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Electronics InSurveying

JA 197E1 INTERNATIONAL

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RESET0... NEWS . . . . PROJECTS.. . . MICROPROCESSORS. . . . AU

WATFORD31 CARDIFF ROAD,AIL ORDER. CALLERS

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WELCOME. Tel. Watford

TL 74*

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electronics toti6.4%),internationali&V

FEATURESELECTRONICS IN SURVEYING 24 Looking around electronically

LETTERS PAGE 28 Readers make their pointsWALLS HAVE EARS 41 How private is private?

WIRELESS SHOW REPORT 50 Down tube lane at the V&ASOFTWARE GAMES 56 Fun and games with calculators

DIGITAL ELECTRONICS PART 4 67 Flipping and flopping

PROJECTSCMOS HOUSE ALARM 16 Building and installing to protect

HAMMER THROW GAME 29 Led into a throwawayRACE TRACK GAME 36 Place yer bets here

DRUNKEN SAILOR PUZZLE 46 Can you solve it - sober?SYSTEM 68 - CUTS CARD 61 Getting a bit taped

NEWSNEWS DIGEST 11 Electronics news travels fast here

DATA SHEET 53 A new family of bi-fet op -ampsAUDIOPHILE 70 Class E sprays and a supeofi cassette

MICROFILE 74 The MPU mans news pagesELECTRONICS TOMORROW 77 Games for soft tellys!

INFORMATIONWANT TO WORK FOR ETI? 14 Two jobs- one here one down under

ETI PRINTS 15 You asked it - and now you've got itSUBSCRIPTIONS 39 Give yourself a treat!

NEXT MONTHS ETI 44 Preview of February ETIELECTRONICS TOMORROW 48 Our best special yet - got yours?

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52 All our wares on display55 Time to keep time64 Books from ETI75 Finish it oft professionally

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COPYRIGHT: All material is soteect to wodd wide Copyoght PHSIcsIMa. All MMOneMe care is taken in the preparation o1 HMe M.P.., m ensureaccuracy but ETI cannot be held responsible for it legally. Where errors do occur a correction Po0 be published as soon as possible afterwards.

PAKS - PARTS - AUDIO MODULESPANELMETERS

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The AL30A is a Man oueloy audio amplifier modulereplacing our ALPO Si 30 The versatility of its design

mskes ideai for record players. rape recorders stereo

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Enpy the Trah, of a magnetic Cartpdge will)

g'pr.:"';',7.Z7,"',;,`,A:',T7rT;,,,,,2:17.e.,9mast Canridges 10 be used wham loci;exist for the use of ceramic cartridges onlyit is plod with a standard DINinput socket for ease of connectionFull instructions supplied UN)

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CAProducts from: p,yonn

ELECTRONICSFairchild, General Instruments. L --I

Liton. Litrarus. Mostek. 68 Ebberns Road, Tel. 0442-62757Motorola, National Semi, Hemel Hempstead, HP3 90RP.S.M.C., Vero.

TYPE SPECIAL FEATURESCLOCK CHIPS & KITS

CCIEIP EKIT 74C00 Quad NAND BITOS25& BVITS02.2 1K71 RAM 2.11NINI5309 7 sag . BCD RESET ZERO

.1." 111g 'C'S "" 'n""r '" VIr4d101:x6:4"CMOS VI!,5311 7 se + BCD74C10 Trtple NAND . 0.25

INM5314 7 sstes//-17'B'ATIC CLOCK 71 Ta: 7.0074C157 Quad Selector 2.2574C153 4. counter 1.15 61611702Q 25578 EPROM 11.90

)721.14 1K74 RAM.. 2:1.t=MI ; mg + BCD 4 [KNIT ONLY 5 65 74C42 BCD Decoder . 0.95

N1195315 7 seg + BCD RESET ZERO/ :0' 'CI" P'" re's'er - '." 1Z5,72:';'6'2'47V,U,1MM.'S Non -max ALARM 74,1135 SIPS sews. 1.15

NIM5318 7 seg + BCD External chg.+ select .... 0.93 8.00 74C1 73 35 Quad latch 0.95 31.15N1M5371 ALARM. 50 Hz 12.19

