the deviation needed for

wideband FM.What this boils down to is that we mustfind some other solution. As figure 1 in-dicates we have still used a free -runningoscillator (VCO), which is modulated bythe microphone signal via an amplifierand a pre -emphasis stage. This takes careof the frequency deviation but in order toattain 'crystal -like' stability a sort of AFC(Automatic Frequency Control) system hasbeen included. This is done by puttingthe oscillator into a frequency locked loop(FLL) in which the frequency of the VCOis controlled by a crystal oscillator (XTO).

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Figure 1. In order to keepthe transmitter frequencyas stable as possible theVCO is continuously ad-justed by a crystal -controlled AFC system.

Figure 2. All the variousparts of the blockdiagram are easilyrecognized in the circuithere. The circuit can fitonto quite a small printedcircuit board in spite ofits complexity.

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6-49

3 wireless microphoneelektor june 1984

The signals from both oscillators are fedto a mixer (block X) and any differencesbetween them are noted by a frequencydiscriminator from where a signal is fedvia a low-pass filter to the VCO to correctits frequency.The oscillator signal is then amplified,filtered, and fed via a matching circuit tothe aerial.

The circuitHaving seen the block diagram the maincircuit diagram of figure 2 is easier tofollow. The division is roughly as follows:the section around T5 ... T8 is formicrophone signal amplification and pre -emphasis, T3 is the heart of the VCO, Ti isconnected as the crystal oscillator, T2serves as the mixer, and T4 is the outputstage. As the diagram shows liberal use ismade of dual -gate MOSFETs. These haveexcellent HF characteristics and a conve-nient side -effect is that they require aminimum of external components.Starting with the VCO; the low capaci-tances and small temperature rise of theMOSFET used here give this oscillator.even without AFC. a stability that wouldnever be possible with an ordinary bipolartransistor. The oscillator circuit itself is amodified Colpitts type circuit whereby thecondition for oscillation is that the sourceof T3 is fed back to the first gate via acapacitive tap from the L3/C8/C9 circuit.The amplitude of the signal at this gate islimited by diodes D6 and D7 in order toprevent the frequency stability from beingaffected by too high a voltage level.

Part of the oscillator signal is fed via L4 togate 1 of mixer T2. The signal fed to theother gate comes from the crystaloscillator based on T1. This oscillatorworks at a frequency 455 kHz lower thanthat of the VCO. The output signal fromthe mixer should therefore have a constantfrequency of 455 kHz. If this is not thecase the VCO frequency has altered so it_must be corrected by the AFC. To do thisthe 455 kHz signal is fed to a frequencydiscriminator consisting of filter FLI,diodes DI and D2, and resistors R3 andR4. The frequency -dependent phase shift-ing of the 455 kHz ceramic discriminatorfilter is used to good effect. When the in-put frequency differs from the ideal thereis a voltage difference across the diodeswhich is converted to a control voltage bymeans of low-pass filter R5/C7. This isthen used to drive varicap diode D3 in theoscillator circuit.The output of the modulation amplifier isalso connected to the varicap. Thisamplifier consists of two stages (T5, T6and T7, T8) with pre -emphasis networkR11/R12/C25 in between. The modulationindex is set by adjusting the amplificationof the first stage with Pl, which is a low -noise preset. If the component valuesgiven here are used the input is suitablefor (high impedance) electret micro-phones. The values of R8. R18. and PImust be changed for different microphoneimpedances. For a dynamic microphoneof about 500 ohm they are: R18 = 470 Q,R8 = 680 2, and PI = 100 k. A limiter (C26,C29, D4, D5) is included between themicrophone amplifier and the varicap as a

Figure 3. Small though itis, this double -sidedprinted circuit board willnot fit into most commer-cial microphone cases.We chose the alternativeof fitting it in a separatecase that can be carriedin a pocket. Both sides ofthe board are shown onthe service pages in thisissue.

Parts list

- Transmitter

Resistors:(all 1'8 WIR1,R9,R14 = 47 kR2 = 3k3R3,R4,R12,R17 = 10 kR5.137 = 100 kR6= 220kR8 = 6k8RI0,R11,R16 = 1 kR13 = 12 kR15 = 1k8R18' = 4k7Pr = 1 M preset

Capacitors:

C1` =5p6C2* = 27 pC3,C11 . . C14 = 10 nceramic

C4,C28 = 100 nC5 = 220pC6 = 1nC7 = 47 0/63 VCEV.C17',C19' = 68 PC9' = 330 pC10 = 3p9C15' = 20 p trimmerC16`,C20* = 47 pC18* = 15 pC21.,C22` = 80 p trimmerC23 = 1 0;10 VC24 = 560 nC25 = 4n7C26,C27.C29 = 470 n

6-50

wireless microphoneelektor june 1984

II GO 00

*0 w ale Figure 4. The screen seenin the prototype here.between the HF and AFsections, can be made oftin or copper. Its positionis indicated by a dottedline on the printed circuitboard.

Inductors:= 20-12

L2 = 470 pHL3 = VHF coil, MC 120style, no. 100078 (Ambit)

1.4: a 4 turns. b = 2turns, of SWG 31 (0.3 mmlCuL on a 3.5 x 3.5 mmferrite bead

L5 - 1 pHL6 = 4pH7L8,L9 = 0 H33L10 = 15 turns, with a tapon the third turn fromground, of SWG 19 ... 2111 0.8 mm) CuLwound on a normal roundpencil

Semiconductors:D1,02 = AA 119D3 = BB 405. BB 10504 . D7 - 1N4148TI = 8F494

0 T2.T4 - BF 900, 8F 907.BE 981

T3 - BF 905. BF 907,BF 981

T5,T7 = BC 550CT6,78 - BC 547BIC1 -- 78105

Miscellaneous:FL1 = 455 kHz ceramicdiscriminator, e.g. 455Dfrom Toko(Ambit)

S1 = switch. SPSTX1' = third overtonecrystal, 35 . _ 40 MHz

Note: = see text

4

safety measure to prevent the frequencyswing from exceeding the maximum per-mitted value.The modulated output signal from theVCO is taken from the source of T3 togate I of output amplifier T4. All the har-monics in the amplified signal are thencarefully removed by an extensive filternetwork before being passed, via match-ing circuit LIO/C21/C22, to the aerial. Atelescopic aerial should be used but a1 metre length of cable is also suitable. Ifthe output filter is correctly set up the3 ... 10 mW produced by T3 results in aneffective radiated power (E.R.P.) of about1 mW.

Other frequenciesNo doubt you have been wondering whatis the meaning of all the asterisks infigure 2. Even though it is designed forone frequency band this transmitter canalso be used for other frequencies. Withthe values stated the circuit is set to35 ... 40 MHz but by changing the com-ponents marked with an asterisk it canwork at up to 90 MHz. For frequencieswithin 20% of the 35 ... 40 MHz rangeeither the capacitors or the inductors inthe filters must be changed, but for otherfrequencies the values of both must bealtered.

ConstructionThe double -sided printed circuit boardshown in figure 3 is a model of compact-

ness. Construction is simplified by mount-ing many of the components vertically. Asmall metal screen (indicated by the dot-ted line) is needed between the HF andAF sections of the circuit.All the coils except L4 and L10 can simplybe bought. One winding of L4, namely a,is 4 turns, and b is 2 turns, of enamelledcopper wire 0.3 mm in diameter (SWG 31)on a ferrite bead of about 3.5 x 3.5 mm.Inductor LIO consists of 15 turns of0.8 ... 1 mm enamelled copper wire(SWG 19 ... 21) wound on a normal roundpencil (which is then removed, of course).The tap off point that connects to L9 is onthe third turn from earth.The MOSFETs used are available invarious different packages (see figure 2)and there could be some confusion aboutthe various pin designations. If possible,we recommend that type 'c' should beused as this is the only one whose pinscannot be mixed.When choosing a crystal remember thatits frequency must be 455 kHz lower thanthe desired output frequency. A transmis-sion frequency of 39.7 MHz requires acrystal frequency of 39.245 MHz. A third -harmonic crystal must be used and it mustbe suitable for parallel mode with 10 pFparallel capacitance. A serial -mode crystalcould possibly be used (30 pF seriescapacitance) but as this gives a frequencyof about 2.2 kHz higher in our design thecrystal frequency must be reduced ac-cordingly; in the example just given itnow becomes 39.243 MHz.The case used must be metal but apartfrom that the only requirement in this

6-51

wireless microphoneelektor june 1984

Figure 6. This test circuitis needed to enable thetransmitter to becalibrated. The metershown could simply bean ordinary multimeter.

regard is that the aerial connection bekept as short as possible. The supply forthe transmitter may be between 9 and18 volts so a 9 V battery is quite sufficient.

