January 1987 or g ,Anfics · 2019. 7. 18. · or g,Anfics glectjw January 1987 UK £1.30 IR £1.89 (incl. VAT) ONGS TO THE PHOTO Processing digital signals Cossor Radar: the first

org ,Anfics

glectjw

January 1987

UK £1.30IR £1.89

(incl. VAT)

ONGS TO THE PHOTO

Processing digital signalsCossor Radar: the first 50 years

770268 451005

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(Tel: 01 208 1177, Telex 922800)305 EDGWARE ROAD, LONDON W2, Tel: 01 723 0233

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PLEASE ADD 50p p&p & 15% VAT(Export: no VAT, p&p at Cost)

Orders from Government Depts. & Collegesetc. welcome.

Detailed Price List on request. "Stock items axe normally by return of post.

please mention ELEKTOR ELECTRONICS when contacting advertiser

Universal controlfor steppermotorsp. 38

Inside a WorldWar 2 radarstationp. 47

A handful of lightp. 27

January 1987Volume 13

13 Editorial Number 141

14 News News News

ELECTRONICSTECHNOLOGY

27 The future belongs to the photon: as the maximum attainable speed of electrons in semiconduc-tor materials is approached, a new technology isbeing developed that uses light as the means oftransporting energy.

47 Cossor Radar-the first 50 years: the first of atwo-part article that looks at the role Cossor hasplayed in developing that important British inven-tion: radar.

58 Digital signal processing: a brief look at what isinvolved in this new technique.

60 Software for the BBC computer-the BBCBuggy: description of a commercially availablesmall but versatile robot.

PROJECTS20 Indoor unit for satellite TV reception -3: the final

part of the article describes the AFC, scan andremodulator facilities, as well as the LNB theftalarm.

30 Top -of -the -range preamplifier -3: the constructionof the preamplifier and a discussion on the prosand cons of using various types of capacitor in AFcircuits.

38 Universal control for stepper motors: a fullyuser -configurable control board with powerful out-put drivers, a standard 8 -bit input, and a facility forthe precise positioning of almost any type of step-per motor.

53 MSX extensions -4: a compact plug-in I 0 andtimer cartridge providing 32 programmable I 0 linesand two counter' timer blocks.

INFORMATION36 New literature; 37 Corrections; 62 New products;66 Readers services; 68 Terms of business; 77 Info -

and data -cards.

GUIDE LINES71 Switchboard; 74 Buyers guide; 76 Classified ads;76 Index of advertisers.

glimpsetntothe

uturef

As the sun rises over the early JanuaryEssex

landscape,a COSSOr

experimentalMode S

TOCIOrantenno

seemspoised

to give us a

glimpseinto the luiure. Al least

tar as the

electronicsworld is concerned,that

future is

exciting.New devetoprnents,

some of which

ore describedin this issue,

and a reviving

marketsee page '14) Offer

bright prospects

tot A987, both in a technicaland in a com

mercialsense.

If71,,

In our Februaryissue: Digital sine -wave

generator PCB design on

the BBCcomputer

Satellite TVreception: yourquestionsanswered

Voice machines VLF add-on unit

for oscilloscopes Electron

ROM -card

EE

January 19874

WITH SOUND PRINCIPLES

Complete Monitor Amp kit for less than 1115Complete Hi-Fi kit for less than £140* 40 watts RMS per channel into El 4, 80 watts into 4* High current output, stabilised PSU for power amps* Minimum capacitor passive equalisation design* MM/MC With infra cut. CD, Rad, Tape 1 & 2 inputs* Rugged TO3 complementary output & PSU transistors* Comprehensive instructions, quality components

Much is said about amplifier design_ Specification and technical performance alone nolonger rules supreme. Concepts such as musicality are regarded as Sacred by thefraternity. The state of the art is for amplifies to have high output current capability, highoverload margins, be "neutral sounding yet articulate and dynamic". High feedbackdesigns are definitely out and cables affect the sound.

Where does the engineer stand in all this? We think you would like an amplifier withreal state of the art features. but riot over the top in insignificant design detaiL You areunhappy at paying for a mass produced product. You appreciate a top class system butcannot Pstify the price of more exotic products. Building your own to an exclusive andwell engineered design has a definite attraction_

GATE ONE utilises the latest audiophile techniques in its design. Great attention isgiven to the layout with separate signal and component earths. RIAA equalisation andtone controls (with in/out switch) are of a passive design_ A low lift switch lets you tailorresponse to compensate for loudspeaker defficiency. A unique volume control circuitIncreases overload margin and optimises S/N ratio.

You can buy a GATE ONE in kit form for £139.61 inc_ or a GATE MONITOR ONE stereopower amp with 3 line inputs for £114.85 inc. Both have a professionally -finished caseand include all components. Both are available fully assembled and tested. Order nowor send for farther details. Go on, when did you last buy yourself a Christmas present?

GATEHOUSE AUDIO (E) Money backguarant

virustPO Box 6, Evesham, Worcs. WR11 4NP. returnedd.

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BEST PRICE COMPONENTS - SAME DAY DESPATCHALL THE LATEST FASTEST DEVICES AS USED BY INDUSTRY. DO NOT CONFUSE WITH SLOWER OLD STOCKOFFERED ELSEWHERE. WE ONLY STOCK COMPONENTS PRODUCED BY ESTABLISHED MANUFACTURERSWHOSE PRODUCTS HAVE BEEN SUBJECTED TO LONG-TERM U.K. TESTING, DATASHEETS AVAILABLE ON ALLITEMS AT £1 EACH.

MEMORIES

DRAM 5v NMOS 15011S(Not Texas)4164 64k x 1 £0.9041256 256k x 1 £2.204416 16k x 4 £2.8041464 64k x 4 £5.90

SRAM 5v NMOS 150AS2114LP lk x 4 £1.502128LP 2k x 8 £2.50

SRAM 5v CMOS 150nS6116LP 2k x 8 £1.306264LP 8k x 8 £2.3062756LP 32k x 8 £25

EPROM 5v NMOS 250AS2716 2k x 8 £2.702732 4k x 8 £2.652764 8k x 8 £1.9027128 16k x 8 £2.1027256 32k x 8 £3.40

EPROM Sv CMOS 250nS27C64 Bk x B £3.5027C256 32k x 8 £10

EEPROM 250AS2816A 2k x 8 £13.502864A 8k x 8 £45

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10% DISCOUNTON ALL ORDERSOVER £25REGARDLESS OFMIX.ADD 15% V.A.T.SENT POST FREE.ORDERS UNDER £25ADD 15% V.A.T.PLUS £1.00 P&POVERSEAS: -EUROPE £2 P&PELSEWHERE £5 P&P(NO V.A.T.)

OW&74LS TTL LOGIC

74LS00 _ .20p741S02 ..20p74LSO4 ..20p741505 ..20p74LS08 ..20p741.509 ..20p74LS1O .20p74LS11 ..20p74LS14 ..32p74LS20 ..20p741/21 ..20p741S30 ..20p741532 _ .20p74L551 ..20p741.574 .20p741S86 ..20p74LS93 ..45p7415123 .60p741.5125 .40p7415138 .40p74LS139 .40p74LS153 .45p74LS154 .85p74LS157 .40p7418158 .40p74LS 16I .55p74LS163 .55p74LS164 .55p74LS165 .60p

741.5166 .60p74LS174 .40p741.5175 .55p74LS193 .60p741S194 .50p74LS240 .65p74LS241 .65p74LS244 _65p74LS245 .80p741.5257 .547415973 .65p74LS280 .75p741.5365 .40p741S367 .40p741,5373 .65p74LS374 .65p74LS393 .60p74LS395 .60p

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74HC00 . . .25p74HCO2 ...25p74HC04 ...25p74HCU04..25p74HC08 ...25p74HC 10 . _25p74HC 11 . . .25p74HC 14 . . 40p74HC20 ...29p74HC21 ...29p74HC27 ...27p74HC32 _ _ 35p74HC42 ...49074HC5174HC74 _39p74HC85 ...59p74HC86 ...49p74HC107 ..49p74HC 113 ..49p74HC123 ..55p

74HC125 ..55p74HC132 . .49p74HCI38 ..99074HC139 ..49p74HCI51 ..59p74HC153 ..59p74HC157 ..55p74HC158 ..55p74HCI61 ..55p74HC163 . .55p74HC164 ..55p74HC165 ..75p74HC166 ..60p74HC173 . .55p74HC174 . .55p74HC175 ..55p74HC193 ..75p74HC240 ..89p74HC241 ..79p74HC242 ..790

74HC243 ..79p74HC244 ..89p74HGT244 .95p74HC245 ..95p74HC257 ..55p74HC259 ..70p74HC273 ..89p74HC354 . _85p74HC365 ..59p74HC367 ..55p74HC373 ..95p74HC374 _95p74HC393 ..69p74HC4040 .69p74HC4060 .69p74HC573 £1.2074HC574 £1.2074HC640 £1.2574HC643 £1.2574HCE88 ..85p

TELEPHONE ORDERSPHONE BL 1WLEN 8.0AM & 12.0 NOONBANKERS CHEQUE CARD HOLDERSONLY WHO ARE TELEPHONE SUB-SCRIBERS. COMPONENTS SENT SAMEDAY BY FIRST CLASS RECORDED POSTWITH 7 DAY INVOICE.£1 surcharge to covervalidation & recorded post 472

MICROKIT LIMITED TELEPHONEBLAKESLEY, TOWCESTER, NORTHANTS NN12 8RB.. 0327 860130

Please mentionELEKTOR

when ordering

please mention ELEKTOR ELECTRONICS when contacting advertisers

EE

January 1987

Managing Editor: Len SeymourAsst Editor: J BuitinyAdvertisement manager: S Brooks

Elektor ElectronicsStandfast HouseBath PlaceHigh Street, BarnetHens EN5 5XETelephone:

Editorial (UK): 01-441 6098(Europe): -31 4402 89444

Advertising: (0227) 661013Telex: 22828A Kluwer Group CompanyOverseas editions:Publitron Publicacoes Tecnicas LtdaAv Ipiranga 1100, 9° andarCEP 01040 Sao Paulo - BrazilEditor: Juliano BarsaliElektor sariRoute Nationale; Le Seau; B.P. 5359270 Bailleul - FranceEditors: D R S Meyer:G C P RaedersdorfElektor Verlag GmbHSiisterfeld-StraGe 25100 Aachen - West GermanyEditor: E J A KrempelsauerElektor EPEKaraiskaki 1416673 Voula - Athens - GreeceEditor: E XanthoulisElektor Electronics PVT Ltd.Chhotani Building52 C, Proctor Road, Grant Road (E)Bombay 400 007 - IndiaEditor: Surendra lyerElektuurPeter Treckpoelstraat 2-46191 VK Beek - the NetherlandsEditor: P E L KersemakersFerreira Et Bento Lda.R.D. Estefania, 32-1°1000 Lisboa - PortugalEditor: Jorge GoncalvesIngelek S.A.Av. Alfonso XIII, 141Madrid 16 - SpainEditor: A M FerrerIn part:Kedhorn Holdings PTY LtdCnr Fox Valley Road &Kiogle StreetWahroonga NSW 2076 - AustraliaEditor: Roger HarrisonElectronic Press ABBox 63182 11 Danderyd - SwedenEditor: Bill CedrumInternational co-ordinatingEt technical manager:K S M WalravenInternational editorial secretariat:G W P v Linden; M Pardo

Distribution:Seymour Press Ltd., 334 BrixtonRoad, London SW9 7AG.Typeset Er composed in theNetherlands by GBS, Beek IL).Printed in the Netherlands by NDB,Zoeterwoude.

Copyright - 1987 Elektuur

ABC

And there will be light...

It is sometimes hard to believe that it was only a hundred years agothat Heinrich Hertz first produced radio waves (1887); less than a cen-tury ago that Johnstone Stoney introduced the term "electron" (1891);just over eighty years ago that the name "photon" was first used(Einstein's Photon Theory: 1905); and but two decades ago that thefirst chip appeared on the market.

In the wake of the practical applications of these inventions anddiscoveries, our ways of life have undergone tremendous changes inthe intervening years.

Yet, although electronics is only a relatively young technology, en-gineers are already beginning to realize that it can not be ex-panded and developed without bound.

The main drawback encountered in modern electronics is the speedat which electrons travel through semiconductor materials (about5x105 mis in silicon). And there is also a limit to miniaturization: notonly is it becoming more and more difficult to etch into ICs narrowerand narrower paths along which electrons travel, but there is alsothe increasing risk of cross -talk, i.e., the leakage of charges from onecomponent to another.

It is for these reasons that scientists and technologists have for sometime been developing a new technology: photonics, in whichphotons-quanta of light-are used as the means of transportingenergy. The light used in photonics is created by lasers, which canoperate in the ultraviolet, infra -red, or visible light regions.

Photonics is already replacing electronics in telecommunicationsand optical memories (such as the compact disc). But lasers are notrestricted to these areas: they can also be used in chemical syn-thesis, defence (SDI), surgery, semiconductor processing, and chipmanufacturing.

In telecommunications, the main use of photons is as yet in fibre op-tics. This year many thousands of kilometres of conventional cablewill be replaced by optical fibre cable all over the world. Most ofthese cables can support operation at up to 140 Mbitis, but work iscontinuing to improve on this performance: one experimental BritishTelecom link already carries telephone traffic at 1,200 MbitIs.

Already, the first international undersea optical fibre cable-linkingBritain and Belgium-was taken into use last October. Laying of theTAT -8 cable, linking the USA with Britain and France, is due to starttowards the end of the year. An optical fibre cable spanning thePacific is planned on a similar time -scale, and many other opticalsystems, both long and short, are under active discussion.

It is heartening that British universities, more particularly Heriot-Wait,and organizations such as British Telecom, Mercury Telecommuni-cations, Standard Telephone and Cables, Belling -Lee, BICC, andmany others, are in the forefront of this exciting new technology,both as regards R&D and commercial application.

VIU R Ti. AUOirFlifFIE.H.11:4= ORCIAATIOP.S

EE

January 1937

NEWS NEWS NEWS NEWS NEW1

West EuropeanElectronicsMarket to growby 7.5% in 1987Benn Electronics, in their 14thedition of the Yearbook of WestEuropean Electronics Data, ex-pect the total market for elec-tronics equipment and com-ponents to reach US$113 billionin 1987-a growth of just over7.5% compared with the marketin 1986 at constant 1985 values.Growth during the remainder ofthe 1980s is expected to beslightly slower at an annualaverage rate of approximately6°/i, with the European elec-

tronics market projected toreach US$135 billion in 1990.The driving force behind mar-ket expansion in Europe con-tinues to be the burgeoningElectronic Data ProcessingSector (EDP), comprising com-puter systems, peripherals.word processors, and on-linecash registers, which is pro-jected to grow at an annualaverage rate of 11.2% over theperiod 1985-1990. In 1990. thetotal EDP market is expected torepresent 37% (in 1985: 30%) ofthe total electronics sector.A significant trend in the EDPmarket will be the growingmaturity of many applications inthe latter part of the forecastperiod, slowing growth fromover 13% in 1985-87 to less than

EUROPEAN ELECTRONICS MARKET,,nstr.tn v4c,5 vat..., A. Kst.s.

zzi

EUROPEAN ELECTRONICS MARKETConstant Eoch.3nge Rat.,

vl

10% per annum in 1988-90. Thistrend reflects the current diffi-culties in the USA computermarket, which Europe lags byseveral years in terms of appli-cation maturity.Liberalization of PIT procure-ment procedures in manyEuropean countries is leadingto greater price competition inthe TelecommunicationsEquipment Sector, leading toan anticipated annual growthaveraging nearly 6% over theperiod 1987-90.France had one of the lowestmarket growth rates for elec-tronic equipment and compo-nents in 1985 at 2.5%, butimproving economic prospectsfollowing its change of govern-ment leads Berm to forecastgrowth at around 7% in 1986-only a little below the Europeanaverage-increasing to some8.5% in 1987.The other country to improvesignificantly is the IrishRepublic, up from 2% growth in1985 to nearly 12% in 1986. TheUnited Kingdom, which had agrowth of 6% in 1985, is forecastto grow at 8.5% in 1986, with afurther 7% growth projected in1987.However, West Germany willretain its position as the country

with the highest growth rate -over 10% in both 1985 and 1986,and around 8% in 1987.The Yearbook of WestEuropean Electronics Data 1987is priced at USS550 and is avail-able from

Benn Electronics PublicationsLtdChiltern House146 Midland RoadLutonBeds 1,112 OBL

US order forFerrantiFerranti Defence Systems Ltdhas been awarded a £250.000contract from Aeromet of Tulsa,USA, for the supply of special-ized mirror systems for highaltitude atmospheric research.The mirrors are designed toprovide an accurate and stableview of the direction of electro-optical sensors.

Ferranti Defence Systems LtdElectro-optics DeptSt Andrew's WorksRobertson AvenueEdinburgh MU 1PX

Satellites are baked and frozen during their testing cycle in astainless steel chamber at Hughes Aircraft Company in ElSegundo, California. The combination oven -refrigerator enablesengineers at Hughes Space and Communications Group to putthe satellites through the temperature extremes that occur inspace. Technicians are seen here monitoring the antenna systemof an HS376 communications satellite with the aid of microwave -absorbing material mounted on portable test stands.A J Wallis Ltd 38 Ernie Road Wimbledon London SW20OHL

EE

January 1987

NEWS NEWS NEWS NEWS NEBEAMA productliability seminarBEAMA will hold a seminar atthe Royal Lancaster Hotel, Lon-don, on January 28 to considerthe implications to industry ofthe EEC Directive on ProductLiability which will become lawin the UK early this year.The introduction in the direc-tive of the concept of "strictliability" renders suppliersof raw materials, componentmanufacturers, finished articlemanufacturers, anyone who at-taches his label to a product,importers of goods horn out-side the EEC, and others, liablein the event of a claim beingmade against them UNLESS theycan prove the existence ofone of the defences permit-ted under the directive.It should be noted that

under the directive, com-pliance with a standard,whether UK or international,will not be a defence unlesscompliance with that stan-dard is a mandatory require-ment of law.

BEAMA Ltd8 Leicester StreetLondon WC2H TBN

New ITT plantITT Semiconductors hasopened a new custom VLSIdesign and fabrication facility atShelton, CT, USA. The plant islocated in the centre of thenortheast industrial heartland,an hour from New York City,and with ready access to majorairports.

British Telecom has completed the first phase of an £80 millionprogramme to computerize inland directory enquiries. At the 186centres where the Directory Assistance System-DAs-has beeninstalled to give nationwide coverage, operators now call upnumbers on to a screen at a touch of a button. This has cut by aquarter the average time taken to handle an enquiry, reducing itfrom 52 seconds to 39 seconds. Pictured here is Mrs MandyCook, an operator at British Telecom's directory enquiry centre inKeybridge House, London, at her DAS position. By her side is atower of 106 phone books, containing the information she cannow provide at the touch of a button.British Telecom Press Office 81 Newgate Street LondonEC1A 7AJ

Part of ITT Semiconductors' new plant at

ITT Semiconductors145-147 Ewell RoadSurbitonSurrey KT6 6AW

The Unisite 40 Universal Pro-grammer from MSS uses tenstate-of-the-art pin driver cardseach of which includes acustom gate array, custom lin-ear chips, and 540 surfacemount devices. It will programall package types, includingLCC and SOIC, so that thedesigner is free to choose thedevices that best suit hisneeds.

Microsystem Services Limited Lincoln Road Cressex In-dustrial Estate HighWycombe Bucks HP12 3XJ

Shelton, CT, USA.

UK -Belgium 5openedThe world's first internationaloptical fibre undersea cable,running between the UK andBelgium, was opened on 29October last.Codenamed UK -Belgium 5, thecable was laid by BritishTelecom International's cable -ship Alert. The 12 cablesalready in use across the NorthSea have a total capacity of justover 23,000 telephone circuits;the new cable will add morethan 11,500 circuits.The new cable forms anotherimportant part of BritishTelecom's plans for digital sub-marine cables. The TAT8 trans-atlantic digital cable is plan-ned to be in service next year.The first undersea communi-cations cable between Englandand the European mainlandwas laid in 1853. That cable con-sisted of four copper wires in-sulated with gutta-percha, atype of natural rubber product,and provided a total of fourtelegraph lines.

British Telecom81 Newgate StreetLondon EC1A TAJ

EE

January 1987

NEWS o NEWS NEWS NEWS NEW1First all -opticalregeneratorThe world's first all -opticalregenerator for use in opticalcommunications has been suc-cessfully demonstrated byBritish Telecom Research Lab-oratories at Martlesham Heath.The regenerator functions as adecision gate which retimesand restores the levels of an op-tical data stream with no in-termediate electronic stages.It is based on the principle thata Fabry-Perot semiconductorlaser has non-linear output-power/input-power character-istics because its refractive in-dex varies with optical powerlevel. At some wavelengths thisnon -linearity leads to bistability(see Fig. 1).To form a regenerator, an op-tical clock waveform consistingof a train of pulses with peakpower just below the bistablethreshold is combined with thedata stream and coupled intothe amplifier. When the data islow, a slightly amplified clock

pulse appears at the output.When the data is high, the ad-ditional power is sufficient toexceed the threshold and theoutput jumps to a higher level,which is insensitive to the datapower, and reverts to low onlyat the end of the clock pulse.The output is the regenerateddata in return -to -zero form,retimed by the clock.The output is at the samewavelength as the clock. How-ever, the input data can beseparated by multiples of theamplifier node spacing whichin turn is determined by thelength of the laser cavity.The amplifier in the experimen-tal system (Fig. 2) was a double -channel planar buried-hetero-structure laser fabricated atBritish Telecom's research lab-oratories with facet reflectivityreduced to 3%. The wavelengthand mean power of the clockwaveform were set to 1514 rimand 6 uW in the amplifier inputfibre, just below the bistablethreshold. Small clock pulsesappeared at the output.Data input was provided from a

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Fig. 4. Regenerated data at1514 nm.

distributed feed -back (DFB)laser. As continuous powerfrom the DFB laser was gradu-ally increased, a threshold wasreached at which the outputpulses abruptly jumped to ahigher level.When the DFB laser was modu-lated with a 140 Mbit/s return -to -zero pulse pattern, produc-ing an optical data stream at1526 nm (Fig. 3). the regen-erated pattern appeared at1514 nm with a mean power inthe output fibre of 20 uW(Fig. 4). Error rates of 3 in 108were obtained with a 2'0-1 bitnon -return -to -zero pseudo-random data stream of meanpower 3 W.

British Telecom81 Newgate StreetLondon EC1A TAJ

Olivetti: newprices andnew modelsIn line with market demands formore powerful and fully con-figured personal computers,Olivetti has announced new PCconfigurations and reduced

prices: the latter born out of in-creased volume productionand the shift towards 80286 -based systems.Highlights include lower pricesand larger configurations of the80286 -based M28 series; a re-duced price for the M24SP;larger configured M24 systems;and lower prices for the M19series.The two new models in the M28series, offering 40 Mbytes ofhard disk storage with optionaltape streamers, are aimed at themulti-user and networking mar-ket.The price reductions and thenew models keep Olivetti in themost competitive price/per-formance bracket for 80286 -based systems, which is rapidlybecoming the standard for pro-fessional personal computing.They bring 80286 processingpower from a major PC supplierwithin reach of buyers of stan-dard PCs. without jeopardizingcompatibility by removingproduct features.

British Olivetti LtdP 0 Box 8986-88 Upper Richmond RoadLondon SW15 2UR

Jeff Pitman has becomemanaging director of FactronSchlumberger Europe, and willrun the division of thecompany from Factron'sEuropean headquarters atFerndown, Dorset. He suc-ceeds Art Buckland who wasrecently promoted to vice-president of FactronSchlumberger worldwide.

EE

January 1987

NEWS NEWS NEWS NEWS NEWElectronicgraphicalsymbolsThe British Standards Institutionhas published a revision ofElectrical and electronicgraphical symbols for schoolsand colleges, which makesavailable to teachers andstudents a selection of symbolsfrom BS3939 (Graphical sym-bols for electrical power.telecommunications, and elec-tronics diagrams).This booklet, together with anassociated wall chart, bringsthe 1981 edition into line withBS3939:1985, which is itselfidentical with IEC617 pub-lished by the InternationalElectrotechnical Commission.Although in this revision theactual symbols are unchanged,they are shown with one thick-ness of line in most cases, oftensimplified (e.g., by omittingenvelopes on semiconductordevices), and are designed on agrid pattern. These changesshould prove helpful to thoseusing the symbols in computer -aided design-CAD.The booklet and machine -folded wall chart-not availableseparately-are priced at £7.50plus VAT from

British Standards Institution2 Park StreetLondon WIA 2BS

Improvedresults at MicroFocusMicro Focus Group PLC hasreported a net revenue of £5.65million (1985: £5.68 million) forthe six months ended 31 July1986.

Pre-tax losses were reduced to£0.48 million compared with£2.81 million for the sameperiod in 1985.The group's investment in im-proved and new products hascontinued, much of it in associ-ation with leading computermanufacturers.

In the summary to his State-ment, the Chairman, BrianReynolds, said that the grouphad stabilized after the changein immediate fortunes resultingfrom the upheaval in their in-dustry, and that he felt confi-dent that 1987 would bring thebeginning of a revival in marketopportunities and a return tothe prospect of growth for thegroup.

Micro Focus Group PLC26 West StreetNewburyBerks RG13 1JT

RAI ordersmore LogicaequipmentIn a major expansion of itsteletext operations, RAI, theItalian broadcasting authority,has returned to Logica for itssecond generation originationsystem.The new PAVANE implemen-tation, which will be handled byLogica General Systems in Italy,will be completed later thisyear, and will provide RAI withextensive up-to-date facilitiesfor organizing and running itsteletext service.The new RAI system will be

one of the largest PAVANE in-stallations to date. The editorialcentre in Rome will have the ca-pacity for up to 64 inputs. In ad-dition to terminals, there isprovision for a number of auto-matic and remote inputs.

Logica PLC64 Newman StreetLondon W1A 4SE

New EPROMprogrammerTechnomatic have announcedtwo additions to their alreadylarge stock of equipment: theMPROMER, an add-on for thehighly popular EPROMER HEprom Programmer, and theWinchester Drive Multiplexer.The MPROMER is intended toprogram single chip microcon-trollers of the Type 8741, 8748,and 8749. It plugs into the ZIFsocket on the EPROMER II.The Winchester Drive Multi-plexer allows up to four BBCcomputers to share a singleWinchester drive. The unit isavailable in two versions: a dualunit for two computers, and aquad unit for four computers.

Technomatic Ltd17 Burnley RoadLondon NWIO lED

This fuse and socket tester, shaped like an ordinary 13 A plug,will test six fault conditions on 13 A mains sockets and plugfuses. Available at £14.95 incl. p&p and VAT, fromGalatrek Limited Scotland Street Llanrwst GwyneddLL26 OA L

This new plug-in timer, whichgives multi -programmeswitching for any electrical ap-pliance up to 3 kW, is availablefrom: Cirkit Distribution Park Lane Broxbourne Herts EN10 7NQ

Daymarc'sFrench con-nectionDaymarc Corporation, one ofthe world's leading manufac-

turers of automatic test andhandling equipment, is open-ing its own French Branch at LaTour d'Aigues in the south ofFrance. The branch will beheaded by John Bird, seen inthe photograph with his wife.Eve.

Daymarc Systems Ltd3 The PinesGuildford GU3 6B11

EE

January 198718

`ird

ACA computersupplement

NEWS NEWS yEWS

The American Cryptogram As-sociation has recently startedpublishing a Computer Supple-ment for people who would liketo apply their computers to thesolution of ciphers. The Associ-ation intends to publish the sup-plement twice a year. at a costof SUS2.00 per issue surchargeon the regular ACA subscrip-tion of SUS15.00. In countrieswhere obtaining small dollaramounts is expensive, specialarrangements can be made. In-terested readers should write to

Mike Barlow5052 Chestnut AvePierrefondsQuebec H8Z 2A8Canada

You can't buycheaperEvery video buff knows that theaudio-visual department atBoots enjoys a fine reputationfor a wide selection of the latestand greatest equipment. Now

Boots has further enhanced thatreputation by extending its Youcan't buy cheaper policy to anextensive range of top namevideo and TV equipment. Youcan't buy cheaper is a promisefrom Boots that if you can findthe same item at a lower pricein your town within seven daysof purchase (from Boots), theywill be happy to refund the dif-ference.All items covered by the Youcan't buy cheaper promise willbe clearly marked with greencards.

BISS Lancaster PLC180 Wardour StreetLondon W1V 3AA

Conductivewindows im-prove immunityRecent tests at ERA Technologyhave shown that very thin metalcoatings on glass can providean effective electromagneticscreen to radio frequency inter-ference. Glass panels coatedwith a very thin layer of conduc-ting material have potential ap-plication in the reduction of

VSI Electronics was recently awarded a franchise agreement tohandle ETRI's range of AC and DC fans and accessories. Seenhere are II to r) Kevin Mott. Distributor for ETRI UK; John Clax-ton. Managing Director of ETRI UK; Mel Child. Managing Direc-tor of VSI Electronics (UK) Ltd; and Keith Rolfe. Passives andElectro-mechanical Product Manager of VSI.VSI Electronics (UK) Ltd s Roydonbury Industrial Park Horsecroft Road Harlow Essex CM19 5BY

emissions from computing de-vices and in providing protec-tion from incoming high -inten-sity radiation from radar trans-mitters.A report covering this work,ERA Report 86-0056R The Elec-tromagnetic Screening Effec-tiveness of Coated Glass Panels,is available from

Publication SalesERA Technology LtdCleeve RoadLeatherheadSurrey KT22 7SA

Rheinmetall touse MarconiradarRheinmetall GmbH are pur-chasing from Marconi Com-mand and Control Systems aRanging Radar 282 for use on itstest range in Federal Germanyfor projectile ballistic measure-ment. This is the first exportorder for this new radar system.The Ranging Radar 282 will beused with an electro-opticaltracker to provide range co-ordinates, which allows a singletracking station to determineprecisely the location of theprojectile in flight. The equip-ment is capable of providingreal-time information onsystems under test with a rangeaccuracy better than one metreout to ranges of 20 km.

Marconi Command and Con-trol Systems LtdChobham RoadFrimleyCamberleySurrey GU16 5PE

Conference -

room echoeseliminatedEchoes resulting from loud-speakers in conference roomscan be eliminated, it is claimed,

by an electronic echo -cancel-ling unit developed by GECVideo Systems.Echoes usually arise becausethe output from the loud-speakers around a conferenceroom are picked up by themicrophone and re -transmitted.The echo -canceller, Type 245,samples the audio signal,estimates the echo content, andsubtracts it from the speech be-ing transmitted.

GEC Video Systems79 Silver StreetReadingBerks RG1 2SZ

Jaguar drivesdrive JaguarWhen Trevor Wheatley, Chair-man of Control Techniques,recently selected his new car,he wanted the best that Britainhad to offer. And he appliesexactly the same attitude to theJaguar drives he supplies toIMO. So it was particularly satis-fying to him when IMO an-nounced that Jaguar Cars,renowned for their exactingproduction standards, had

chosen no fewer than 19 Jaguardrives for conveyors in theirnew customer assurance de-partment at the Browns Lane as-sembly plant.