74151 " '''' 2-"'c '." grIO'l WO'n1'171=2185MM5378 CAR Clock Crystal control. LED 9 86 10.00 DM8035 35 Hex buffer 1.75

MM537g CAR Clock Crystal control. Gas discharge 9.66 DM8095 1nY 8095 1 75 91145307AA Saud Rate Gen 12.68MK5025 ALARM SNOOZE 5 50 9.00 DIVIBIL595 35 8 0 I buff 1,45 14.45303 tAY.5.1013) DART 6.34MK50395 IlOtOOVVN Counter - 6 One. 12.10 15.10 "157 It S96 Inv 95 1.45 Mal for 5307 TBAN1K50396 LIP/DOWN Counter - 111.10113SS . .. 13.10 15.10 DM817597 35 4.4 honer 1.05 DM8578 Citer Gen 15.20MK50397 UP/ DOWN Counter - MMSS 99 . 12.10 15.10 0M811.5.. ii, 97 1.05 f.th CAB 6 8VVF eyed ,

FCM7001 AtARN1. SNZ. CALENDAR. 7 seg . 9.00 12.50FCM7002 ALARM. SNZ CALENDAR. BCD . 1700CT7003 ALARM SNZ CALENDAR. Gas discharge . 9.00FCM7004 ALARM. SISZ CALENDAR 7 seg 9.00 12.50 CLOCK MODULESAVS, 1202 7 sag.4 digit LT601 Alarm Clock odule. Simi MA1002 6.00AT5. 1230 7 seg. ON and OFF ALARM 5 26 ESA MT X1001 Transformer 0.90All above clock kits include clock PC board. steek chip, socket and CA3081(Inver IC. MH15378 also includes crystal and Dimmers. When ordering kitplease use prefix NIHI, e.g. MHI 5309.

OLDE CLOCKSDISPLAYS In kit MDT or built these clocks ere based on designs nundreds of years old

Wood stone and non are used to reproduce authentic -eichr woride walt131707. 704. 701 0.3" 1.70 Litronix class 2 product clock. in futl det. The kits contain all you need tncludtng glue. screwsDS727, 728. 721 0 5" 12 dig DL707E /1 etc and very comprehensive inslrochons Stones lor weights are exctuded

4.31 DL727E 12 dig ) For coloured brochure picas. send 15p stampsD5747. 750. 7460.8" 3.82 017475 1.80

MHI DISPLAY KITS111707/ 4 don 0.3" 7.60 MHI707E74

1/1112;',71 0 5" 1g I1770V71

21=71 0 5"51H1747/13 ..

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4 305 705 307307 20

. .... 9.90Any one MUER RION aboyeE11s;aVevoltintlevierface detect, WI. any

CASES w SOCKETSVERO 1 8" 7 ;200 24 28 or 40 pin 0 60VERO 2 5" 2 3.00 Soldercon Drip Mks 50 pms 0.30

PAYMENT TERMSCash oath o.er Access Barclaycard Immo, quote your number, Cred 1=Lar.attaccrnt holders 15,6 handkng charge ort goora

All prices exclude 915then

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alma 7,000 EL FCTRONICS68 Ebbw., Road3=Tel 0442 5,757

ELECTRONICS TODAY INTERNATIONAL - JANUARY 1 978

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CLOCKS617 PRICE

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MetacBARGAINS

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ELECTPONICS TODAY INTERNATIONAL - JANUARY 1978

. . . . news digest

Join the DigitalRevolution

Understand the Idevelopments in Calculators.stsgsgtsr. ...Ng. meshes...

lye instrurtlent

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£7.10

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ELFCTRONICS TODAY INSERNAVONAL - JANUARY 1978.

:ro'41,:e't:s'a;'Prif=r30Tr2n6L°4 andcan be used votb any ca. rad.° ,lape una It re s.PlYoened rn woes wan tne ex.sirnp spealung leads a. p,con,u c1.on wan our speakers S1.5 produCes

rem. performanceure .s

r oil by sPns.. popper Pne of e

rabno /he need for an

TenremMtrby 'r=rn,gath9'r=11a=1:very easy processine 515 nes been SpeCoey despned for car 1.19e and

=ne:4:1To=rtV:::ZoT'ar tee' "'C3/16

p

Frequency Response 50nn 30411t1.0 Impedance 80 nomma1Input Sons.1..y volis RM.S.Im 15 watts output

C1,15Pnc.17 + P2.21 VAT P&P free

2" 40ve Tweeter20o+ Gera,. Me,.