The receiverAs we dealt with the receiver in detail inthe September 1983 issue we will keepthis section as short as possible. Very fewmodifications are needed to change thefrequency range from 87.5... 104 MHz toabout 33.5 ... 40.5 MHz. The changes areclear from the circuit diagram of figure 6.Only LI, L2, L3, R1, R2, and C2 are givendifferent values and an extra LF output

6AA 119

P)20 kn:v

O840532

can be made via C24. The sensitivity ofthe receiver is about 2µV and with a50 cm aerial the microphone signal can bereceived at distances of up to 100 metres.The receiver's intermodulationcharacteristics are not really good enoughfor it to be used effectively with morethan one microphone at a time.

CalibrationThe microphone is tested and calibratedas follows:1. Check that the crystal oscillator

operates. This is done by connectingthe test circuit of figure 7 as closely aspossible to Ll/C2. If the meter deflectsthe crystal oscillator is working.2. Check the VCO by connecting the test

circuit parallel to L3. Again the metershould deflect.3. Check the operation of the receiver. As

the 'personal FM' also receives at thethird harmonic of its VCO a few strong FMbroadcasts should be faintly audible.4. Inductor L3 must be set by connecting

a high -impedance probe from a fre-quency counter to gate 1 of T4 and trim-ming the coil to the correct frequency.Fine-tuning is possible by connecting thecounter to the aerial output and trimmingthe core of L3 until the voltage measuredwith a voltmeter connected across C7 isas low as possible (0.000 V).4b. Adjusting L3 without a frequency

counter. This is not recommended foranybody with a weak heart or a quicktemper because it will put a strainboth. Connect a (20 kcl/V) voltmeteracross C7 and start by winding the core ofL3 out as far as possible. By slowly turningthe core in try to find the correctdiscriminator point. This point is recog-nized by the symmetrical change in thevoltage across C7 before and after thepoint in question. If the adjustment iswrong one voltage will have a muchsteeper slope than the other.5. Adjusting C15, C21 and C22. The test

circuit of figure 7 is connected acrossC20 and C15 is then trimmed to give themaximum meter deflection. Trimmers C21and C22 can be adjusted with a fieldstrength meter after the aerial has beenconnected. The receiver could possiblybe used as a field strength meter ifnecessary.

Wireless microphones and thelawThe most important points to note are:Wireless microphones for use in Britainmust be licensed and therefore requiretype approval. Two frequency bands arestrictly forbidden for this purpose:26.1... 29.7 MHz and 88 ... 108 MHz. Ap-plications for type approval should be ad-dressed to: 14

Department of trade and industry.Directorate of radio technology.Waterloo Bridge House,Waterloo Road,London SEI 8UA.

6-52

6 wireless microphoneelektor june 1984

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Parts list

- ReceiverEPS No.: 83087

Resistors:

R1* = 33kR2` = 3k3R3 = 2k2R4 = 47 kR5 = 68 kR6,R9 = 10 kR7 = 100 kR8 = 18 kR10 = 10QP1 = 10 k ten turn potP2 = 22 k log. pot

Capacitors:

C1 = 68 p ceramicC2' = 6p8 ceramicC3 = 4n7 ceramicC4,C5.C20 = 10 n ceramic

C6= 1 A/6 VC7,C19 = 47 n ceramicC8 = 2n2C9,C12 = 3n3C10,C13 = 180 p ceramicC11,C15 = 330 p ceramicC14 = 100 nC16 = 220 p ceramicC17 = 150 nC18 = 220nC21 = 10 p/6 VC22 = 220 p/10 VC23 = 100 p/6 VC24' = 220 n

Semiconductors:DI = BB 105D2 = AA 119T1 = BF 494T2 = BC 640

T3,T4 = BC 549CIC1 = TDA 7000manufacturer: Philipssupplier. Technomatic Ltd.

IC2 = LM 386

Inductors:L1,L2 = 1pH5L3 = OpH82L4 = inductance made withcopper tracks on theprinted circuit board

Miscellaneous:

S1* = single pole toggleswitch

Note: ' = components thatare changed.

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549C

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Figure 7. It is quite easyto modify the 'personalFM' to act as the receiverfor the microphone. Inthis case, however, usingthe headphone cable asthe aerial is not recom-mended.The output canbe taken from the aux-iliary AF output that hasbeen added or it can bemade audible by in-cluding an extra amplifier(such as an LM 386) andusing a loudspeakerrather than headphones.

SOO %...rr..

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woe 6-53

merging BASIC programselektor june 1984 As a programmer's skills grow there is more and more temptation to

use scraps from different programs to make a new one. This is aninteresting idea but it is not immediately obvious how it could be putinto practice. The program given here, however, was written to dojust this. It is a utility designed for the Junior Computer with DOSthat can be adapted for other systems as long as the DOS (or BASIC)used has an input/output distributor that allows the memory to beconsidered as a peripheral device, as the Junior does.

merging BASIC programsa utility programto merge twodistinct basicprograms andmaking use ofutility softwarefrom the OSdisk 2

Table 1. Unlike most ofour recent software offer-ings this program is writ-ten in BASIC, or at leastone part of it is. Thismakes the job of adapt-ing it for systems otherthan the Junior Computerthat much easier.

The purpose of the program given here isto merge different BASIC programs or toplace them one after the other. This alonemakes it interesting and it is doubly so asit uses an interesting property of theJunior Computer's DOS and BASIC;namely that the memory can be used asan input/output device. This is acharacteristic that the Junior shares withthe majority of modern personalcomputers.The distributor is a software switch which,when programmed accordingly, allows theworkspace memory to be equated to theconventional peripheral devices (key-board, VDU, parallel or serial printer, etc.)and also to the main memory, and this isthe interesting point as fas as we are con-cerned. In the 0565D DOS system thenumber of the memory as an input/outputdevice is 5. For any system other than theJC's it will be necessary to refer to theuser's manual to find the informationneeded to modify the program.The distributor is managed by the DOSbut it can be used directly in BASIC. TheLIST 5 instruction, for example, causes theBASIC file to be transferred from theworkspace ($3A7E ...), where it is in com-

pact (tokenized) form, to $8000 and fromthis address on it is found in intearalASCII format so that it can appear as eas-ily on a VDU screen as on a printer. Ad-dress $8000 is set by the DOS but this caneasily be changed by the user if he sodesires.To understand this operation it is import-ant to know that the file is compacted inthe interpreter's workspace. The BASIC in-structions appear there in shortened formas indicators (tokens) or markers ratherthan as a series of ASCII codes cor-responding to the letters making up thereserved words of the instructions. In thenormal memory, on the other hand, wefind the file in the familiar form after theLIST 5 instruction has been executed.The I/O distributor allows the memory tobe used as an input device just as thekeyboard is. The merging program makesabundant use of the possibilities thisopens up.

BASIC and mergingThe program given here consists of amachine -code section (table 2) and aBASIC part, which is where we will now

2060 FOPy=1T024:FRINT:NE-T2016 PRINTTAB, 10."2020 PPINTTA810:.'-FILE MERGE UTILITY. -2030 FFINTT,48. 101.°20-16 PRINT:FRINT:PRINTT.4E. 16, "written bv A. Nachtmann2650 PPINT:PPINTTAB( 19 "feb. 19. 19842060 PRINT:PPINT:FRINT2070 PRINT'Be sure that both files to be linked ha -e different line numbers.2080 PRINT'If both files have some common line numbers boot up your system2090 PRINT'with the RSE0 utility to renumber the lines.2100 PRINT:INPUT'In which drive are the files to be merged A7B/C/B':Bs2116 &.S=LEFTS,.D5.1):O=A8e-D4):IF De.ASC('A') OR. O>ASC'O') THEN26002120 PPINT:INPUT'enter first file name -:Fs2130 INPUT'enter second file name'ISS2140 PRINT:INPUT'are you ready';IS2150 IF LEFTS(IS.1).7.)'Y' THEN21402160 REM ---RESET MEMORY INPUT POINTER2170 POKE9093.0:POKE9099,1282130 DISK!"SE A':DISK!'CA E400=12.7': DISK!'SE '+DS:DISK!'130 E481'2196 A1=8*16'3+11: A2=8*16'3+24i16+42206 REM --2210 A=A12220 FORX=1 TO LEN(FS>2230 POKE A.ASNMIDSCPS.X.1,):A=A+12240 NEXT2250 REM ---2260 A=A22270 FOR X=1TO LEN(5t)2280 POYEA.ASUMIOS(SS,X.1));A=A+12290 NEXT2300 POKE8993.16