IMO Limited1000 North Circular RoadStaples CornerLondon NW2 7113

19 EE

January 1987

NEWS

Intelligentprocessmonitor

NEWS NEWS NEWS NEW

Analogic has introduced theControl Master Series of 41/2 -digit, microprocessor -baseddigital panel meter which, it

is claimed, offers the uniquecapability of single- or dual -

channel monitoring, and an un-precedented degree of intelli-gence, convenience, and accu-racy.

Analogic Limited68 High StreetWeybridge KT13 8BN

The Model CH -330 PortableSolar Battery Charger fromChronar will recharge two HP7(AA) size rechargeable NiCdbatteries (supplied) in aboutthe same time (12-14 hours) asa conventional mains charger.The CH -330 will work in ar-tificial light, but best resultsare obtained when the panel isplaced in direct sunlight. TheCH -330 retails at E19.95, incl.VAT.Chronar Ltd 49 AlbemarleStreet London W1X 3FE

1111.M.10.

. . 1-=-771,

-0 10-,z mir-~YR=

The Marconi Type 2382 Spectrum Analyser (100 Hz -400 MHz).with-above it-the Type 2380 Display Unit, is available for hirefrom Electroplan Rental.

Power sources& supplieseventThe Power Sources & Suppliesevent, to be held as part of the1987 (28-30 April) British Elec-tronics Week at London's Olym-pia Exhibition Centre, will bededicated to the latest devel-opments in battery technology.The associated conference isintended to reflect recent in-novations in electronics andelectrical engineering whichhave resulted in an unpre-cedented growth of productsneeding self-contained powersupplies operating from bat-teries.British Electronics Week is be-ing organized by

Evan Steadman Communi-cations GroupThe HubEmson CloseSaffron WaldenEssex CBIO 1HL

New lasers fromSTC

STC Defence Systems hasbegun production of its secondgeneration low threshold laserswhich offer significant advan-tages in price, performance,

and reliability over otheravailable devices.The new laser's ridge wave -guide configuration, requiringonly a single epitaxial growthprocess, achieves the lov:threshold characteristic nor-mally associated with buriedheterostructure designs, butwith substantially lower pro-duction costs.The structure is applicable to1300 rim and 1500 nm lasers ofboth the conventional Fabry-Perot structure and to DFB-distribute d feed-back-typeswhich produce stable singlespectral line emission. The

devices have also performedwell when modulated for datarates up to 2.4 Gbit/s.

STC Defence SystemsOptical Devices DivisionBrixham RoadPaigntonDevon TQ4 7BE

Menvier Hybrids has been ableto reduce lead times for theirextensive range of thick -filmresistor networks and hybridassemblies to about 6 weeksthrough the introduction of a£150,000 laser trimmer suppliedby Chicago Laser Systems (seephotograph).Menvier Hybrids Ltd Southern Road Banbury Oxon OX16 7RX

An ultra -thin half -page solid-state display that uses a new elec-trolurninescent technique has been developed by Lohja. Thescreen, known as the Finlux MD 640.200, is intended primarily foruse in portable computers, desk -top terminals and process in-strumentation.Lohja Corporation Karri Kuusikko Olarinluoma 9 SF -02200Espoo Finland

EE

January 198720

INDOOR UNIT FORSATELLITE TV RECEPTION 3

by J R v. Terborgh

eN . eV)

This is the final, optional board in the IDU. As promised in thepreceding instalments of the series, it comprises the AFC, scan

and remodulator facilities, as well as the LNB theft alarm.

The circuit board described inthis article is not, strictly speak-ing, indispensable for a fullyoperative indoor unit. But then,the optional add-on circuits arerelatively simple to build on asingle PCB, and may provideyou with a number of quiteuseful extensions.

Circuit descriptionThe circuit diagram of the op-tional extension board is shownin Fig. 18. The various functionsit offers are best discussed bystarting from the three possiblepositions of the front panelmode switch, &a -b.1. TUNE: S4a.b is set to position1, as shown in the circuitdiagram. Oscillator ICG isdisabled by the low level at its

RESET input, pin 4. Electronicswitch ESE, is closed, while ES:is opened, so that the DC -coupled video signal, CVBS-1(see Part 2) is routed to TVmodulator ICIG. The operationof this versatile RF chip will bereverted to.The RF board tuning voltage,Vtur,e, is taken from the outputof summing opamp A2, which isdriven with the tuning controlvoltage (terminal T, controlsPs -P7), and the output voltage ofAFC amplifier A,.If AFC switch Si is opened(AFC off), ESE, and ES7 are offand on, respectively, whichmeans that the voltage at the -i-input of AI is a fixed level, de-termined with P9. Vtune will,therefore, track the voltage atpoint T, just as if there were no

amplifier of any type in func-tion.Switching on SG, however,causes Bnc, rather than thevoltage at the wiper of P9, to befed to the + input of A. Thiscreates a feedback loop in thetuning voltage circuit. It willbe recalled that Bnc is thesmoothed direct voltage com-ponent of the baseband videosignal. Tracing its origin will re-veal that Bnc is the proportionalequivalent of the PLL-generatedtuning voltage across varactorD2. i.e. it can provide infor-mation about the instantaneouscentre frequency of the PLLsubcarrier (see Part 1).Assuming the AFC function tobe switched on, and assumingthat the selected oscillator, LOLor LOH, starts to deviate from its

set frequency-which may wellhappen owing to thermal ef-fects-the PLL will conse-quently alter the voltage acrossD2-and hence Bnc-to matchits VCO frequency with that ofthe incoming carrier at about610 MHz. The AFC circuit nextresponds to the assumed fluc-tuation of BDC by correctingVmne such that the oscillator re-mains at the set frequency, i.e.BDC also remains constant!The practical limitations of theproposed AFC circuit mainlyconcern the response speed ofthe loop, and the AFC holdrange. The AFC circuit shouldbe insensitive to the demodu-lated video component, which,of course, is also the PLL actionto an FM input signal. This func-tion is taken care of by C50 (see

EE

January 1987

18

ESt

ESS

23.s last

aluddas

a.

Si I=2= SCAdi3= TEST RfJeCe_

cast

Cd

0 = 10 HZ 1.w. 4 V. 15a =21 t.w. = triangular wave..f1= 156-25 kHz VW. 11 Vt, 1S.--- 31 r.w. = rectangular waveS = -r 7.5 V All values are twice' and within 10%.T= 10 Hz t.w. 30 Vt: IS.---- 2) AO voltages measured with respect to groundU =0_8-30 V 15.-= 1: turn Prl with a DhIM (Z.,, .- 1 Mel.V = 2-4 mA

r

Se e-d..

Wertai tea

141.16.1CH=40010ES1-ES4 C12=110668ESS-E58=C13=40660M-44./C1C.13024

Ctt Ott

"C

1211sesewftresi

12V

1.21J.ZE=001621

E6062-3-111

Fig. 18. Circuit diagram of the optional extension board in the 113U.

Part 2), as well as Cl]. Feedbackresistor R64 defines the AFChold range, i.e. the span of Vtunethat ensures a constant BDC

voltage. The stated value of thisresistor fixes the amplificationof A, at about 3 Ptil +R63)/13.631,which will ensure sufficientAFC action in most practicalcases.2. SCAN: S;= -b is set to position2. ES, is closed, and ICaoscillates at about 10 Hz. Thetriangular wave at pins 2 & 6 isamplified to about 30 Vpp bymeans of A3, which conse-quently causes the relevant os-cillator, LOL or LOH, to producea swept output frequency overits entire mixer injection band.The purpose of the SCAN fa-cility is to facilitate the initialdish positioning procedure. Assoon as the dish "sees" thesatellite, there will be a markedchange on the TV or monitor

screen from stable noise to arather unsteady flicker, causedby the receiver sweepingacross the incoming transpon-der signals. Also, the S -meterwill show some deflection andhence can be used to find theinitial aerial position.

3. TEST REMODULATOR: S4a-b

is set to position 3. ES1 isopened, causing ICa to oscillateat 156.25 kHz, or 10 times the TVline frequency. Counter ICIDsupplies two sequential 7 gspulses; one for use as a lineblanking pulse (Q3), and one fora white vertical bar (Q6). Thesepulses are combined by meansof ES2 arid ES3 to form what canhardly be referred to as a com-posite video signal, yet is en-tirely satisfactory for the pres-ent purpose. Resistors R57 andR58 have been dimensioned fora blanking/white ratio of about

1:3. ESL is closed. while ES5 isopened, so that the video testsignal is passed to TV modu-lator IC16.The remodulator test facilityenables ready tuning of the TVset to the modulator output fre-quency, thereby slightly allevi-ating the possible difficulty insetting up a satellite receptionsystem for the first time.

LNB theft alarm (ICis;T13).The relevant circuit section is

so simple as to obviate the needfor a detailed description. Withthree jumpers installed asshown by the dashed lines, LEDD15 and buzzer Bz, will warn ofattempts to steal the costly LNB.The jumper block and the po-tential -free relay contactsshould enable a straightforwardconnection of the LNB theftalarm to many types of existingalarm system. Table 3 showssome of the possible alarm con-figurations plus associatedjumper positions.

Table 3.

Alarm configuration jumpers/wires

LED and buzzer only c -d e -f h -Ire to external alarm; a -c e -g d -f h -IIDU alarm disabledexternal 20 mA seriesloop (OR function)external alarm drives

a -b g -e c -f h -I

a -b d -f g -f h -IIOU alarm

EE

January 1987

Parts list(Note: parts are coded to BS1852;

see Infocard 500)

Resistors (+5%1:

Rss=1K0RS6 =15K

RS7 = 1K8

=4K7Rs0=-82OR

R60=8211

R62 =9K1F

1363;Rss;R66;R73... R76 incl.= 10KR64; R = 22K

136, =21(7

Res;117t;R72= 100K

Ros =12KF

Rro=47K1177;f176=12K

Rrs;R51;Raz=560RRai =82K

Res=6K8R66=300RF

Ps=25K multitum presetPs= 51(0 multitum preset

Capacitors:

Crs= see textCso=220p 5% styroffexC61;Cs1;Cs3=10p;16 V tantalum

Ca2;Cet;Ca6=100n

Csr:Cas;Cts;Croo= 10n ceramicCas=40;63 V axial electrolyticCsr;C:2=470nCts=560p ceramicC93 = 18p ceramic NPO

Cu = see textCss;Css:Csr =10p ceramic

Cra=22p foil trimmer (green)C101... C10/ incl. =ln ceramic

Inductors:

LI8 = 7T1S assembly (Neosid)*Lis= KACAKI769HM (Toko)Leo= small VHF balun core(appr. 7 x 5 x 4 mm)

1.21;L22=0.68pH axial choke Home-made inductor; see text.

Semiconductors:

Dts= LED redICs =7555 (do not use a 555)IC10=401711

IC11=-401068

1C12;IC/3=40668

ICU= LM324!Cis = T1L111 or 11L311

IC16=TDA5660P (Siemens)`1-12;T13=BC547B

Miscellaneous:

Bzr= 12 V self -oscillating buzzer¢12 mm

Ki= BNC, phono or Belling -Leesocket (VHF output).

SA= 2 -pole, 3 -way rotary switch.Ss= miniature SPST switch.)(1= 48 MHz crystal; HC18 case;

series resonant 30 pF AT cut.

PCB Type 86082-3 Isee Readers

Services).0.1 inch pitch jumper block;2 rows of 5 pins; jumpers as

required.37 off soldering pins.

Available from UniversalSemiconductor Devices Ltd;Telephone: (01 348) 9420/9425;or from ElectroValue; Telephone10784) 33603 or (061 432) 4945.

Fig. 19. Track layout and component mounting plan for the IDU extension board.

Remodulator (IC16).The Type TDA5660 fromSiemens is an all -in -one TVmodulator chip which can beconfigured for a wide variety ofTV standards. In this design, itprovides a double-sideband,AM vision, FM sound, TV signalat 48 MHz, which is roughlychannel 2 (48.25 MHz, Band I).Operation on channel 3 or 4 isalso possible by simply usingan appropriate crystal in the X,position. The circuit may also

be modified to output a UHF TVsignal (470-790 MHz), but this israther more complicated thanexchanging the crystal, and is,therefore, only recommendedfor experienced RF construc-tors. The matter will be revertedto in the section on construc-tion.The audio input signal to the TVmodulator chip is passedthrough a fare -emphasis net-work, R83-CB8 50 us). Themodulator chip provides wide -

band FM modulation at theaudio sub -carrier frequency of6.0 MHz, as set with 109. TheVHF output signal is available atsymmetrical outputs pins 13 and15. A double pi -filter, C95 -1,22-

C96 and Os7-L21-C9a, precedes300R -to -75R balun Leo, formwhich the TV signal is taken byCiao. Trimmer Cgs is used to setthe modulator output filter foroptimum balance. The dashedlines around the remodulatorcircuit denote metal screens

EE

January 1987

which serve the preclude strayradiation.

ConstructionIf you have made it so far inbuilding the IDU, you are notlikely to encounter serious diffi-culties in getting the presentextension board up and run-ning.Fig. 19 shows how PC boardType 86082-3 is to be com-pleted. Only three points re-quire special attention, namelymaking Lis and L20, and fittingthe extension board on top ofthe vision-sound-PSU board de-scribed in Pan 2 of this series.In order to avoid unnecessarilyrepeating the suggestions formaking one's own inductors, itis recommended to re -read thepassage on preparing Lis; thiscan be found in Elektor Elec-tronics, November 1986, p. 53.With reference to Fig. 20 andTable 4, oscillator coil Lla ismade as follows (note that thewhite ABS former as part of theType 7T1S inductor assembly isdivided into two equally longsections by means of a smallrim):1. Starting from f, and observ-ing the indicated winding di-rection, close -wind 11 turns inupward direction onto thelower section of the formerbody; doing so will neatly fillthis section. Connect to b (notto e!).2. Starting from e , and oncemore observing the correctwinding direction. close -wind 4turns upward onto the uppersection of the former; the firstturn should rest against the rim.Connect to a.3. Check for any short-circuitsbetween the windings, andverify correct continuity at thepins.4. If you have a GDO, checkwhether the inductor can betuned to about 50 MHz with a18p capacitor temporarily fittedacross f -b.5. Mount the former plusscreening can onto the PCB.Adjust the yellow -tipped coreuntil its top is level with the holein the screening can.As to La, the construction ofthis balun (balanced -to -unbal-anced transformer) is evidentfrom the six -step instructionshown in Fig. 21. Almost anytype of small, two -hole ferritebead rated for at least 100 MHzean be used in this circuit. Theinductor is wound with bifilar

Fig. 20. Pin assignment of os-cillator tank inductor L,u.

Table 4. Home -wound inductors

InductorSWGwire turns remarks

Lie f' -be' -a

30 enam.30 enam.

11

4Closewound on Neosiddie. 4 mm former Type7T1S; see Fig. 20.

Lze 30 enam.bifilar

2x3 RF transformer; seeFig. 21.

LUHF. 24 silv. 3 Space windings to obtainoverall length of 5 mm.Internal dia = 3 mm.

Lx; LI,' 24 enam. 5 Space windings to obtainoverall length of 8 mm.Internal dia = 3 mm.

' Only required for UHF -band operation of remodulator.

21

-1- 3 turns

1 ? 1 II etEm ff 0 ?2 2 `

? RJR I ES?

4.-c)

... ?

T 2x SWG30

I II

3 turns

III

1'3'a b

11 s

I d.. I eriei2 ...........--.-.. 223 ....--. 2 MI

- ak--.-- -3 -- e . ii_4(VA

4 4 iiiiiilaiiii p 4' 4 4 wiaall FW4 c 4 walaiii, -'44

M

2141d

n

EL Y IT1

Fig. 21. Suggested construction of balun L -o.

wire, which is simply made bytwisting two lengths of enam-elled copper wire. After wind-ing two times three turnsthrough the bead holes, thestring ends are split in order toidentify the four individualwires by means of a resistancemeter or a continuity tester(step IV). At this stage, it is agood idea to check the wiresfor internal short circuitscaused by the insulatingenamel coating being damagedas the windings are tightenedaround the ferrite bead.After making the balun and fit-ting it onto the board, it is timeto check whether this is cor-rectly populated. There shouldbe six wire links in all, and the

jumpers in the LNB alarm cir-cuit should be fitted as re-quired. Positions C79 and Cs.-are vacant as yet. Make surethat all ceramic capacitors inthe remodulator section aremounted with the shortest poss-ible lead length. The crystalcase must not be grounded.The position of the 12 mm highmetal screen around theremodulator circuit, and thelengthwise fitted screen acrossIC16, is governed by 9 solderingpins. A single strip of 12 mmwide thin brass sheet or tinplate is readily cut and bent tosize. Remember to drill twosmall (4, 3 'mm) holes in thescreen to enable feedingthrough the shielded wire to

the audio input. and, if re-quired, the 4 3 mm coax cablefrom the RF output to K4 on theenclosure rear panel.The completed extensionboard is mounted on top of therear side of the vision-sound-PSU board. i.e. as close as poss-ible to the enclosure rear panel.Remodulator output socket K4

can be fitted at a suitable lo-cation in the rear panel, whilstbeing connected direct to therelevant pin on the PC board,Le. without a length of coaxcable. Note, however, that thismounting method requiresmaking a suitably sized hole inthe previously mentionedscreen, allowing for the passingof the socket.

EE

January 1987

The lowest possible mountingheight of the present boardabove the vision-sound-PSUboard is determined mainly bythe height of the fuseholder onthe latter PCB. Sufficient stab-ility of the "sandwich" con-struction is ensured by usingtwo conventional 15-20 mm longPCB spacers in the two rearpositions.It goes without saying that theoverall height of the two -boardunit should enable the IDU tobe closed properly. Also, thevision-sound-PSU board shouldbe fully operative and correctlyaligned, since many of its ad-justment controls are no longeraccessible with the extensionboard fitted on top.The wiring of the boards shouldbe fairly' straightforward, requir-ing no further remarks otherthan that the audio, BDC andVrune connections should bemade in conventional shieldedmicrophone cable, while theCVBS-1 connection is made in

3 mm coax. In all cases,ground the cable shield at thelower board only.Finally, the external loop con-nection can be made withwhatever type of socket or ter-minal strip is thought most con-venient; a 3- or 5 -way DINsocket is satisfactory.

24

Setting upBefore detailing a suggestedsetting up procedure for thepresent board, it must be madeexpressly clear that attemptingto use the completed extensionPCB along with as yet un-oper-ative RF and vision-sound-PSUboards needlessly complicatesgetting the IDU to function cor-rectly. Therefore always buildup the receiver as detailed inPart 2, and familiarize yourselfwith the various adjustmentpoints and their typical re-sponse, before adding the pres-ent board.

1. Set S4 to TUNE, and switch offthe AFC (Ss). Turn P7 (coarsetuning) to check whether Vtunevaries from about 1-30 V. Tuneto a satellite programme andcheck the presence of com-posite video at pin 10 of IC16.Do the same for the audio atpin 1.Measure BDC, note the value,and adjust P9 for an identicalvoltage at its wiper. Switch onthe AFC and check its holdrange by turning P7; reception

should remain unaltered over acertain portion of the tuningcontrol travel, then suddenly belost.2. Set S4 to SCAN, and switch offthe AFC. Use a scope to checkmeasuring points and J.Vtune should be an undistortedtriangular wave, i.e. it shouldhave clearly defined points ofinflection, and no clipped topsor appreciable offset. Ifnecessary, R62 and R69 may beredimensioned to achieve thecorrect wave -form and ampli-tude respectively.Set Ps to the centre of its traveland observe the monitor screento see the effect of the SCANmode when a satellite is re-ceived. You may want to experi-ment a little with the value ofCal to obtain the bestnoticeable effect on the screen.Try to remember what it lookslike!3. Set S4 to TEST REMOD., andconnect a TV set to Tune theTV to channel 2. Adjust the corein Lis until the test signal-awhite vertical bar two thirds tothe left of the screen-can beseen with good definition. Ad-just Ps for optimum synchroniz-ation, or use a frequency meter

for the presence of the statedrectangular wave (see Fig. 18).Fine-tune the TV set to the testsignal, and switch the IDU onand off a few times to verifywhether the 48 MHz oscillatorstarts properly; correct the ad-justment of Lia, if necessary.Set S. to TUNE and observe thetransponder signal on the TV. Itmay be necessary to re -do thesetting of Pt and Lla, as well asthe TV tuning, for optimum pic-ture quality.

Turn up the volume control onthe TV and peak L19 for bestsound reproduction. A suitableceramic capacitor (10-100p) maybe fitted in the C94 position, incase L19 can not be tuned lowenough.Finally, tune the TV set to alower UHF band harmonic ofthe remodulator, and adjust C913for minimum signal strength.Unfortunately, the presence ofharmonics can not be ruled outaltogether, given the relativelylow frequency of operation ofIC16. Depending on the degreeof crystal activity, it may beworth while to fit a damping re-sistor (1K0 -10K) across pins f andb of Lis.Run a quick check on the oper-ation of the LNB theft alarm bydisconnecting the downleadcable at K1. Please note that thealarm circuit is fed from theunswitched +12 V supply.Therefore the + Bz, terminal onthe PCB should be wired to thebuzzer as well as the ap-propriate connection of S2 (seePart 2).Finally, if the setting of Ps fails togive a satisfactory compromisebetween the operation of theSCAN function and that of theinternal test pattern generator,try fitting a number of smallcapacitors in the C79 position.

Remodulator on UHFThe circuit diagram of Fig. 22shows how to modify the on-board, TDA5660-based, TVmodulator for operation in theUHF TV band (470-790 MHz). Asthis modification is not sup-ported by the PCB layout, alter-ing the circuit is recommendedfor experienced RF construc-

tors only.Preset P is used to set thedesired output frequency,which must be well removedfrom the PLL VCO frequency toavoid carrier interference.Therefore do not tune IC16 tothe generally used modulatorchannel 36.The small ceramic NPO capaci-tors can be fitted in a three-di-mensional construction, alongwith oscillator inductor UHFwhich can be spaced or com-pressed slightly to set the initialoutput frequency. The 11)5

capacitors are. of course, fitteddirect across the relevant ICpins at the PCB track side.The modulator output filtermust also be altered as shownto allow for the higher fre-quency. Use a suitably ratedbead for Leo, and wind two turnsthrough each hole, rather thanthree as in the VHF circuit. Thedata for LUHF, Lx and Ly can befound in Table 4.

Aerial positioning unitThe circuit diagram of Fig. 23aand the photograph of Fig. 23bshow a simple, yet indispens-ible accessory unit for the IDU.It is a hand-held remote metercircuit which is connected tothe IDU over a length of 6- or7 -way cable, enabling the userto monitor the S -meter indi-cation while lining up the aerialfor optimum reception.It should be noted that the cir-cuit diagram and practical re-alization are but suggestions;other configurations, as well asmore sophisticated controls areperfectly feasible, and con-structors should have little diffi-culty in tailoring the aerial

Fig. 22. Modified circuit for the remodulator, if this is to operate in the UHF band.

Test set-up to examine the performance of the BFG65 prestage in -the IDU. Display indications, left to right: frequency (MHz); as-sociated gain (dB); noise figure (dB). Courtesy of SSB Elec-tronics, Iserlohn, Federal Germany.

Fig. 23. Circuit diagram (23a) and practical outlook (23b) of theaerial positioning unit.

positioning unit to their specificrequirement.With reference to Fig. 23a, themeter should be a more sensi-tive type than that incorporatedin the IDU. Either a switch,mounted onto the IDU rearpanel, or a socket contact, isused to break the S meter driveroutput to the front -panelmounted meter, and route thesignal to the aerial positioningunit. A buzzer is fitted to enablethe person remaining at the IDUto notify the other person at theaerial that the IDU is switchedfrom SCAN to TUNE followingthe slightest sign of receptionon the TV or monitor screen.In practice, the aerial position-ing unit may be used as follows(note that a detailed aerial posi-tioning method will be dis-cussed in next month's finalinstalment of this series):1. Set the IDU to SCAN, LOL orLOH depending on the satelliteto be received; connect thepositioning unit cable, and, ifpossible, install a helper at theIDU.

2. Take the positioning unit tothe aerial site (on the roof, in thegarden, or wherever receptionis thought feasible).3. Set the unit to maximummeter sensitivity and line up thedish until some deflection isseen. Hopefully, the person in-side has noted the SCAN effecton the screen, and, via thebuzzer, notified you that themeter indication will be lost foran instant as he tunes to sometransponder.If no help is available, leave thedish roughly positioned and goinside to switch from SCAN toTUNE yourself. Reception ofthe satellite may still be weak atthis stage, but you have at leastmanaged to find a stable signal.4. Go outside again and line upthe aerial for highest meterdeflection. -turning down thesensitivity any time the meterreaches its fsd indication.

Threshold extensionThe following is a necessarilybrief examination of a numberof experiments with the PLLdemodulator, IC2, on the RFboard. As these experimentsare not supported by the PCBlayout, their being carried out isonly recommended for ex-perienced RF constructors.Also, since the objective of theproposed modifications is tofurther lower the PLL noise

EE

January 1987

threshold so as to improve uponreception with relatively lowC/n ratios (8-10 dB), there is nopoint in altering the PLL circuitif your specific outdoor unit en-sures a C/n output of more thanabout 12 dB.When the C/n ratio at the inputof the PLL demodulator ap-proaches the noise threshold,the received picture is more orless impaired owing to noisespikes occurring primarily inthe saturated colour areas. Thiseffect is mainly due to insuf-ficient open loop gain of thePLL at the chroma subcarrier,4.433 MHz (PAL system).Incorporating a chrominancefilter in the secondary PLL loopmay improve reception to someextent, but it should be notedthat the effect depends on thetransponder deviation andbandwidth. For instance, thesignal from Teleclub Switzer-land could be slightly improvedby peaking the chroma filterwhilst observing the few re-maining sparklies in the ochrerectangle at the lower right ofthe test chart. Correct tuning ofthe series filter will enable thesharp white -to -black transitionsin the chart to appear with aclearly improved definition.The practical circuit of thechroma filter extension isshown in Fig. 24a.It will be recalled that C20 andC21 define the secondary loopresponse and hence the oper-ation of the PLL at a specifictransponder deviation. It is im-portant to realize that, at pres-ent, there is no single standardfor the peak -to -peak deviationof transponders, not even if

these are part of one and thesame satellite. Research carriedout by the EBU and the CCIRhas provided evidence for theproposition that, given aspecific C/n ratio, S/N riseswith increasing deviation. It is,therefore, arguable that future satellites will hold transponderswith larger output bandwidth;after all, a number of the pres-ent generation of TV satelliteswere originally designed to

operate in data communicationnetworks.It may be interesting to experi-ment with the values of C20 andC2, while observing the signalfrom a relatively weak transpon-der. The range of values thatcan be fitted in the stated ca-pacitor positions is quite large-see the small inset table inFig. 24a. Fig. 24b shows how

EE

January 198726

24

RB

1= 4.433 MHza 0>10

L9RU

*C20

7170621 1 81

PO in

IC2PLL

SL1451

1 AGC V 2 pp in

91 121

C21RV

1F6 y

603*

86082-3-24a

L9

RB

b

11

C20NMI7330P

1 21 81

el = 20...28 MHzPP

IFS' PO in

1C2PLL

SL1451'4 V _ LFB

AGC 2 RF in

121

RV ef

700n700nIM=1

66092-240

Fig. 24. Experiments in attaining a possibly low noise thresholdfor various levels of transponder deviation.

Fig. 25. Pass band curve of an incorrectly aligned (25a) and a cor-rectly aligned (25b) IF chain on the IDU RF board.

the secondary loop differentialamplifier is converted into asingle -sided type by decoup-ling the LFB2 input and the Voutput with 100n ceramic ca-pacitors. This modification iscalled for when receiving satel-lite signals with a peak -to -peakdeviation of the order of25 MHz. It should be noted thatsuch a high deviation valuedoes not necessarily mean ahigher bandwidth; in nextmonth's article we will examinethe exact relationship betweenthese terms.Finally, interested constructorsare advised that Plessey haverecently introduced the TypeSL1455 quadrature FM TV de-modulator, which is stated toachieve a noise threshold ofabout 7.5 dB, i.e. it is some 1 dBbetter than the SL1451 con-figured for optimum operationgiven a specific deviation.

RF boardmeasurementsThe IF amplifier chain on the RFboard was studied with respectto its frequency vs amplitudecharacteristic. Use was made ofa 0-1800 MHz spectrum analyzerplus associated sweep unit.Fig. 25a shows the curve of awrongly adjusted IF chain; oneof the four bandfilter trimmershas obviously been set at toolow a frequency, causing amarked peak outside the re-quisite pass band.While adjusting the bandfilters

to obtain a satisfactory filterresponse, it was found possibleto locate the pass band any-where in the 450-650 MHz band,while the bandwidth was neverless than about 35 MHz. There-fore, constructors not in pos-session of an RF sweep gener-ator or other sophisticatedequipment to measure the IFbandwidth need not worry toomuch about the overall pass -

band of the RF board. As longas all trimmers can be tuned forstable noise output. the initialalignment is satisfactory.Fig. 25b shows the band passcurve obtained after very care-fully peaking the trimmers foroptimum reception of the testchart broadcast by TeleclubSwitzerland on ECS-1. Thecurve thus obtained may becompared to the theoreticallyrequired one shown in Fig. 25c.The latter is used by the EBU tospecify the minimum require-ment for Eutelsat-1 receivingstations.

Next timeNext month's concluding articlein this series will tackle a widevariety of questions raised inconnection with satellite TVreception. So. should anyaspect of the present subjectmatter still puzzle you, seewhether it is among the sub-jects qualified for closer exam-ination in Part 4.

RGK;Bu

25c I I I

b

The figure is symmetrical relative to centre frequency

I= IF pass band requirementRF pass band requirement

A B C D a b

cd

e(MHz)(MHz)(MHz) (MHz) (MHz) (dB) (dB) (dB) (dB) (dB)

28.8 36.0 45.25 60.0 0.6 2.5 (10.0)* (25)* 0.3

* There is no requirement for out -of -channel filtering in the transmit equipment.However, it is recommended that out -of -channel filtering be provided in thereceive equipment.

86082-3.25c

Fig. 25c. Theoretical requirements as to bandwidth of RF and IF sections in satellite TV receivingequipment (Courtesy of EBU, Brussels).

19.7

THE FUTURE BELONGS TO THEPHOTON

Electronics has been the main engine of innovation since theinvention of the transistor 40 years ago. Most of tomorrow's

interesting technologies will work by manipulating light, notelectricity.