PO Imrt1114,;=7.--

pedance

SI 5 ?nee per pair P17 74 -pr2 21 PAP., freeTWO YEARS GU,t1R,gojg ON ALL OF OUR

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ELECTRONICS TODAY INTERNATIONAL - JANUARY 197B

digestET starts dm - Eked m

Used asell mune noMmg and

hem° Publosed Nem, liege., Hanover and ..est. Odo Wog shown sv.th pipe ds the photo,shexarrhmng a puhhoo Naito wall the advertsin g andOtOdualon managers

tot, tt'syroerWaurll octou nts

lweh m eaan theat h o

NTS shoo

VaharPS:'e ng so°thatwe have deoded maths f Ms new method of PCBOteguetion a regular ETI feature

Incase you sove mond out On ETIPStiNTS thusler Mev are a complete PCB pattem already to rub

tIrTgrarantoT4'escrte=ihy 'Wrron.N r SI. SU

h1V;M=:1=71,'"'"7"'"n"47:Unnl haw Me only ETIPRINT evadable hes been

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ORDER TODAYEtgauglr P.0 leasable to ETI Magazine, to,

Ygr:=STREET, LONDON. OSP. INN

75p Inc, VAT and P & P,

PILI% TItIV:Xlars14;preent al"S

sou

itE

HOUSE ALARMIN these days of increasing crime and vandalism an alarm system for the home can

add greatly to ones peace of mind. To be effective however, not only must thealarm circuitry be well designed, it must also be correctly installed. This article

describes a sophisticated alarm system and how best to commission it.OUP MARLA 1.51.1E last year carried a I eature go,cry sensors

gVle, 'Zvatlar'Z'VZWZ1Z2s'eiZdosm ZZ7i,g,,77:::%:r71:7,7= ' ,7:::"::::'"could make their domiciles more secure and Mos les eotrance,

P

the burglar A wide varrely of means bYurity ol the home could be im

such forcedroo1or very oc

.ort tee, forced eat t the walls o,

garage

mutes ' to the use of noAdriong 1.A.E Mita,. of burglar alarms 'be feature did The srmplest and most rehab fo.ode any circuits 1urlable alarm alarm ins..tons N the meg^

consists of a qv °Harrow°

'11'ddc:n:=4;r1"''s .rrn....., Sealed Om ene.It have developed the design

rnphabie enough though that a,alan:s'ys'e"m'l no matter hOw saphrstrcaled - canonly he juse d it is installed correctly FunberFthe

l'11'n''en*t7o179nr°f:ePan l':'ioT'sri:c:u'ut i'°Ily 5oVr4A:i,dsc7reisiodF:n171irle

AbnIrrnn nit'ar=y'inTern"al.T:ibation ofalarmtmdshow the specification of our alarm evolved

How They Get In

Nearly 3096 of Al burglA furtherezna=7=1 loos and m

'erhus'enea'err171O==dpsO.1:4albreaems canavoided ha install, adequate door and WrndOW °e

se Acadia., locks on all external flOOIS TheSecan'only be opened with. key - even IromIlx=

r-riroze7EinT'g':,in:i:esnn;ttoreFolrns7i,nmhz,:ned and

un=1.IT 'n.=:ralgebt,Vnclow7c117ng

""c7ram'ed'u'aZdt:ht.n.dOr:/s7AU'r1::rrorVbreakglass our leW will 110 oirmbing through a wind..frame Aitb broken glaSS in 11

T. precautions outlined abovees el berng burgled about O,D

amino 2096 can be reduced to Arrest zerObvvmiaoing eurgia, alarm inevemph.SZ.,on the word good a poor alarm mo off eA

noi at all

16

tuhe and a...A..1.011y at Ale rgap between Men)

vwen magnet brought ne

the feeds Irarg,

switches AZ'

he protected

Aftlst these ar

11

reed switch Ale

Zn"Xlene"

=1:1:01e

Aagnets mote that tbemagnet A to ..11dOwl

VOndow glass may be 1/1010f led by Ace., on afa°P AommAmlo, lor as, a self adnesbe

lbeIrsouv. FA butbular .