6-54

HEXDUMP: E480,E4FF0 1 2 3 4 5 6 7 8 9ABCD2F

2408: 50 4F 48 45 38 39 39 33 2C 31 OD OA 80 OD 8A 44 POKE8993,1E410: 49 53 48 21 22 4C 4F 20 28 20 20 28 20 20 22 3A ISK!'LOE420: 4C 49 53 54 23 35 OD OA 44 49 53 49 21 22 4C 4F LIST#5..DISK!'LOE438: 28 20 20 20 20 20 20 22 3A 4C 49 53 54 23 35 OD ':LIST#5.E440: OA 44 49 53 48 21 22 47 4F 20 45 34 35 32 =2 OD .DISK! 60 E452'.E458: 0A 80 AE 91 23 AD 92 23 SE 66 E4 SD 67 E4 A2 682460: SD 00 E4 Fe 18 SD FF FF EE 66 E4 DO 03 EE 67 E42470: AD 66 E4 SD 91 23 AD 67 E4 SD 92 23 ES DO El 60E480: 60 A2 00 A9 80 8E 66 E4 SD 67 24 A2 OD DO DI FFE490: 00 FF 80 FF 00 FF 00 FF 80 FF 00 FF 00 FF 88 FFE4A0: 80 FF 00 FF 00 FF 00 FF 00 FF 80 FF 00 FF 00 FFE480: 80 FF 80 FF 00 FF 00 FF 00 FF 00 FF 00 FF 84 SFE4C0: 00 FF 00 FF 80 FF 00 FF 00 FF 80 FF 80 FF 00 FFE4De: 80 FF 00 FF 80 FF 00 FF 00 FF 00 FF 88 FF 00 FF24E0: 80 FF 08 FF 00 FF 00 FF 00 FF 00 FF 00 FF ee FF24F8: 00 FF 00 FF 80 FF 00 FF 00 FF 08 FF 08 FF EE 212500:

HEx:DUMP: 2200.22510 1 2 3 4 5 6 7 89ABCDEF

2200: A9 01 SD 52 26 20 BC 26 A9 2A 85 FF 20 54 27 802218: FE 20 07 29 AO BF 28 EC 22 FO 63 88 DO F8 SC 002228: 23 20 AC 15 20 9E OF 20 94 15 20 73 20 OD BA 2D2238: 2D 20 44 49 53 48 20 32 20 2D 2D OD OA OA 00 4C2240: E6 2A 20 20 20 20 20 20 20 20 20 20 28 20 20 202258: 20 51

begin. As soon as it knows the unit wherethe files can be found (D$) and theirnames (F$ and 5$ are two arbitrary namesthat must be in the directory of the unitdesignated by D$ - lines 2000... 2160)the processor initializes the pointer in-dicating the start address where the filetransferred to memory can be found. Itthen loads a machine code program and alook -up table at $E400 (from sector 7 oftrack 12; this is part of the space after thedirectory!). The machine language pro-gram is started by the GO instruction atline 2180. This loads the series of instruc-tions found in the right side of table 2 indirect mode (Le. without line numbers) in-to the area from $8000 on. From line 2190to line 2290 the BASIC program places thenames of the files that are to be merged(FS and 55) in direct mode after the twoLO instructions that have just beenloaded. The instruction at line 2300 pro-grams the distributor to make the memorythe input divice. The BASIC editor thenreceives the sequence of instructionsstarting at $8000 as if they were input one -by -one via the keyboard and it then ex-ecutes them one after the other. What thismeans is that it loads file F$, transfers it to$8000 (LIST 5), and then loads file S$ andtransfers it, in turn, to the space after FS. Itthen executes the DISK! "GO E452" in-struction which is the last it receives indirect mode from the memory as an inputdevice.The machine -code program at 5E452places a POKE 8993,1 instruction in directmode after the two files loaded at address$8000 and as this instruction has no linenumber it will be executed as soon as theinterpreter meets it. The purpose of thislast command is to reestablish the input

distributor in its original form where thekeyboard is the input device. Now theBASIC editor loads files F$ and S$ into itsworkspace to form a single new file whichit compacts and lists as it goes along.When it arrives at the last numbered linein the second file it finds the POKE 8993,1instruction which it executes in directmode thus making the keyboard again theactive input device.If a LIST instruction is now given thedisplay on the screen will show that theworkspace does, in fact, contain files F$and SS.

RSEQIn order to be able to effectively mergeexisting files it is essential to be able toeasily manipulate the numbering of thelines in both files and then later of thesingle file resulting from the merger. Ondisk 2 of the 5 supplied with the OhioScientific DOS is a utility program calledRSEQ that could be used to perform thistask. Until now none of the myriad articleson the various aspects of the Junior Com-puter have dealt with adapting disk 2 forthe Junior. The hexdump given in table 3does just that, enabling JC users to easilychange the line numbering of BASIC files,especially those that are to be merged.The adaptation procedure is quite simple.First copy the master diskette (this isalways advisable as a safeguard) and thenload track 0 of disk 2 by means of theTRACK 0 R/W UTILITY (RA200) at address$A200 (or elsewhere). The contents of thistrack must then be changed according tothe hexdump in table 3 and the modifiedfirst page of track 0 is then reloaded tothe diskette (VVA200/2200,1). And that's all,folks! 14

merging BASIC programselektor june 1984

Table 2. The second partof the MERGE utility islisted in this hexdump.This complements theBASIC program given intable 1.

Table 3. Diskette 2 fromthe set of 5 supplied withthe Ohio Scientific DOScontains a utility, RSEQ,that can be used torenumber lines in a file.The hexdump given herelists the modificationsneeded to adapt this forthe Junior.

6.55

echo sounderelektor june 1984

F. Kuhnke andP.W. Putters

echo soundersonar for yachts

sonar is an acronym ofsound navigation ranging

MMV = monostablemultivibrator

FF = flip-flop Ibistablemultivibrator)

Figure 2. The blockschematic is self-evident:the neon lamp has beenreplaced by a digitaldisplay. Underwatersound projector andhydrophone are housed ina common case, whilethe transmitter andreceiver are contained inone IC. Furthermore, a'shallow depth' alarm hasbeen provided.

Running a yacht aground does not necessarily mean its destruction,or even that there is any damage, but no skipper is happy with it. Atbest, it means a lot of effort to get the craft afloat again; at worst,well that does not bear thinking about . . . It can safely be said thatmany such mishaps could have been prevented by the judicious useof some sort of sounding apparatus!

In the past, sounding. that is. measuringthe depth of the sea bed, was carried outby a weighted line, the sounding -line.Nowadays, these are found almost ex-clusively on board yachts only. They con-sist of a ball of lead (the weight) and aline that has been marked suitably atregular intervals, so that when the leadtouches the sea bed the depth can beread off the line. The big disadvantage ofsuch a sounding -line is that it can only beused at low speeds and at shallow depths.The echo sounder does not suffer fromthese disadvantages and, moreover, its in-dicator may be mounted in the wheel-house near the other navigational aids. Anecho sounder is a sonar system thatmeasures the time interval between thetransmission of a burst of ultrasonicenergy and reception of the consequentreflected waves. In this, a speciallydesigned electro-acoustic transducer isused of which the transmitter is called anunderwater sound projector, while the

return echo is detected with ahydrophone.The usual configuration of an echosounder is shown in figure I. The soundprojector transmits a pulse in the frequen-cy range 150... 200 kHz. This pulse isreflected by the sea bed and detected bythe hydrophone. The hydrophone convertsthe echo into an electrical signal which isused to fire a small neon tube which ismotor -driven at uniform speed along aconcentric, calibrated disc. The neonlamp thus fires at a scale division cor-responding to the depth sounded. As thepulse is transmitted at exactly the momentthe neon lamp passes through zero, thedepth can be read off directly. Experi-enced skippers are also able to deducethe type of sea bed. For instance. sandyground causes a narrow flash of light.stony ground a wider one with a frayedtop, and soft ground an even wider onewith a frayed bottom.The present design has a digital read-out

6-56

which, unfortunately, does not allow an in-dication as to the type of sea bed, but ithas the advantage of being somewhatsmaller, and the depth can be read moreaccurately. It is also easier to buildyourself as the block schematic in figure 2shows. An important simplification is alsothat the sound projector and hydrophoneare contained in one and the same hous-ing which is connected to one IC(9), typeLM 1812 manufactured by NationalSemiconductor.