The electronics revolution isyoung. The electron was ident-ified less than a century agoand the microchip, on whichtoday's information -technologyindustry utterly depends, hasbeen around for fewer than 20years. The successes crammedinto these two hectic decadeshave created the impressionthat electronics is a technologycapable of limitless improve-ment.It is not. Electronics will giveway to a superior technologybased not on electricity but onlight. Physicists did not realizeuntil early in this century thatlight came in the separatepackets they now call photons.But science has made startlingprogress in manipulationphotons. A photonics revolutionis already in the making.The first shot of the electronicsrevolution was the transistor.Photonics' first shot was the in-vention, in 1960, of the laser. Un-til then, those trying to do trickswith light had to make do with ajumble of disorderly wave-lengths. Lasers create a sourceof light with a uniform wave-length and with each wave mov-ing in step with its companions.This is a tool of immense power.Lasers can-or so PresidentReagan hopes-destroy ballis-tic missiles thousands of milesaway. They can cut metal in fac-tories and repair blood vesselsin human eyes. Hospitals uselaser beams guided throughoptical fibres to shatter people'skidney stones. A French inven-tor has replaced the strings of aharp with laser beams. Liketransistors, lasers have shrunk:they can now be generated by achip the size of a grain of sugar.This is paving the way for awholesale switch from elec-trons to photons.Why is the switch worth mak-ing? Because photons travelfaster than electrons; because

they have no mass; because (un-like electrons, which interferewith each other) photons can bemade to pass through eachother unperturbed; becauselight behaves both as a particleand as an electromagneticwave-which means that opticaldevices could be based onmuch the same operating prin-ciples as those already used inelectronics.Moreover, electronics is dis-covering its limits. One is thespeed at which electrons travelthrough semiconductor ma-terials. So long as electrons re-main the information carriers ofcomputers, this sets an absolutelimit on the speed-and hencepower-of computing. Elec-tronics has not reached thatlimit yet, but it is drawing closeenough to worry engineers.The customary way to makecomputers cheaper and fasteris to squeeze electronic compo-nents closer together. Thenumber that can be fitted on asingle chip has grown from

Laser majesty

about a dozen 20 years ago to2m today. But miniaturization,too, is bumping against limits.Engineers are running out ofways to etch into chips ever -smaller paths along which elec-trons can run. And when com-ponents get too close, the chipsare plagued by "cross talk'!-theleakage of charges from onecomponent to another.If computers are to work fasterstill, a new approach is needed.The best bet is "parallel pro-cessing'?-the notion that com-puters ought to be able to per-form a lot of operations simul-taneously, instead of channel-ling all their calculationsthrough one bottlenecked cen-tral processing unit. Here, too,the case for a photonic solutionis compelling. Sending severalelectric currents through onechip at the same time riskscross -talk and disaster. Not sowith beams of light: a chipcould process several at oncewithout their interfering witheach other.

Still sceptical? Consider howrapidly light has nudged elec-tronics out of two pillars of in-formation technology: telecom-munications and the storage ofinformation.In communications, telephonecompanies are tearing out theircopper cables as quickly asthey can afford to and replacingthem with hair -thin opticalfibres made of glass. Light is abetter messenger than elec-tricity. It wastes less heat and isimmune to electromagnetic in-terference. Better still is light'senormous bandwidth. Becauseit spans so many frequencies,light can squeeze in far more in-formation than electricity can.The quality of the optical fibresthemselves has improved dra-matically. In early (circa 1970s)fibres, light ran in a disorgan-ized zig-zag through a relativelylarge core within the fibre. Theresulting collisions with thefibre's cladding absorbed muchof the light, requiring frequentrepeaters to refresh the signals.In 1977, experimental fibrestransmitted up to 140 megabitsof data a second, and needed arepeater every six miles or so.Today, one experimental fibrenetwork installed in Britaincarries telephone traffic at1200 megabits a second, with30 miles between repeaters.The first transAtlantic fibres willbe carrying data and telephoneconversations between Europeand America in 1988. Yet thetechnology is on the thresholdof another luminous leap.This will not come fromchanges in the fibre itself, butfrom the devices used to sendand receive the optical signals.The first step is to combine in asingle device all the parapher-nalia that optical fibres re-quire-lasers to send signals,detectors for receiving them,and a rag -bag of lenses, mirrorsand electronic controls.

EE

January 1987

The second step is to transmitlight beams "coherently"L-ie, intightly -defined wavelengths-into a receiver that can betuned to select the requiredwavelengths and sort out theseparate streams of data. Inprinciple, coherent trans-mission enables a single fibreto carry 10m telephone conver-sations or 10 000 digital tele-vision channels at once.The optical assault on datastorage-that other pillar of in-formation technology-hasbeen as impressive. Musiclovers were in the van with theircompact discs. The music isturned into digital signals,burned on the disc as a seriesof minute pits and then de-coded for playback by a low -

power laser.Audio discs like these are onlythe first big success of atechnology restlessly seekingnew applications and markets.Optical discs are beginning toreplace magnetic ones as a wayto store computer archives.Because they are tough, thediscs can be stored insidespecially -constructed juke-boxes. One 4.7 -inch disc canstore about 550m bytes ofdata-the equivalent of 1500floppy discs or about 250 000printed pages. Which means ajukebox can store the archivesof an entire government depart-ment.

Optical discs suffer from onedrawback: erasing them orwriting new information onthem is difficult. This has im-peded their marriage with com-puters, but has also promptedan imaginative hunt for appli-cations in which data must bestored permanently withoutalteration.Discs sold under a standardformat known as compact -disc read-only memory (CD-ROM) are enabling data -basecompanies to sell archival infor-mation to subscribers cheaplyby post instead of expensivelyby telephone. Grolier, anAmerican publisher, has put itsAcademic American Encyclo-paedia (30 000 articles, 10 000pages) on one -tenth of one disc,which it sells for less than $200.A new generation of discscalled WORMs (write -once -read -many -times) is half -waythere. These are sold blank, sothe end user can store whateverdata he likes on them, althoughthe information, once stored, isthere to stay. But the technology

28

for a fully -erasable disc willprobably be perfected by theend of the decade. Two ideasfor making them are alreadyshowing particular promise.One is based on a magneto -

optical process. The disc's re-cording layer is an alloy of ter-bium, iron and cobalt. To storeinformation, a laser heats up atiny spot on this layer, creating avertical magnetic field. The in-formation is read by anotherlaser whenever it encounters amagnetised spot, the light'splane of polarization is rotated.The information can be erasedby reheating the spot.The other approach is chemi-cal. Here, a laser is used toswitch the structure of a tel-lurium alloy back and forth be-tween amorphous and crystal-line phases, which reflect lightdifferently.Impressive as they are, theprogress made by optical discsand fibres do not amount to arevolution. Photonics will notcome fully of age until it equals,and then surpasses, the centraltriumph of the electronics revol-ution: the computer.At the heart of the computersits the transistor. A transis-tor, remember, is a switch, adevice that can flip backwardsand forwards between twostates. Computers are chains ofswitches. They treat sequencesof ons and offs to denote num-bers (in which case ons and offsare read as the ones and zerosof binary counting) or to denote"true or false" (in which casechains of switches can be usedas the building blocks ofalgebraic logic). The challengefor photonics is to invent adevice that does for light whatthe transistor does for elec-trons.

Into the heart of thecomputerIt has virtually happened. AtAT&T's Bell Laboratories andBritain's Heriot-Watt Universityin Edinburgh, small and primi-tive circuits of the kind thatcould one day grow into com-puters are already running onlight. The switches they use-known variously as bistable op-tical devices (BODs) or trans-phasors-are essentially opticaltransistors. Light emerges fromthem as a strong beam (on) or aweak one (off). Put a bunch oftransphasors together, shinelaser beams through them, and

A handful of light

you have the basic ingredientsof an optical computer.To understand how atransphasor works, think of it astwo partially -reflecting mirrorsfacing each other. If a beam oflight is shone through themsome of it gets trapped, bounc-ing backwards and forwardsbetween the mirrored surfaces(see diagram on next page). Asthese waves cross each otherthey can either interfere withand weaken the beam or alignwith it and reinforce it. Thisphenomenon is the basis of asimple instrument-used tomeasure wavelenghts-in-vented by two French scientists,Charles Fabry and Alfred Perot,in 1896.The Fabry-Perot interferometeremits a strong beam or a weakbeam depending on whetherthe waves are being reinforcedinside the cavity. On its own,however, it is not a switch: auseful switch needs to be ob-viously on or obviously off.Common sense says that agradual change in the intensityof the beam shining in will pro-duce a gradual change in thebeam getting out, not the ab-rupt change that is needed. Inordinary circumstances, com-mon sense would be right. Inthe case of the transphasor, it isnot.To make the Fabry-Perot in-terferometer into a switch,physicists hit on the idea of mar-rying it with a phenomenonknown as optical bistability,first observed at Bell Labora-tories in 1976. The secret is inthe cavity between the mirrors.

If this were filled with an or-dinary medium-air, say, ormost solids-the intensity of thebeam passing out of the mirrorwould, indeed, change in pro-portion to changes in the inten-sity of the beam shining in.Transphasors, however, use afamily of materials (such as in-dium antinomide and zinc sel-enide) that are "non linear". If alaser beam shines into thesematerials, a slight change in itsintensity can trigger the wave -reinforcement and make thebeam coming out of the trans-phasor suddenly brighter-andmake it stay that way until thetrigger is released.Bell Laboratories and Heriot-Watt have made different sortsof transphasors, but they bothwork. Heriot-Watt's are entirelyoptical: the laser beams areshone into bistable plates madeof zinc selenide. Bell is trying ahybrid approach. Its devices,made of gallium arsenide. useelectro-optical interferencewithin the cavity to trigger thereinforcement effect. In an op-tical computer, these deviceswould be the "chips". and the"wires" would consist of laserbeams.To make a computer, it is notenough to be able to turn justone switch on or off. Computersare complex arrays of switches,each of which feeds signals intothe next. So optical switchesmust be "cascadable'=thebeams of light emerging fromone transphasor must be able toflip the next, and so on. Theymust also be able to receiveand send several signals at the

29 EE

January 1987

Let there be light: how a transphasor works

'On'Incomingbeam

-

el

Forward beamResulting wave

. -----N /77%

'Off'

Forward andreversebearnsreinforce

beam

/01 in\ / \ f1 0 1 1-1 i

: %I 1 ii 1 / 'r''

Resulting wave

\ 1.. 1 11 1 1; 1' 1 1'

Forward andreverse beamscancel out

Reflectedbeam

- Reverse beam

.Partiallyreflectingmirror I- Reverse beam

Source: Sciertfc Arne.=

87009-1

same time (properties knownrespectively as "fan -in" and"fan -out").These obstacles are tumblingfast. Last year, for example, theteam at Heriot-Watt Universityshowed that its zinc-selenidetransphasors could be keptnear their threshold by aholding laser, then switched byturning on a small extra beam.Earlier this year, the team an-nounced that it had placedseveral transphasors in a cyc-ling loop.Optical switches should, intheory, be able to operate 1000times faster than electronicones. But do not throw yourelectronic computer away justyet. For the present, trans-phasors are primitive. They stillhave to be pumped by toomuch light, and they are stillbulky, separate devices-theyhave not yet been squeezedtogether on chips in the wayelectronics switches have. Evenso, optical switching works.

Hybrid vigourLaboratories everywhere arerushing to bring optical andelectronic switches together.One motive is to make even bet-ter use of optical fibres. Exist-ing optical networks do notwork at the speed of light,because the messages thefibres carry are shuttled be-tween machines such as tele-phones and computers thatrun-for now-on electricity,not light. So at each end of eventhe niftiest optical fibre sits acumbersome device whose jobis to transform optical pulsesinto electronic ones and viceversa.

To speed this procedure,engineers are creating op-toelectronic chips. To do so,they have had to conquer a dis-advantage of the photon-its in-ability to carry an electricalcharge. Picking signals off theend of an optical fibre demandssome way to sort out waves oflight and send them to differentdestinations. Electrons can beshunted by the application of anelectric field; chargelessphotons are impervious to suchmethods.The answer has been to chan-nel the light through "wave -guides" etched into chipsmade of materials with unusualoptical properties. Thesematerials change their ability toconduct light when an electricfield is applied to them. Usinglithium niobate, engineers havebeen able to make a widerange of optoelectronic modu-lators, switches and other de-vices.But there is another reason forwanting to bring the photon andthe electron together parallelprocessing. Britain's Plesseyhas developed a BOD in whichthe bistability comes from in-serting a photochromic ma-

terial-one whose chemicalform changes when exposed todifferent wavelenghts of light-into the cavity. Plessey believesthe device could be used forparallel processing. The idea isto squeeze an array of BODs ona single two-dimensional plate.Each then becomes an in-dependent switching centrethat can be addressed simul-taneously by an incoming laserbeam (see diagram below).This approach comes into itsown in applications such asimage -processing, in which thevalue of thousands of pictureelements (pixels) must be in-dividually calculated to buildup a whole picture. Plesseyaims to get around this data-processing bottleneck by usinglight to process all the pixelsat once. The optical switchesare not yet as fast as elec-tronic ones, but that hardly mat-ters when they work simul-taneously. Plessey reckons thatwith its photochromic BOD, adevice the size of a finger -nailcould process 4m pixels in oneten -thousandth of a second.Photonics has come a long wayin the quarter century since thearrival of the laser. But entirelynew ideas for manipulating andexploiting light are still pop-ping up. These range from themundane (mechanical and bio-logical sensors based on op-tical fibres) to the franklyquixotic (travelling to the starsby giving spacecraft sails thatcatch photons). Physicists havebegun to use laser beams totrap individual atoms so theycan be observed in detail.Engineers envisage massivecomputer memories with dataencoded within the light -waves

of a hologram.Why this sudden flowering? Inthe 1970s, physics made awealth of discoveries about theways in which light interactedwith matter. These discoveriesare now finding applications.The properties of non-linearmaterials-which made thetransphasor possible-are oneexample, but there are others.In some circumstances, lighttravelling through a materialsets up internal sound wavesthat contour themselves like adeformable mirror, sending thelight backwards out of thesubstance on the path alongwhich it entered. In 1972, DrBoris Zeldovich and colleaguesat the PN Lebedev Physical In-stitute in Moscow used this pro-perty to make something calleda phase -conjugate mirror.This is no ordinary mirror it cantake an image that has been dis-torted and then straighten outthe jumbled -up waves to recon-stitute the original image. Likeso many technologies, the mir-ror was treated as a laboratorycuriosity at first. It is now beingpressed into service by astron-omers to take the twinkle out ofstars, and by star -wars generalsto shoot laser beams throughthe turbulent atmosphere. Themirrors can also be used to pro-ject three-dimensional imagesthrough optical fibres and toetch tiny components on micro-chips. One way or another, lightlooks like the wave of the future.

Reproduced with permissionfrom The Economist

EE

January 198730

TOP -OF -THE -RANGEPREAMPLIFIER -3

This concluding part of the article deals with the construction ofthe preamplifier. Additionally, it gives a detailed discussion of the

various types of capacitor, both myths and realities.

The preamplifier contains threeprinted -circuit boards: motherboard, bus board, and supplyboard. The dimensions of theboards have been chosen toallow the unit fitting in a stan-dard 19 inch cabinet with aheight of 2 units (88 mm). Themains transformer is fitted in aseparate aluminium enclosure.the dimensions of which are notcritical. In addition to the PCBs,two foils are available throughour READERS SERVICES: onefor the front panel and one forthe rear panel.

High -qualitycomponentsIt is important to use only high-

quality components to ensureoptimum performance. All re-sistors should be metal filmtypes with a tolerance of 1%,although that of R7 and Rashould preferably be 0.1%. Ifthese prove unobtainable, sel-ect a pair of 1% resistors that are

identical in value, or very nearlyso, with the aid of a digitalmultimeter.All opamps are Type OP -27,while the dual transistors areMAT -02s. Do not use the OP -37in the line amplifier, becausethis type has off -set compen-sation only for gains greaterthan 14 dB.All capacitances in the signalpaths are formed from a parallelcombination of an MKT and anMKP capacitor (M= metal; K=plastic; T= polytherephthalate;P = polypropylene). Frequency-

determining capacitors in theIEC compensation section (C9,Clo , C11) are I% MKS (S=poly-styrene) types. Electrolyticcapacitors in the power supplyare all PCB mounting types.Decoupling capacitors shunt-ing electrolytic capacitors maybe MKT or ceramic types.It is advisable to use silver-or gold-plated phono inputsockets: these guarantee free-dom from oxidation and conse-

quent contact potentials be-tween plug and socket.The relays on the bus printmust, of course, be of primequality. Four possible types areshown on the component list.The excellent SDS type is unfor-tunately polarized, and its coilconnections are exactly the re-verse of the others: if this type isused, therefore, its coil connec-tions must be reversed.The volume control poten-tiometer must be of the highestquality: in the prototype astereo version from Alps wasused with excellent results.The balance potentiometers arerather less critical, but shouldstill be of very good quality:they should definitely not becarbon types, but conductiveplastic or cermet. Bourns orSpectrol models are rec-ommended.The switches are not criticalcomponents, since they onlyswitch direct voltages to therelays.

A few tips to make the total costcome down somewhat. TheOP -27 may be replaced by a5534, which is a lot cheaper andstill a good -quality device, but itmay give off -set problems. TheMAT -02 may be replaced by anLM394, but the overall qualitywill come down slightly. In thiscontext, if moving -coil pick-upsare unlikely to be used, onlyone MAT -02 per channel is re-quired as already explained inPart 2. Cost reductions on thecapacitors should be well con-sidered: whatever you do, neveruse electrolytic capacitors inthe signal paths - at the veryleast MKT types should be usedthere.

ConstructionThe mains transformer, whichcan either be of the laminatedor of the toroidal type, shouldbe mounted in an aluminiumcase (see Fig. 13). From one endof this case the-non-earthed-

EE

January 1987

mains cable should emerge,and from the other a fairly heavythree -core cable terminatedinto a suitable plug. This plugmates with a correspondingthree -pin socket at the rear ofthe preamplifier enclosure.This arrangement is absolutelyessential to keep any hum fromthe preamplifier circuits.Next, the supply board shouldbe completed. The voltageregulators should be fitted ontoadequate heat sinks, which canbe fitted to the board with self -tapping screws.When- the board is completed,it can be mounted at the right-hand side of the enclosure. Donot forget a screen between itand the mother board. Thealternating voltage from themains transformer is taken tothe board via the double -polemains switch.Mains on -off indicator D12

should now also be connectedto the supply board.The earth connection on thesupply board is then connectedto the enclosure via a shortlength of heavy-duty cable.The supply may then beswitched on to test whether thedirect voltages are present ifso, they should be set to +18 Vwith the aid of the two presets-P1 and P2.

The bus board can be completefairly quickly. First screw all thephono sockets to the board (in-puts at the track side). Tightenthem by hand and then solderthem lightly to the board: thisprevents them coming loosewhen later the correspondingplugs are withdrawn andplugged in again. Then tightenthe socket nuts with a suitablespanner. After that all othercomponents, including therelays, can be fitted onto the

board.Some resistors are soldereddirect to the centre terminal ofthe sockets.The connections betweensocket and board at the tapeand line outputs are madewith a short length of equip-ment wire. The remaining con-nections are provided withsoldering pins to make themeasily accessible during the re-mainder of the work.Remove any resin from theboard with a brush dipped intowhite spirit or alcohol, and thenseal the track side with a suit-able plastic spray. Take carethat no spray gets into thesockets or relays. This cleaningand insulating of the board re-duces the risk of cross -talk to aminimum.The board is then mounted tothe rear panel of the enclos-ure with the aid of insulatedspacers: this obviates any possi-bility of the tracks or socketstouching the enclosure.The earth connection adjacentto the sockets must be connec-ted securely to the enclosure tobecome the case earth: thissame point should be connec-ted to the central earth point onthe supply board via a shortlength of cable.The mother board should becompleted in the followingorder: resistors; capacitors;mechanical parts; semiconduc-tors. Make sure that non -insulated capacitors (if at allused) can not touch the screen-ing at the top. Do not usesockets for the ICs.At the front of the board, threesupply rails have to be pro-vided. To do this, first fit

soldering pins in all the holes;then cut narrow strips of brassor tin sheet, and solder these to

Parts list (Fig. 15)Components for one channelonly are given: the corre-sponding ones for the otherchannel (dashed 1'1 in thedrawings) are, of course,identical

Resistors (all metal film):

=2ORF

R2 =49R9F

R3= 100RF

RERs6=1KOF

Rs =49K9F

R6= 150RF

117;Fle=1K5F

R6:111D;R17=392RF

R12=348RF

R13 = 3K48F

R14 = 3K16F

flis=22KIFR16= 1K21F

R17 = 16R5F

R16;l141;R43=2K2F

R19 = 1210Rzo = 475KF

R21;Rsz=20KFF122;R23=15KF

R23 = 4K75F

R21= 3K92F

F12025;R17 =1MOF

Rzz = 475KF

Rte = 27K4F

R21= 182RF

R3D;R33;R31;R3E:R51;R33;1356;

R57 = IORJ

R31;1332= 22RJ

Ris=6K8JR46;1346;R61=10KF

R53 = 100KF

P1 = 10KJ log potentiometer(e.g. Bourns Electronics')

P2= 10KJ log stereo pot meter(e.g. Alps RKGA-2 10k AX2-I

Capacitors:

C1 = 220pJ polystyreneC2;C3= 100pJ polystyreneC1= 47pJ polystyreneCs;CEC12;C14-,C42=100,1 MKT

Cr.CtEC41=4u7J MKPCs = 10rrOJ polystyrene

CEC1, =330nOF polystyrene

Cio=lnOFCis =24r2J MKP

CIECI7=470nJ MKT

C16= 10014M;3 V: tantalum

electrolytic

C16;C21:C22;C2s;C2s;C3l;C32:

C12;C4r,C46;C.42=220nJ MKT

C2D;C26;C3o= 100i4M; 25 V

C23;C21;C27;C26;C11:C15:C15;

C14 = 10000M; 25 V

C3I = 100nJ MKTC66;Cs1;Cs2;Css:Cs4;Cts=22n0K

ceramic

Semiconductors:

D7=1N4148Ds= LED redT,:T2;T3= MAT -02

T1= 2N2291

1C1;IC2;IC4;ICs =0P-27'IC3= LF411

Miscellaneous:

S, =2 -pole DIP switchS2=8 -pole DIP switchS3 = SPST miniature

ReG =sub -miniature PCB mountingrelay; 2 -pole change -over 12 Vle.g. Meisei M1-12 or M1B12H;

Siemens W11V23102-A0006-A111- -; Omron G2V-2;SDS DS2E-M-121*

16 saver- or gold-plated phonochassis sockets

PCB 86111.3

'Distributors in UK:Cambridge: HiTek; telephone

10223i213333

Sevenoaks: Jermyn Distribution;telephone 107321 450144

Harlow: STC ElectronicServices; telephone (0279)26777

Armon Electronics; telephone01-902 4321

- Efectrovalue; telephone(0784) 33603 or 061-432 4945

*May also be available fromElectromail; telephone

10536/ 204555General note: many special audio

components are available fromSage Audio, Bingley, WestYorkshire, telephone 102741

568647

or fromKord Audio Products. The Green,Nettleham, Lincoln, telephone:(05221 750702

Fig. 13. The mains transformer must be housed in a separatemetal case.

Fig. 14. Illustrating the three supply rails on the mother board.

EE

January 1987

15

Fig. 15. The mother board.

EE

January 1987

16

Fig. 16. The foils for the front and rear panels.

Fig. 17. Template for drilling the tront and rear panels.

the pins a few millimetresabove the board (see Fig. 14).Next, all connecting pointsshould be fitted with solderingpins. At this stage, only thepin for the earth connection tothe supply board should besoldered to the screening layerat the top of the mother board.Finally, the board is cleaned,and its track side insulated withplastic spray, in the same man-ner as the bus board.

The mother board can then bemounted in the enclosure. Allconnections to switches andpotentiometers can then bemade, as can those between themother and bus boards (at theright of the motherboard at theline section). Screened cable isnot necessary for the latter, asthese connections are only afew centimetres long.Next, the connections betweenthe supply and mother boards

are made.The switching connections tothe bus board may be madefrom flat cable terminated atboth ends into a plug to matewith the corresponding socketson the boards. It should benoted that socket K, on thebus board is fitted 180° differ-ent from the position shownin Fig. 4 on page 43 in theNovember issue of EE. In re-ality, pin 1 is located where

pin 10 is shown.Finally, the connections be-tween the MC -MD sockets andthe associated inputs at themother board, and those be-tween the MC -MD amplifieroutput on the mother board andthe bus board should be made.These should be in good -qual-ity screened audio cable orflexible coaxial cable (TV type).When all connections are madeand checked, the mains may be

EE

January 198734

Table 3

Technical specification

Input sensitivityPhono: MC (low)

MC (high)MD (low)MD (high)

Tape, tuner, auxCD

0.1 mV into 47K0.2 mV into 47K2 mV into 47K4 mV into 47K200 mV into 45K400 mV into 20K

Maximum input voltage at 1 kHzInput -line out:Phono: MC (low) 1 mV

MC (high) 2 mVMD (low) 20 mVMD (high) 40 mV

Tape, tuner, aux 2 VCD 4 V

Input -tape out:Phono: MC (low)

MC (high)MD (low)MD (high)

6 mV12 mV

120 mV240 mV

IEC (RIAA) correction±0.2 dB over the frequency range of 20 Hz to 20 kHz. Standardinput impedance: 47K; standard input capacitance: 50 pF. Valuescan be preset from 1OR to 47K and from 50 pF to 500 pF.

Output (line out)Nominal output voltageMaximum output voltageOutput impedanceMaximum output current

Third -harmonic distortion(at 1 kHz)

1.2 V10 V<100R20 mA

output voltage 100 mV 1.2 V 10 VPhono: MC (low) <0.1% <0.01% <0.02%

MC (high) <0.05% <0.01% <0.02%MD (low) <0.01% <0.005% <0.02%MD (high) <0.01% <0.005% <0.02%

Tape, tuner. aux <0.005% <0.005% <0.02%CD <0.005% <0.005% <0.02%

lover range 20 Hz to 20 kHz and output voltage of 1.2 V)Phono: MC <0.02%

MD <0.01%Tape, tuner, aux <0.008%CD <0.008%

Intermodulation distortion(60 Hz: 7 kHz; 4:1; SMPTE)Tape, tuner, aux, CD <0.003%

Signal-to-noise ratio(inputs short-circuited; output 1.2 VIPhono: MC (low) >70 dB

MC (high) >76 dBMD (low)MD (high)

Tape, tuner, auxCD

Line amplifier(terminated into 47K)Frequency range

Phase charac-teristic

Cross -talk (at 10 kHz)line inputs (L--11)L/R to other inputs

Slew rate

>86 dB>92 dB>105 dB>105 dB

10 Hz - 50 kHz ( +0.1 dB)1.5 Hz - 500 kHz (-3 dB)

< + 0.5° 115 Hz - 120 kHz)

< -70 dB<-80 dB>4 V/ps

18

pulse generator

1 VPP

50Hz

to differenceinput ofoscilloscope

test -C 1 mV/div

1k

25k

86111.18

Fig. 18. Circuit for making comparative measurements of differ-ent types of capacitor.

switched on. Adjust Pi and P2 toobtain exactly +18.5 V op thesupply rails on the motherboard.Next, measure the directvoltage at the output (pin 6) ofthe LF411 (IC3); this should notbe more negative than -14 V. Ifit is, lower the value of Ills tillthe reading is -14 V. Thisvoltage depends to a large ex-tent on what of input tran-sistors is used; normally. R15need not be altered from the

stated value. As a safety check,measure the direct voltage atthe output (pin 6) of IC2: thisshould be not more than 5 mV,and preferably 0 V.The preamplifier should amplymeet the specifications givenearlier, which are minimumvalues. The prototypes ex-ceeded the figures given inalmost all cases: for instance,distortion measurements gavevalues that were only about halfthe figures stated. 14

EE

January 1987

Table 4

Capacitors: myths and realitiesCapacitors come in all shapes, sizes, and qualities. Until not all that long ago, many types of capacitor had never been seriouslyassessed as to their behaviour in audio circuits. Today, the pendulum has swung to the other side: among many audiophiles thereis a manic obsession with certain types of capacitor.

Serious research started in the USA in the late seventies, and in 1980 Walter Jung and Richard Marsh published a detailed accountin the influential magazine AUDIO of their findings as to the behaviour of virtually all types of capacitor in audio circuits. Thecapacitors specified for the present preamplifier were selected on the basis of that article and on the research in our own labora-tories.

Of the many types of capacitor on the market, the most important for audio applications are, in order of merit:polytetrafluoroethene (PTFE; Teflon; Fluon);polystyrene;metallized polypropylene;polypropylene;metallized polycarbonate;polycarbonate;metallized polyethene;polyethene;mica;glass;electrolytic.Electrolytic capacitors may be sub -divided into:bipolar;solid (aluminium);dry (aluminium);wet (aluminium);tantalum.The research in our own laboratory consisted, among others, of measuring the distortion when the various types of capacitor wereconnected in the (audio) signal path. The results were, to say the least, surprising. Although our distortion measuring equipmenthas a lower limit of 0.005%, only the electrolytic capacitors gave clear readings over the audio range up to 50 kHz. Not listed here,but tested none the less, were ceramic capacitors. Not surprisingly, these were found to be totally unsuitable for use in audiocircuits.

Jung and Curl devised a fairly simple method for the measuring of, among others, the dissipation factor and the dielectric absorp-tion under dynamic conditions. The relevant test circuit is shown in Fig. 18. The two RC circuits are provided with a rectangularpulse from a low -impedance source. The output signals are applied to a sensitive oscilloscope, where one is subtracted from theother. The result is a measure of the difference between the two RC circuits. If one of the circuits uses a high -quality capacitor,such as a PTFE or a polystyrene type, the performance of the other can be assessed with reference to it. The 100R potentiometerserves to compensate for the equivalent series resistance of the reference capacitor it is assumed that this capacitor always hasthe lower series resistance. The frequency of the input signal must be fairly low to obtain a readily visible difference on the oscillo-scope, and is normally about 50 Hz.

In our research, the reference capacitor was a metallized polypropylene type, because PTFE and polystyrene models are availablein fairly low values only, and this would make testing of high -value capacitors impossible. The percentages quoted below indicatethe deviation caused by the relevant capacitor with respect to the absolute value of the input pulse. The main differences betweenvarious types of capacitor are a non-linear performance during the positive part of the pulse, and an incorrect following of thevoltage jump. All metallized polypropylene (=MKP), polypropylene, and polystyrene (styroflex) capacitors showed a deviation of not greater

than 0.01%. The popular metallized polytherephthalate (=MKT) capacitors, as well as metallized polycarbonate (=MKC)and polycarbonate

types gave average deviations of 0.03%. Aluminium as well as tantalum electrolytic capacitors caused deviations in all cases of not smaller than 1%: in some instances

well above this figure.Parallel combinations of capacitors have a dynamic behaviour that is never better than that of the poorer of the two.

In 1987The analogue chip now beingdeveloped by Micro -Linear ofCalifornia may come to com-mercial fruition. It is envisagedthat this chip will be able to per-form up to four fifths of alltypical analogue functions.DATAQUEST reckons that theanalogue chip market may beworth close to £2 billion in five

years' time.There will be an acceleratingshift towards bipolar IC tech-nology with STC Semiconduc-tor in the forefront.An increasing number of newand faster gallium arsenide -GaAs -microprocessors willcome onto the market. Therecently announced VitesseElectronics Type VE29G01, for

instance, performs a 4 -bit addoperation in 15 ns, which isalmost three times as fast asavailable silicon or GaAs de-vices.There is likely to be a tremen-dous increase in the use of sur-face mount components: someobservers expect a fivefold in-crease in the market by 1991.Texas Instruments already has

90% of its eligible componentsavailable in SM; Motorola has50%, but is working hardtowards 100%; and NationalSemiconductor hopes to havemost of its component typesconverted during the first fewmonths of the year.