Amydoor by Roof, wal3,Floor entryOf on ore.6%

manipulate door locksby jemmy or pressure 14.4%Open doors by WOO. keys ass

Entry through unlocked doors and windows 79.2%

Fig 2This sketch shows how criminals generallyenter a house. Note the very high percentageof entries nude vie doors and windows foundunlocked.

Vibration sensors may be used to protect large areasof glass but these are prone to false triggering duringthunderstorms etc.Many other types of intruder sensing devices may alsobe included in the system. Pressure mats for examplecan be placed under carpets in strategic passageways- or even under the door mat. The mats contain alarge number of normally open contacts some of whichwill be closed when the mat is trodden on. The system

sunalso include more sophisticated intruder detectors

ch as infra -red type sensors.The intruder alarm itself should be reasonably

accessible to people entering and leaving the premisesvia a silent entry' door, but will hidden from the sightof an intruder. The alarm's output stage should be arelay which latches when an alarm signal is received.

Warning DevicesFor household use a good quality 12 Volt bell shouldprove an adequate warning device. Being me hanicallyresinant, bells have a very high conversion efficiency,

Fig 3 Set the reeo switch two the window Paine andthe ',Now into the moving part

ELECTRONICS TODAY INTERNATIONAL - JANUARY 1978

e louvres 1.,FOrCe windows

ssferrnarOSS

Break glass in window andOpefMatch

in fact, the average bell draws less than 500 mA at12 V yet can be heard several hundred metres away.

Good sirens can be heard well over a few kilometresaway, but they draw a lots of current and cost morethan a good bell, Small cheap sirens cannot berecommended.

If at all possible, householders should make mutualarrangements with neighbours to contact the police ifthe alarm is heard. Similar arrangements should also bemade so that neighbours can switch off the alarm whenthe police arrive.

An alarm which resets after a period of time,silencing the bell or siren, is a useful device that will bemuch appreciated by the neighbours. Care must betaken to ensure however. that the alarm when triggeredand reset, still provides some measure of protection tothe property.

Whatever the warning device chosen, it should bemounted unobtrusively high up in an inaccessibleplace. The leads to the device should be of an adequategauge to avoid any voltage drop associated with a long

Fig. 4. To oioteet ed., set the reedswitch pro the archoVa.

HOUSE ALARM.

T'

Fig 5 CIICUd tlogram of the A' board

run. The wires should be concealed from view.We strongly recommend that a seperate 12 Vbattery

be used in any burglar alarm. This should be checkedat regular intervals to ensure it is still in good conditionand should be replaced as a matter of course when ithas been in service for a period of one year.

Alarm UnitThe specification of our alarm unit is shown in Table 1From this one can see that the alarm has seven'normally closed' circuits (42-A8) plus a silent entrycircuit (Al) which allows about 30 seconds on entry toturn the alarm off. This feature also gives a 30 seconddelay between turning the alarm on and the sensorsbeing armed, this allows time to leave the house.

It is possible to connect two or more alarm switchesin series for each external circuit but if so doing ensurethat any such series -connected switches are groupedtogether.

The reason for providing a number of seperate alarmcircuits is to do with the problems involved withresetting a triggered alarm mentioned above. Mostalarms work on a system where all the windows anddoors have normally closed reed switches all wired inseries so that opening any one breaks the loop and setsthe alarm off. The alarm then rings for ten minutes and

18

hZr

Fig 5 Ceiguit diagram or the '8' board.


UNLIKE SOME ALARMS that use a singlesensing loop with all the switches wired inseries, this design features a number ofdifferent alarm groups. These are brokendown into two groups designed fornormally closed (NI, C) switches -Penmeter Group (inputs A-05) andInternal Group (inputs 13,-B.m) - togetherwith one group for normally open (N/0)switches (inputsto Al

The inputs to each of the circuitsdescribed above have their own Inputcircuitry.