The circuitThe ultrasonic pulse travels a distanceequal to twice the depth of the sea bed.As the average speed of sound in water is1500 m/s (at 20°C and salinity of 2 percent), the time taken to travel to and froma depth of, say, 7.5 m is 10 ms. If thereforethe clock frequency for the counter in ICIis 750 Hz and pulses are registered for10 ms, it has effectively 'sounded' a depthof 7.5 m. However, as the counter can onlycope with complete pulses, a depth of7 m would be indicated. To provide amore accurate indication of depth, theclock frequency is increased to 7500 Hzand this allows depths to be read indecimetre steps.The counter, backing store, and 7 -segmentdecoder are contained in ICI. The counterreceives a stop pulse from IC9 when theecho is detected. The counter position isthen passed to the decoder by the back-ing store and indicated on a three -digitdisplay.A reset pulse from IC5 starts a new countcycle. As ICS generates a pulse every200 ms, 1500 pulses can be counted. Thismeans that the circuit is usable for depthsup to 1500 decimetres = 150 m. The resetsignal serves two further functions: it startsthe transmit pulse, and it sets off the alarmvia MMV4 and FF2. This means that theoutput of FF2 generates a 'shallow depth'alarm if the output level of the MMV islogic high at the moment the echo isdetected. The alarm threshold can be setbetween 1 m and 10 m with P1.The various functional blocks of figure 2can be found back readily in figure 3.Monostable MMV3 ensures that thedisplay is switched off when no echo hasbeen detected for some time: this timecan be set with P2. When no echoes arereceived, LED D2 also remains ex-tinguished. The display remains switchedon until MMV2 changes state. When anecho is detected, D2 starts to flashimmediately.As IC9 is the heart of the circuit, it'sworthwhile having a closer look at it. Theindividual stages contained in the IC areshown in figure 4, together with thenecessary peripheral elements. If IC5 pro-vides a 0.5 s pulse to pin 8 of IC9 every200 ms, the on -chip modulator is actuatedand generates the pulse for the soundprojector, in this case at a frequency of200 kHz. The modulator and 2nd h.f.amplifier have tuned circuit L1/C14 incommon. During transmission, this circuit

1

permanentmagnet

hydrophone

neon lamp

t - 2d/va = d/750where t is the travel time ins, d is the depth in m, andva is the average speed ofsound in water.

motor

pulse generator

amplifier

/ Figure 1. A commonmethod of depth sound -

underwater ing: the underwatersound sound projector transmitsprojector a burst of ultrasonic

energy which is reflectedand detected by thehydrophone. The echo isamplified and used to

,2, light a neon lamp which- is motor -driven around a

depth -calibrated disc.

6 MHz

1C3

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ICA

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6-57

echo sounderelektor June 1984

Figure 3. The circuit ofthe echo sounder con-sists basically of theultrasonic transmit-ter/receiver IC(9). clockgenerator IC3/IC4, pulsegenerator IC5. counter/store/decoder IC1. andthe LED display. The'shallow depth' alarm isset with P1 and the alarmis sounded by buzzer Bz.

is connected to the modulator and duringreception to the amplifier. This has, ofcourse, the advantage that the transmitand receive frequencies are identical and,moreover, the absolute frequency is notterribly important.The 200 kHz pulse from the modulator isamplified in the output stage and appliedto the sound projector via driver T8 andinductor L2. This inductor, together withthe self -capacitance of the sound projec-tor and C22, forms a circuit which istuned to 200 kHz.In the interval between transmit pulses,the echo is detected and evaluated. It isapplied to the 1st h.f. amplifier and then,via P4, to the 2nd h.f. amplifier which is

now connected to Ll/C14. The poten-tiometer enables setting the sensitivity ofthe echo sounder. The output of theselective amplifier is applied to athreshold detector which only reacts tosignals which lie above a certain level.Noise pulses on the signal are suppressedby a combination of pulse recurrencedetector and integrator. If the pulse trainis interrupted, the pulse recurrence detec-tor evaluates the received echo asspurious and causes integrator capacitorCI5 to discharge. If the received pulsesaxe too short (as, for instance, noisepulses). C15 does not charge fully and thepulses are rejected as spurious. If thedetector is fed with a true echo, the

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6-58

4 echo soundereiektor june 1984

display driver is switched on. A protectioncircuit briefly switches the receiver off ifthe display driver has been on too long.This is effected by the charging ofcapacitor C19 from the signal at the driverstage; when C19 is charged, an on -chiptransistor is switched on.Capacitor C9 ensures that the gain of the2nd h.f. amplifier is low immediately aftera pulse has been transmitted to preventany ringing of the transducer beingevaluated as an echo. This causes theminimum depth that can be sounded tobe around 2 m. If this is not acceptable,the value of C9 may be reduced. Note thatthe sensitivity in that case must also bedecreased.

Construction and assemblyThe most important aspect is, of course,the fitting of the transducer: somepossibilities are shown in figure 5. It isessential that it is fitted perpendicular to aline drawn through the length and to onedrawn through the width of the vessel. Itmay be necessary to mount the transduceronto a suitably shaped adapter as shownin figure 5c. If the hull is of fibre -glass, thewhole assembly may be fitted in -board.The cable from the transducer to the elec-tronic pan of the echo sounder must notbe tied together with other cables, as thismight give rise to noise pulses whichwould upset the proper operation. An im-portant point here is NOT to shorten thecable provided with the transducer!If you already have an echo sounder,there's no need to buy another transducer,as the one you are using already is almostcertainly suitable for the present circuit.

The VDO Echo Sounder Modis 120(operating on 200 kHz), or Spaceage,Euromarine, or Seafarer (all operating on150 kHz) have transducers which canhardly be told apart. All these transducersare available at most ship's chandlers ormarine electrical suppliers.Construction of the electronic part of theecho sounder on the printed -circuit boardshown in figure 6 is child's play comparedwith the fitting of the transducer. InductorL2 must be hand -wound, but Ll may bebought ready made.The three -digit display is constructed onthe printed -circuit board shown infigure 7. The voltage regulator and its heatsink should be fitted at the track side ofthe board onto suitable (insulated) spacersor, properly insulated, at one of the side -walls of the case. The two pc boardsshould be screened from one another byan earthed metal plate. Same -name ter-minals on the two boards should be con-nected to one another.Warning! The earth connection of CL(figure 7) is not at the same side of theboard as CL. Terminal DS on the sameboard should be connected to earth witha wire bridge, and DP should be wired to+5 V.The case should be plastic or metal and- important - splash -proof. Spindles ofpotentiometers and switches, LEDs, andsockets, must be sealed during fitting. Thered perspex display window must befixed to the case with water -proof glue. Donot forget the connections to the 12 V± 2 V supply. Before fitting the boardsinto the case, the circuits have to becalibrated.

Figure 4. The blockdiagram of the ultrasonictransmitter/receiver IC9 isshown here to give a bet-ter idea of the operationof the circuit. Thereceiver sensitivity is setwith P4. while P3 enablesa good measure of noisesuppression. Tuned circuitL1/C14 is common to thetransmitter and receiver.Fine tuning of the circuitis possible by means of

6-59

echo sounderelektor june 1984

Figure 5. A number ofuseful tips on positioningthe transducer (figure 5a).Figure 5b shows how thetransducer may be flush -fitted or otherwise.Figure 5c shows how thetransducer may bemounted in -board whenthe vessel has a fibre-glass hull.