EE

J.,97 -u3:-. 1987 36

NEW LITERATURE NEW LITERATURE

IntegratedCircuits andMicropro-cessorsby R C HollandISBN 0 08 033470 9 (soft cover);0 08 033471 7 (hardback)Price: £18.00 (hardback); £9.00(flexicover)200 pages - 227x148 mmThis book is a concise learningpackage describing all themajor IC types and their appli-cations. It describes the threemain categories of ICs-digitalcircuits; analogue circuits;microprocessors and their sup-port chips-as well as miscel-laneous devices. Most otherbooks on electronics tend todescribe just one of thesecategories, and the presentwork is therefore welcome in itsattempt to assemble all essen-tial information to give thereader a reference for all typesof ICs.The book also includes a rigor-ous analysis of faultfinding pro-cedures in modern electronicsystems, as well as a number ofexercises (with answers), usefulappendices, and a glossary ofterms commonly used in elec-tronics.The book is aimed at the elec-tronics student or practisingengineer who has a rudimen-tary knowledge of electricaland electronic principles. Itsupports the principal elec-tronic and microcomputermodules of most courses inelectronic engineering.

Pergamon Press LtdHeadington Hill HallOxford OX3 OBW

ProbabilitySignals, Noiseby Jacques DuprazISBN 0 946536 70 8Price: £40.00 (hardback)344 pages - 234x156 mmThis new book, ably translatedby A Howie, provides a com-prehensive and coherent treat-

ment of signal theory andprobability in engineering. Itsrigorous approach will make itan invaluable working tool forall those interested in telecom-munications and informationtheory,.Suitable as a course text, thebook takes the student from thefairly standard concept of a ran-dom variable through to themore sophisticated ideas of ran-dom vectors and signals, whilstcovering the fundamentals ofprobability theory,.The author avoids abstractmathematical references andfocuses on practical appli-cations. Numerous exercisesand examples will enable thereader to assimilate the con-tents of the book and solve theproblems which face him.Jacques Dupraz is a lecturerin communications theory atthe Ecole Superieure d'Elec-tricite in Paris and at the EcoleNationale Superieure de l'Aero-nautique et de l'Espace inToulouse. He also managesthe Communications SystemsGroup of CIT ALCATEL.

North Oxford Academic120 Pentonville RoadLondon Ni 9JN

SuppressionComponents,Filters, andScreening forEMCERA Report No. 86-0006This report contains the pro-ceedings of a seminar and exhi-bition held by ERA Technologyin February last year at theHeathrow Penta Hotel.The subject of the seminar waschosen because of the rapid in-crease in the use of electronicsystems in all forms of equip-ment. This had led to many newproblems in screening or sup-pressing electromagnetic emis-sions and hence preventingelectromagnetic interference.The relevance of this topic wasdemonstrated by the interest inthe seminar which attracted

nearly 200 delegates and in-cluded an exhibition areawhere 26 manufacturers dis-played related equipment, sup-pression devices, and services.This report is essential readingfor all those involved in theseeking of solutions to prob-lems associated with elec-tromagnetic interference. Suchinterference was once causedmainly by household ap-pliances and electrical equip-ment, but today there are manymore sources, such as controlunits and digital and comput-ing equipment. Moreover, ap-pliances have become smallerand are often enclosed in plas-tic cases with minimal screen-ing and earth reference planesare often hard to find.The report is available at £45to members and £50 to non-members from

ERA Technology LimitedCleeve RoadLeatherheadSurrey KT22 7SA

Computers inSystems forMeasurementand Controlby Dag BjorklofISBN 91 7810 553 6Price: £17.50 (soft cover)286 pages - 237 x172 mmThis is a very welcome, pro-fessional book dealing withcomputerized systems formeasurement, analysis, andcontrol. It is of particular in-terest to the reader who, with-out being a computer expert,wants to understand and effec-tively use a personal computerin technical applications. It isintended to serve as an infor-mation guideline for engineersas well as a complete textbookfor technical students.Computers in systems (286pages) covers the followingareas:* Computers and their role in

technical 'systems* Instrumentation and system

techniques

* Computer interfacing andcommunication

* Digitizing measurement sig-nals

* I/O management by com-puters

* Basic -programming formeasurement, analysis and

control* GPIB - the instrument bus

(IEEE 488/IEC 625) and itscontrol by means of various per-sonal computersGeneral hardware and softwareproblems associated with dif-ferent types of controllers areput in their right light andtreated with emphasis on inter-facing and programming of per-sonal computers. The bookcontains numerous pedagogicand relevant short programexamples on the Basic -level.The author, Dag Bjorklof, is as-sociate professor and head ofthe Instrumentation Laboratoryat KTH, the Royal Institute ofTechnology in Stockholm,Sweden. He is an expert in ap-plied measurement techniquesand has a broad experiencefrom various international en-gagements.

Daxab ElectronicsBox 102S-181 22 LidingoSweden

NewTechnology inElectricalServicesby Dr Noel Meeke andLynn SteerGloucestershire College ofArts and TechnologyISBN 0 582 002184 4Price: £3.5064 pages - 297x205 mmThis report is the outcome of aproject carried out by a teamfrom the Gloucestershire Col-lege of Arts and Technology.The project was commissionedby the Further Education Unit-FEU-on behalf of the Depart-ment of Education and Science-DES-PICKUP programme.The report says that a hard look

WEEJanuary 1987

NEW LITERATURE NEW LITERATURE

needs to be taken at the currenttraining of electricians who in-stall and maintain new tech-nology equipment. It also main-tains that the various organiz-ations and examining bodies in-volved with both initial trainingand updating courses need totake urgent account of the extrademands being made on theelectrical contracting and ser-vices industry because of newtechnology.Surveys conducted both locallyand nationally showed that,where new technology is con-cerned, the main areas of in-volvement are lighting control,energy conservation, and in-truder and fire alarm systems incommercial, industrial, anddomestic premises.Since the number of systemswith which the electrician islikely to come into contact isalready large, and still growing,a study of them in only a shortperiod of time would only leadto surface knowledge. Theauthors therefore suggest, andgive examples of, a bank of ob-jectives which could be usedselectively.The report is essential readingfor anyone involved with thetraining, be it initial or up-dating, of electricians.

Longman Resources UnitFREEPOSTYork YOl 1TU

NewCataloguesNote that catalogues listed heremay not be free of charge,although many of them are.Furthermore, not all businesses

publishing a catalogue areprepared to accept orders fromother than professional or tradecustomers.

There are two new cataloguesfrom Cirldt: the electronic con-structor's catalogue (Winter1986: £1.20) and the 1st edition ofthe Components Catalogue.They are available from

Cirkit Holdings PLCPark LaneBroxbourneHerts ENIO 7NQTelephone: (0992) 444111

Electrovalue's latest cataloguehas 56 pages crammed withthousands of items needed byhome constructors, ex-perimenters, manufacturers,laboratories, educational in-stitutes, and many others.Very many items are by Siemenswith whom Electrovalue enjoypreferential delivery arrange-ments: an important aspectwhen special items are re-quired urgently.Purchases may be made at oneof the Electrovalue shops inEgham or Manchester, or bymail, a service with which thecompany established itselfmore than 25 years ago.The needs of industrial andother large-scale users forwhom competitive quotationsand delivery times are often ofparamount importance aredealt with separately.

Electrovalue Ltd28 St Judes RoadEnglefield GreenEghamSurrey TW20 ORBTelephone: (0784) 33603

Or

Electrovalue Ltd680 Burnage LaneManchester M19 1NATelephone: 061-432 4945

The 1987 Greenweld catalogue,packed full of componentsand equipment at low prices,should be part of the cataloguecollection of anyone interestedin electronics.New items of test equipment in-clude power supplies; oscillo-scopes; frequency counters;CB testers; while the range oftelephones and accessories hasbeen greatly expanded.There are numerous pricereductions to give the construc-tor a better deal. A by -returnpostal service is offered for allex -stock parts.Also included is Bargain List 26:nine pages of surplus bargainsfrom component packs to key-boards.But the main attraction of thecatalogue must be the offer of3 days hotel accommodationFREE! Two vouchers are givenfor orders over £200 and twovouchers are to be won everymonth in a draw open to allcustomers spending over £10!The catalogue is available at£1.00 post paid from

Greenweld Electronics Ltd443 Millbrook RoadSouthampton SOl OHXTelephone: (0703) 772501/783740

INMOS's The Memory Spec-trum, detailing the company'srange of Static and DynamicRAMs, is available from

Rapid SiliconRapid HouseDenmark StreetHigh Wycombe HP11 2ERTelephone: (0494) 26271orRapid Silicon28 High StreetNantwichCheshire CW5 5AATelephone: (0270) 627505

The Winter 1986-87 catalogueof West Hyde, the electronicenclosure specialists, offers104 pages of details on all exist-ing ranges of enclosures. Alsoincluded are several new prod-ucts, among which the award -winning Internorm 19 -inch rackcase, and many new ranges ofplastic cases for desk, work-bench. or hand-held use.There are also new handles,bezel LEDs, and cases for com-puters and keyboards. All thesetop quality cases and ac-cessories are competitivelypriced.The catalogue comes with twovouchers, making it even bettervalue for money. Each vouchercan be used to obtain a £1 dis-count on an order worth £10 ormore.To obtain the catalogue send acheque or PO for £2 to the ad-dress below. Credit card ordersare also accepted by post ortelephone.

West Hyde Developments Ltd9-10 Park StreetIndustrial EstateAylesburyBucks HP20 lETTelephone: (0296) 20441

CORRECTIONSElectronic balance(December 1986-p. 34 ff.)Two pages in this article were inad-vertedly interchanged at the printer's.The correct order is p. 34-36-37-35.

True-RMS meter(December 1986-p. 45)In the circuit diagram, Fig. 7, the 101)ndecoupling capacitor at pin 3 of IC4 must

be C11. Constructors wishing to make

their own PCB should note that thecomponent side layout, shown in Fig. 8and on p. 71, must be processed withreversing film prior to etching.

EE

January 1987 38

UNIVERSAL CONTROLFOR STEPPER MOTORS

With good quality stepper motors widely available at reasonablecost, this flexible, computer -driven, control board will make it

rather hard to hold on to the belief that stepper motors are theexclusive realm of industrial electronics. If you are suspicious

about "universal", just glance at the speficications Table below; ifyou are into industrial electronics, well...

Stepper motors come in an as-tounding variety of types andsizes, and they are frequentlyspotted items in electronicsurplus stores and on hobbyvenues. Sheer curiosity hasprompted many a home con-structor to purchase one at afraction of its original price.However the number of wirescoming from the device, andthe fact that it is often found farmore difficult to get going thana simple servo motor, moreoften than not causes the per-plexed owner to carefully puthis price possession in thejunkbox, together with other"possibly useful" materials.In Stepping Motors, ElektorElectronics April 1985, thegeneral methods were exam-ined for the the driving of step-per motors. Also that articleprovides a useful discussion ofstepper motor terminology,used further on in this article.The main specifications of theproposed control board aresummarized in the shadedTable on this page. The board isreadily tailored to suit the user'srequirement, but it should bemade quite clear at the onsetthat each of the following sec-tions is to be read closely to beable to decide on the mostfavourable circuit configurationfor a specific application. A de-tailed discussion of each of thetechnical features is, therefore,indispensable to a good under-standing of the operation of thisfully user -configurable inter-face board between computerand, for instance, robot limbs, apantograph, or a plotter.

Technical specification

Drive capacityfor motor types:

Max. outputcurrent:

one 4 -phase bipolar type;two 2 -phase bipolar type;one 8 -phase unipolar type;two 4 -phase unipolar type.

L293E fitted: 1 A; phase.L298 fitted: 2 A; phase.Software -controlled polarityand 32 -step current flowdefinition.

Driver type: Switch -mode current sources.

Digital 110:

Supply:

8 -bit data input and 2 -bithandshaking to Centronicsstandard.

10...35 V with L293E fitted.10...45 V with 1298 fitted.Regulation not required.

Stepper motors:some problemsThe following is a necessarilybrief discussion of the main dif-ficulties to be overcome whenusing stepper motors.Limited speed range: the statorwindings constitute an induc-tive load, which limits the com-mutation the coilcurrent. Also, the revolving,permanent magnet rotor causesan inductive voltage whichfurther worsens the commuta-tion. These effects limit themaximum attainable step rate(also: pull-out rate), but can beovercome by utilising currentdrive control.Resonance: the undampedcharacter of a stepper motoroperating at a relatively lowstep rate causes its movementto be rather halting. The upperoscilloscope trace in Fig. 1shows the considerable over-shoot after each step. Shouldthe step frequency equal that ofthe underdamped oscillations,resonance inevitably occurs,causing a powerful, jerky move-ment of the spindle. Mechan-ical damping devices havebeen developed to ensure asmoother spindle movement,but these permanent loadstypically cause the already lowefficiency of the stepper motorto fall below the acceptablelevel.The lower oscilloscope traceshown in Fig. 1 providesevidence for the propositionthat micro -step operation canprovide a marked improvementin linear spindle movement,

1

- to

Fig. 1. Comparison between normal (upper curve) and micro -step(lower curve) operation of a stepper motor below its resonancefrequency. Overshoot is largely ruled out by the latter mode.

thus enabling the direct transferof motor power via a set ofgears.Low efficiency: an energizedstepper motor dissipates anamount of energy in the re-sistive load formed by its statorwindings. When the spindle isheld stationary, this resistanceis the sole current limiting fac-tor; also the stall torque is oftenneedlessly high. Current drivesystems may enhance the dy-namic characteristic of the step-per motor to some degree, butlinearly controlled currentsources, unfortunately, exhibit avery low efficiency.The present design is based onthe use of high efficiency,switch -mode current sources,thereby going round the prob-

2

esC

.c

data

addressdecoder

referencevoltage

latch

40kHzosc.

5V 14_logic

supply

latch

D/A

H. sync

PWM

mainpowersupply

V

DRIVER

enable

ense

latch

D/A

ync

PWM

DRIVER

- enable

ense

latch

D/A

sync

PWM

4, 4,

DRIVER

enable

sense

D/A

syncPWM

DRIVER

enable

sense

87O03-2

Fig. 2. Block diagram of the stepper motor control board.

39 EE

January 1987

lems associated with thepreviously mentioned systems.Also, the proposed currentdriver has the advantage of be-ing uncritical of its input supplyvoltage; extensive regulationand smoothing circuits are,therefore, not required-an im-portant fact in view of the poss-ibly high currents involved inoperating the stepper motor. Asthe current through the wind-ings is fully programmable, theuser can arrange for the overalldissipation of the stalled motorto be significantly reduced.Limited resolution: steppermotors are classified accordingto the number of steps perspindle revolution. Using themicro -step mode, this specifi-cation becomes less important,and a specific type of motorcan, therefore, be tailored farbetter to the task it is to per-form.

Block diagramAfter these preliminary con-siderations, it is time to have alook at the block diagram of thestepper motor control board-see Fig. 2. This design is inessence a quad bipolar powerdriver. Each driver consists of abridge circuit and can supplyboth negative and positive out-put current from a singlesupply. Starting at the inputside, it is seen that each drivercomprises a latch and a D/Aconverter to enable program-ming the level and the polarityof the current fed to each in-dividual stator in the steppermotor.The switch -mode currentsources are essentially voltage -controlled pulsewidth modu-lators (PWMs), driven with thedifference between the objectamount of stator current and theactually measured current.These two values are obtainedfrom the D/A converter and aDC current sense amplifier, re-spectively. The four drivingPWMs are synchronized via acommon 40 kHz oscillator sig-nal, which ensures a favour-able switching frequency-theswitch losses are still accept-able, and the signal is inaud-ible-as well as the absence ofbeat signals.At the top of the block diagram,there are some more circuitfunctions common to the fourdrivers. An address decoderuses the two MS (most signifi-cant) bits to discriminate be-

EE

January 198740

3

L298

*sea 121

al:

A

A LM336

12_35(45)VK1 0

.57

DID2

Di

D5

06

37E

019

0 "200

0 2

R2

5V

0

0

1.44

6

o

.0 SO

12

4

N 1_116 = ICS = 4069; 74HCT04A 1...A4 = IC15 = LM324AS...A8 = IC16 = L M324MMV 1. MMV2 = IC17 = 11E556MMV3. MMV4 = IC 18 = 818556

106 = 45.56;74HCT3910 = 40174; 74HCT174

a.a.

DS II

04 5

03 13

02 14

01 3DO

7.

DO 4

DS OS

04 0403 0-02 IC7 0201 01

DO GO

CIA

R26

ETA Al

3

12

15

5

2

1

DI 3

L4/03 13

DS 605 II

De 2

07

as'

DI 01

D2ica

0203

04 01

CS 050-

SV

IC11

ZN436/ZN426

Ref

4

51

5 12

12 2

EI

AD 1/2 CO:1

Al 106 Cs03 :71

0 a b

U1

0OC

93

U2si t3

L293 E

12-35(45)V91 *

0 INN

0

00

C5

2t2

4

/ 05 11

/;104:2'03/ 02DI

NCO

,47.01

/,02703

405

0.05

0413 a,14 IC9

3 DI4

C5

04

03

2001

7

Ref in

4

*IC12

711436/ZN426

SI 101 11

630

A2

Ca

417

417

12

53A3

R31

EMI

5V RIO C12

O EIM1316

251

Ins

3

40

ScMMV1 0

6

614

R6

rn

1111114

15

813

11 14MV2

5V

019

2V1

O ons5V

C13

1nS

7

LM336017*

R27

2 PiaMEI

673

0673 R35

12

55

2

513

12

14

13

6

5V

0-9

0: 1C37805

a.0. 02

Dt 01

03

02" IC1004GS GS

CLR

2

15

12

13

*IC13

ZN436/ZN426

F-4(

1125

SV

CIA

632

A6

12 2

7

10

119f in

IC14Ref111

ZN436/ZN426

.121

.o

417

4n7

C11

d 13A7

R33

t14

ets4 A

V

4 13

03

Es

02

01

* 04ICI

L298

T',se217

RI

ENEA4

R23

EOM

R7

R19

MEM

2

12...45V ,..k(L298)

0

02 D1

Dt D313

0A

3

06 A 05

oa 7

3

DI 138 = BYV27

5V

O

R24 R20

5V R12

O um020

251

Cu

Ins

3

ii MMV3 0T

6

R16

fla

KM:I

815

a

sense 1

Vs

qa

5

13c

11

ft MMV4 0

5V

9

20

II

13 12

D21

R13 275

O UMC15

5V MS

O 0 0 0 0 0C20 IC7 IC 11

ci ICS ica 1c15 IC 17C2

ICIO IC'14 IC16 1C1822y ACV 8.

100n O 0 a 0 0 0MEN

N6

0220.1

3

* 1,`,... 1C2'

E1Ez

02

01 112

set e 2

R eIC4

(7)555

7

2

65

C6

13n It-

12...35V;taa(L293E)

0

3

010 D9

1312 D11

13

to

014 A 013

016 T 13/6

17

R9

R25 921

109.*

..016 = BYV27

57023-3

Circuit diagram of the universal control for stepper motors. The choice between the L293E and L298 motor driver is left to the user.

tween the control data sent toeach of the four driver circuits.Provision has been made to usehandshaking with the computerfor optimum reliability of the ofdata transfer to the board. A ref-erence voltage source makes itpassible to use D/A converterswithout an internal referencecircuit. Finally, a 5 V supplypowers all logic circuits on theboard.Depending on the applicationyou have in mind for the step-per motor control board, thisneed not incorporate all of thepreviously introduced circuits.For instance, the relatively ex-pensive D/A converters may beomitted if you do not envisageusing the micro -step facility, butwould still want to be able toprogram semi -step operation.The proposed board makes itpossible to drive a four -statorsystem, even with two separatetwo -stator motors. It is possibleto operate one motor in themicro -step mode, while theother one is controlled in thestandard way, i.e. by means of a"stripped down" driver circuit.The user is offered a choice oftwo possible types of driver IC,which can be fitted as requiredby the expected output current.As you can see, our use of theword "universal" in the title ofthe present article is fully justi-fied.

Circuit descriptionIt is not very difficult to spot thevarious functional blocks in thecircuit diagram, Fig. 3. As to theaforementioned common cir-cuits on the board, IC3 is the 5 Vregulator, ICI the 40 kHz oscil-lator, ICe the one -of -four driverdecoder, and zener diodes D17and D18 may be used to provideDACs IC, 1-IC14 with a highlystable 2.5 V reference.On receipt of a computer -gen-erated STB or STB (strobe)pulse, ICo decodes DO and Di inthe sent dataword and enablesthe corresponding sextuplelatch, IC7... IC10, to clock the6 -bit value which determinesthe output current level sup-plied by the driver (Do...D4) aswell as the polarity (Ds).Therefore, only five bits of thesix or eight -bit DACs are used totranslate the latch output into avoltage between 0 and 2.5 V in32 increments (25). Each of theDAC output voltages is used todrive the inverting (+) input ofopamps As, A3, A6 and A7. How

these in turn are capable ofdetermining the stator outputcurrent is detailed in the nextsection.Returning to the handshake cir-cuit composed of IC6, Ni andNz, it is seen that both positiveand negative -going strobepulses can be used by fittingthe appropriate wire jumper, a(STB) or b (STB). Note, however,that in many Z80 -based systemsS1B is an input signal. and RDY(ready) is an output signal, i.e.the signals are reversed as com-pared with the Centronics stan-dard. Jumper a is to be fittedwhen driving the stepper motorboard with either a Z80 PIO, or a6522 VIA. while jumper b ac-comodates the use of a Cen-tronics port. More informationon the handshaking circuit canbe found in Table 4, while Z80PIO users may consult MSX ex-tensions - 4, elsewhere in thisissue.

PWMs and currentdriveIn order to make clear the oper-ation of the switch -mode cur-

rent driver circuits in thisdesign, it is necessary to studyFig. 4. From a functional pointof view, the Types L298 andL293E from SGS Ates are largelyidentical; these devices merelydiffer in respect of the maxi-mum available output current.The L298 is twice as powerful asthe L2993E and is, therefore,housed in a Multiwatt' -15 SILenclosure, rather than a 20 -pinDIL package as is the L293E.Each IC holds two indepen-dently controllable bridge cir-cuits plus associated logicdrivers. Since these ICs are tobe driven with logic voltagesonly, there would seem to be noway of controlling the bridgecurrents with a linear regulatingsystem. However in each driverthe emitters of the lower bridgetransistors are brought out topins, enabling the connectionof an external current sense re-sistor which provides a voltagedrop proportional to the statorcurrent. Fig. 5 further illustratesthis principle, which forms thebasis of the negative feedbackcontrolled switch -mode currentdriver.

Any duty cycle of the currentdrive system starts with ICsgenerating a 1 ys negative resetpulse for all four monostablemultvibrators MMV,... MMV..Taking MMV, and the uppersection of IC, as an example,the reset pulse causes Cl2 to bedischarged to the zener voltageof D18. Simultaneously, MMV, istriggered, and provides an out-put period determined withnetwork Rio -C12 as well as theDC level applied to the controlvoltage input, pin 3. This level isinternally compared with thevoltage across Cl2 and hencedetermines the length of theoutput period. Since the com-parator internal to the Type 556MMV is incapable of linear op-eration with input control volt-ages below 1.5 V, D18 leavessufficient residual charge in Cl2for the MMV to produce suffi-ciently short output periods.From this it is seen that theMMVs in the circuit essentiallyfunction as voltage -controlledpulsewidth modulators, en-abling the power output stagescontained in IC, and IC2 for theduration of their output periods.

4

L293E

L298

°ss0

Iro

1112

0EnA0

o

OUTZ our]0

MITA,

2

6

_D3

;c

15

SENSE A 5EftSE 8 87003-4

Ina

0En111

0

Fig. 4. Internal organization of the SGS stepper motor drivers L293E and L298.

EE

January 198742

Therefore, current sense re-sistor R6 carries the stator cur-rent and hence produces aproportional voltage drop.which is averaged in networkCls-R14 and raised in amplifierAi.Opamp A2 compares themeasured current (- input)with the object current (+ in-put), and corrects its outputvoltage to MMV, until these twovalues equal. Simple as this mayseem at a first glance, there is,however, a snag in the measur-ing of the stator current. As longas the bridge is enabled, statorcurrent h flows through Rsense,and its voltage drop is simplyIsRsense volts-see Fig. 5, line a.The disabling of the bridge im-mediately breaks the currentthrough Rsense, but not thatthrough the stator winding,whose inductance causes itto supply a lagging current,which is driven into the supplyvia free -wheeling diodes-seeFig. 5, dashed line b. In es-sence, the self-inductanceof the stator winding has asmoothing effect upon thestator current. Therefore, theaverage value of URser.se is not adirect measure for the statorcurrent, since it does not com-prise the free -wheeling current.With most types of steppermotors, the period L/R of thestator winding is long as com-pared to that supplied by thePWM drivers (T=1/40 kHz =25 its). In practice, the variationin free -wheeling current in be-tween driver pulses hardlycauses any ripple, and the errorincurred by only measuring thecurrent through the sense re-sistor is, therefore, caused bythe duty factor variation. Ingeneral, a relatively small dutyfactor variation suffices to give aconsiderable stator currentspan. As soon as the duty factorrises above some 50%, and thefree -wheeling period starts tooverlap the bridge on -time, Isrises relatively quickly. The re-quired duty cycle giving maxi-mum stator current is a functionof the ohmic resistance of thestator winding and the supplyvoltage level. The higher thatvoltage, or the lower that resist-ance, the stronger the tendencyto large variations in Is around a50% duty factor.The foregoing considerationscan not but lead to the conclu-sion that the output signal of AIneed not be exactly pro-portional to the stator current.

Fig. 5. Current flow during the bridge -on period (a) and duringthe bridge -off period (b, free -wheeling operation).

Fortunately, the overall linearityis still acceptable, and occa-sional deviations can be com-pensated by suitable software.

Returning to the circuit dia-gram, Fig. 3, the remainder ofthe circuit functions are quiteconventional designs.Timer IC4 provides the nega-tive -going 40 kHz synchron-ization signal for the R and Tinputs of the MMVs. In theabsence of a common syncsignal, the input supply wouldbe corrupted by a good manyinductive voltage peaks, whichwould readily lead to the MMVsbeing triggered in error and theentire circuit operation beingupset in consequence.Network Ri-D22 prevents 5 Vregulator IC3 from being dam-aged by too high an input volt-age. As the maximum input volt-age for IC3 is 35 V, the use of theType L298 stepper motor driver(Vs(rnax)= 45 Vpeak) necessitates

fitting the voltage limiting net-work. But even with the L293Efitted in the circuit, it is still agood idea to use 121 and D22, asthey also afford protectionagainst inductive voltage peakson the unregulated supply rail.The use of the 2.5 V referencediodes D17 and D17' is notobligatory, and their use will bereverted to in the section onconstruction.The logic sections of the circuitare composed of CMOS ICsonly. This means that the logicdrive to the board must becapable of supplying CMOS-compatible signals. Should youwant to drive the board withTTL signals from a Centronicsport, the stated CMOS ICs mustbe replaced by the suggestedHCMOS versions.

ConstructionBefore embarking on the con-struction of the present board,

Parts list

Resistors (4-5%1:

RI= '''R2= 100K

132;Ris...R2, incl.= 10KR.= 18KRs= 1K0

R6_. _R9 intl.=R113...R13 incl. = 22K

R14...R17 incl. =8K2R22...R:s incl. =39KR25... R29 incl. =4K7R33. - .R33 incl. =470K

Ru;Rts= 3

Capacitors:

C1=22p; 40 VC2:C2= 1p; 6V3 tantalumCa:Cr =10nCs = 2n2

C6 = 1n0

incl.=4n7Cis incl. =1n5

Cie_. _Cis incl.= 120nCoa...Coo incl.= 100n

Semiconductors:

DI...DIs = BYV27 11N4001 alsousable with L293EI

D17 or D17.= LM336

Die...D2i =2V1; 0.4 Wzenerdiode

Dzi=IC1=1238 or ICI' = L293E(SGS Ates)

IC2= L298 or IC2' = L293EISGS Ates)

IC3 = 7805

ICA =555 or 7555

IC5=4069B or 74HCT04IC6=4556B or 74HCT139IC2...1Cm Inc -L=401748 or74HCT174

ICII...1Cta incl. =ZN436 orZN426 3

1C15:1C15=L14324

1C12:1C0=556 or 7556

Miscellaneous:

Ki= 20 -way angled plug for PCBedge mounting

K2= 64 -way a&c DINbusconnector lif required!

Heatsink for ICT;IC2 as requiredPCB Type 87003 (see ReadersServices)

Notes' See Table 1

'1 See Table 23 See Table 3

' Available from Universal Semi-conductor Devices

17 Granville Court GranvilleRoad Hornsey London

N4 4EP. Telephone: 101 348)

9420/9425 Telex: 25157usdco g.

EE

January 1987

Table 1.Input supply JVJ

<25 25-30 30-35 35-40 >40

Output driveris RI Dz2 RI 022 RI D22 RI D22 RI On

1 x L298

2 .. L298

1 x L293E

2 x L293E

L298 Et L293E

1 220R I- 330R 115 V 330R 15 V 330R I 22 V

1(}0R 1 - 18OR 115 V 220R' i 22 V 330R` 122 V

100R - 180RIi 15 V 2

47R' - 47R I -100R 10013"

1 lit = wire link; do not fit Dn.2 With only one L293E fitted, supply must not exceed 36 V.- Do not fit. 4 W type, else 1 W.

the type and the number ofstepper motors must be con-sidered in order to be able todecide on the most favourableas well as the most economicalrealization of the circuit.To begin with, there are theL293E and the L298 to choosebetween. The latter should beused with currents in in excessof 1 A per phase. Two L298s canbe bolted onto a common heat -sink, together with regulatorIC3. As all conductive surfacesof these ICs are at ground po-tential, there is no need for in-sulating washers and the like.Relatively low ouput currentscan be handled by the more

motor current is fully program-mable, but in order to attain op-timum resolution in the micro -step mode, the maximum valueof Is must be defined by meansof selecting appropriate re-sistors in the R6 and R9, as wellas in the R22...R25 positions-consult Table 2. As 16-41712X) isalso related to the self-induct-ance of the windings, it is ad-visable to actually measure thecurrent consumption of themotor.The +5 V supply rail is madeavailable at a separate pin of theI/O connector. When feedingthe stepper control board froman external 5 V supply, omit R,,

economic Type L293E, whichcan be fitted in the ICI' andIC2' positions on the PCB. InMost cases, the copper surfacesoldered to pins 5, 6, 15 and 16of these chips provides suf-ficient cooling, while IC3 is bestfitted with an insulated, stan-dard U-shaped vane radiator.Should you decide to use a L298for two stator windings. and aL293E for the other two, do notforget to limit the input voltagein accordance with the maxi-mum specification of the latter.Depending on the type of out-put driver fitted, dimension Rias per Table 1.As already stated, the stepper

0 0 0 00 0IC 2

0 0 0 0 0CIB0 0 0

E°C'15

J43141H

i37

Table 2.

stator Rsv-se at Vs -

current <22 V >22 V 12,

0.1 A 5R6 6R8 , a W

0.2 A 2R7 3R3 14 W

0.5 A IRO 1R2 ',4 W

1.0 A R47 R33 1 W

1.5 A R33 R39 1 W

2.0 A R27 R33 1 W

D22 and IC3. then fit a wire linkin the holes provided for thetwo outer pins of the regulator.As to the D/A converters, thereare a number of types to choosefrom. In principle, the TypeZN436E gives satisfactory per-formance for most applications.Note, however, that it comeswithout an internal reference,so that D17 (117') must be fitted,and Rs must be a 1K2 type,while R9 must be omitted-consult Table 3. Jumpers cand d are not used, and jumpere is fitted to pass the refer-ence voltage to the REF IN pinsof 1C13 and IC14. The TypeZN426-x (the suffix indicates the

Fig. 6. Track layout and component mounting plan for the motor control board.