PERIMETER CIRCUITThe normally closed sensors associated

with the perimeter circuit (inputs to A ,-A,)are connected to the circuitry around IC.and IC,

These ICs am Quad NOR gates which, inthis application are configures as inverters.The sensors am connected to the inputs ofthese gates via the resistors R,. -R Withthe sensor switch closed the output of theassociated IC will be high. If the switch isopened the output will go low as the inputsto the gates are then tied high via resistors

.R. R. is included to ensure that theinputs to the CMOS ICs are terminatedunder all conditions. The capacitors Ctogether with the resistors R,p-R, proVidea filter to ensure that transients on theinput lines do not trigger the alarm.

In each output of IC. and IC, there is aLED which is connected to the SecurityCheck Button (PB,). Upon operation of thisbutton power is supplied to the LEDs whichwill light if the IC they are connected to hasdlow output. ie the input is triggered. Theiodes in series with the LEDs are

necessary because of the low reversevoltage breakdown of the LEDs. Diode D.supplies power to the input circuitry duringthe security check. The input A, providesthe silent entry feature and is describedhelots.

HOW IT WORKSThe other sections Ark, have their

outputs fed via an RC network, whichgenerates a negative pulse upon triggering,inane of the inputs of IC. Thus if any of theinputs are triggered a positive pulse at theoutput of IC,will result.

SILENT ENTRY CIRCUITWith the silent entry circuit a 30 second

delayIC

due to R,..C..endelIC . overrides the

output of immediaty thisaf ter the alarmhas been energised. After time if theinput is triggered the output of IC, will gohigh, having been inhibited from doing sountil now by the high output of IC, ., andwill toggle the RS flip flop formed by IC,and IC,., taking the output of IC , high.After another 30 second delay due to R..C,, the input to IC- will be high and itsoutput low.

TRIGGERING CIRCUITThe same output results if one of the

other inputs is triggered and the output ofIC,goes high momentarily.

This output is used totoggle. via IC theRS flip flop formed by IC, (which is used tocontrol the alarm and resetting circuitrydescribed below.

IC, also has two .her inputs. The first,consisting of the network R., C_, and D...This circuitry disables the alarm functionwhen the Perimeter Switch is In the offposition and fora short period of time afterthe switch is moved to the on position byholding the input of IC, , high. Thisprevents spurious triggering.

The second input to IC, , is from thenormally open input (A), as well as theemergency and alarm test switches. If anyof these switches are taken low a negativegoing pulse is coupled to IC, ;to trigger thelarm. These functions operate even if the

perimeter sensors are off. This input can be

used for emergency inputs such as firealarms.

OUTPUT.The positive going pulse at the_output of

IC ,sets the RS flip flop IL, IC, and tnthis triggeredstate IC, output is low andIC, high.

The delay circuitry uses a CA3130 (IC)configured as a comparator. C

'is normally

charged to IOV until the flip flop istriggered allowing it to discharge via Ru.When the voltage on C,,,has fallen to about20mV (the level set by Ro and R.., on the

).non -inverting input of IC The ouut ofthe IC will go high resetting the fliptp flopsformed by IC, r IC, and IC. , IC,.12., isincluded in the feedback loop to providesome hysteresis.

The output device can either be a relay orsiren circuit. We have provided for both-options. The siren output is formed by two555s, one operating eta high frequency anddiving the speaker via driver transistor Q,and the other at about 2He which is used tomodulate the frequency of the first.

The relay and 555s are energised when Q,is tumed on by the high output. of IC, asthe flip flop is set.

Addition circuits can be added in blocksof four at a time (as Board P) andconneetedto the Aux. input.

AUXILIARY BOARDThe circuitry of board B is almost

identical to that of Board A. The maindifference is that the negative goingoutputs of each IC am ()Red using diodesD -D;,, opposed to a logic gate.

This board can only be energised if theperimeter hoard is powered up. Thecapacitor together with R., and Dprovide a short positive going pulse uponswitch on to disable the main alarm for abrief period of time.

resets. If, however, the window, as is likely, is stillopen, the alarm must be turned off completely toprevent it continuing to ring.