5a

r

b

i I Rue Vass,

ri.,o8wood and ottel

4

ase62 5 a

Photograph. The echosounder must becalibrated such that thereceived signal (secondpulse) on pin 1 of IC9 ismaximum for all trueechoes

scale divisionvertical:upper pulse (IC5 pin 3)5 V/division (d.c.)lower pulses (IC9 pin 1)1 V/division (a.c.)horizontal:1 ms/division

C

al fil nq

111101 5010.°11°

01101011,01101311 fibre glass

11111016,1011 hull

CalibrationFirst, adjust P4 for maximum sensitivity ofthe receiver. Next, place the transducer atright angles, and at a distance of 0.5 m, toa reflecting surface. If the transducer hasalready been installed, place a reflectingsurface similarly in front of it. Then adjustthe core of inductor LI so that the displayindicates 2.3 (metres). This figure resultsfrom the fact that in identical time inter-vals sound in air travels only 0.217 as far asit would in water. Since the simulatedwater depth is 0.5 m, the circuit behavesas if the depth were 0.5/0.217 =2.3 metres. Then vary the distance be-tween the transducer and the reflectingsurface: in air this lies approximately be-tween 0.5 and 1 ... 1.5 m, correspondingto a displayed depth of 2.3 to 4.6 ... 6.8 m.The change in distance must be clearlyindicated by the display; if it does not, thecore of LI must be adjusted until the realmaximum sensitivity has been found.If you have an oscilloscope available,calibration is somewhat easier. But BECAREFUL with connecting a probe to IC9because if any two pins of this IC areshort-circuited, it gives up the ghost. Letour (unfortunate) experience be a warningto you!Connect the probe of the oscilloscope topin 1 of IC9 and trigger the oscilloscopewith the signal at pin 3 of IC5. Then adjustthe core of LI for maximum amplitude ofthe echo which is visible a few milli-seconds after the transmit pulse (seephotograph).The current consumption of the echosounder with the display on is about200 mA or an average of 40 mA at 12 V.

Some final pointsInductor L2 must be home-made on asuitable pot core of about 18 mm diameterand 11 mm height. The inductance of thesecondary winding, L2b, should be suchthat the resonant frequency of the circuitformed by it, the transducer self -capaci-tance, and C22 is exactly the same as thatof the transducer. It may be calculatedfromf = I/2nV LC,where f is the resonant frequency in Hz,L is the inductance in H and C is the totalcapacity in F.

6-60

echo sounderelektor june 1984

Parts list

Resistors:R9 = 10 MR10,R14,R21.R22 = 1 kR11 = 1k2R12 = 470 kR13,R15.1317 _ R20,R25 = 10 k

R16,R23 = 100 kR24 = 1MR26.R27.R28,R31 = 5k6R29,R30 = 100 QR32 = 10 QR33 = 5Q6P1 = potentiometer, 1 M,

linearP2 = preset, 1 MP3 = preset, 100 kP4 = potentiometer. 5 k,linear

Capacitors:C4 = 10 pC5 = 22pC6 = 560 pC7 = 10 nC8,C12,C16,C26 = 100 nC9,C10,C14.C17 = 1 n (seetext for C14)

C11 = 10#4/16 V forvertical mounting on pcboard

C13 = 12 n MKTC15,C18 = 220 nC19 = 680 nC20 = 2n2C21 = 150 p (400 V)C22 = 1n5 (400 V) (seetext)

C23 = 220 ji/25 VC24 = 4700/16 VC25= 100 11/.16 V

Semiconductors:D1,D3 = 1N4148D2 = LED redT5.T7 = BC 5478T6 = BC 16078 = BD 140IC3 = 4060IC4 = 40102IC5 = 555IC6 = 4098 for 4538 - seetext)

IC7 = 4538IC8 = 4013IC9 = LM 1812 (NationalSemiconductor)

Inductors:L1 = 63014H = YAN 60033(Toko) (available fromAmbit)

L2 = see text la suitablepot core, RM 10, whichhowever does not quite fitthe pc board, is availablefrom Ambit)

Miscellaneous:

S1.S2 = SPST toggleX1 = quartz crystal. 6 MHzTransducer. 150 kHz or200 kHz (available frommost ship's chandlers ormarine electrical suppliersas spare for Seafarer,Euromarine, Spaceage,VDO, and other echosounders)

Coaxial socket, panelmounting (to receive thetransducer cable)

Splash -proof caseSocket, panel mounting, for12 V supply cable

Piezo buzzer PB 2720PC board 84062

Figure 6. Layout and trackside of the printed -circuitboard of the echosounder. The boardshould be housed in asplash -proof case.

6-61

echo sounderelektor June 1984 7

Parts list

Resistors:

R1 . R7 22 QR8 = 82Q

Capacitors:

C1 = 10 p/10 V tantalumC2a = 470 p/16 VC3 = 100 n

Semiconductors:

DP2 .. DP4 = 77601D1T2 . . T4 = BC 140IC1 = 74C928IC2 = 7805

Miscellaneous:

Heat sink for IC2labout 5°C/WI

PC board 81105.1

Figure 7. The componentlayout and track side ofthe printedcircuit boardfor the display. Thevoltage regulator, com-plete with its heat sink.may be mounted ontoone of the side -walls ofthe case ion insulatingspacers if a metal case isused/.

By transposition,L = 1/4rt2f2Cwhich with f = 200 kHz, C = 3n2 gives avalue for L2b = 198µHThe corresponding number of turns, N, iscalculated fromN=where Ls is the specific inductance of thepot core. If, for instance, Ls = 250 nH, thenumber of turns works out at 28.If the turns ratio, n, is chosen at 1 : 9, L2amust be 3 turns.When a pot core with different specific in-ductance is used, the above calculationfor N must, of course, be redone; theturns ratio may be kept at 1 : 9. Equally,when a different transducer is used, theinductance of L2 must be recalculated.Furthermore, if the frequency is not200 kHz, capacitor C14 should berecalculated from C14 = 1/4n2f2L1, where fis the new frequency and LI = 630 µH.

The depth at which the 'shallow depth'alarm is actuated may be set with the aidof the following formuladepth (m) = 9 x10-c(P1 +R16 +R17)where PI, R16, and R17 are in ohms.

Where the transducer is not fitted at thedeepest part of the vessel, measure thedistance, Dk, between the underside ofthe transducer and the lowest part of thekeel. Replace the 4098 in the IC6 positionby a 4538, change C9 to 12 n. and connecta resistor Rk in series with R13. The valueof Rk is calculated from:Dk = 9 x 10-XRk +10'),where Dk is in metres and Rk in ohms.Therefore. Rk = 10'Dk/9 - 10'If, for instance, Dk = 1.5 m, the value ofRk = 157 k. The display will then, ofcourse, indicate the depth between thedeepest point of the keel and the seabed, not that between the transducer andthe sea bed.Warning! When setting and calibrating Pl,Dk must, of course, be borne in mind.

6.62

audio peak meter ...nlektor june 1984

A.B. Hill

The display of this versatile audiopeak meter is formed by a row ofLEDs and features a 'peak hold'facility that can be used while thenormal signal levels are monitored.The meter includes an input bufferstage that can be switched to enablethe monitoring of signals at loud-speaker level or at line output level.An optional variable -frequency band-pass filter is also included.

audiopeakmeter. .... with peakhold facility

Figure 1. This diagramshows typical constituentstages in an audio peakmeter.

As the input sensitivity can be matched toeither line level or power amplifier outputlevel, the audio peak meter may be usedwith virtually any sound system. Line levelinputs may lie between 150 mV and 5 Vwhile the power handling capability ex-tends up to 250 W. Other characteristicsare shown in the box at the beginning of thisarticle. The display characteristics may betailored to provide a peak response or asimulated VU response.Like many circuits of this nature, thepresent one can be broken down intovarious stages as shown by the block diagramof figure 1. The first stage is the input bufferwhich includes gain adjustment for the inputlevel matching. The variable band-pass filteris an optional stage that may be useful inparticular applications. The next stageconsists of a full -wave rectifier and providesoverall gain adjustment for the followingpeak and buffer stage. Finally there is thedisplay decode section. The display isformed by a row of LEDs with either'dot' or 'bar' mode of operation.

Specification

Input shaping circuit

output,maximum: 11 V, 20 mA (d.c.)rated: 10 V (d.c.)

input,loudspeaker: 10 ... 250 W peak into

8 ohms for rated outputline: 150 mV . . 5 V (d.c.) for

rated outputcalibration: 950 mV (corresponding to

10 W into 8 ohms)frequency bandwidth at -3 dB of rated

response: output better than 100 kHzlow-pass cut-off frequency 70 Hzfilter: slope -6 dB/octave

(-20 dBldecade)band-pass gain at centre frequency

filter: 0 dB(optional) centre frequencies

200 Hz, 500 Hz, 1250 Hz,3 kHz, 8 kHz-3 dB points 125 Hz,320 Hz, 800 Hz, 2 kHz,5 kHz, 12.5 kHzslope -12 dB/octave(-40 dB/decade)

Display driving circuitLED switching thresholds (dB)-40, -20, -10, -6, -3, 0, +2, +4, +6, +8.+10typical corresponding peak power levels (WI10', 10' , 1, 2, 5, 10, 15, 25, 40, 60, 100input voltage for +10 dB switchingthreshold: 10 V (d.c.)