EE

January 198744

Table 3.

DiA converter jumper

ICI, IC14 c d e R34 R35 D17

ZN436 ZN436 - - x 1K2 - I LM336ZN4261x - x 390R i - -ZN426 - x x

1- 139OR I -ZN426 ZN426 x x - 390R 1390R -I

- Don't care- Do not fit.x must be fitted.

number of bits: 6, 7, or 8) isalso usable but is expected tobe somewhat more expensive,as it holds an internal referencecircuit, which can be used byfitting jumper c or d. depend-ing on the position of the DACon the board, and using a390R resistor in the Ra or Raposition, whichever is appro-priate. Should you want to dowithout the micro -step facilityaltogether, mount two 10K re-sistors as shown in Fig. 7. Com-pleting the stepper motor con-trol board is very straightfor-ward indeed when using ready-made, through -plated PCBType 87003 (see Fig. 6) availablefrom our Readers Services.When using the L293E driverchip, solder it straight ontothe board to effect sufficientcooling by the large coppersurfaces at the track side of thePCB.

ConnectionsIn general, the connection ofbipolar stepper motors is fairlysimple. A two-phase motor re-quires to be driven with onehalf of the control board cir-

cuitry. The actual connection ofthe stator windings is largelyuncritical. Reversing the po-larity of one stator winding, orinterchanging both windingssimply causes the motor to runin reverse. A bipolar four -phasemotor requires to be drivenwith the whole of the controlboard. When using such amotor, observe the correctphase relationship between thestator windings, else thespindle will merely oscillate be-tween two positions, rather thanrevolve.Basically, unipolar motors canbe connected in three ways,as shown in Fig. 8. The firstmethod, shown in Fig. 8a, re-quires passing less than normalcurrent through the series con-nected windings to precludeoverheating and/or saturationeffects in the stator. Also, theincreased stator inductancecauses a considerably lowerpull -in rate.The second method involvescreating a centre -tapped wind-ing-see Fig. 8b. In principle,this arrangement always resultsin one half of the winding beingshort-circuited to the positive

Fig. 8. Basic methods for the connection of unipolar motors.

Fig. 7. Where micro -step operation is not required, each of theDACs in the circuit may be replaced by this resistor combination.

supply rail. As compared withthe above method, there is theadvantage of the lower overallinductance, but the short-cir-cuited half -winding gives rise toan increased motor dissipation,owing to the inevitably high in-duced current, which is onlyadvantageous in that it ensuresgood damping characteristicsand hence a relatively smoothspindle movement.The last alternative is shown inFig. 8c. This method of connect-ing a unipolar motor is basedupon the use of the individualwindings as if these were of thebipolar type. In case the twowindings of a stator are not con-nected internal to the motor,anti -parallel connection is pref-erable. A normal, parallel con-nection immediately results inthe magnetic fields counterac-ting, causing the spindle to re-main stalled.Provision has been made on thePCB to fit a 64 -way, a & c rowbusconnector, K2. Its connec-tions are left vacant to enableusers to configure the bus wir-ing as required. At the otherside of the board is Ri, a 20 -wayangled plug which is used for

the Centronics signals. De-pending on the set-up of thecomputer system in which thepresent board is to be incor-porated, wires may have to berun from K2 to K1, or K2 may beused for mechanical supportonly. Those users intending tomake a stand-alone peripheraldevice of the stepper motorcontrol may want to cut off thePCB section provided for 1C2altogether.

The power supplyAs already stated, the presentboard is rather uncritical of itsinput supply voltage. Extensiveregulation and smoothing of the12...35 (45) V input rail is notrecommended in view of theoverall system efficiency. Whendesigning the power supply inquestion, merely observe thatthe ripple voltage does not ex-ceed 10 to 15% of the outputvoltage.It must be reiterated that themaximum permissible peak in-put voltage for the baord de-pends on the type of bridgedriver IC fitted; for the L298,Vm= 45 Vceak; for the L293E,Vi=36 Weak. In practice, it isrecommended to keep the in-put voltage a few volts belowthese values to allow for the in-duced peaks caused by thefree -wheeling current.A second factor to be con-sidered in the establishing ofthe supply voltage is the ohmicresistance of the stator wind-ings in the stepper motor. As arule of thumb, the supply volt-age for the board must be atleast two times the typical op-erating voltage of the motor op-erated with voltage drive. Inprinciple, therefore, most com-monly available 5 V stepper

motors should work all rightwith a board supply of 10-12 V,but a higher supply is prefer-able for improved current drivecharacteristics and hence ahigher pull -in rate.The total current consumptionof the system goes mainly onaccount of the stepper motor(s).Due account should be taken ofthe fact that the total currentdrain may amount to 8 A whenusing the board to drive 4 off2 A stator windings. Obviously,the mains supply should be de-signed to reliably cater forpossibly high current peaks,and the same goes for thesupply wiring. Also observe the2 times 4 contacts on K1, re-served for the connection of theinput supply; keep the totalcurrent drain in mind and, ifnecessary, use soldering pinsto avoid overloading the rela-tively thin connecting posts inK2.

Driving steppermotorsAs the stepper motor controlboard is essentially only a per-ipheral device, the computer-or more precisely the soft-ware-determines the move-ments of the stepper motorspindle.The key to the driving of themotor(s) is the 8 -bit controlword sent to the board via thecomputer's parallel output port.Fig. 9 shows the bit assignmentfor that control word. The twoMS bits-D6 and D7-are used toaddress one of four stator drivercircuits. Bit D5 provides thepolarization control, while Do -DI determine the stator currentin 32 (2') increments. Note thatsome Centronics output portsare open -collector types, re-quiring the data input lines andthe STB line to be pulled high to+5 V with 470R -1K0 resistors.Quite essential to the operationof the stepper motor is thestator current timing sequence.Fig. 10a shows the timing for fullstep operation, in which thestator current is arranged to re-verse with every step. Semi -stepoperation is illustrated inFig. 10b; during the reversal ofthe stator current, this is held atnought. This basic method isfurther exploited in the quarter -step mode shown in Fig. 10c,while extrapolation of this prin-ciple leads to the stator currentbeing reversed linear with time,

97 6 5 4 3 2 1 0

address polarity current definition87003 10

Fig. 9. Bit -functions in the control word sent to the board.

Fig. 10. From simple to complex: timing diagrams relevant tovarious methods of controlling a stepper motor.

Table 4. Handshake configurations

port type computer I board toto board i computer

wire linkor jumper

note(s)

Centronics b (1); (21STB 1 ACK: BUSYI

Z80 PIO

(outputmode)

a . -READY I STROBE

I

6522 VIA;6821 PIA

DATA READY 1 DATA TAKENCAVCB2 ICA1ICB2

b (3)

(1) Pull-up resistors may be required on board; see text.

delay.

(2) Use of ACK or BUSY is system dependent.(3) Depending on the PCR register contents:MI pulse mode: DATA TAKEN line not requiredII handshake mode: DATA TAKEN forces interrupt;

service routine outputs next byte after required

45 EE

January 1987

as shown in Fig. 10d. In prac-tice, however, the linear com-mutation is slightly problematic,since the sub -steps at the cur-rent cross -over point are in-evitably larger than those dur-ing the start and the end of thecommutation cycle. Moreover,the available torque will varyconsiderably during the sub -steps, as the total stator currentis not constant.During the current reversal, apermanent load fitted to thespindle will cause the rotor todeviate more from the objectposition than during momentsof maximum current. resultingin irregularity of the sub -stepsize. This effect is generallyfound to be rather more mani-fest with dual -stator motors thanwith four -stator types. Up to andincluding quarter -step oper-ation, dual -stator motors have anadequate performance, butfour -stator types are clearly tobe preferred for all applicationsmentioned so far. The reasonfor this is the more constantaverage stator current of the lat-ter motors. In conclusion, dual -stator motors are best operatedwith a constant total stator cur-rent, as shown in Fig. 10e.The commutation characteristicrequired for equal step sizeis mainly determined by thespecific type of motor to hand,and some trial -and -error pro-gramming may be required toattain optimum performance.

Sending bits to theboardThe simplest method of drivingthe stepper motor is probablythe writing of a array whichholds all data for a full com-mutation cycle. Such a cycleessentially involves once re-versing the current, and revers-ing it again to return to theoriginal polarity. In a four -statormotor, this corresponds to 8 fullsteps. A programmed pointer isused to send the datawords tothe board, and can be read, in-cremented or decremented tocontrol the direction of thespindle rotation. To get themotor to run as required, thepointer is programmed to ad-dress the individual array en-tries in a closed loop.Table 5a is a data dump of an ar-ray to control a four -stator motoraccording to the timing dia-gram of Fig. 10d. Note es-pecially the toggling of the

EE

January 198746

Hexadecimal data for one commutation cycle. Table 5a is for a four -stator motor operating asper Fig. 10d, Table 5b for a two -stator type operating as per Fig. 10e.

Table 5a. Table 5b.

I m 1 data M data address data address

M stator 1 stator 2 M

data

stator 1 stator 200 !1F ID 80 3F 3D02 11B 19 82 36 39

04 117 15 84 37 35 S1F 40 180

1823F 60

06 13 11 86 33 31 T 02 1E 41 3E 61

08 ':OF OD 88 2F 2D A 04 10 42 84 3D 62

OA 1 06 09 8A 28 29 T 06 IC 43 186 3C 63

OC i07 05 8C 27 2508 1B 44 I 88 3B 64

OE '03 01 8E 23 21 R OA 1A 45 8A 3A 65

10 21 23 90 01 03 OC 19 46 8C 39 66

12 1 25 27 92 05 07 OE 18 47 8E 38 67

14 29 2B 94 09 OB10 17 48 90 37 68

16 1 2D

18 131

2F33

9698

OD

11

OF

13

12

14

16

15

49 1924A I9a

3635

696A

lA 1 35 37 9A 15 1716 14 46 196 34 68

1C 139 3B 9C 19 18 18 13 4C 198 33 6C

1E l3D 3F 9E 1D 1F1A 12 4D 19A 32 61)

1C 11 4E ISC 31 6E1E 10 4F SE 30 6F

20 5F 50 AO 7F 7D 20 OF 50 A0 2F 7022 5B 59 A2 7B 79 22 OE 51 A2 2E 71

24 57 55 A4 77 75 S 24 OD 52 A4 2D 7226 53 51 A6 73 71 T 26 OC 53 1 A6 2C 7328 4F 4D A8 6F 6D A 28 OB 54 I A8 28 742A 4B 49 AA 6B 69 T 2A OA 55 AA 2A 752C 47 45 AC 67 65 2C 09 56 AC 29 762E 43 41 AE 63 61 R 2E 08 57 AE 28 7730 61 63 BO 41 43 30 07 58 BO 27 7832 65 67 62 45 47 32 06 59 B2 26 7934 69 68 84 49 46 34 05 5A 84 25 7A36 60 6F B6 4D 4F 36 04 58 186 24 7B38 71 73 88 51 53 38 03 SC 188 23 7C3A 75 77 BA 55 57 3A 02 5D IBA 22 703C 79 7B BC 59 5B 3C 01 SE

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58 B1 B3 D8 91 935A 2D 52 DA OD 72

5A B5 137 DA 95 975C 2E 51 1 DC OE 71

5C B9 BB DC 99 98 5E 2F 50 1 DE OF 70

5E BD BF DE 9D 9F60 30 4F 1E0 10 6F62 31 4E 1E2 11 6E

64 32 4D E4 12 6D60 OF DD E0 FF FD 66 33 4C ES 13 SC62 DB D9 E2 FB F9 68 34 46 E8 14 6864 D7 D5 E4 F7 F5 S 6A 35 4A 1 EA 15 6A66 D3 D1 E6 F3 Fl T 6C 36 49 1 EC 16 6968 CF CD E8 EF ED A GE 37 48 1 EE 17 ss6A CB C9 EA EB E9 T 70 38 47 FO 18 676C C7 C5 EC E7 E5 72 39 46 F2 19 666E C3 Cl EE E3 El R 74 3A 45 F4 1A 6570 El E3 FO Cl C3 76 3B 44 1 FS 18 6472 E5 E7 F2 C5 C7 78 3C 43 1 F8 1C 6374 E9 ER F4 C9 CB 7A 3D 42 1 FA 1D 6276 ED FF F6 CD CF 7C 3E 41 1 FC 1E 61

78 Fl F3 F8 D1 D3 7F 3F 40 FF 1F 607A F5 F7 FA D5 D77C F9 FB FC D9 DB7E FD FF FE DO DF

stator address bits and the cur-rent polarity bit. Table 5b is asimilar dump intended as aguide in controlling a dual -stator motor according to thetiming diagram of Fig. 10e. Forboth applications it it advisableto provide for an interrupt -based synchronization facility,as offered by, for instance. theType 6522 VIA.Unfortunately, the fairly largenumber of sub -steps oftenmakes it impossible for themotor to attain its maximumspeed. In this context. there isno doubt about the advantageof machine language subrou-tines over BASIC programs.Should the need arise to havethe motor run at a relativelyhigh speed, it is possible toprogram for more than one stepat a time. At high switching fre-quencies. the stator inductancelimits the current to such an ex-tent. that accurate current drive,and hence micro -stepping, isunattainable anyhow. Howeverthis is of little consequence,since the motor will nonethe-less run smoothly with the steprate well in excess of the res-onance frequency. Micro -step-ping is. therefore, primarily ofuse either for relatively lowmotor speeds. or for accuratespindle positioning.When skipping array entries torealize sufficient motor speed,care should be taken to finishwith the last byte of the rel-evant stator phase. Large stepsshould. therefore, always com-prise sub -steps which arepowers of two (2, 4, 8. 16 or32 steps at a time). TW

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January 1987

COSSOR RADAR:THE FIRST 50 YEARS

The last 50 years have seen an unending struggle to force backthe frontiers of knowledge and advance the development of

radar in its many different forms. Cossor, one of the great namesin the British electronics industry, has played a significant part inthat story of innovation. Undoubtedly, this process of advance willcontinue throughout the second half -century of radar's existence,

when new difficulties will be met. But Cossor has shown that itpossesses the means, the skill, and the determination to meet

whatever challenges the future may hold.

In 1935, the firm of A C CossorLimited had been in existencefor 39 years and had establisheditself as one of the nation's mainmanufacturers of radio valves,radio receivers and associatedproducts. At that time thecompany owned three factoriesin the Greater London Area ofwhich one, Cossor House com-pleted in 1934, was the largest -self -contained radio plant in theBritish Empire. The companywas then marketing a range ofreceivers for domestic use,from a simple 2 -valve battery setto a large radiogramophonepriced at 16 guineas (£16.80, theequivalent of about £420 at 1985prices). Cossor was also turningout large numbers of "MelodyMaker" radios in kit form andby this time total sales were ap-proaching three-quarters of amillion.Significantly for this account, in1935 Cossor produced most ofthe cathode ray tubes beingmade in Great Britain. In thosedays before the mass pro-duction of television, however,the commercial use of thesetubes was confined to a fewspecialised radio applicationsand the Cossor electro-car-diograph for hospitals. Thecompany was producing about300 cathode ray tubes per year,which was sufficient to meet thedemands of the home market atthat time.By the early 1930s the rapidlyevolving technology which wenow call electronics had pro-duced all the pre -requisitesnecessary to build a radar:transmitters that were powerfulenough, receivers that weresensitive enough, antennas thatwere directional enough and

cathode ray tubes that werereliable enough to display theecho signals. And by that timeit was well known that radiowaves would bounce off met-allic objects. The German pion-eer Heinrich Hertz had demon-strated the principle back in the1880s, and in the years to followscientists in several countrieswould propose detection sys-tems based on the idea. Few ofthese were ever built, however,and before 1935 none of themwould be usable for any com-mercial or military purpose.Britain's claim to have led theworld in the development ofradar stems from the fact that itsscientists built the first radars tobe incorporated into a nationalair defence system.The starting point of Britishwork on radar was on 26February 1935 when RobertWatson -Watt, then Superinten-dent at the government NationalPhysical Laboratory at Slough,ran a demonstration to provethat radio signals would bereflected from aircraft and thiscould be used as a means oflong-range detection. The BBCshort-wave overseas transmitterat Daventry in Northampton-shire was used to "illuminate"his target, an old Heyfordbiplane bomber of the Royal AirForce which had flown fromFarnborough for the purpose.In the rear of his mobilelaboratory installed in a Morrisvan, parked in a field atWeedon near Daventry, Watson -Watt and his co-workersswitched on the special re-ceiver they had built to displaythe echo signals. As the lumber-ing Heyford passed high overthe van at a stately 90 mph

(144 knth) the luminous greenspot in the centre of thecathode ray tube began tooscillate up and down with in-creasing rapidity. The oscil-lation decreased sharply as theaircraft's speed relative to thereceiver fell to zero, then in-creased again as the aircraftreceded. The system Watson -Watt had demonstrated was afar cry form radar as we nowknow it, or indeed from anydevice that could be used toprovide warning of enemy airattack. But it proved the techni-cal feasibility of such a detec-tion system, which was all hewanted to do at that stage.On learning of the success ofthe trial the Royal Air Forceeagerly grasped the idea ofradio location as a possiblesolution to one of its most intrac-table problems: how to obtainsufficient early warning of en-emy bomber formations ap-proaching Britain, so thatfighters could get into positionto intercept them. Watson -Wattwas allocated an initial sum of£10,000 to develop his ideas.The word "radar" was notcoined until some years later,initially, to conceal its truenature, the device was code -named "RDF" (short for Rangeand Direction Finding).Watson -Watt and his team built aprototype radar with a speciallybuilt pulsed transmitter, and ranit at their research station nearOrfordness. The prototype im-mediately confirmed that theresearchers were working onthe right lines: by June 1935 theset was tracking aircraft out to42 miles (67 km); by Septemberthe range had increased to58 miles; and by March 1936-

just over a year after the initialexperiment at Daventry-an air-craft was tracked to 62 miles(100 km). In each case, as in allthe early British radar trials, theecho signals were displayed oncathode ray tubes made byCossor.By the end of 1936 the prototyperadar was working well enoughfor it to be ordered into pro-duction Under conditions ofgreat secrecy two civiliancompanies were told of the pro-ject in January 1937: Metro-politan -Vickers were consultedabout building the specialpulsed transmitters, and Cossorthe receivers. By then Cossorwas one of the market leadersin the design and constructionof television receivers for thedomestic market, and these hadmuch in common with the typeof receiver now required for theRDF system: both were high -gain receivers of pulsed signalson frequencies in the 45 Mega-hertz band, and displayed thosesignals on a cathode ray tube.

Inside the receiver room at aChain Home radar station. Thereceiver equipment, made byCossor, was housed in thelarge rack in the background:the WAAF operator with herback to the camera was sittingin front of the cathode raytube, her hand on the gonio-meter control for measuringthe bearings of aircraft.

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January 1987

Watson -Watt had built up agood working relationship withCossor during his work oncathode ray direction findingequipment, and recommendedthat the Air Ministry ask thecompany to build the receiversfor the new radiolocationsystem. The upshot was thatCossor received a contract todesign and manufacture theprototype of a sensitive re-ceiver able to pick up and dis-play weak pulsed echo signalson frequencies between 20 and45 megacycles (the frequencyspread of the productionradars). Further contracts pro-vided for the construction of19 additional receivers. Theagreed price was £1,000 per re-ceiver.The task of designing andbuilding the new receiver, andgetting it into production, wasgiven to Cossor's main factoryat Highbury. Later the devel-opment and production ofCH receivers was moved tothe newly acquired plant atHackney.While work on the receiverswas in progress at Cossor, inMarch 1937 the prototype ChainHome radar station at Bawdseynear Ipswich was handed overto the Royal Air Force. It was thefirst operational radar station inthe world, and during air exer-cises at the end of April aircraftwere plotted out to 80 miles(128 km) from the set.The first part of the Chain Homeearly warning radar system wasfully operational by the time ofthe Munich Crisis in September1938, and had demonstrated theability to plot aircraft out to arange of 120 miles (192 km).Following the promise shownby the initial radar stations, theRoyal Air Force placed ordersfor a greatly extended chainwhich was to provide cover ofthe entire east coast of Englandand Scotland. Before the end of1937 Cossor had received con-tracts for an additional 40 ChainHome receivers.When war broke out in Sep-tember 1939 a total of 19 ChainHome radars were operational.One was situated to cover theapproach to the fleet anchorageat Scapa Flow in the Orkneys,the other 18 gave continuouscoverage along south and eastcoasts between the Isle ofWight and Aberdeen. By thesummer of 1940, when the Luft-waffe began its largescale at-tacks on Britain, the Chain

48

Home radar cover was con-tinuous from Lands End to theShetland Islands. Air Chief Mar-shal Sir Hugh Dowding woulddepend on the sets to providewarning of incoming enemy for-mations. to enable him to de-ploy his outnumbered squad-rons of Spitfires and Hurricanesto maximum effect. Only theskill and bravery of the RAFfighter pilots could have wonthe Battle of Britain, but the lackof the all-important radar warn-ing system could certainly havelost the battle.After the Battle of Britain furtherChain Home radar stations werebuilt to expand the area ofcoverage, until by the end of1941 this took in the entirecoastline of Great Britain andNorthern Ireland. Throughoutthis period there was a con-tinual process of improvementsto the radar, and Cossor engin-eers designed and built a newlightweight receiver that couldbe transported more easily.From the beginning of the warother types of warning radarwent into service to provide im-proved cover on enemy aircraftcoming in at low altitude. Butagainst aircraft approaching atmedium or high altitude theChain Home radar remainedthe primary early warning setuntil the war ended in 1945. Afew of these radars continued inservice as part of Britain's airdefences until the early 1950s,clear evidence of the sound-ness of the original design andconstruction of the equipment.The promise shown by radarwas such that after the RAF theother services began to issuerequirements for specializedsets of their own. One ofWatson -Watt's research teams atBawdsey had built the proto-type of a radar to provide Armyanti-aircraft gun batteries withmedium range warning and ac-curate range information ontargets. The Army issued a re-quirement for 500 of these sets,and in October 1938 placedorders with Metropolitan -Vickers to build the transmittersand Cossor the receivers. Thenew radar, designated theGunlaying Mark I (GL I forshort) operated on frequenciesin the 54 to 84 Megahertz band.Cossor set up a production linefor GL I receivers at its Hackneyfactory and the first pilotmodels were delivered in June1939. The first production GL Iradar went into service in

September 1939 at the time ofthe outbreak of war, and by thesummer of 1940 about 200 Gun -laying Mark I radars were inservice with Anti -Aircraft Com-mand of the Army.Strictly speaking the term"Gunlaying" was a misnomerwhen applied to the GL I radarin its original form, for the sethad not been designed to doany such thing. "Gun -AssistingRadar" is a more accurate termfor it, for although the set gaveaccurate ranges on enemy air-craft, its azimuth indicationswere poor and it gave no elev-ation indications at all. Theradar was, therefore. incapableof directing anti-aircraft firewith any degree of accuracyagainst aircraft that could not beseen visually. These limitationswere clearly recognized at thetime, but it was considered bet-ter to get GL I into service assoon as possible to allow anti-aircraft gunners to gain someexperience with radar. A newradar purpose -designed foranti-aircraft fire control against"unseen- targets, the GunlayingMark II entered production inearly 1941 and Cossor Ltd re-ceived a contract to make thedisplay units. With its greaterpotential for measuring angularaccuracy. the new radar wasmuch more sensitive to sitingthan the GL I/EF had been. Inservice, the GL II was found toneed a much larger chicken -wire mat than its predecessor,in some cases extending out to100 yards from the receivercabin.Cossor maintained its close as-sociation with Anti -AircraftCommand throughout the warand developed the No 9 Predic-tor system, the first electronicanalogue computer for anti-air-craft fire control built in Britain.In the event the No 9 Predictordid not go into production, butthe No 11 equipment developedfrom it was produced in quan-tity after the war.In the spring of 1943 Cossor re-ceived a contract to develop amicrowave radar for searchlightcontrol, the SLC IX. The 55 -indiameter reflector of the radarwas rigidly attached to thesearchlight so that the twopointed in the same direc-tion. The SLC IX was a fully en-gineered searchlight controlradar intended to replace simi-lar equipinents built undercrash -programmes by othercompanies. In May and June

1944 an experimental model ofSLC IX was set up in Hyde Parkand demonstrated its effec-tiveness and ease of operationbefore selected VIPs. Royal AirForce Fighter Command pro-vided a very experienced pilotin a fast aircraft, but in spite ofhis best efforts and violentevasion he was never able to es-cape from the searchlight'sbeam once he had been illumi-nated. Following the demon-stration the Ministry of Supplyplaced an order for 1,000 of thenew searchlight control radars,with delivery planned to com-mence in April 1945. In theevent, however, the first pro-duction equipments were de-livered just too late to seeaction. Following the end of thewar the order for SLC IX was cutback to 300 sets, which Cossorcompleted during 1946.During the closing year of thewar Cossor were closely in-volved in the design and con-struction of the electronicsystems for "Brakemine", a testvehicle intended to establishthe feasibility of radar beam -riding as a method of guid-ance for anti-aircraft missiles.Developed at the Army ex-perimental workshops at ParkRoyal, the Brakemine projectmarked the beginning of workin Britain on surface-to-airguided missiles. In retrospect,however, it is clear that thespecification drawn up for thismissile was over -ambitious inconcept and it pushed too hardat the limits of the availabletechnology. The first Brakeminewas test fired (unsatisfactorily)at the range at Walton -on -the -Naze in September 1944. Duringtest more than 20 Brakemineswere launched, before the endof the war halted funding andthe project ended.

Supporting theoffensiveDeveloped by scientists at thegovernment Telecommuni-cations Research Establishmentat Swanage, GEE was a hyper-bolic navigation system whichemployed a chain of threepowerful ground transmitterslocated about one hundredmiles apart, which radiated in-terlocking pulsed signals in aset order on a single radio fre-quency in the 45 to 55 Mega-hertz band. By means of aspecial receiver an aircraftnavigator could measure the

49 EE

January 1987

minute differences betweenthe times of arrival of thesignals; and by referring theseto a special map he could readoff his position. In effect theGEE transmissions set up an in-visible grid of signals overEurope, with which the crewsof aircraft with GEE receiverswere able to fix their positionprovided they were within 400miles of the most distant trans-mitter. The accuracy of thesystem varied between abouthalf a mile, if the aircraft wasclose to the transmitters, and sixmiles at maximum range. Com-pared with modern systemssuch accuracies are not im-pressive, but in 1941 GEErepresented a considerable ad-vance over the other long rangeposition -fixing methods in usein Bomber Command. At thattime the only alternativemethod that could be used overenemy territory, if groundfeatures could not be identifiedat night, was astro navigation.Under operational conditionsan experienced navigatorcould fix his position to within20 miles from the stars using asextant, but new crewmen freshout of the training schoolscould rarely achieve even thatdegree of accuracy.In Augst 1941, Cossor signed atop -priority contract to build300 GEE airborne navigationreceivers for the Royal AirForce. Much hard work wasnecessary before the receiverwas ready to go into mass pro-duction. The company had tore -engineer the equipment sothat is could be produced econ-omically from existing compo-

The GEE Mark II receiver wasproduced in large numbers byCossor during the war. Fittedto bomber transport andmaritime patrol aircraft, thishyperbolic radar navigationsystem made it possible foraircraft to adhere to plannedtracks far more accuratelythan had previously beenpossible.