This is the reason that our alarm does not use asingle loop but has a number of alarm groups. Further,the alarm is triggered only by a change of state in anyof its alarm loops. Thus if the alarm is triggered by thechange of stage in any of its sensing loops when awindow, say, is open, it will not be retriggered whenafter a period of time it resets and the window is stillopen. This affords some protection to the premisesunder these conditions.

We have provided a test button so that a check onthe security of the house can be made before the alarm

set. indicating immediately which window or door isopen.

As well as the external circuits the system hasprovision for connecting a number of internal circuits.These may be actuated by normally closed switches -in which case they should be connected to B1-84 - orby normally open sensors connected to A9.

It may well be worth considering installing a seriesof emergency push buttons. Such switches should bemounted on the architraves of the front and rear doorsor in a reachly accessible position near the doors. They=sable the occupant to set off the alarm if a caller forces- s way into the house when the door is opened.

t'_S-RONICS TODAY INTERNATIONAL -JANUARY 1 978

PB

Fig 7 Winng of thetches and pushbuttons.

HOUSE ALARM

A3

Ag

NB 9 Component overlayof the 'Ed board

A

129

82 4

K

AU

A

(-tAl- -t .43 i--4Pso 1.-- -fr-1,2

4.(51.9

.1,q.

Al2

A9

IA: 2 1i"Al All,2

TO RELAY

11001

IOWISO

(7374.

T TCFI RJ- t'8 B9

---rr 7-, -

cri -f*00

0 (3014 N BOARD A

LEE a

A.OV

F19 B. Component overlay o

0

TO POINT ABOARD A

84H -

N

' board

20 ELECTRONICS TODAY INTERNATIONAL - JANUARY 1978

Although this is not a common event, emergencyswitches provide elderly or timid people with a feelingof security.

Use good quality bell pushes for these circuits andconnect them to the A9 inputs on the circuit board.

Fire Alarms

Fire sensors may be wired across the A9 input. Theactual fire sensors should be mounted in the ceilings ofrooms in which there is a fire hazard - kitchen, livingroom, rooms with electrical or heating applicances orwhere people smoke (don't forget the bedroom ifyou've a habit of smoking in bed!). Sensors should alsobe installed in the roof of the garage especially if this isattached to the house - the laundry, workshop etc.

Construction

Due to the number of components, it is recommendedthat the unit should only be built using the PCBs shownhere.

BOARD ARESISTORS all '% W 5%

R18,54 22kR9,37,,40,546,5153 47kR10-25,48,52R26 38 42 4417R27.34,36,43,49 IMR35 10k1440 100R04.4 220kR45,47 6808R50 2k2 MISCELLANEOUS

PCB as pattern.

Assemble the components, watching the connectionof all the polarised components. Also solderthe CMOS ICs last and then solder pins 7 and 14 first.This allows the protection diodes inside the IC to be'effective. The LEDs should be mounted parallel to thePCB as shown in the overlay as these have to protrudethrough holes in the chassis.

Boxing of the alarm unit is largely a matter of choice.Our layout can be seen in the photographs. Note thatwe did not fit a key switch to our alarm, but installed itin a locked cupboard which could also be used for thestorage of valuables.

Security Sense

May we say again that the installation of an alarmshould only be part of a co-ordinated campaign todissuade burglars. Details of the various preacutionsthat can be taken were detailed in our feature lastMarch. Your local Crime Prevention Officer will also beprepared to give help on most matters of security.

PARTS LIST

CAPACITORS

CI -8,16,18,22,23C9-15,17C19020,21C24,26025,27

SEMICONDUCTORS

10u 16 V tantalum47n polyester22u 16 V tantalum100n polyester15n polyester100u 16V

IC1-3,5 CD 4001IC4 CD 4068IC6 CA 3130IC7,8 555LED18 .2" type LED01 TIP 295502 SCI 09DI -11 1N914D12,13 1N4001

MISCELLANEOUSPCB as patterr,12 V I858 relay

BOARD BRESISTORS at % W 5%

RI -4R5,10R6-9,11-14RIOR15.18

22k47k1k47k1M

ET1

CAPACITORSCI 33u 16 V electrolyticC2-5 10u 16 V tantalumC6-9 47n polyester

SEMICONDUCTORS

ICID1-11LEDI-4

CD 40011N914.2" type LED

GENERAL FOR BOARDS A & B.SWITCHES

SWISW2SW3PB1.3

SPOT toggle switchSPDT toggle switchDPDT toggle switchsingle pole press toMake push type.