The circuit diagramThe input shaping circuitThe various inputs to be monitored are selec-ted by switch Sla in the input buffer stageof the circuit diagram shown in figure 2a.Position 1 of Sla connects the input to earthand this is therefore the 'off" position.Position 2 selects a calibration signal input,of which more later. The loudspeaker powerlevel input is selected by position 3 whilevarious line outputs are selected by positions4, 5, and 6. This method allows the meterto be used readily for monitoring in widelydiffering situations. The gain of the inputamplifier is adjusted automatically byswitch S lb. The addition of suitable resistorsto positions 4, 5, and 6 enables the peakmeter to cater for a wide range of inputlevels.The next stage consists of a variable -fre-quency band-pass filter which enablesselective metering of the signals as in areal-time analyser. The stage has unity gainand may be omitted as required by simplyconnecting the output of input amplifier Al

1

0

0oo

input buffer

variableband-pass

filter

full waverectifier

andgain adjustment

peaksampling

and bufferdisplay

840E5-1

6-63

audio peak meter ...elektor june 1984 12a

MONITORLOUDSPEAKER

O

Figure 2a. The input signalshaping circuit completewith the optional band-pass filter based on A2.

Al ... A4 = IC1 = TL 084A5... A7= %IC2 = TL 084A8 ... All = IC3= LM 339Al2...A15= IC4 = LM 339A16 ...Ala= %ICS= LM 339N1 ... N4 = IC6= 4011N5 ... N8 = IC7 = 4011N9 ... N10.= `,41C8 =4011N11 ...N14= IC10=4081N15 ...NIB= IC11= 4081N19 ... N20 = 'h.IC12= 4081N25 ... N30= IC13= 4049N31 ... N35 = IC14 = 4049

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4 0O S10

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10k

Al

m

470n

R93

nR7

0

R8

R94

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R14

R13

R12

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C7

18n

C6

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C5

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C4

In

In

2 1300

524

R22

6a

ceten

R15

C94n7

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1111

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Cl'In

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R21

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R9

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770n

84065.23

directly to the non -inverting input of op -amp A4 with switch S2 in position 2. Theother positions of S2 select the requiredfilter response.Position 1 provides a high-pass responseand constitutes a rumble filter. Position 3connects the non -inverting input of A4 toearth, which switches off the opamp. Theremaining positions, 4 ... 8, select variousfrequency bands that are provided by aWien bridge band-pass filter constructedaround opamp A3.The output of the variable band-pass filteris passed to a precision full -wave rectifierconsisting of A4 and A5. Preset P2 in thefeedback loop of opamp A4 provides gainadjustment applicable to all input levels: itis adjusted at the appropriate calibrationinput level. Operation of the rectifier is asfollows: opamp A4 increases the magnitudeof both positive and negative signals by theforward voltage drop across diodes DI andD2. The resultant signal is rectified by A5and the consequent drop across D3 and D4cancels that introduced by D1 and D2.The rectifier is followed by a peak chargingstage, opamp A6. The peak sampling re-sponse is selected by switch S3: it is effectedby the discharge of capacitor C15 via switch -selected resistors R28 . . . R30 in series withR31 and/or R32.In position 4 the discharge resistor has beenomitted: this results in a very slow dis-charge rate which is only due to the inputcurrents of opamps A4 or A5 and thereverse (leakage) current of diode D6.In position 5, the charge and discharge rates

(via R32 and R33 respectively) are aboutequal and produce a simulated VU response.The final stage of the input shaping circuitconsists of an output buffer, opamp A7,which adjusts the gain in the 'peak' and 'VU'positions.

The display drive unitThe display (see figure 2c) consists of a rowof LEDs: the switching threshold for eachLED is determined by resistors R38 ... R61.The reference voltages, Ur, fixed by theseresistors are applied to one of the inputsof comparators A8 . A18, while the inputsignal from A7 is fed to the other inputs.Note that the polarity of the comparatorinputs depends on the input signal and onUr. When the level of the input signalexceeds that of one of the thresholds, therelevant comparator switches off and itsoutput is pulled up to +9 V.Switch S4 selects a moving dot or bardisplay. In the bar mode, the outputs ofgates N1 NIO are held high. When anycomparator switches off, the correspondingAND gate, N11 . N20, receives a secondhigh input and thus provides a high output.This results in the LED in that particularchannel being switched on.In the dot mode, the outputs of gatesN1 . N10 are dependent on the state ofthe output of the next higher comparator.When a given comparator output is highwhile the next higher output is low, both in-puts of the relevant AND gate, N11 ... N20,are high so that the appropriate LED lights.However, when a given comparator output is

6-64

2b audio peak meter ...elektor june 1984

R27

C>135

ICI IC3 IC6 IC10

IC2165 1C8 1C12

high while the one above is also high, boththe NAND and AND gate outputs will below, and the LED will remain off. In the dotmode, therefore, only the topmost compa-rator with a high output causes an LED tobe switched on.A further facility of the display is that of'peak sampling', which means that thehighest LED that lights will remain on untilthe 'peak display' function is disabled. Thefour R -S latches of IC9 are controlled byswitches S5 and S6 and provide the peaksampling. The latches are enabled when bothswitches are closed and reset by the briefopening of S6. Each latch reset is also con-nected to the outputs of all higher latchesvia diodes D7 ... D12. The latches are setwhenever their LED is switched on by thedisplay logic. However, the diodes effec-tively provide an OR reset to the latcheswith the result that only the uppermostlatch to be set will hold an LED on. Theoperation of the normal dot or bar mode isindependent of the peak display and alatched peak LED will therefore not holdlower LEDs off. This means that a peaklevel may be held while the normal dot orbar mode continues to function.

Calibrationit will be patently obvious that any levelindicating mechanism is only as good asits calibration, a fact any pilot who surviveda duff altimeter will tell you!Initially, the calibration input level shouldbe set to suit the power levels to be moni-tored: the one used here is 950 mV (d.c.)which corresponds to 10 W (peak) into an8 -ohm load. All preset potentiometersshould be set to the middle of their travel,

and switches S1 ... S3 set to the followingpositions:Si - position 2 (calibration input)S2 - position 2 (filter bypass)S3 - position 2 (peak response)Adjust P2 to the correct output fromopamp A7. It may be necessary to adjustP3 if the reading cannot be achieved with P2alone. The output may be monitored on aDWI (digital voltmeter) or an LED display.Next, move S3 to position 5 (VU mode) andadjust P4 for the appropriate reading. Theloudspeaker input can now be calibrated bysetting S1 to position 3 and adjusting P2.Calibration of the line inputs is more sub-jective. If a line input is to be used with atape recorder, the recorder metering may beused for comparison, particularly if itresponds to peaks. In that case, a steadyaudio tone from a test record or oscillatoris required, but inter -station hiss replayedfrom tape is an alternative. It should benoted that the line output should be usedwhen the recording level of a tape recorderis monitored.Where tape recorder metering is not used,the line level may be calibrated to a directvoltage derived from equipment specifi-cations or by calculation. It may then benecessary to multiply r.m.s. values by 1.414(N,i) to get peak values. A line voltageoften used for 0 dB (the Dolby level) is500 mV peak. Whatever method is used, P1should be adjusted to obtain the appropriatelevel at the output of opamp A7. Switch S1must be set to one of the line inputs (4... 6)while switches S2 and S3 should remain inposition 2 (filter bypass and peak responserespectively). 14

9V0

0IC13IC14

9V

Figure 2h. The full -waverectifier, gain adjustment,and peak charging stages.

The 'normal' level used inaudio engineering is 1 mWinto 600 n I= 775 mVacross 600 in and isconventionally designated0 d8m.

6-65

audio peak meter ...elektor june 1984 2c

Figure 2c. The displaydrive circuit is not nearlyas complicated to build asit looks.

91/

* sae te.