Method of operation of "Oboe". The "Cat" tracking station guided the aircraft along an arc of con-stant radius passing through the target, by transmitting dots if the aircraft was to the right oftrack, dashes if it was to the left and a steady note if it was on track. A second ground trackingstation, the "Mouse", carried out continual range measurements on the aircraft and transmitted thebomb release signal when the aircraft reached the target.

nents wherever practicable.Jigs and special tools had to bemade to produce those partswhich could not be bought in asstandard items. Members of theworkforce had to be retrained(and in some cases recruitedand trained from scratch) to pro-duce the new equipment.In time of war no radio or radarsystem of importance can ex-pect to remain free from jam-ming for long, once an enemylearns of its method of oper-ation. Because of this the RAFwithheld the use of GEE duringlarge-scale attacks on enemyterritory, until there wereenough receivers to equip asizeable proportion of the nightbomber force and sufficientnavigators had been trained tooperate the device.Royal Air Force Bomber Com-mand first used GEE during alarge scale attack in March1942. From the time of its in-troduction the new system-af-fectionately nicknamed "GoonBox'greatly improved thenavigational accuracy of RAFnight bombers operating overenemy territory. By May 1942sufficient bombers carried GEEto allow Bomber Command toadopt the so-called "BomberStream" tactics: from then un-til the end of the war nightbombers flew in concentratedraiding forces. Since even in thecentre of the stream it wasunusual to see more than acouple of other bombers in theforce. each bomber crew had tonavigate individually andadhere as closely as possible tothe briefed route and timingpoints. With these tactics it was

often possible to saturateenemy night fighter and Flakdefences in the area, which re-duced their effectiveness andthe number of bombers theywere able to shoot down.The success of GEE did notpass unnoticed in Germany,however. Within three weeks ofits introduction the Luftwaffe in-telligence service had securedan almost -intact receiver from acrashed Wellington bomber.The method of operation of thenew device was soon deter-mined and the Luftwaffe paidGEE the compliment of launch-ing a top priority crash pro-gramme to counter it. TheGerman Post Office hastily con-verted several speech transmit-ters into makeshift jammers, toradiate spurious pulses to con-fuse GEE. RAF crews firstreported interference on GEEin August 1942. Within a shorttime the improvised Post Of-fice transmitters were sup-plemented by "Heinrich", anew and more powerful jammerspecially designed to counterGEE. Soon Heinrich transmit-ters were operating all overGerman-occupied Europe, oneeven found its way to the top ofthe Eiffel Tower in Paris.After the initial order for 300GEE receivers, Cossor re-ceived large scale follow-onorders and the equipment re-mained in production through-out the conflict. The answer toHeinrich was the Mark II ver-sion of GEE, also built byCossor, which had five separatechannels of operation spreadover the frequency band 20 to85 Megahertz so that navigators

could choose those signalsleast affected by jamming. Oneblock of GEE frequencies waswithheld for the Normandy in-vasion in June 1944, and wasfirst used by the armada oftransport aircraft which carriedthe airborne troops to theirlanding zones; the move wassuccessful and there was nointerference from enemyjamming. For the remainder ofthe war GEE Mark II was able toprovide accurate fixing overlarge parts of enemy -held terri-tory, and over all sea areas andfriendly territory.When the war in Europe endedin May 1945, more than 60,000"Goon Boxes" had beendelivered. The Royal Air Forcedid suffer heavy cumulativelosses during its bombing of-fensive; but had the nightbombers been denied the useof the concentrated stream tac-tics which GEE made possible,their losses would certainlyhave been far higher.Another important radar sys-tem made at Cossor's Londonfactories employed two re-lated equipments code -named"Rebecca" and "Eureka". It wasthe company's first encounterwith secondary radar. a fieldwhich represents Cossor's mainactivity in the 1980s. The ChainHome and Gunlaying systems,for which the company hadpreviously built the receivers,were both primary radardevices; that is to say theirtransmitters radiated high pow-ered pulsed signals in a beam,aircraft within that beam re-flected signals and the resultantechoes were picked up by the

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January 1987

radar's receiver. Range wasmeasured by timing the intervalbetween the transmitted andthe received pulses and bear-ing was measured using adirectional antenna. Secondaryradar operated on a differentprinciple. A less powerfultransmitter radiated pulsedsignals in the same way. Butwhen these signals were re-ceived by a transponder (acombined receiver -transmitter)some distance away, they trig-gered the transmitter whichemitted a coded reply signal.The coded reply was thenpicked up by a receiver locatedbeside the original transmitterand the range and bearing ofthe transponder could bemeasured by normal radarmethods. Secondary radar wasnot a replacement for primaryradar, but it opened up a wholenew field of possible appli-cations of its own.In the case of Rebecca -Eureka,which worked in the 214 to 234Megahertz band, the Rebeccatransmitter -receiver was car-ried in the aircraft and the as-sociated Eureka transponderbeacon was positioned on theground at a point where the air-craft was required to go. Thesystem gave ranges in excess of50 miles. With Rebecca the air-craft navigator could read offthe range of the transponder,and by using homing antennashe could give the pilot accuratedirections to fly to the beacon.In another important use ofRebecca -Eureka, transponderswere issued to resistancegroups operating in occupiedterritory. The Eureka beaconswere used to mark clandestinedropping zones, enablingAllied transport aircraft to makeaccurate drops of containerscarrying weapons and sup-plies. A particular advantage ofEureka for this purpose. com-pared with a conventional radiobeacon. was that it did nottransmit until it was triggeredby the Rebecca equipment ofthe aircraft approaching tomake the drop. As a result it wasusually impossible for theenemy direction -finding ser-vice to locate the droppingzones in sufficient time fortroops to be sent to interferewith the operations.Cossor also produced Lucero,an attachment to the primaryradar equipments carried bybomber, night fighter, maritimepatrol and naval aircraft which

50

enabled these sets to functionas secondary radars in the samewas as Rebecca. The modifi-cation provided separate anten-nas and radio frequency sec-tions for the transmitter andreceiver chains which weresimilar to those of Rebecca; butLucero used the intermediatefrequency amplifiers and dis-play equipment of the originalradar. Lucero provided fa-cilities for air-to-air or air -to -ground homings on beaconsoperating in the 170 to 180

Megahertz band. The Mark IIversion of the equipment whichwas manufactured by Cossorfirst went into service in thespring of 1944 and the systemwas widely used during oper-ations. One very useful featureof Lucero was that after a mis-sion it enabled aircraft carryingthe device to home on groundbeacons located at their baseairfields.In a quite different applicationof the secondary radar prin-ciple, the TelecommunicationsResearch Establishment devel-oped the "Oboe" precisionbombing system. Oboe can beregarded as "Rebecca -Eurekain reverse", in the sense that theinitial triggering transmitter andfinal receiver were on theground. and the transponder(manufactured by Cossor) wascarried in the aircraft. Oboe ex-ploited the fact that radartechniques make it possible to

measure range with con-siderable accuracy, and that ac-curacy does not diminish withdistance. A ground station(known as the "Cat") trans-mitted pulses to trigger atransponder carried in the air-craft, and on receipt of the replypulses the ground operatorsmeasured the aircraft's rangevery accurately. The groundstation then transmitted radiocommands to the pilot, direc-ting him to fly along an arcwhose radius equalled thedistance from the groundstation to the taraet. In otherwords, the bomber was routedto its rarget along the cir-cumference of a circle whosecentre was the Cat station. Sim-ultaneously a second groundstation, the "Mouse" situatedabout 120 miles from the Cat,continually triggered a secondtransponder in the aircraft andmeasured the latter's range as itapproached the target. Whenthe Mouse station observed theaircraft reaching the bomb -release point, it broadcast thesignal to release the bombs.Oboe Mark I operated on fre-quencies in the 212 to 236Megahertz band and first wentinto service at the end of 1942.During many of the attacksusing Oboe, the ground stationnear Dover in Kent acted as"Cat" and that near Cromer inNorfolk served as "Mouse". TheOboe system had the draw -

Paratroops descending on Landing Zone 'X' to the west ofArnhem on 18 September 1944. Cossor made the lightweightground Eureka beacons which guided the transport aircraft ac-curately to their dropping zones for this operation. Imperial WarMuseum.

backs that one pair of groundstations could control thebombing run of only one air-craft at a time that might last upto 10 minutes; and the curvatureof the earth limited its range to280 miles from the more -distantground station. On the otherhand Oboe was, for its time,very accurate-it could putdown half the bombs releasedwithin 400 yards of a targetanywhere in its operatingrange; moreover. the 280 -milemaximum range of the systemtook in a large slice of westernGermany. Oboe was fittedmainly to Mosquito aircraft ofthe Pathfinder Force, whichused the system to drop theirtarget marker bombs with greataccuracy. The crews of heavybombers of the main forcewhich followed the Pathfindersaimed their loads on the dis-tinctively coloured flares whichthe markers scattered on theground.The enemy made strenuous ef-forts to jam or confuse OboeMark I. but before they coulddo so effectively the Mark IIoperating in the 3135 to 3240Megahertz band began enter-ing service to replace it inmid -1943. The microwave ver-sion of Oboe enjoyed inter-ference -free operations untilApril 1945, less than a monthbefore the war ended inEurope.Another device produced inquantity by Cossor to aid thebombing offensive was "Mo-nica", a tail -warning radaroperating on frequencies in the175 Megahertz band whichwarned bomber crews of en-emy night fighters closing in toattack from behind. Monica wasfirst used in action early in 1943,and by the end of the year it wasfitted to the majority of Lan -casters and Halifaxes.By the end of the war almostevery single combat aircraft op-erated by the Royal Air Force,and many of those of Allied AirForces, carried at least one itemof equipment made by Cossor.Even the smallest single -seatfighter was not exempt: thesecarried the "Walter" radarbeacon manufactured by thecompany, which assisted in lo-cating aircrew who had bailedout of their aircraft. Walter trans-mitted on a spread of fre-quencies around 175 Mega-hertz, and its signals could bereceived by any aircraft whoseradar operated on that fre-

EE

January 1987quency or which was fitted witha Lucero attachment. Walterweighed 2 pounds 2 ounces(about 1 kg) complete with bat-tery and telescopic antenna,and in the stowed condition itwas small enough to fit into thestandard dinghy pack whichclipped on an aircrewman'sparachute harness. The distressbeacon remained a standarditem of aircrew survival equip-ment long after the end of thewar.As well as complete equip-ments. Cossor factories pro-duced valves and cathode raytubes which were used in thegreat majority of radars madein Great Britain during the war.To meet the enormous demandfor these components theCompany erected a large newfactory on a green -field sitenear High Wycombe in 1941. InJanuary 1942, just seven monthsafter the first sod was cut, theplant was complete and hadbegun making components. Bythe end of the war in August1945 the factory had producedmore than 300,000 cathode raytubes and huge numbers ofvalves.

Swords intoploughsharesFollowing the end of the warand the immediate cancellationof most of the orders for equip-ment for the fighting services,Cossor wasted no time in put-ting its considerable ex-perience in radar to peacetimeuse. One clear need seemed tobe a simple, cheap and reliableradar for merchant ships and asa private venture the companybegan work to develop such aset. One feature of this equip-ment was a special long -after-glow coating on the cathode raytube, which allowed the oper-ator to track the relative move-ment of contacts by observingthe "tail" trailing behind each.In December 1945 a prototypeCossor Marine Radar, operatingon a wavelength of 3 cms, be-gan sea trials on the M.V. Atlan-tic Coast belonging to CoastLines. The coaster plied be-tween London and Liverpooland was the first cargo vessel ofits size to carry radar duringcommercial operations.The new Marine Radar quicklyproved its value in the con-gested waters and poorweather conditions which are a

daily part of operations aroundthe British Isles. Whether ornot a ship had this equipmentcould make the difference be-tween catching or missing atide, and on that could dependwhether a competitively bidcontract made a profit or aloss. Commercial shipownersare not noted for their open-handedness, but gradually theycame to realize that moneyspent on a radar could prove acost-effective investment evenin the short term. Shippingcompanies began to take noticeof the new Cossor radar. Thefirst to be sold was fitted to theNorwegian whale factory shipSirJames Clark Ross, which car-ried the set and a Cossor en-gineer to service it during awhaling expedition to the Ant-arctic. The radar was found tobe particularly useful for de-tecting icebergs. In October1946 a Cossor Marine Radarwas on the 83,000 ton luxuryliner Queen Elizabeth whenshe set out for her maidenpassenger -carrying voyagefrom Southampton to New York.Merchant ships both large andsmall began carrying Cossor's

new radar, and during the dec-ade following the end of thewar some 200 of these sets weresold at home and abroad. Tokeep these radars in operationthe company established aworld-wide servicing organis-ation.When the commercial airroutes in Europe reopenedafter the war, Cossor equip-ment developed during theconflict played an importantpart in assisting safe operations.During the late 1940s BritishEuropean Airways equipped itsViking, Dakota and Ambassa-dor airliners with GEE re-ceivers. Cossor also built theground transmitters for the newGEE chain established to coverScotland and the offshoreislands. Early in the 1950s a GEEchain with three ground trans-mitters was set up in Kenya forthe aerial photographic surveyof East Africa. The navigationaid enabled the high flying air-craft to adhere accurately totheir planned flight tracks, en-suring the task was completedusing as few flights as possible.For the Festival of Britain in 1951the organizers asked Cossor to

Antenna for the "Monica" tail warning radar, fitted below therear gun turret of a Lancaster bomber. Cossor produced -Monica"in large numbers. Garbett Goulding collection.

exhibit one of its radars along-side items of high technologyequipment manufactured byother companies, at the mainSouth Bank site beside theThames. The company decidedto use the occasion to demon-strate a new type of radar, aland -based set for the control ofships entering or leaving har-bour in poor visibility. A basicCossor Marine Radar was modi-fied with a larger scanner to im-prove definition and an en-larged display, and installed inthe main exhibition hall wheremembers of the public couldsee on the screen traffic pass-ing up and down the river. Itwas a convincing demon-stration of the value of radar sur-veillance for harbours and atthe time it aroused consider-able interest. The Cossor har-bour control radar based on theSouth Bank equipment was of-fered for sale and the first waspurchased for installation atWallasey to assist ferries pass-ing between there and Liver-pool during periods of poorvisibility. Other sets were in-stalled at Douglas on the isle ofMan, and Gladstone Docks atLiverpool.At about the same time a har-bour control radar was modi-fied for use as an airfieldcontrol radar and tried out atthe Royal Aircraft Establishmentat Farnborough and the newLondon airport at Heathrow.The trial established the valueof positive radar control forcivilian air traffic. As a resultCossor received a contractfrom the Ministry of Civil Avi-ation to develop the ACR 6, anambitious ground based air-field control radar operating ona wavelength of 10 cms and de-signed for use at major airports.The ACR 6 incorporated severalfeatures which were con-sidered novel at that time: it wasfitted with a moving target indi-cator to cancel out groundreturns (it was the first British -built radar to incorporate thisrefinement); the radar used cir-cular polarization to reduce theeffects of weather clutter, thedisplay incorporated a systemwhereby local map featurescould be overlaid on the radarpicture electronically; andthere was a built-in test systemwith comprehensive monitor-ing and metering.The first ACR 6 to go into com-mercial service became oper-ational at London's Heathrow

EE

January 1987

Airport in 1955. Similar radarswere erected at other importantairfields in Great Britain. A fewACR 6s were exported: twowent to Switzerland where theywere used at Geneva andZurich; two more went toHolland and were set up atSoesterberg and Gilze Rijen. Inservice the ACR 6 proved ex-tremely reliable and continuedin operation for many years.Even when the radars them-selves were replaced by othersincorporating more -moderntechniques, the superb Cossorantennas were retained. One ofthe antennas continues in use tothis day a Heathrow, others areat Stansted and Gatwick, proofof the farsightedness of theirdesigners more than 35 yearsearlier.The facilities ACR 6 providedmade it a desirable piece ofequipment for any commercialairfield with a high flow of traf-fic, but the high cost of theradar limited its installation to afew large airports. Cossor rec-ognised the gap in the marketand to exploit it the companydeveloped a simplified low-costairfield radar with a new anten-na using some componentsfrom the ACR 6. This was theCR 21 airfield surveillanceradar, which first appeared in1957. The CR 21 was smallenough to fit into a trailer andsold in moderate numbers. TheCR 787 which appeared in 1961was an up -dated version of theCR 21, featuring a travellingwave tube amplifier to improvereceiver sensitivity. There wasalso an innovative system forwriting information on thescreen, which then followedthe blip from the aircraft as ittracked across the screen.Altogether some fifty CR 21sand CR 787s were built and atthe time of writing several CR787s are in operation through-out the world.In a further bid to extend thecivil applications of its range ofradars, Cossor designed andbuilt the Windfinder Radar CR353 to meet a requirement fromthe British Meteorological Of-fice. This was based on theNaval Type 993 radar for whichCossor built the transmittersand operated in the 2,800Megahertz band allocated tometeorological use. The set wasfitted with a conical scan lock -follow system to enable it totrack the ascent of balloons car-rying radar reflectors. By fol-

The Cossor ACR 6 airfield control radar first went into oper-ational service at London Heathrow Airport in 1955 and wasacclaimed as a major advance in this type of radar. The pre-cision -built antennas for the ACR 6 were so good that even whenthe radars themselves were replaced by others incorporatingmore -modern circuitry, the original Cossor antennas were re-tained. At the time of writing these antennas are still in use atHeathrow. Gatwick and Stansted airports, clear proof of thefarsightedness of the Cossor designers 35 years earlier.

lowing the movement of theseballoons, the radar operatorcould measure the strength anddirection of the wind at differ-ent altitudes. Examples of thisradar were bought by govern-ment meteorological servicesin New Zealand and severalother countries.No history of Cossor during thepost-war years is complete with-out mention of some of thefar-reaching changes to thecompany which took place dur-ing this period. By the early1950s a huge financial invest-ment was necessary to pur-chase the equipment requiredfor the mass production of radiovalves and domestic radio andtelevision receivers. It wasdecided to concentrate theavailable resources on thedevelopment and production ofradars, and Cossor's valve, radioand television divisions weresold off. Then in 1958 Cossormoved en -bloc from thecramped and ageing factoriesat Highbury, to the modern fac-tory complex at Harlow in Essex

which remains its home to thepresent day. In 1961 A.C. CossorLtd was acquired by Raytheon,an American electronics giantwhich had made distinguishedcontributions of its own inradar for example, duringWorld War II Raytheon devel-oped a process for the massproduction of magnetrons,which was to enable the Alliesto deploy microwave radars inquantities sufficient to have adecisive influence on the con-flict. Today Raytheon is one ofthe world's largest manufac-turers of high technology elec-tronic systems and the associ-ation has greatly increased theresources available to Cossor,while allowing the Britishcompany considerable in-dependence in deciding whichequipments it should developin order to meet market re-quirements.During the 1960s Cossor tookthe positiye decision to concen-trate its main design, develop-ment and production activitieson secondary radar systems for

civilian and military use, as willbe described in Chapters 6 and7. Interest shifted away fromprimay radar systems, thoughthe company retained the abili-ty to move back into that area ifthe prospects appeared favour-able. In 1965 Cossor obtained alicence from a then associatedRaytheon company, Selenia inItaly, to re -design thatcompany's ATCR-2 surveillanceradar to meet British re-quirements. The resultant radarbecame the CR 901 which ap-peared in 1967. One examplewent into service at the Arma-ment and Aircraft ExperimentalEstablishment at BoscombeDown, but it was decided that itwould not be cost-effective toupgrade the design to the ex-tent necessary to match com-peting radars and no more werebuilt. At the time of writing theCR 901 is the last primary radarproject undertaken by Cossorfor the civil market.

New military radarsand systemsThe company's first completelynew military equipment to gointo large scale production afterthe war was "Orange Putter", a3 cm wavelength tail warningradar designed for installationin the Canberra jet bomber.The company took over thedevelopment of this equipmentfrom the TelecommunicationsResearch Establishment atMalvern in 1947, and built morethan 700 for the Royal Air Forceand foreign air forces.

The final part of this article willappear in the February 1987issue of Elektor Electronics.

The article is based on thebooklet of the same name byDr Alfred Price.

Eluary 1987

MSX EXTENSIONS 4

I/O and timer cartridge

Fourth in our series on simple to make extension boards for theMSX series of computers is a versatile, cartridge -size, input/output

plus timer module, primarily intended to drive thecomputerscope featured in our September and October 1986

issues.

This article presents thosemany owners of an MSX com-puter with an interface exten-sion board featuringI 32 (4 times 8) I/O lines;I 4 programmable timers;I user -definable address de-

coding;II daisy -chained interrupt con-

figuration.All of these functions havebeen realized on a single, car-tridge -size board which can behoused in a common musiccassette box. Although the firstaim of this design is to providean interface between an MSXcomputer and the computer -scope, the I/O and timer car-tridge can fulfil a variety oftasks. For instance, there is thefield of robotics where steppermotors are to be driven via acomputer interface (see Univer-sal control for stepper motors,elsewhere is this issue). Thepre extension board is

1

datatm

!Oconee!

I

expansion control

ergarisionaddressdecoder

cartridgeaddressdeetder

pulite!VO

pavane!VO

titimers

fro

VO

timer I/O

E6125-1

Fig. 1. Block diagram of the MSX I/O and timer cartridge.

also tailored to drive an MSXEPROM programmer, whichwill be detailed in a forth-coming issue of Elektor Elec-tronics. However the presentarticle will mainly focus on howto use the I/O and timer car-tridge in conjunction with thecomputerscope.The previous instalments of thisseries were published in theJanuary. February and March1986 issues of Elektor Elec-tronics.

Block diagramFigure 1 shows the various func-tional blocks comprised in theI/O and timer cartridge.The cartridge address decoderdefines the I/O channelsthrough which the card is ac-cessed by the Z80 microproces-sor. It will be recalled that MSXcomputers use I/O mapping

EE

January 1987

based on 255 (2a-1) channels,rather than reserving a specificaddress area in the system RAMto transfer I/O data and I/Ostatus/control words.After the processor hasselected the cartridge bymeans of an appropriate I/O in-struction, the expansion ad-dress decoder is enabled toselect either one of two parallelI/O blocks, or the timer block.The expansion control bus pro-vides the peripheral blocks

54

with information as to the natureof the word then present on thedatabus, since this is used tobidirectionally transfer bothdata and status/control words.Each I/O block comprises twosets of 8 I/O lines plus associ-ated peripheral handshakinglines; the cartridge, therefore.has 32 I/O lines in all. i.e.

enough and to spare for all sortsof applications.The timer block comprises 4 in-dividually addressable coun-

ter/timer units in a single chip.

The cartridgehardwareWith the use of three LSI chipsfrom the Z80 peripheral supportfamily, the circuit diagram ofthe I/O and timer cartridge,shown in Fig. 2, closelyresembles that of the blockdiagram.Cartridge address decoder ICs

teFn Z -V,, A F:0

MOSI

compares a preset 4 -bit addresswith CPU address bits A4 -A2,and activates its A=B outputwhenever the two configur-ations match, i.e. when the com-puter accesses the cartridge.The previously mentioned 255I/O channels can be addressedvia the least significant byte onthe CPU address bus (AL' -AT).while IORQ indicates a CPUI/O cycle rather than a memoryaccess cycle. In MSX BASIC, in-put and output instructions aresimply INP (xxx) and OUTxxx,n, respectively, where xxxis the I/O channel and n is thebyte to be output.Since I/O channels 64 through255 are reserved for standardMSX software and hardware, AE.and A7 in the preset addressnibble are hard -wired toground (logic low) so as to avoidI/O contention problems be-tween the cartridge and resi-dent I/O mapped hardware.Table 1 shows the jumper con-figurations to define the16 -channel I/O block throughwhich the cartridge is to be ac-cessed.Address comparator ICs neednot be strobed with ro-R-0 as theperipheral LSI chips ICI, IC2and IC: each have theirIORQ input to this effect. IC- isa dual 2 -to -4 line decoderwhich provides the PIOs (Par-allel Input/Output) and theCTC (Counter/Timer Control-ler) with rE (chip enable)pulses. These three peripheralfunctions are selected by an ap-propriate bit -configuration ofaddress lines A2 and Al, pro-vided, of couse, the A =B outputof ICs is logic high. Note thatoutput 3 of decoder 1 in ICI (pindenotation: IQ3) is used to drivethe active low E2 (strobe) inputof decoder 2; decoder 1,

therefore, merely functions toinvert the A=B output from IC5.If selected with CE. the PIOsand the CTC have access to theCPU data bus as IORQ goeslow. The direction of the data

cartridgeI/O block(decimal)

jumpers

0-15 a b

16-31 a d

32-47 c b

48-63 c d

Fig. 2. Circuit diagram of the multi -I/O and timer extension for MSX computers.Table 1. The cartridge addressblock assignment.

111 EE

January 1987

flow-i.e. CPU to peripheral, orvice versa-is determined bythe logic state of the RD line.Provision has been made toprocess PIO or CTC-generatedinterrupts by connecting theINT outputs of ICI, IC2 and 1C3in a wired -OR structure. Thedaisy chain connection of theIEI and 1E0 (interrupt enableinput and output, respectively)signals is essentially a methodof interrupt priority assignment.In the cartridge, ICI has thehighest interrupt priority, IC3the lowest. Once ICI activatesits INT output, 1C2 and IC3 aredisabled from outputting inter-rupt requests to the processor.In this system, high -priorityperipherals automatically over-ride NT requests from devices"further down" the daisy chain.Upon receiving an INT pulse,the CPU polls the peripherals todetermine the origin of the INTrequest. This is done by meansof an INTACK (interruptacknowledge; MI AND MM)pulse, which causes the rel-evant peripheral to respond byputting a vector byte onto thedatabus. This vector is used asthe LS address byte for the in-terrupt service routine. In aZ80 -based system, pulses MTand 'ORO are used to form theINTACK pulse, while the inter-rupt vector is loaded into thedevices during the initializationroutine. PIO ICI has beenassigned the highest priority onthe cartridge since PIO IC2 andCTC IC3 are not used in thedriving of the computerscope.The chips on the cartridgeboard are either fed from thecomputer +5 V supply, or froman external supply connectedto pins 21 (GND) and 22 (+5 V)of 50 -way output connector IC(remove link e). If all chips inthe cartridge are of the CMOStype, the supply capacity of thecomputer should be adequate,and link e can, therefore, be leftin place. In theory, the appli-cation of standard NMOS chipsin the IC,, IC2 and IC3 positionsrequires the cartridge to be fedfrom an external supply, as thetotal (worst case) current de-mand of the board is then about320 mA, exceeding the avail-able 300 mA supply capacity ofthe computer slot. In practice.however, we measured a cur-rent demand of about 100 mAwith NMOS chips fitted in thecircuit, which could, therefore,be fed from the computer with-out overloading the internal

+5 V supply.From these observations it canbe seen that it is good practiceto measure the actual currentconsumption of the cartridgebefore deciding on computeror external supply.

Programming thePIOsThe Type 7.80A PIO from Zilogfeatures two 8 -bit ports, whichcan be set to one of four poss-ible operating modes bywriting an appropriate byte tothe command register in thechip. The logic state at the B/ASEL input determines whichone of the two ports is to beread from or written to (port Aor B), while the bit at C/17) SELindicates transfer of a con-trol/status word (C) or a dataword (Th via the 8 -bit databus.Address lines Act and A, driveB/A SEL and C/D- SEL, respect-ively, enabling the user to con-figure each PIO for any one ofits four possible modes. MODE43 selects the port A & B byteoutput mode, MODE 1 the byteinput mode, MODE 2 the byteinput/output mode, and MODE3 the bit programmable in-put/output mode.Modes 0, I and 2 operate on thebasis of interrupts, and can,therefore, only be used with theZ80 CPU programmed tooperate in its interrupt mode 2.This requires running amachine language program todefine the address of the inter-rupt service subroutine. In thecase of the MSX computer,however, the VDP-generated in-terrupts must first be disabledwith instruction VDP (I)=VDP(1)AND 223. Following the servic-ing of the cartridge -generatedinterrupt, the display interruptsmust be enabled again by re-programming the Z80 for mode1 interrupt operation and nextrunning command VDP(1)=VDP(1) OR 32.Considering the complexity ofthe foregoing programming se-quence, it was thought useful tofurther examine PIO MODE 3,which enables ready program-ming-i.e. in BASIC-of the car-tridge without the need toobserve the intricacies of inter-rupt service subroutines. ThoseMSX users interested in usingPIO MODE 0 I, or 2 should con-sult Zilog's copiously detailedComponents Data Handbook,or their 280 Applications Hand -

CTC bit

function

notetsllow (0) high (1)

Do vector control byte

Di - software reset

Di no time constantfollows

time constantfollows

D7 trigge uponloading timeconstant

clock/ triggerpulse starts timer

timer mode only

Di falling edge rising edge CLK/trigger edgeselect

135 :16 prescaler :256 prescaler timer mode only

Dc timer mode counter made

D7 enable INT disable INT

Table 2. Bit functions in the Z80 CTC control register.

book.The following instruction se-quence initializes MODE 3 inthe PIO:Mode Control Byte = &HFF(define MODE 3);I/O Register Control Byte =&Hxx (see example below);Interrupt Control Byte = &H07(interrupts disabled);Interrupt Disable Byte =(may not be required);

The byte written to the I/Oregister in the PIO determineswhether the individual lines areinputs (logic 0) or outputs (logic1). Example: sending byte &HFOto the I/O A register sets portlines A. AI, A2 and A3 to in-puts, while Az, As, As and Ai areset to output operation.After the initialization routine,data can be output and input viathe port lines. Evidently, each ofthe ports must be initialized asset out above. This is done byselecting the appropriate chip(I/O address lines A2 and A3),the appropriate port (A/I1), andcontrol/data access, as re-quired. All of this is ac-complished by a sequence ofwrite instructions to addresseswithin the cartridge I/O block.

Programming the CTCThe Type Z80 CTC comprisesfour individually configurablecounter/timer circuits. Thefunction of each bit in the CTCcontrol byte is shown in Table 2.The stated time constant (bit D2)determines the number ofpulses before the ZC/TO outputgoes high. Each timer/counterwill continue to operate until asoftware (DI) or a hardware

reset (pin 17) is received by theCTC.

ConstructionSince the proposed I/O andtimer module is to function as aplug-in cartridge for MSX com-puters, there can be no doubtabout the need for a ready-made, double sided, andthrough -plated PCB-see Fig. 3.As there are relatively few com-ponents on this board, no prob-lems are envisaged if due careis taken to solder accurately:many tracks run quite close toanother and are, therefore, indanger of being accidentallyshorted by excess solder.There is an important point tonote before actually starting topopulate the board. Make surethat it fits into the preparedmusic cassette holder-, it may benecessary to do without ICsockets to ensure the absoluteminimum height of the board, inorder that the cassette box canbe closed properly. The reelposts and any other studs in thecassette box must be removed,and a rectangular slot should becut as shown in Fig. 4.The home-made cartridge mustbe sufficiently sturdy to be ableto withstand being plugged inand removed again quite fre-quently. without developingcontact problems on the con-necting copper tracks at theslot side of the board.

MSX software for thecomputerscopeThe general programming

EE

January 198756

Parts List

Resistor:

Ri =12K

Capacitors:

Ci =1004;6 VC2;CEC4=100 n

Semiconductors:

ICi:ICz =280A PIO 'IC.=ZMA CTC IC& =741-1CT138

IC5=74HCT85

+CMOS version is preferred;

see text.

Miscellaneous:

3 off jumper pins for link e1 off 2 3 contacts jumper block3 off jumpers for above blocksKi= 50 -way plug for PCB edge

mounting (right angle type)

PCB Type M251 music cassette box (see text).

Fig. 3. Component mounting plan for the I/O and timer cartridge.

4

6L

1_ 27

109

65

16.9

Fig. 4. Dimensions of the rectangular clearance cut into themusic cassette box.

methods for operating the corn-puterscope (see ElektorElectronics, September andOctober 1986) in conjunctionwith an Electron, C64, or BBCcomputer, also apply to theMSX software supplied with PCboard Type 86125. However thelimited screen resolution ofMSX computers necessitates aslightly different position forthe oscilloscope controlstexts-see Fig. 5. The variousscope "controls" can beselected as required by meansof the function keys on the MSXkeyboard, while the cursorpositioning keys permit settingthe requisite parameter value.In view of the previously men-tioned limitation imposed onthe attainable resolution of theMSX screen (192 x 256 dots), it

was found impossible to retainthe quantifying figures along-side the vertical and horizontalaxes.The function keys Fl through F9on the MSX computer are pro-grammed to do the following:Fl sets the required amplitudeand merits no further comment.F2 and F3 serve to set the ver-tical offset and the trigger level,respectively. This involves thedisplaying of an absolutevoltage level, and, since thetrigger level is comprised in thesample byte. changing the ver-tical offset causes the triggerlevel to be changed accord-ingly. The computer displaysthe trigger threshold thus ob-tained by a small, blinking, bar.The screen division (graticule)can be defined either in 1 -pixel

5

-.-1. ,-;

.

. r,,

1ii

I , rI

iii

i

In -1 r ,4

----,ka ,

.,

s

I

._

+17 ,T'sir, I i 2;f-JCIFtlirif'di-11-tOrriti

]. i_ 1 '-41-- Getrit,

i 20ps

-FS slc.r-e:r:cs

Yic

I111

, :,

, , -244.l

II 111111.

,.

-T.. i 1 NI,

I t.:11 TR:r5eEFEI 11

÷1---F-'?' 7 1

I -

61:- ir)ie r

1:7 1-i-Drri.

,e

Fig. 5. Two examples of the use of the screendump optionoffered by the computerscope software.