MISCELLANEOUSCase to suit, 12 V battery !HP1 or 2 X 991/tarrninal strip.

Types Of Inputs

Silent Entry

Perimeter Circuits

Internal Circuits

Emergency Circuits

Current Drain AndBattery Life (Type HP1 or similar)

Emergency onlyAlarm activeAlarm sounding

Alarm Time

Silent entryPerimeter circuitsInternal circuitsEmergency circuits

Single circuit,30 s exit delay,30 s entry delay.

7 circuits, N/C contacts,can be expanded in units of 4.

4 circuits, N/C contracts,can be expanded in units of 4.Any number of N/O circuits.

Any number of N/O circuits.These circuits are active evenif perimeter and internal circuitsare switched off.

2.5 mA (4000 hours)9 mA 12000 hours)500 mA (10 hours)

12 minutes.


HOUSE ALARM

Fig 10 Connection o,terminal

Fig. 12. PCB fa,IPartern u'furl size I]5 x OSmm).

22

BUY LINES

The components for thisproject should be available frommost suppliers, Watford, Marshalls, Maplin etc., or,probably, from most local shops. The Siren used is amatter of choice, but please make sure it's up to the job.


SOC20.

The most powerfulMonolithic IC amplifier

in the world.20 watts output (continuous sine wave) ...

Less than 0.2% total harmonic distortion at all powers,allfrequencies

And totally electronically indestructible!Until recently, all monolithic IC chipssuffered from two basic designweaknesses. First, thermal runawaycausing heat to build up as currentincreased; and second, short circuiting.

- L -

Standard plastic package with copper slug.

Until the SOC20 IC chips Thisextraordinary new power amplifier chipis uniquely designed to improve thermaldissipation. It also has two separatebuilt-in circuits, one of which measureson -chip temperature. If this should riseabove 150°C the output transistors areswitched off thus preventing thermalruneWaY

And short circuits? The other circuitcontinuously monitors both current andvoltage. If the product of current andvoltage rises above a critical level, the

SOC.) plastic package with chipdirectly soft -soldered to copper slug,

drive is adjusted to bring the transistorswithin safe operating limits.

The amplifier can drive speakers ofany impedance maximum power willonly fall outside the recommended

80 range.And any pin on the chip may be

shorted to any voltage in the system forany length of time ... and no damagewill occur!Superb quality ...extraordinary powerThe SOC20 isn't only safe ... it's alsoextraordinarily sophisticated. Totalharmonic distortion is less than 0.2% atall powers and all frequencies - and innormal use is well below 0.1%.

If power is at a premium, use twoSOC20 amplifiers in 'Full Bridge' to giveover 40 watts continuous into 80speakers.

The SOC20 is naturally guaranteedunconditionally for one year. Althoughwith the SOC20's unique patenteddesign, we think you'll have little causeto make use of any guarantee,

SpecificationMaximum supply voltage

± 22 0 144 V total)Output power

20 watts continuous 412 or 80Open loop gain

100 dBSupply voltage rejection

50 dBInput noise voltage

4 flyNumber of transistors

18

Supplied with free printed circuitboard, heat erne mounting bracket,comprehensive instructions, andsuggested applications_

The SOC20 will work on any supplyfrom 12-44 volts and therefore can beused for in -car as well as domesticapplications. Apart from its obviousaudio uses the fact that it is DC coupledthroughout makes it ideally suited forservo systems - in radio -controlledmodels for example.

Incorporate the SOC20 in yourequipment today!SOC20's cost f4.95 each, or f7.95 apair for, say, stereo applications. Only afew readily -available components areneeded to build a full amplifier unit.

Of course, the SOC20 comes with a10 -day money -back guarantee.Science of Cambridge Ltd,6 Kings Parade.Cambridge,Cambs.,C621SN.Tel: Cambridge (0223) 311488.