Ur.O

960

R57

956

961

R59220k 2

95622k 6

954 955f51-r= -7r1 -t

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95333k

R51

27k

94912k

R46 R47

120k 27k

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942

R41

R39

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A- l 8

A17

A- 16

Al 5

Al 4

945185

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6-66

elektor june 1984

Miniature solid state relaysNorbain Electra -Optics Ltd. has launcheda completely new range of switch -DIPminiature solid state relays. Manufacturedby MSI, the device range consists of threed.c. and seven a.c. types covering a widerange of voltage and current optionswith opto or transformer isolation andsynchronous or zero voltage switching.Housed in standard 14 and 16 pin sealedceramic DIL packages to improve herme-

ticity and aid the conduction of heatenergy, the devices employ thick -filmhybrid techniques to achieve a high powerhandling capability in a small package.Heading the new range is the E24E-2H16 pin package which has a 1A RMSrating and input to output isolation of400 V RMS. The device switches at thezero voltage point of the a.c. waveform,requires an input signal of 8 mA at 5 Vand has a peak voltage rating on the out-put switch of 600 V. Anti -parallel SCRs inthe power switch ensures enhanced DV/DTsurge current and thermal characteristics.Other devices in the range include theE40-1 capable of switchings a.c. and d.c.currents to = 80 mA at I 60 V, the E41 -2Hrated at 1 A RMS a.c. with a triac outputrated at 600 V, the E43-1 designed for d.c.switching current of 500 mA at 60 V andE43-2 designed for 200 mA currentswitching at 250 V d.c.

Norhain Electra Optics LimitedNorbain House,Boulton Road,Reading,Berkshire RG2 OLTTelephone: 0734 864411 (2961 Ml

Capacitor and coil testerFieldtech Heathrow has recently in-troduced to the U.K. market a capacitorand inductance tester which is generatingmuch interest in the electronics industry.Designated the LC53 the unit provides theengineer with a range of test functionsnever previously available in one unit.The unit is claimed to be unique because itis the only tester on the market which willdynamically test capacitors, coils, SCRsand TRIACs and will find an amazing 75%of defective capacitors which value -onlymeters will miss.The unit, which is fast with 100% auto-matic ranging, tests capacitors for leakagecurrent under full load, with up to 600volts applied. It checks capacitor dielectricabsorbtion, and has the capability toreform electrolytics. It will check forall coil defects in or out of circuit, itautomatically tests coils for effective CI

using a U.S. patented ringing test. It teststransmission lines for distance to open orshort circuits within feet and it willalso test dielectric strength to 600 volts. Itmay also be used for high potentialleakage tests up to 600 volts. The unit isalready being successfully used in majorelectronics companies giving broadcast,T.V., and video engineers quick reliableresults with a unique range of test func-tions.Fieldtech Heathrow Limited,Huntavia House,420 Bath Road,Longford,Middlesex UB7 OL LTelephone: 01 897 6446 (2963 M)

World's smallest lithium batteryMatsushita Electric Industrial CompanyLimited of Osaka, Japan, parent companyof Panasonic U.K. Limited, announcesthe introdustion of the world's smallestpin -type lithium battery. The 3 voltbattery measures a mere 2.2 mm in diam-eter and 11 mm in length and initiallywill be marketed for use in ultra -smallfishing floats with LED for night timefishing. The battery is expected to bewidely adapted for use in small electronic

1 1 1 1 1 1 1 1 1 1

products - wrist watches, calculators,memory cards, memory back-ups, micro-phones, hearing aids and toys.Due to the rapid gains in IC, LSI andVLSI technology the trend has beentowards miniaturization in electronicequipment, therefore small high per-formance batteries have been in strongdemand. The new battery has been devel-oped through use of the maker's precisionproduction technology and accumulatedtechnological expertise in the field of

poly -carbon monofluoride lithium batter-ies. To achieve mass production of the2.2 mm battery, dimension tolerance hadto be decreased to one -tenth of previousmodels, in the drawing process of thealuminium case and in the areas of plasticmoulding technology, seal packing andassembling technology of the battery.

Features:

Requires little space in a product;keeps constant operating voltage whencharged.maintains long shelf life,three -volt battery is twice the voltage ofsilver -oxide and mercury batteries,capable of lighting LED,superior temperature characteristics.

Panasonic U.K. Limited,300/318 Bath Road,Slough,Berkshire SL 1 6JB.Telephone: 0753 34522. (2970 M)

DIP diode networksIskra has introduced a new range of DIPdiode networks, the BD series. Developedfor logic circuit and similar applicationsrequiring densely packed arrays of diodesor zeners, each network contains eightdiodes mounted in a 16 -pin plastic DIPmeasuring 21.5 mm x 8.5 mm x 4.6 mmtall (excluding pins). Pin spacing is thestandard dual -in -line pitch of 0.100" andeffective pin length is 3.2 mm. Diodetypes to be offered in this package are,initially, the 1N4148 100 V, 75 mA

silicon planar epitaxial signal diode andthe BZY 88C 4V7 4.7 volt zener butthe manufacturer will shortly be offeringa complete range of diodes in the DIPpackage including rectifier, fast recoveryand zener types.The packages, which are encapsulated in'Crastin' 5 K 615 FR flame retardantepoxy resin, are straightforward arrays,each diode being terminated separatelywith anodes brought out to pins on oneside of the DIP and cathodes broughtout on the other side. The new packagesoffer the circuit designer advantages incomponent packing density, in productioncosts and in handling and storage. Ad-ditionally, combinations of arrays ofdiodes, resistors and links can be suppliedin the same packages.

Iskra Limited,Redlands,Coulsdon,Surrey CR3 2HT.Telephone: 01 668 7141. (2972 MI

6-67

Multimeter incorporatesfrequency meterThe model 1504 from Thurlby Electron-ics is a bench DMM which offers thebonus of a built-in frequency meter.Frequencies up to 3,999.9 kHz can bemeasured directly with a resolutionof 100 Hz. A hi9h accuracy figure of± 0.0025% over 10.30-C is guaranteed bythe 6 MHz crystal timebase. Sensitivityis typically 30 mV rms.As a conventional multimeter it has a4% digit liquid crystal display extendingto 7 32,000 counts. 32 ranges are providedenabling measurement of a.c. and d.c.voltage, resistance, diode test, and a.c. andd.c. current up to 25 amps. The meter hasimpressive sensitivity figures of 1010 mn and 1 nA as well as an excellentaccuracy of 0.05%. All a.c.- ranges aretrue R MS responding which enablesaccurate measurements to be made onnon -sinusoidal waveforms, a feature essen-tial for engineers who require powerrelated measurements on switching wave-forms.

The unit is housed in a newly designed highimpact ABS case which incorporates amulti -position tilt-stand/handle. A carryingcase is available for portable applications.The meter operates from internal batteriesor from a.c. line power and weighs only2% lbs.

Thurlby Electronics Ltd.New Road,St lees,Huntingdon,Cambridgeshire PE17 46.G.Telephone: 0480 63570 (2957 M)

The 'Stringy Floppy'Astec Europe Ltd has introduced a newconcept in data storage, the 'StringyFloppy', which combines the low cost ofa simple cassette with the fast accesstime of a floppy disk. The wafer cassettemeasures approximately 6.5 cm x 4 cmand can store up to 13 K bytes of for-matted data on a 50 foot endless loop oftape. The data is recorded at a tape speedof 10 IPS at a rate of 21 K bps. A highspeed mode allows any data to be foundwithin a maximum of 35 seconds andthe cassette has been optimised for pre-cision tape tracking at high speeds. An'intelligent controller with a serial portprovides a high-level command structureand a flexible file management system.The data is stored in a disk -like blockstructure to allow maximum utilisationof the tape. Since the data format on thetape is standard, data interchangeabilityacross different systems will be assured

even if the interfaces run at differentspeeds. It is ideal for any computerwith an RS232 port.The 'Stringy Floppy' will be available invarious forms: - a basic transport mech-anism with read/write and motor controlcircuit; a basic transport mechanism withread/write, motor control circuits and anintelligent controiler capable of servingtwo transports; a completely freestandingunit packaged to include drive mechanism,read/write, motor control logic, RS232interface, PSU, integrating software and allassociated cabling. Astec's research anddevelopment division is already workingon variants of the device with storagecapacities of 256 K/bytes per 50 feet oftape. Eventually it is anticipated thatcapacities in excess of 1 megabyte willbe obtained using dual track heads.Astec Europe Ltd.,Telephone: 0734 509411. (2971 M)