EE

January 1987

IF

f

t

increments (cursor up/down),or in 8 -pixel increments (cursorleft/right). This arrangement isalso valid for function 7.F4 selects the trigger mode:automatical, manual, or exter-nal. The automatical triggermode causes the computer toestablish the trigger level afterdepression of the space bar. Inthe manual and external modes,the computer waits for thespacebar to be pressed a sec-ond time, indicating a manualtrigger pulse, or a triggerenable pulse (EXT).F5 selects input mode AC, DC,or GND (0 V).F6 sets the timebase.FT sets the horizontal position ofthe trigger instant.F8 selects a positive or anegative trigger slope.F9 selects the display mode:single (+ delete), continuous(+ delete), or continuous. Press-ing the DEL key causes the dis-play to be erased beforeshowing a new image.F10 permits outputting thescreen page contents to aprinter (screendump mode).The initialization routine in theMSX computerscope programis specific to the Smith Coronaseries of printers; other typesmay require rewriting theroutine to suit the relevant bitimage mode and the print headlayout. With some skill inmachine language program-ming. writing one's own screen -dump subroutine is con-veniently started by carefullystudying the Smith Corona ver-sion supplied.Table 3 shows a straightforwardtest program to check the per-formance of the cartridge andthe computerscope board, in asimilar manner as already de-tailed for the BBC and Electroncomputers. The cartridge isconnected to the corn-puterscope as shown in Fig. 6.It is seen that the PIO handshak-ing lines ARDY (port A ready)and ASTB (port A strobe) arenot used in the basic set-up.However to improve upon theoverall speed of the communi-cation between computer andcomputerscope board, one ofthe unused inverters N1E-Nis onthe latter may be connected asshown in Fig. 6 to effect inver-sion of the READY output of thecomputerscope board. It mustbe noted, however, that theMSX software supplied is basedon PIO MODE 3, as already de-tailed, and therefore does not

support the use of the hand-shaking lines. Experiencedprogrammers may have a go atwriting an interrupt servicingroutine that does permit the useof ASTB, while ensuring thatthe MSX screen timing (VDP)remains correct. In all, thewriting of a subroutine satisfy-ing the foregoing conditions israther specialized work, and ifyou feel not quite sure about itall, simply leave the Ang lineopen and the set-up will still besufficiently fast.Finally, MSX users interested infurther details on machinelanguage programming willfind invaluable information inThe MSX red book, by AvalonSoftware. and in Behind theScreens of MSX, by Mike Shaw.Both books are published byKuma Computers Limited;Pangbourne; Berkshire. Tele-phone: (07357) 4335; Telex849462 TELFAC. These newpublications will be reviewedin the New Literature colUmnsin a forthcoming issue ofElektor Electronics.The next instalment in thisseries of articles will deal with aMSX EPROM programmer,which operates in conjunctionwith the I/O and timer car-tridge.

10 SCREEN 220 A=3*1630 DA=A÷4: 013=A.,5:40 OUT CA, 255: OUT CA, 0: OUT CA, 7: OUT DA, &H1050 OF=O: IN = 1: Nt=0: TH=0: TB =8: AM=8: TR =060 OUT CB, 255: OUT CB, 0: OUT C8,770 OUT DB, (OF,64+128*IN): OUT DA, &H1480 OUT DB, (N14-64÷ 128*TH): OUT DA, &H1290 OUT DB, (TB+ 16*AM): OUT DA, &H11100 OUT CB, 255: OUT CB, 255: OUT CO. 7: OUT DA, 0: OUT DA,

&H40: OUT DA, &H10110 HO =TIME+ (TB,- 1)*50120 IF HO>TIME THEN120130 IF TR =0 THEN OUT DA, EtH30140 IF TR =1 THEN OUT DA, &H38150 IF TR<>2 THEN 160 ELSE IF INKEYS= " " THEN OUT DA,

EtH90 ELSE 140160 HO = TIME+ 3*(T13 11*50170 OUT DA, 0: OUT DA, &H20: OUT DA, 0180 CLS190 PSET (0,85)200 FOR 1=0 TO 255 STEP 2210 LINE -(112, 150-INP(DB)12)220 OUT DA, &H40: OUT DA, 0230 OUT DA, &H40: OUT DA, 0240 NEXT250 OUT DA, &H20260 FOR 1=256 TO 512 STEP 2270 LINE -11/2, 150-INP(DB)/2)280 OUT DA, &HBO: OUT DA, &H20290 OUT DA, &H60: OUT DA, &H20300 NEXT310 GOTO 50

AR Table 3. MSX-test computerscope.

6

2

4

6

8

10

12

14

16

18

1

3

5

7

9

11

13

15

21

insi.

A7 PA78

7

6

5

4

3

2

1

17

16

15

14

13

12

11

10

9

1920

A6 PA6

A5 PA5

A4 PA4

A3 PA3

A2 PA2

Al PA1

A0 P A,0'

ASTB READY

07 BP7

B6 PB6

B5 PB5

B4 PB4

B3 PB3

B2 PB2

01 PB1

BO PBO

.6 mie.

msx cartridge computerscopesee text

READY

Fig. 6. Overview of connections between the cartridge and the computerscope.

EE

January 198758

DIGITAL SIGNAL PROCESSING

Compact disc players have been with us for some time. Digitaltelevision receivers are becoming commonplace. These, and

other apparatus, have an important aspect in common: digitalsignal processing. But what is really involved in this?

Digital circuits only respond todiscrete values of input voltageand produce discrete values ofoutput voltage. Usually, thesecircuits operate between twodiscrete voltage levels, i.e., highand low (logic) levels. It istherefore clear that before sucha circuit can operate theanalogue signals have to beconverted into digital (= binary)signals.

Some fundamentalsFig. 1 shows the basic set-up ofa digital processing circuit. Theincoming analogue signals at Xare digitized, in an analogue -to -digital (A -D) converter, pro-cessed in a (digital) signal pro-cessor, and then reconvertedinto analogue signals in a D -Acircuit.The A -D converter produces astream of binary values byquantization. In this method, theincoming waveform is dividedinto a finite number ofsubranges each of which isrepresented by an assignedbinary value within thesubrange. In a compact discplayer, a 16 -bit A -D converter isperfectly adequate, while invideo circuits 8 -bit convertersare satisfactory.Since the signal processoroperates by computation, it canhandle only a finite number ofpulses in unit time. It is the taskof the A -D converter to ensurethat the input capacity of theprocessor is not exceeded, andthis in turn determines the sam-pling rate.Sampling is a technique inwhich only some portions of the(analogue) input are used toproduce the set of binaryvalues to represent the infor-mation contained in the wholesignal. To ensure that the outputvalues represent the inputsignal without significant loss ofinformation, Nyquist's SamplingTheorem states that the rate of

sampling of a periodic quantitymust be at least twice the fre-quency of the input signal.A -D converters in CD playerstherefore produce about 45 000sixteen -bit values for each sec-ond of music. The signal pro-cessor in these players needtherefore be only moderatelyfast, as they have some 22 ps be-tween consecutive compu-tations. A video signal pro-cessor must be much faster asthis has to carry out more than10 million computations persecond.

Requirements andapplicationsThe set-up of Fig. 1 can performall the functions of an analoguecircuit, and more. It is farsuperior to a complex combi-nation of resistances andopamps in summing, substract-ing, multiplying, and raising toa power.For example, the volume settingin an analogue circuit involvesthe signal being attenuated byresistance(s), being distorted intransistors, being subjected tohum from the main transformer,and finally being output by ascratchy volume control wiper.In a digital circuit, it is merely

divided by a variable divider ormultiplied by a variable factor.Filtering in a digital circuit isalso simplicity itself: the basicoperations of multiplication andaddition enable virtually anykind of filter to be realized. Ofcourse, the filter designer mustbe thoroughly familiar withfilter theory, and Fourier andLaplace transforms. Apart fromthat, the filter can be adjusted,altered, and varied with the aidof software.For instance, in a digital tele-vision receiver, the tuner is con-nected to the various outputstages by digital circuits. Thesecircuits filter (compute!) fromthe video signal the sound andchrominance subcarriers, ex-tract the quadrature compo-nents from these anddemodulate them; cut off anynoise pulses; eliminate any con-version errors and picture inter-ference (within limits); arrangethe volume of sound, stereobalance, tone, colour saturation,brightness, and optimum con-trast. These circuits are cur-rently contained in special VLSIchips.As yet, there is no (pre-) ampli-fier for CD players with directdigital input. But progress israpid ...

Fig. 1. Basic set-up of a digital signal processing unit.

Signal processorsAs already mentioned, virtuallyall requirements are met by thebasic operations of multipli-cation and addition. Also, it wasshown that the signal processordoes not have all that much timeleft for each computation. Sig-nal processors have, therefore,microprocessors with typicalinstruction codes; they are rela-tively small but, none the less,quite fast.Sequences such as:"fetch value 1; fetch value 2;multiply values 1 and 2; addvalue 1 to the result; load the ac-cumulator at the position ofvalue 1 and increase the ad-dress counter"as a rule have only one oper-ational code. Moreover, whilean instruction is being pro-cessed, the next instruction andthe next two values areretracted from the memory(pipelining). This means thatsuch an instruction takes threeclock pulses from start to finish.With a 10 MHz clock, a 16 -bitmultiplication and addition lastsonly 300 ns.Even faster are signal pro-cessors that use the Harvard in-stead of the von Neumannarchitecture. In the latter, dataand instructions are stored in acommon memory, whereas inthe former separate memoriesare used (see Fig. 2). InHarvard -type processors, in-structions and data (in someeven two sets of 16 -bit data) arefetched from the memory simul-taneously. This means that twoto three times as many oper-ations can be carried out persecond as compared with a vonNeumann device.The software for the requiredfunction is first computed andloaded into a normal computer,with which the run of the pro-cessing cycle is simulatedbefore the PROM of the signalprocessor is loaded.To conclude, and specially for

2

n in

data ROM

data RAM

'data

signalprocessor

'out

n °peados

command RAM

command PROM

Fig. 2. Modern signal processors use the Harvard structure inwhich the memories for data and commands are separated.

Fig. 3. Basic recursive filter. Output signal ylt) is stored in anintermediate memory and used as input signal y(t-1) for thenext computing cycle.

Fig. 4. Basic non -recursive filter. Output signal ylt) is built upfrom a succession of inputs: x(t)...y(t-n). Secondary memoriesare required for each of the inputs.

5

Table 1

StartClearClsB=0.5V% =205Defline 1Dim X1%164)Dim Yl%(64)Dim Z1%(64)For I% =1 To 64X1%11%)=1% *10-5

Next 1%Polyline 64,X1%(),Y1%0 Offset0,V%

DoMouse X%, Y%, T%If T%=1If T1% = 1X% = Int(X%110) 4 1

Y% =Int(Y%/10)*10+ 5Y1 %(X%)= Y% -V%Polyline 64,X1%(),Y1%0Offset 0,V%

ElseCls

EndifEndifT1% =T%Exit If T% =2

LoopFilter:Print At(1,1);Input "Select filter order:(1...9)";Ord

For 1=1 To 64Z1%(I)=Y1%(1)

Next IFor 1=1 To OrdFor I% =1 To 64Z1%(l%) = B*Z1%(1%)(1- B)*Z1%(I%-1)

Next I%Next IClsDefline 2,1,0,1Polyline 64,X1%(),Z1%() Offset0,V%

Deffine 1,1,0,1Polyline 64,X1%(),Y1%0 Offset0,V%

DoMouse X,Y,TExit If T=2

LoopAlert 1, "Change filter?", 2,

"New filter; end", ZIf Z=1Goto Start

EndifIf Z=2Goto Filter

EndifEnd

Table 1. Example program inBASIC for an RC low-passfilter of the nth order and itsgraphical representation.(Fig. 5).

59 EE

January 1987

those readers who want todesign a digital filter and arenot too familiar with Fourier orfilter theory, a sample designfor a personal computer.Basically, there are two types offilter: recursive and non -

recursive. Figure 3 shows anexample of the simplest type ofrecursive filter, where the out-put signal is available for furtheruse a computation cycle T later.This type of filter can be usedfor high- or low-pass purposes.Non -recursive filters are formedby inserting the input signal(s)into two or more successivefilter sections as shown inFig. 4. Each section must, ofcourse, have a secondarymemory. This type of filter issuitable for use as a transverseor comb filter.A low-pass filter is easily com-puted from the followingmathematical relation

y(t)=ax(t); by(t-1)

where y(t) is the output signalresulting from an input signal xat time t;y(t-1) is the output signal onecomputing cycle before y(t);

b=1-a;0<a<1;0<b<I.

The following example pro-gram was written in GFA-BASICfor the Atari -ST. If the GFA in-terpreter is not available, theRun Only Version can becopied (free of charge) at anyAtari dealer. It can, however, bemodified for use with othertypes of computer relativelyeasily, particularly if Pascal isused.

EE

January 1987 60

SOFTWARE FOR THEBBC COMPUTER -2:THE BBC BUGGY

--(*1111'7Th I tilt_

1.gyvvvvi-,---yrots

This article deals with a remarkable combinationof versatile hardware and ingeniously written,

learn -as -you -program, software. The BBC Buggy isa computer -controlled little robot with some quite

astounding capabilities.

Although this series ofarticles is primarily in-tended to discuss corner-cially available softwarepackages for the BBCmicro, it was deemedworthwhile to introduce theBBC Buggy and its associ-ated control programs tothe many owners of a BBChome micro.

Available from Econom-atics' Education Division,the Buggy is in essence asmall vehicle, composed ofFischer-Technik parts, andcontrolled over a length offlat ribbon cable connec-ted to the standard periph-eral port on the BBC ma-chine.The principle of a steerable

turtle, known from in-teractive programminglanguages such as LOGO,has been put into practicein the case of the Buggy, asit is a tangible vehiclerather than any kind ofgraphics figure movingabout on' the screen andprogrammed to makedrawings by means of a set

of user -definable com-mands. In principle, theBuggy is therefore but atool in learning about struc-tured programming. How-ever the fact that it is aprecisely engineered ve-hicle offers possibilities notcommonly available withsimulation -based (joystick& screen) systems.

The BuggyhardwareIt would be beyond thescope of this article to givea detailed description ofthe Buggy's construction;the accompanying photo-graphs should give readersa good impression of whatthe vehicle looks like.Two powerful steppermotors, controlled via atop -mounted interfaceboard, ensure a highdegree of positional accu-racy at a remarkably lowprogramming effort. TheBuggy can carry a pencilto leave a trace as it com-pletes its task route; thechain -driven wheels andthe rear -mounted ballbearing enable the Buggyto revolve around its ownaxis, leaving only a dotfrom the electro-magnetoperated pencil as thewheels revolve in oppositedirection.Provision has been madefor the incorporation of alarge number of optionalhardware add-ons, such asa grab arm, a bar-codereader (BCR), and a front-

mounted light -dependentresistor (LDR), which can beused to track down lightsources. The fully equippedBuggy is an agile, semi -

intelligent creature thatcan find and remember itsown way through almostany "landscape'; no mat-ter how many purposelycreated obstructions it en-counters while seeking itsway to the finish.The grab arm is a stunningexample of the combinedpower of the Buggy hard-ware and software; the con-trol program, through adigitizer, monitors the cur-rent consumption of thegrab arm motors, and thusprevents lifted objects frombeing crushed. Actually,the Buggy was tested byhaving it lift, carry, and putdown an egg without mak-ing a mess of it.The optional BCR enablesthe Buggy to travel over atrack consisting of onemetre or so of bars whichmay represent, for instance,the notes of a piece of(computer) music; the BCRsystem is comparable to

that used for the digitalreading of price dataprinted on many shop-ping items. However, sincethe Buggy travels at ahighly accurate speed, nosynchronization bars are re-quired in the coded pat-tern. A few try -outs showedquite conclusively that theBuggy can be relied on tosupply 100% faultless BCRdata to the computer. It isalso possible to have theBuggy read its route direc-tions from pieces of BCRstrip located at a fewplaces in the landscape.

The BuggysoftwareWhatever the performanceof the Buggy's hardware,the vehicle would be but aclumsy toy without the sup-porting software. Econ-omatics, in our view, de-serves credit for the pro-duction of software that is,in a word, unbeatable evenby experienced machinelanguage programmers.The BBC BASIC interpreter isexploited to the full, andthe same goes for thegraphics features of themachine. The Buggy com-mand set comprises 10simple to program instruc-tions, while the user is freeto add his own for specificpurposes. PENEDIT can beloaded from disk to supportthe use of the software -controlled pencil; again,the degree of accuracyachieved with the Buggy'spropulsion system is as-tounding: with some skill inprogramming, writing one'sname on a sheet of paperis feasible.The programs supplied byEconomatics are user-friendly and readily ex-tendable for specific pur-poses. Most instructionsrelating to the Buggy's,movements can be definedin the necessary number ofincremental steps; e.g.128he. FORWARD, TURN 3FnexLEFT, SPEED=7Che., etc.Economatics supply acopiously detailed instruc-tion manual with theBuggy; a large number ofhighly instructional pro-gramming examples are

given, as well as a step-by-step construction methodfor the fully-fledged versionof the project.

ApplicationsAs already noted, the maininterest for the BBC Buggylies in the educationalfield; the fact that a tan-gible vehicle can be seento move about with ap-parent intelligence ishighly stimulating to furtherexploration of program-ming methods. The Buggytherefore comes in whenscreen-based turtles fail toarouse further interest inwriting structured programsleading up to sophisti-cated applications in thefield of robotics and its as-sociated science, cyber-netics.The so-called Buggy Park isan outstanding example ofthe resourcefulness ofEconomatics in devising abench -mark for other re-mote -controlled vehicles.In essence, the park is arectangular space bor-dered by a "wall"; the in-struction manual gives fulldetails of the suggestedconstruction, as well as ofthe way the exact size of thepark is entered in the rel-evant control program.SUNSEEK can be run to showthe Buggy's ability to trackdown a small light sourcelocated anywhere in thepark. Neither the dis-placing of the bulb, nor theraising of obstructions dur-ing the performance willkeep the Buggy from find-ing and remembering its

EE

January 1987

way to the light. On arrivalthere, a triumphant cry isproduced.Sceptical onlookers can beinvited to a game of MANVS BUGGY, which effectivelydemonstrates the skill ofthe latter in finding a par-ticular location within anarea, relying on limitedsensors (LDR, touch -sensi-tive bumpers) only.

ConclusionsThe BBC Buggy is a most in-structive extension of theBBC computer. Its hardwareand software operate ina purposeful manner, en-suring both optimum pro-cessing of instructions andease of extension by theuser.The BBC Buggy comes as aFischer-Technik Kit, togetherwith the associated soft-ware and instruction man-ual, and requires nospecial tools for assemb-ling.More information on theBBC Buggy and its hard-ware and software optionsare available fromEconotnalics EducationDivision4 Orgreave RoadHandsworthSheffield 513 9/Q.Buggy: £129.98: PEN KitE19.85; Grab Arm £79.00.

EE

January 198762

Of PRODUCTS NEW PRODUCTS NE1AAnalogue anddigitalmultimeterFeedback's new ADM663 com-bines the traditional analoguemoving coil multimeter with adigital multimeter, providing atruly practical measuring tool.Whilst the LCD display allows aprecise reading to be made, aglance at the pointer allows theuser to get a feeling for thetrend of the measured valuewithout having to try to resolvethe rolling digits. This is es-pecially useful when measur-ing maximum or minimumvalues.The analogue movement is aclass 1.5 multimeter with 10 MQinput impedance and 25 mV/200 pA DC and AC ranges.Overranging of 25% is providedon each scale and these are alllinear, including, unusually, theohms range.The digital side is equally im-pressive with 2000 counts andaccuracy of 0.1% and the highcontrast liquid crystal display islegible even in poor light con-ditions.An important feature of bothanalogue and digital facilities istrue RMS measurement of alter-nating voltage and current. Thisprovides accurate measure-ment of the RMS values ofsignals rich in harmonics. withcrest factors up to 5 at midrangeor 2.5 at full range. A typical ap-plication is the measurement ofthe signal-to-noise ratio of a re-ceiver. The AC bandwidth is25 kHz. The meter has 8 func-

tions and 35 ranges, all with ex-ceptional protection againstoverload; protection on the am-meter function is by fuse and allvoltage and ohms ranges willwithstand 380 V without dam-age. Auto -polarity switching isprovided and the taut -bandgalvanometer enables theADM663 to withstand theshocks expected from a lifetimeof being carried in a toolbox.Feedback Instruments LimitedPark RoadCrowboroughSussex TN6 2QR.Telephone: (089) 26 3322Telex: 95255

(3520:13:F)

MicroprocessorRTC moduleA real time clock module nowavailable from IQD is specifi-cally designed for use in micro-processors. The RTC 58321features a built-in 32.768 kHzstandard clock quartz oscillatorwhich eliminates the need forregulation and aids rationalis-ations. It also incorporates bat-tery back-up, time counter(hour, minute, second), datecounter (year, month, date andday), a 12 hour/24 hour clockswitchover function and auto-matic leap year setting, andcounter start, stop and resetfunctions.The clock module has an inte-grated circuit with an output of

1 Hz, and standard signal outputcan be set at 1024 Hz, one sec-ond, one minute, one hour. A4 -bit bi-directional bus line isemployed for data, which iswritten to and read frommemory. Installation is madeeasy by its DIP-16PIN design.IQD is a major producer ofquartz crystal units, oscillatorsand filters. Its 150 -page cata-logue now contains the mostcomprehensive selection of fre-quency control devices in theUK.

IQD LimitedNorth StreetCrewkerneSomerset TA18 TAR.Telephone: (0460) 74433Telex: 46283

(3546:2)

Graphicsevaluation kitfrom TIJust on offer from VSI is TexasInstruments' new low-costgraphics design kit. A com-plete package which brings asimple and comprehensive full -colour bit -mapped graphics tothe designers' fingertips.Operating with any 8-, 16-, or32 -bit CPU this videographicskit will support systems withscreen resolutions from256 x256 to 4096 x 4096 pixelsand any number of colours.A new contept with new inte-grated circuits to match has re-duced the active device count

to six. Video system controllerTMS 34061 for video RAMseliminates separate text andgraphics subsystems. A ver-satile video palette, althoughlow in cost, provides all the cir-cuitry normally contained in asubstantial p.c.b. Two multiportvideo RAMs not only providevirtually unlimited memorybandwidth but also eliminatethe usual problems betweendisplay, refresh and update.This new approach to colourgraphics, which unifies the textand graphics into a totally bit -mapped system brings manyadvantages to the user. Re-duction in component countmeans smaller size and greaterreliability. New system architec-ture allows conventional hard-ware functions to be im-plemented in software. It pro-vides the ability to select draw-ing algorithms to fit applicationand performance needs.Lower costs, increased flexi-bility and simplicity of use sum-marize some of the advantages- others include full sup-porting hardware and softwarefrom TI for extended systems.The complete design kit costs£99 + VAT, and comprises sixchips, one 68 -pin socket, and acomplete package of sup-porting literature which in-cludes six separate publi-cations.

VSI Electronics (UK) LimitedRoydonbury Industrial ParkHorsecroft RoadHarlowEssex CM19 SBY.Telephone: (0279) 29666Telex: 81387

(3546:4:F)

PRODUCTSPower driverICs interfacelogic to high -

current loadsA trio of quad -gated powerdriver integrated circuits fromRCA Solid State provide thehigh current levels needed tointerface logic circuitry to theresistive and inductive loadsfound in digital control systems.instrumentation and other ap-plications. Two of the devicesoffer complementary operation:The CA32I9AE is an invertingpower driver while theCA3252E provides the samedrive function in non -invertingform. The third member of thefamily, the CA3242E, is an in-verting power driver that offersthe additional advantage ofshort-circuit protection shouldthe load current exceed a pre-determined value.All three drivers can switchload currents of 600 mA withoutspurious changes in the output -state voltage. The input gates ofeach driver are compatible witheither TTL or CMOS logic de-vices operating from 5 V powersupplies. All drivers contain in-ternal diodes connected acrossthe power -driving transistors toprotect against voltage tran-sients caused by inductive -loadswitching.

RCA CA3219AE/3252E 3242EPower Driver ICs

Short-circuit overload protec-tion is the unique feature of theCA3242E. Overload protectionis activated when a load currentof about 1.2 A causes thecollector -to -emitter voltage(VcE45,,,r)) of a driving transistorto rise above 1.3 V for longerthan a built -in -time delay of ap-proximately 35 us. If the timerdelay is exceeded, the transis-tor is shut down by its protec-

0 NEW PIRODUCTStion network. but withoutaffecting the other driving tran-sistors. The corresponding in-put or the Enable pin (pin 14)must be toggled to reset theprotection network.All three types can handleeither resistive or inductiveloads. Typical load -driving ap-plications include relays.solenoids. AC and DC motors.heaters, incandescent andvacuum fluorescent -displays.

RCA Limited Solid StateDivisionLincoln WayWindmill RoadSunbury -on -ThamesMiddlesex TWIG 711W.Telephone: 093 27 85511

(3520:3:F)

versionof 64K EEPROMHitachi are launching a 64KEEPROM that uses low powerCMOS technology and, at thesame time, achieves excellentspeed characteristics.The EEPROM -the HM58C65-is organised as 8K x 8 and hasbeen designed with a variety offeatures - such as a single railsupply and on -chip latches andtimer - which makes it simpleto use. Also included are poweron/off data protection circuitry.The device offers three erasingmodes - byte. page and chip,

with erasing times of 10, 10 and20 ms respectively. Byte andpage write times are also just10 ms and access time is 200/250 ns.The device's CMOS technologyreduces operating current tojust 10 mA (typ) as opposed tosix times this amount for a con-ventional NMOS device. Stand-by current is reduced evenmore dramatically to 1 mA -just 4% of the standby power ofan equivalent NMOS EEPROM.The device is packaged in28 -pin dual in -line and SOPplastic packages.

Hitachi ElectronicComponents (UK) Limited21 Upton RoadWatfordHertfordshire VIDI 7TP.Telephone: (0923) 46488Telex: 936292 hitec g

(3546:16:F)

Single boardgives IBM' PCminicomputerpowerA single -board co -processorfor the IBM' PC/XT/AT andcompatible machines is nowavailable from PPM Instrumen-tation Limited.The Pro68 from Quin SystemsLimited is based on the high-speed Motorola 68000 (68010

optional). The board providesfull 16/32 -bit minicomputer likeprocessing power at low cost. Itfeatures a 10 MHz no -wait -statedesign and simply plugs into anavailable full-size PC slot.The 0S9 operating system pro-vides a UNIX. type multi-usermulti -tasking environment. Asecond operating system isavailable - the proprietaryDOS68, it provides IBM' PCDOS compatibility eliminatingoperator confusion.

Future memory growth atminimum expense is providedby using 256 K bit chips allow-ing memory sizes from thebasic 512 Kbytes to 1 Mbytes tobe built up. The board also in-cludes provision for the 32081math processor giving in ex-cess of 20,000 floating point op-erations per second.Applications potential is enor-mous and brings the PC userinto such areas as scientificprocessing, and creation andtesting of UNIX' compatibleapplications.

' IBM is a registeredtrademark of InternationalBusiness Machines Inc.

UNIX is a registeredtrademark of Bell Laboratories.

PPM Instrumentation LimitedHermitage RoadSt JohnsWokingSurrey GU21 1TZ.Telephone: (04867) 80111Telex: 859181

(3457:12:F)

EE

January 1987

OAT PRODUCTS NEW PRODUCTS NEVFlexible VAW/dBmeterNow available from PPM In-strumentation Limited is theBallantine 3501A. The four -function 41/2 -digit multimetergives true RMS measurement ofAC and DC voltage, current,power and dB levels.Of particular interest is thewide range of dB measurementoptions, the standard scale be-ing 0 dB to 1 mW in 600 ohms.Further characteristic im-pedance levels between50 ohms and 1 Kohm areavailable making conversiontables redundant. Relativegain/loss levels are thussimplified and outputs can beread directly.When used as a Wattmeter realload delivery is computedusing applied voltage, load cur-rent and power factor data.Power ranges cater formeasurements from microwattlevel to a maximum 7.5 kHz.Power ranging is semi -auto-matic.Voltage and current functionsgive selectable AC or AC/DCcoupling, floating -input andtrue RMS measurement. Volt-ages are autoranged between200 mV and 750 V. Currentranges are push-button selec-ted and are between 200 NAand 10 A, front panel indicatorsflag out -of -range settings.The versatile 350IA is a wide-ranging and powerful tool forgeneral, production and fielduse. An optional interface withIEEE 488 general-purpose in-strument bus allows the unit totalk to output data in automated

system applications. The unit isoperated from a 115/230 Vmains supply.PPM Instrumentation LimitedHermitage RoadSt. JohnsWokingSurrey GU21 1TZ.Telephone: (04867) 80111Telex: 859181

(3457:6:F)

"Better thangold"connector-

platingalternativeA plating system whichremoves the need to com-promise connector perform-ance and reliability on thegrounds of the price of gold isbeing used on IDC connectorsnow available from Dage asstock items.The Robex plating system isclaimed to perform "better thangold" because 10 microinch ofRobex outperforms 30 micro -inch of gold when comparedusing standard corrosion andporosity (nitric acid) tests.Thickness for thickness, Robexexhibits inherently lowerporosity compared with goldbasically because the crystalsize grain structure of Robex issmaller than that of gold and thecrystals lie closer togetherthereby enabling Robex to

cover up surface imperfectionsmore effectively than gold isable to.Robex gives the reliability ofthick gold plating but withoutinvolving the customer in thehigh cost associated with gold.Results of comparative testsshow that in terms of porosity,environmental corrosion resist-ance. solderability and wear re-sistance Robex outperformsgold yet in terms of initial con-tact resistance there is nosignificant difference betweenthe two alternatives.

Ideal for heavy industrial andtelecommunications appli-cations. Robex can be used inany type of IDC system. So farIDC connectors carrying pinsusing Robex plating (TR20 -20 microns) have been grantedBritish Telecom approval(D2632A) for use throughout itssystems. Robex is also BT224qualified.

Dage (GB) LimitedEurosem DivisionRabans LaneAylesburyBuckinghamshire HP19 3RG.Telephone: (0296) 33200Telex: 83518

(3457:11:F)

New multi -

standardcolour monitorReflex Limited have introduceda new highperformance colourmonitor from Electrohomewhich is the first in the industry

that is compatible with theColour, and ProfessionalGraphic Adapters (CGA, EGAand PGA) in IBM' or compat-ible computers. In addition, themonitor can be used with awide range of other computerswith horizontal scan fre-quencies between 15 and34 kHz.Known as the ECM 1311, thishigh resolution 13 inch colourmonitor incorporates vari-scancircuitry which enables themonitor to automatically lockon to the video signal from thecomputer. There is no need tomake any adjustments apartfrom the usual horizontal andvertical position of the pictureusing easily accessible controlson the back of the monitor.All the user has to do is followthe instructions on installing aCGA, EGA or PGA board of hischoice and the Electrohomemonitor will automatically ad-just itself accordingly.

The ECM 1311 accepts eitheranalogue or TTL input signals.The wide bandwidth videoamplifier in the monitor andthe high quality picture tubeprovides crisp clear imagesof even the most complexgraphics.The ECM 1311 is housed in cas-ing of the same colour as IBM'PC/XT/AT's, and measures just36.4 cm x 34 cm x 39.6 cm(14.38 x 13.39 x 15.63 inches).Weight is 13.2 kg (29.1 lb).

IBM is a registered trademarkof International BusinessMachines Inc.Reflex limitedWellington Industrial EstateBasingstoke RoadSpencers WoodReading RG7 lAW.Telephone: (0734) 884611Telex: 848927

(3457:3:F)

EE

January 1987

OAT PRODUCTS NEW PRODUCTS NEI1

Electronic ig-nition controllerAvailable now from WI Elec-tronics is the SGS Type L497electronic ignition controller.designed for breakless ignitionsystems using Hall effect sen-sors. This new device wasalready introduced in ElektorElectronics, October 1986.The L497 can drive an externalNPN Darlington transistor tocontrol the ignition coil current,providing stored energy withlow dissipation.One of the special features ofthe chip is the programmabletime for the recovery of the cor-rect dwell ratio when the coilpeak current fails to reach 94%of the nominal value. Conse-quently the spark energy isnever less than 94% efficienteven during fast acceleration orcold starts.VSI Electronics (UK) LimitedRoydonbury Industrial ParkHorsecroft RoadHarlowEssex CM19 5BY.Telephone: (0279) 34577Telex: 81387

(3457:13)

MultipurposeinspectionlampBriticent has updated its well -established Elwis fluorescenthandlamp to conform to thelatest British Standard safetyregulations. In addition to the240 V version, inspection lampsare now available to operate

from 110 V AC and 24-42 V ACor DC supplies, extending therange of applications that canbenefit from the proven advan-tages of portable fluorescentlighting.Giving the same amount of lightas a 50 W filament bulb, the 8 WElwis lamp saves some 80% ofthe energy costs and providescool. glare -free illumination.The lightweight but rugged unitis ideal for the most awkwardsituations, designed to clip orhang on suitable projectionsand not to roll if laid on slopingsurfaces. It is totally insulated.resistant to oil and petrol, and isdust- and water -tight to IP67.The lamp comes with 6 m ofstandard flexible cable. Thefluorescent tube has approxi-mately 6000 hours life and iseasily replaced.Briticent International LimitedCrow Arch LaneRingwoodHampshire BH24 1 NZ.Telephone: (0425) 47617Telex: 418333

(3457:9:F)

High -powervariablecapacitorsTelecomms of Portsmouth cannow supply the new NevadaTypes TC-250 and TC-500 vari-able capacitors. The TC-250 is asingle, the TC-500 a twin tuningcapacitor with a capacitancerange of 13-250 pF.The units are available ready -assembled or at a lower price inkit form to suit radio amateurs

building aerial tuning units etc.The capacitors use a specialAcrylic Perspex, 6 mm thick, forthe end plates capable of with-standing extremely high volt-ages (7.8 kV) and with excellentRF properties.For commercial broadcastequipment a version is availableutilising ceramic end plates tosatisfy the most stringent ofspecifications.The TC-250 and the TC-500retail for £15.61 and £19.50. re-spectively.Telecomms189 London RoadPortsmouth P02 9AE.Telephone: (0705) 698113Telex: 869107 Telcom G

(3457:5:F)

Extensive rangeof quartzcrystalsA new range of quartz crystalfilters from Piezo Products in-cludes a large variety of stan-dard designs for use in HF, VHFand UHF communications,spanning the 100 kHz to100 MHz frequency range. Thefilters are also available tocustom specification, and canbe selected in a large variety ofenclosure styles.Made by the specialist firm, CRSnelgrove of Canada, andavailable in the UK from Piezoproducts, the filters come with awide range of selectable at-

tributes including sharp selec-tivity, low insertion loss, highstop -band rejection and ex-cellent intermodulation charac-teristics. Linear phase filtersand filters with precise groupdelay characteristics are alsooffered.

The HF range includes typesfor many standard frequenciesincluding 99.8, 250, 455, 1400,

1500, 1748, 1750, 1751 and4400 kHz, plus 35.4, 40, 45, 68.6,75 and 100.2 MHz types for roof-ing filter applications. The VHF/UHF range covers 9.9 to 31 MHzin a variety of standard fre-quency selections.This range of standard quartzcrystal filters also includes 200,500 and 700 kHz versions formiscellaneous applications.Piezo Products LimitedMillstream Trading EstateChristchurch RoadRingwoodHampshire BH24 3SD.Telephone: (0425) 479337Telex: 418336

(3520:20:F)

EE

January 198766

READERS SERVICES READERS SERVICE

All items may be ordered fromElektor ElectronicsSteadfast HouseBath PlaceBarnetHertfordshire EN5 5XETelephone: 01-441 6098Telex: 22828Office hours: 08.30-12.30 and 13.30-16.30

Software is also obtainable from Technomatic Limited (for address see in-side front cover).

In Sweden. printed -circuit boards should be ordered fromElectronic PressBox 63S-182 11 DanderydTelephone: 08-753 03 05

For orders on Elektor Electronics, use the order form opposite.

Excluding subscription, all prices shown are net and should be increased by15 per cent for VAT (UK only - not books or magazines) and postage andpacking costs as shown below. For convenience, the VAT amount to beadded by UK customers is shown where relevant.

UK Europe Other countries Other countries(surface mail) (airspeeded)

Books (each) 75p 11.00 11.50 12.50Orders for other items(up to 500 g) 75p 11.00 11.50 12.50Over 500 g to be advised

SUBSCRIPTIONS

United Kingdom 115.00UK students 113.50Europe Er Ere airspeeded 118.00Middle East & North Africa airspeeded 121.00South East Asia airspeeded 124.00Central Er southern Africa airspeeded 124.00USA Ea Canada airspeeded 124.00Central & South America airspeeded 124.00Australia & New Zealand airspeeded £26.00Far East & Pacific airspeeded E26.00

Student applications must be supported by evidence of studentship signed by the headof the college, school, or university faculty.

Payment may be made by cheque (made payable to Elektor Electronics); postal order;money order; Access credit card transfer lonly if the subscription goes to the card-holder's address); or by direct transfer to our account 0303636 with IJoyds Bank PLC,841 High Road, London N12. Subscribers outside the UK may also pay by Sterling Draftthrough their own bank. Cheques, postal orders, and money orders should be crossedand made payable to "Elektor Electronics".

The standard subscription order period is twelve months. If a permanent change of ad-dress during your subscription period means that copies have to be dispatched by amore expensive service, no extra charge will be made. Similarly, no refund will be made,nor expiry date extended, if a change of address allows the use of a cheaper service.

As the quality of airfreight and airmail services varies in different situations. we reservethe right to use the best available service compatible with cost and speed of delivery fora particular territory.

Subscriptions can be sent by surface mail only if specifically requested; rates for thisservice are identical to those for airspeeded subscriptions.

At least six weeks advance notice of change of address is needed to ensure that copesmay reach the new address when required. It is requested that the address portion fromyour latest mailing wrapper is enclosed with your new address instructions.

Mixing issues will be replaced within reason, providing that the relevant claim is re-ceived within two months (outside Europe and North America - three months) of thecover date of the missing issue. Requests for issues outside this period should be ad-dressed to our Back Numbers Department who will advise the cost of replacing theissues concerned.

Apart from sterling cheques, USS. Canadian S. and Euro cheques can be accepted atthe exchange rate prevaffing at the time your order is received. Note, however, thatthese should be increased by 12.50 to cover the Bank's negotiating fee.

Please note that new subscriptions take about six weeks from receipt of order to be-come effective.

It is regretted that new subscriptions can under no circumstances be backdated.

LETTERS

Letters of a general nature, or expressingan opinion, or concerning a matter ofcommon interest in the field of elec-tronics, should be addressed to TheEditor. Their publication in Rektor Elec-tronics is at the discretion of the Editor.

FAST ISSUES

A limited number of past issues can besupplied at the current cover price pluspostage & packing as detailed above.

BOOKS

The following books are currentlyavailable: these may be orderedfrom certain electronics retailers orbookshops, or direct from ourBarnet office.

300 Circuits 15.50301 Circuits 15.50302 Circuits E5.50Automate your model ra4way .

MARCH 1986Stezwoofer

No.

85357

Price VAT1E1 Ill

840 1.26

BINDERS

Elektor binderIJan '86 onwards) 12.95 MSX 13b bias board 93303 1815 273

APRIL 1986Portable rrox 86)121

86312-24530 080533 0.8)FRONT PANELS

eryn2-25 3.60 0.54No. Price VAT 860124 6.00 0.9)

(1) (El Satetite loudspealds 8W16 3.15 0.4E1

Programmable timer 85047-F 14.90 2.24Real-time clockVariable dual power

8601796019-1

3_65 0.587.20 106

Sweep generator 85103-F 5.15 0.78 supply 8111182 4.05 0.61Portable mixer 86012-1F 2.85 0.43

86012-2F 3.15 0.48 MAY 198686012-3F 5.00 0.75 Printer buffer 85114-1 11.75 1.7786012-4F 5.10 0.77 85114-2 5 05 07686012-5F 4.70 0.71 Portable meier 86012-3A 53) 0.8088012-61 3.45 0.52 E601239 4.70 0.71

a: e power 1 kW AF Mier 86031 1803 2.7086018-F 4.60 0.69

=aa.e- JUNE 198686041.F 3.55 0.54 Singletrace CRT

.

ir 'or satellite86082.F 3.50 0.53

COrr.ftetr8 -way relay board1 SW anspPrier 2

86013E603986)67

rat aye/able5.80 0.871160 174Lie RMS :T;etet 86120-F 6.35 0.% Rain gauge 86068 360 0.54Top-athe-range Portable nii,er M012-5 595 0.90

preamplrfiet 86111-F 5.10 0.84

JULY 8 AUGUST 1986Car radio Mann 86406 not a-caiat2te

SOFTWARE Guitar fuzz urztNiCd charger

8642786437

Car bens monitor 8E447

Software in IEIPROMs No. Price VAT CIAT.la indicator 86448 not ar.-a_an -IC1 Stepper motor rag rata 86451 2.8 U-_

Sideway RAM for BBCand Electron 9E452 1_95 0.39

morse program for the Icarrained mitt 86351)Junior Computer Heart beat rnoni-tor 86453 240 O_Xi1 x 2716 518 7.30 1.10 SMD de 86451 1_95 0.3)tees program for the icorntined Writ. 86452iJunior Computes Speech processor E6459 riot ova :fable1 a 2716 519 7.30 1.10 Revolution counter 86461 49) 0.74ASCII keysoft RMS-to-DC convener 86-1 1.70 0261 2716 520 7.30 1.10 Rodenk.deterrent 86490 2_00 0.30character generator arid Lae -noise aerial booster 86504 290 0.44video routines for DOS Battery 86569 net avzxhitreJunior1 2732 - 1 27t6 521 16.40 2.46 SEPTEMBER 1986character generator aridvideo routines for ex-

FITTY intrifeserowypEasar impedance

8839 7.60 1.14

tended Junior meter 99)41 6.75 1.021 x 2732 2 2716 522 24.00 3.60 Computerscape 89333 24.60 3.69character ger.erator Headphone arreakfer 8056 4.05 0.61

1 x 2732 523 9.00 1.35 Ursivbsal peripheral1 x 2716 524 7.30 1.10 equipment 9E0901 1% 120universal terminal860912 2 55 0 451 x 2732 525

wind direction indicator1 x 2716 526eabyrinth1 x 2716 527EPROM copies1 x 2716 528analytical video display1 x 81S23 529

9.00

7.30

7.30

7.30

4.80

1.35

1.10

1.10

1.10

0.72

OCTOBER 1986Equo5zer for guilesIDU ra satuhte

receptionStkOrt-Vaee receivesilirwer.i RP board)Computer.ope 2

9E061

asce2-1eso:o

8610)

5 0.8)

12193 1.891.9) 027

2.85 0.43

typewriter interface2 x 2716 530tiP-eontroBed frequencymeter 1 x 2732 531

14.60

9.00

2.20

1.35

Video bterfase forAtan-ST

956-5

86103

2.C5 0.31

6.20 0.9.3

X -Y plotter NOVEMBER 1986= 2732 532

programmable time:9.00 1.35 IC sateEte reception 90312

noise gen850 1.50

1 a Z732 535 9.00 1.35 %CBI 1.55 0.27

GHz pre -scaler A;: -_c - 86110 4.9550-871 a 2732 536 9.00 1.35 Pre 7 861111 10.40 1 84

automate yourmodel ra9erey

--.eneratorbalarce

86116 not avaaab=e

1 x 2716 537marine computer

7.30 1.10 11CD beard' 61012-2 310 0.55

1 ti 2716 538 7.30 1.10 DECEMBER ISMJumbo clock Temperature probe for2x2716 539 14.60 2.20 131.1).1 83312 105 0.19Graphics card Infra -red rernate Control 861151 2-95 0.432 x 825123 543 9.60 1.44 66115 2 3.30 0.50printer buffer True RMS inmate, 93120 9.75 1.471 a 2716 545 7.30 1.10 D A conieertv for 1 0

bus 3PRINTED CIRCUITS

JANUARY 1907IOU foe satedite TV

No. Price VAT reception 99E82-3 6.9) 1.041E) Top of the -range

JANUARY 1386preamplifier 86111-2 2250 3.38

Stead state ignition 85123 3.87 0.57 MSX cartridge for uPVariable Hier for DX 66Cs/1 12_136 1.81 ost6owope 86125 8_45 1.22

AF power Unaersal control hearrindies 85:C4 3.33 0.50 stepper motors 87003 15 40 2.31

Infra red tight switch 9:036 3 45 0.52

FEBRUARY 1986uniseesat RF board 250)) 1.80 0.27MSX-Cam boom 85130 4.80 0.72Graph,., C.C.4947

exte,s: c -89380-2 11.65 1.78Batter,

N.Cd 8E022 5.80 0.87Car tr,,rgar a'arrn 96005-1 4.85 0.70

8005-2 2. 0.40

79 EE

January 1987

1ZOMPUTER WAREHOUSE tsaFOR CALLEff

THE ALLADINS CAVE OP COMPUTER AND ELECTRONIC EQUIPMENTNOT UNE DATA RASE

*DISTEC-PThe ORIGINAL FREE OF CHARGE dial up database. Buy, browse or place YOUR OWN AD forgoods or services to sell 1000's of stock items,

spares and one off bargains. Updated daily.ON LINE NOW. CCITT, 8 bit word, no parity.

For 300 baud modems call 01-679 1888For 1200-75 baud modems call 01.679 6163

FREEYoounlyr m o i t of ftrom it smceosmapLt eprIEI For

HIGH QUALITY' COLOUR TV SETThe fabu bus TELEBOX an INVALUABLE MUST for the owner 01ANY video monitor teethe composite in put colour or monochromeMade by a major UK Co as a TOP QUALITY. stand alone UHFtuner and costing OVER £75 to manufacture this opportunity togee your monitor a DUAL FUNCTION must not be missed! TheTELEBOX consists of a compact stylish two tone charcoalmoulded case, containing ALL electronics tuner, power supply etcto simply plug in and convert your previously dedicated computermonitor into a HIGH DUALITY COLOUR* TV SET, giving a realbenefit to ALL the f antilyr! Don't worry if your monitor doesit havesound -THE TELEBOX even has an integrate watt audio amplifierfor driving an external speaker. PLUS an auxifiary output forsuperbquality television sound via your headphones or HI Fl system etcOther features include Compact dimensions of on 15.75- w75- d a 35" tt latest technology. BRITISH manufacture. fully -tun eabie7 channel push button tuner. AutoAGC circuit SAW fifter.LED status inacatoc fully isolated 240v AC power supply for totalsafety. Mains ON -OFF switch eta Many other uses

UMITED QUANTITY- DON'T MISS THIS 0 FF E Ft!!

DON'T MISS THE CPM DealOF the CENTURY

The FABULOU CPM TATUNG PC2000Professional Business System

A cancelled export order and months of negotiation enables us to offer this proiless analPC. CPM system, recently on sale at OVER £1400. at a SCOOP price just over the cost ofthe two internal disk drrvest' Or less than the price of a dumb terminal'Not a toy, the BIG BROTHER of the EINSTIEN computer. the DUAL PROCESSORPC2000 comprises a modern stylish three piece system with ALL the necessities for theSMALL BUSINESS. INDUSTRIAL EDUCATIONAL or HOBBYIST USER Used withthe THOUSANDS cr proven_ tested and ayanable CP).1 software packages such asWORDSTAR. FAST. DBASE2 etc. the PC2000 specificatron at our prices. CANNOTBE BEATEN!'Tne central processor plinth contains the 84K, Z50A processor. DUAL TEAC 55F 53/4 '

Double sided 40/80 track disk drives (1Mb per drivel. PSU, 4K of memory mapped screen RAM disk controller, RS232,CENTRONICS and system expansion ports. and if thats not enougn a ready to plug into STAN DARD 8 DRIVE port for up to FOUR8- disk drives, either in double density or IBM format The ultra slim92 key detachable keyboard features 32 user definable keysnumeric keypad and text editing keys even its own integral microprocessor which altOws the main ZBOA to devote ALL its time toUSER programs, etimi nati ng -lost character probt ems found on other machines The attractive detachable 12 monitor combinesa green. anti -glare etched screen, with full swivel and tilt movement for maximum user comfort Supplied BRAND NEWwith CPM2.2. user manuals and full 90 day guarantee. Full data sheet and info on request PC2000 Wordprocessor System

PC2000 System PC2000 Business System with CPM with CPM and TEC FP25 daisywheelwith CPM Etc. and 'Ready to Run' FAST Sales and pnnter

COST OVER £1400 Purchase ledger. supports up to9000 Accounts. VAT etc

COST OVER £1700

ONLY £29.95 OR £24.95 if purchased with ANY of ourvideo monitors. Supplied BRAND NEW ...nth full instructions and 2 EARwarranty. Post and packing £3.50 'When used with colour at

COLOUR & MONOCHROMEMONITO SPECIALS

'SYSTEM ALPHA 14 COLOUR MULTI INPUT MONITORMade by the famous REDIFFUSION Co. for their own professional computerSystem this monitor has all the features to suit your immediate and futurerequirements Two video inputs RGB and PAL Composite Video, allow directconnection to BBC/IBM and most other makes of micro computers or VCR'aincluding our very own TELEBOX An internal speaker and audio amp may beConnected to computer or VCR for superior sound quality. Many other featuresPIT. tube. Matching BBC case colour. Major controls on front panel SeparateContrast and Brightness - even in RGB mode Separate Colour and audiocontrols for Composite Video input BNC plug for composite input 15 way'f7Plug for ROB input mor.t.ilar construction etcetc

This Must Be ONE OF THE YEAR'S BEST BUYS. PC USERSupplied BRAND NEW and BOXED. complete with DATA and 90 dayguarantee. ONLY E149.00 as above OR IBM PC Version £165.0015 Day 'Cr skt £1.00 BNC sot 75p BBC interface cable £5.50DECCA 80 16 COLOUR monitor. RGB input.Little or hardly used manufacturers surplus enables us to offer this specialconverted DECCA RGB Colour Video 1V Monitor at a super low price of only£99.00. a pace for a colour monitor as yet unheard of! Our own interfacesafety modification and special 16' high definition PK tube. coupled with theDECCA 80 series 1V chassis give 80 column definition and quality found onlyon monitors costing 3 TIMES OUR PRICE The quality for the price has to beseen to be believedl Supplied complete and ready to plug direct to a BBCMICRO computer or any other system with a TTL RGB output Other featuresare: internal speaker, modular construction. auto degaussing circuit attractiveTEAK CASE. compact dimensions only 52cm W x 34 H a 24 D. 90 dayguarantee AIM gh used units are supplied in EXCELLENT condition.ONLY £99.00 +CarriageDECCA 80 16 COLOUR monitor. Composite video Input Same as abovemodel but fitted with Composite Video inwt and audio amp for COMPUTER.VCR or AUDIO VISUAL use. ONLY £99.00 + Carr.REDIFFUSION MARK 3, 20- COLOUR monitor. Fitted with standard 75 ohm

ite video input and sound amp This large screen colour asplay is idealfcrcomposite

SHOPE/S. DISCOS CLUBS and other AUDIO VISUAL appli-cations Supplied in AS NEW or little used condition ONLY £145.00 + Carr.

BUDGET RANGE EX EQUIPMENT MONOCHROME video monitors.All units ate fully cased and set for 240v standard working with composite videoinputs Units are pre tested and set up for up to 80 column use Even whenMINOR screen bums exist - normal data displays are unaffected 30 dayguarantee12 KGM 320-1 8/W bandwidth input. will display up to 132 a 25 lines. £32.9512" GREEN SCREEN version of KGM 320-1. Only £39.959- KGM 324 GREEN SCREEN fully cased very compact unit Only £49.00

Carriage and insurance on all monitors £10.00. TT U T LS

GOULD OF443 enclosed, compact switch mode supply with DC regulated outputsof -5v7i5.5a, +12v313.5a. -12v '110.1a and -23v c:'0,02a. Dim 18 . 11 - 6 cm.110 or 240v input BRAND NEW CALL OUR SALES OFFICEGOULD 6640A 5v 40 amp switch mode supply NEW E130.00ACiDC 'Linear PSU for DISK drive and SYSTEM applications. Constructed on a rug-ged ALLOY chassis to continuously supply fully regulated DC outputs of +5v3 amps -5v 3.0.6 arr..,. and -24v 5 amps Short cacuit and overvoitage pro-tected. 100 or 240v AC Dim 28 125 7 cm NEW E49.94

2.,,,rage PSU's £3.03

L:t41:11/ Manufacturers BRAND NEW surplusDEC LA34 Uncocled keyboard with 67 quality gold plated switches on X -Ymatrix- ideal micro conversions etc £24.95AMKEY MPNK-114 Superb word processor chassis keyboard on single PC8with 116 keys Many features such as On board Micro, Single 5v rail full ASCII

coded character set with 31 function keys. numeric keypad cursor padand 9600 baud SERIAL TTL ASCII OUTPUT! Less than half price

Only £89.00 with data. Carriage on Keyboards £350

NOW only f.799NOW only £499

Carnage InSurance E12 00 MODEMS-PRESTEL - VIEWDATA - TELEXPLESSEY VUTEL, ultra compact unit, slightly largerthan a telephone features A STANDARD DTMFTELEPHONE (tone diall with 5 CRT monitor aridintegral modem eta for direct connection to PRESTELVIEWDATA etc. Designed to sell to the EXECUTIVE atover £603! Our price BRAND NEW AND BOXED atonly £99.00DECCAFAX VP1 complete Professional PRESTELwstem in stimline desk top unit containing Modem.Numeric keypad. CPU, PSU etc Connects direct tostandard ROB colour monitor. Many other featuresinclude: Printer output Full keyboard input ceeeetteport etc BRAND NEW with DATA A FRACTION OFCOST only £55.00ALPHATANTEL Very compact unit with integral FULLALPHA NUMERIC keyboard Just add a domestic TVreceiver and you have a superb PRESTEL system andvia PRESTEL the cheapest TELEX service to bet oung Many features CENTRONICS Printer outputMemory drailin etc Supplied complete with data andDIY mod for RGB or COIT,GDE!E . :..1,:. .::.;roUts ASNEW only £125.00

Post and packzng on a, - - , r- : _ _ - :, ... z 50

EX -STOCK INTIMATED mown4164 200 ns D RAMS 9 for £11 4116 x-£1.50 2112 £10.00 2114 £2.50 21 02 E2006116 £2.50 EPROMS 2716 £4.50 2732 cac:2764 £4.95 271 28 £5.50 6800 £2 fi : 6821 r'68A09 £8 6B1309 £10 8085A £5.50 508 6 £ I8088 £8 NEC765 £8 W02793 £25 8202A£22 8251 £7 8748 £15 ZBOA DART £6.5:280A CPU £200. Thousands of ICs EX STOCKsend SAE for list

DISK DRIVESJapanese 5,.. half height 80 track double sided diskdrives by TEAC CANON. TOSHIBA etcSold as NEW w in 90 day guarantee ONLY £85.00TEC F0-503 Double sidedliiH 40 TRK NEW £75.00SUGART SA400 SS FH 35 TRK £55.00SIEMENS F00100 SS F11 40 TRK £85.00carriage on 5Yr- drives £5.50Brand NEW metal 5lt.' DISK CASES with internal PSU.DSKC1 fort HH or 1 FH drive £29.95 +KIE4.00DSKC 2 for 1 I -1H drive £22.95 +pp £3.50DKSC 3 As DSK1 LESS PSU £1 2.95 +pp £2.50DSKC 4 As DSK2 LESS PSU £10.95 +pp £2.008 IBM format TESTED EX EQUIPMENT.SHUGART 800/801 SS £175.00 +pp £8.50SHUGART 851 DS £250.00 +pp £8.50TWIN SHUGART 851'62 MOtotal capacity in smart casecomplete with PSU etc. £595.00MITSUBISHI M2894-63 8' DS 1 Mbequrv. to SHUGARTSA85011. BRAND NEW at £275.00 +pp £11.50DYSAN 8 Alignment disk £29.00 + pp £1.00Various disk drive PSUs Ex Stock SEE PSU section.HARD DISK DRIVESDRE/DIABLO Series 30 2.5 Mb front load £525.00Exchangeable version £295.00. 1.1E3029 PSU £95.00DIABLO 44/DR E4000A, B 5+5 Mb from £750.00CDC HAWK5-F5 Mb E795.00. CDC9762 SO MbRMOOetc. £2500.00.PERTEC D3422 5+5 Mb £495.00RODIME 51/4 Winaiters ex -stock from £150 CALLClearance items- Sold as seen- No guaranteeICL 2314 BRAND NEW 14' Mb Removable pack haredisk drive cost over £2000 with data ONLY £99.00BASF 8172 8' 23Mb Winchesters E199.00Unless stated all drives are refurbished with 90 dayguarantee Marty other drives and spares in stock - cal

sales office for details

Join the communications revolution with our superrange of DATA MODEMS Prices and SOeCificafionsto suit all applications and budgets -BRAND NEW State of the art productsDACOM DSL2123 Multi standard 300-300. 120375Auto answer etc £268.00DACOM DSL2123A0 Auto dial. smart modem withmulti standard AUTO SPEED detect and data butterwith flow control etc £385.00DACOM DSL2123GT The CREAM of the intelligentmoderns auto dial auto call index, bufferetc etc £498.00Steebeck 581212 V22 1200 baud FULL DUPLEXsync or asyna optional auto dial £465.00TRANSDATA 307A Acoustic coupler 300 baud fullduplex. originate only, RS232 interface £49.00

Ex BRMSH TELECOM full spec CCITT. ruggedisectbargain offers Sold TESTED with data. Will work onany MICRO or system with RS232 interface.MODEM 13A 300 baud unit only 2' high fits under

. phone CALL mode only £45.00 _MODEM 201. 75-1200 baud Compact unit for useas subscriber end to PRESTEL TELECOM GOLD.MICRONET eta £39.95 +pp £6.50MODEM 20-2 1200-75 baud Same as 20-1 but forcomputer end £65.00 +pp £6.50DATEL 2412. Made by SE Labs for BT this two pailunit is for synchronous data links at 1200 or 2400baud using 2780/3780 protocol etc Many featuresinclude 2 or 4 wire working self test auto answer etcCOST OVER £800. Our price ONLY £199 +pc £300DATEL 4800, RACAL MPS4800 baud modern EXBE good working once- ONLY £295.00 ertio £8.00

SPECIAL OFFERMODEM TG2393. Ex BT. up to 1200 baud fullduplex 4 wire or half duplex over 2 wire line ONLY£85.00 PER PAIR +pp £1000

For information contact our Sales Office.

MATRIX PR T 4 SSPECIAL BULK PURCHASE of these compact highspeed matrix pnnters Built in Japan tor the HazeltineCorporation this unit features quality constructiongiving 100cps bidirectional full pin addressablegraphics, 6 type fonts up to 95 single sheet ortractor paper ham:Sing. RS232 and CENTRONICSParallel interface Marty other features BRAND NEWarid BOXED. COST £420. Our price Only £199.00

Dry Fit MAINTENANCE FREE by Sonnenschein& YuasaA300 07191315 12v 3Ah NEW £13.95A300 07191312 6v 3Att NEW £9.95A300 07191202 6-06v I.8Ah TESTED Ea

Equip £5.99

VDU TE MINALSStandard VDU data entry terminals

at give away pricers!!QUME OVT108. Current product state of brie artterminal with detachable keyboard. 12 Green screen.2 page RAM. TVI 925. Hazeitine. ADMSA emulations.software setup. 25 a 80. Clock. Swivel and tilt basePrinter pon, Function keys etc BRAND NEW andBOXED AT ALMOST HALF PRICE Only £425.00AJ510 - EX RENTAL Z80 controlled 15 greenscreen 24 a 60 display. graphicS, cursor addressing.printer port etc Very good condition TESTED completewith manual only £225.00ADDS 520 - Dumb terminal, used. 12 01w screenR5232 interface and printer port TESTED.ONLY £125.00. Carnage on terminals £1000100s of other terminals in stock. CALL for more detais.

tiAll prices quoted are for U.K Mainland. paid cash with order in Pounds Sterling PLUS VAT. Minimum order value £2.00.Minimum Credit Card orderE10.00. Minimum BONA FIDE account orders from Government Depts.. Schools. Universities andestablished companies£20.00. Where post and packing not indicated please ADD £1.00 4- VAT_ Warehouse open Mon -Fri9.30-5.30. Sat 10.30-5.30. We reserve the right to change prices and specifications without notice Trade. Bulk and Export

, ri r r T r: 1114 I 32 Biggin Way, Upper Norwood, London SE19 3XFLLLL I 1\1)111!..-1 Telephone 01-679 4414 Telex 894502 Data 01-679 1888 .

please mention ELEKTOR ELECTRONICS when contacting advertisers

1987 BUYER'S GUIDE TO ELECTRONIC COMPONENTS

Pick up a copy of our new 1987 catalogue from allbranches of W.H. Smith for just £1.50.Or post this coupon now, to receive your copy by post for just£1.50 ÷ 40p p & p. If you live outside the U.K. send £2.50 or11 International Reply Coupons. I enclose £1.90.

Name

Address

Post Code

AVAIL/WI FIN BILL

W.II, SOWSTORES

ORDER VOWCOPY NOW!

MAPLIN ELECTRONIC SUPPLIES LTD.Mail Order. P.O. Box 3. Rayleigh, Essex SS6 8LR.reef:hone: Southend (0702) 554161

SHOPS BIRMINGHAM Lynton Square, Perry Barr. Tel:021-356 7292 LONDON 159-161 King Street, Hammersmith, W6.

Telephone: 01-748 0926. MANCHESTER 8 Oxford Road, Tel:061-236 0281. SOUTHAMPTON 46-48 Backs Valley Road, Tel: 0703 79;831. SOUTHEND 282-284 London Rd, WestchThon-Sea, Essex.

Telephone: 0702-554000Shops closed all day Monday.

Documents

January 1987 or g ,Anfics · 2019. 7. 18. · or g,Anfics glectjw January 1987 UK £1.30 IR £1.89 (incl. VAT) ONGS TO THE PHOTO Processing digital signals Cossor Radar: the first