Copperfoil tapeCost savings of 90% over the cost ofprinted circuit boards can be achievedusing a novel tape produced by CopperfoilEnterprises. It is produced from 99.999fine copper. Tested and approved at 24 V,5 A d.c. and conforming to BS safety

elektor june 1984

regulations, it is supplied backed with ahigh -temperature resistant adhesive whichbonds monolithically to all insulatingsurfaces including plastic and paper. Itsolders simply without loss of integrity.Copperfoil is used for circuit tracks,burglar alarm systems, proximity switches,moisture detection, bus bars and otherelectronic applications. It is of particularvalue in the repair of printed circuitboards and for production of prototypeboards. Widths available are 4,4.75,6, and8 mm in 33 m rolls.Copperfoil Enterprises,141 Lyndhurst Drive,Hornchurch,Essex RM11 1JP.Telephone: 040 24 56697 (2960 MI

New extraction toolA new extraction tool - the Model507M from EREM - for extracting14, 16 and 20 pin DIPs from printedcircuit boards, is now available from UKdistributor Nietronix Ltd.The 507M extracts the DIPs withoutdamaging the components and extractioncan be done within close proximity of

other components. The flat, steel headis shaped so that tracks on the circuitboard cannot be scratched or damaged.Nietronix LimitedSmith's Forge,North End Road,Yarton,Avon BS19 4AU.Telephone: 0934 838656 (2969 M)

6-68

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DEPT. EK 28'29 BURNT MILLHARLOW. ESSEX. CM20 2HU U K OPENING HOURS: MON-FRI 9am-6.30pm. SAT 10am-5pmTel. HARLOW 102791 443521 Telex 81'd894 AKHTER G We welcome callers. no parking problems.

mretun -Massive range of componentsfor your hobby...insist on Maplin quality!

MAPLIN'S TOP TWENTY KITSTHIS LAST

MONTH DESCRIPTION OF KITORDERCODE

KITPRICE

1. (1) M 75W Mosfet Amp Module LW51F £12.952. (2) 0 Modem LW99H £44.95

Case also available: YK62S Price £9.95.3. (4) Car Burglar Alarm LW78K £6.954. (5) Partylite LW93B £9.455. (3) ZX81 I 0 Port LW76H £9.256. (19) Spectrum Keyboard LK29G £28.50

4 XAO4EBest of E&MM4 XAO4E9 XAO9K

Also required: LK3OH £6.50; Case: XG35Q £4.95 - Total £39.95.Also available complete ready -built: XG36P £44.95.

7. (9) Syntom Drum Synthesiser LW86T £11.95 Best of E&MM8. (8) 0 VIC20 64 RS232 Interface LK11M E9.45 7 XAO7H9. (7) 8W Amp Module LW36P £4.45 Catalogue

10. (10) M Harmony Generator LW91Y £17.95 Best of E&MM11. (15) Logic Probe LK13P £9.95 8 XAO8J12. (6) Keyboard for ZX81 LW72P £23.95 3 XAO3D

Case also available: XG17T £4.95. Complete ready -built: XG22Y £32.5013. (14) Ultrasonic Intruder Detctor LW83E £10.95 4 XAO4E14. (11) Spectrum RS232 Interface LK21X £17.95 8 XAO8J15. (171 Hexadrum LW85G £19.95 Best of E&MM16. I-) Noise Gate LK43W £9.95 Best of E&MM17. (-) Guitar Tuner LW9OX £10.75 Best of E&MM18. I-) Freq. Meter Adaptor LK2OW £8.99 9 XAO9K19. (16) Car Battery Monitor LK42V £6.25 Best of E&MM20. (20) M ZX81 Speech Synthesiser LK01B £16.95 6 XAO6GOver 80 other kits also available. All kits supplied with instructions.The desriptions above are necessarily short. Please ensure you knowexactly what the kit is and what it comprises before ordering, by checking theappropriate Project Book mentioned in the list above.

DETAILS INPROJECT BOOKBest of E&MM sop "`

5 XAO5F 1111-1:4$

41t

MAPLIN'S FASCINATING PROJECTS BOOKSFull details In our Project BooksPrice 70p each.In Book 1 (XAO1B) 120W rms MosfetCombo -Amplifier Universal Timerwith 18 program times and 4 outputs Temperature Gauge 6 Vero Projects.In Book 2 (XAO2C) Home SecuritySystem Train Controller for 14 trainson one circuit Stopwatch withmultiple modes Miles -per -GallonMeter.In Book 3 (XAO3D) ZX81 Keyboardwith electronics Stereo 25W MosfetAmplifier Doppler Radar IntruderDetector Remote Control for TrainController.In Book 4 (XAO4E) TelephoneExchange for 16 extensionsFrequency Counter 10Hz to 600MHz Ultrasonic Intruder Detector I 0 Portfor ZX81 Car Burglar AlarmRemote Control for 25W Stereo Amp.In Book 5 (XAO5F) 300 Baud DuplexModem to European Standard 100W240VAC Inverter Sounds Generatorfor ZX81 Central Heating Controller

Panic Button for Home SecuritySystem Model Train ProjectsTimer for External Alarm.

F411:104 NiKPLEN.

111.41Wire... 01.4?.

- 4 =M. ...-01441.11- .

In Book 6 (XAO6G) Speech Synthesiser for ZX81 & VIC20 Module toBridge two of our Mosfet Amps to make

350W Amp ZX81 Sound on yourTV Scratch Filter Damp Meter Four Simple Projects.In Book 7 (XAO7H) Modem (RS232)Interface for ZX81 VIC2O Commodore64 Digital Enlarger TimerController DXers Audio Processor SweepOscillator CMOS Crystal Calibrator.In Book 8 (XAO8J) Modem (RS232)Interface for Dragon 32 & Spectrum Synchime I 0 Ports for Dragon 32 Electronic Lock Minilab PowerSupply Logic Probe Doorbell forthe Deaf.In Book 9 (XAO9K) Keyboard withElectronics for ZX Spectrum Infra -

Red Intruder Detector Multimeter toFrequency Meter Converter FMRadio needs no alignment Hi -ResGraphics for ZX81 Speech Synth-esiser for Oric 1 VIC20 Extendiboard ZX81 Extend -RAM Dynamic NoiseLimiter for Personal Cassette Players. TTL Levels to RS232 Converter Logic Pulser Pseudo -Stereo AMRadio Ni-Cad Charger Timer

1984CATALOGUE

A massive 480 big pages ofdescription, pictures and dataand now with prices on the page.The new Maplin catalogue is theone book no constructor shouldbe without. Now includes newHeathkit section. On sale in allbranches of W.H. Smith. Price£1.35 - It's incredible value formoney. Or send £1.65 (,ncludingp & p) to our mail-order address.

Adder-Subtracter Syndrum's Inter-face Microphone Pre -Amp Limiter.In Book 10 (XA1OL) CassetteEasyload for ZX Spectrum 80mAmateur Receiver Auto Waa-WaaEffects Unit Oric 1 Modem Interface 2.8kW Mains Power Controller Extendiport for Dragon 32 12V Fluor-escent Tube Driver 32 -LineExtension for Digi-Tel.

GREAT PROJECTSFROM E&MM

Our book "Best of E&MMProjects Vol. 1" brings together21 fascinating and novel pro-jects from E&MM's first Year.

Projects include HarmonyGenerator, Guitar Tuner, Hexa-drum. Syntom. Auto Swell.Partylite, Car Aerial Booster.MOS-FET Amp and othermusical, hi-fi and car projects.Order As XH61R. Price £1.

rPost this coupon now for your copy of the 1984catalogue. Price £1_35 - 30p post and packaging.it you live outside the U.K. send £2.20 or 11International Reply Coupons. I enclose £1.65

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Mail Order. P.O. Box 3. Rayleigh, Essex SS6 8LR. Tel: Southend(0702) 552911 Shops al 159-161 King Street, Hammersmith,London W6. Tel: 01-748-0926. 8 Oxford Road, Manchester. Tel: 061-236-0281. Lynton Square. Perry Barr. Birmingham. Tel: 021-356-7292. 282-284 London Road, Westcliff-on-Sea, Essex. Tel: 0702554000. 46-48 Bevois Valley Road, Southampton. Tel: 0703 25831.All shops closed all day Monday.All prices include VAT and carriage. Please add 50p handling chargeto orders under £5 total value (except catalogue).