7,7rarrE17:7.71Please send me lcItY1SOC20 Monolithic IC Amplifiers(f 4.95 each or f J.95 per pair,inclusive of p&p and VAT at 8%1.

I enclose cheque/money order/

postal order for

Name

ETI

ELEC-RON`CS TODAY INTERNATIONAL - JANUARY 1978 23

TRANSFORMERS'x::::::2'.ttc7=0;!%7:,;".tar

0. OR 20 VO

66 51.

VADR, 1141. Pap PA P

BAYDIS

TECNNALOGICS PROUDLY PRESENT

THE "LOGISCAN Mk. II"COLOUR TELETEXT DECODER

WITH

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YOU CAN NOW BUY A TELETEXT DECODER TO THELATEST BBC/ IBA/BREMA JOINT SPEC. (NB. Manyother decoders are not full spec. display.)

THE LOGISCAN Mk. II OFFERS THESE EXTRAS.* Double/Single Height 1r Background Colour Fix* Conceal/ Reveal Switch * Untie (revert to black)* Discrete Graphics * Continuous Graphics* Graphics Hold /Release (Instant Colour Changes)* Auto Newsflash * Roll Mode* Flash/Steady Display * Subtitle Inserts* 6800 MPU Compatible * DMA Capability

Completely self-contained in attractive earthed case,suitable for most Colour TVs, the Mk. II is available asa kit at E1135 + 121/2% VAT; Built E250 + 121/2%VAT. Details large SAE. Also Bch Touch Tuner, AerialI /P TV Pattern Gen., SAE.

TECHNALOGICSMAIL ORDER 8 EGERTON STREET FULL

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24

um:umIN SUPINE

THE PRACTICAL ASPECT of a professional surveyor'sjob requires measurement of the size, shape and position(relative to other such defined shapes) of pieces of landranging from the small household plot to the size of acountry. It may also involve the application of the samemethods for the measurement of large manufacturedobjects, such as buildings, bridges and other engineeredstructures. Such tasks commonly require measurementof distances and lengths ranging from a few metres tothousands of kilometres to precisions as small as amillimetre and angles to precisions down to less than anarc second.

Combinations of length and angle measurements, ona basis of measurement using triangles, are used invarious ways to define shape and size. Definition ofdirection, with respect to North, and with respect to alevel surface or a vertical plane, also enters into asurveyor's daily needs.

In many cases, for reasons of convenience, themeasurements made are not quite those actuallyneeded: conversion or correction is required and, as themathematical process must be performed within 5 to 7decimal figures of precision, the calculations needed canbecome tedious. As an example, when measuring thedistance between two pegs in sloping ground it is thehorizontal distance to a point vertically above the pegsthat is often needed. The distance measured in practiceis more often than not the slope distance between theactual position of the pegs.

Enter electronicsUntil the 1950s the most precise method formeasuring long lengths used a steel -tape hung incatenary, this method having developed from the lessaccurate chain of iron links. Another optical method,called tacheometry, used the telescope of the theodolite

Figure 1 Using telescope to del rmine range by lacheometry.

ELECTRONICS TODAY INTERNATIONAL -JANUARY 1978

\ICSTING

A quiet revolutionhas taken place inthe field with theadvent of electronicmethods.Dr. P. Sydenhamexplains how.

or level to determine range by observing a knownlength -interval of a measuring staff (placed at the farpoint) within a given observed angle defined by two linesin the telescope's field of view - see Fig. 1

By the late 1950s the surveying instrument makers- traditionally they were then mainly from Europe -had acquired generations of skill with optics and finemechanics, but little knowledge and experience withelectronic technique. Because of this they were, at thattime, understandably reluctant to develop and marketelectro-optical devices for surveying. However, by themid -1960s the industry had built up its confidence inelectronic methods and today we are in the midst of aquiet revolution.

This revolution began in earnest with thedevelopment and acceptance of an electro-opticalmethod of long-range determination around 1945. Itwas called the Geodimeter and was made by AGA ofSweden to designs produced earlier by Dr E. Bergs -hand.(History records the fact that Galileo proposed an optical

you,. 2 Sellurommar modal MRAS. uses the microwave method tomeaure Ms once ham m to 50 ern to an accuracy bed. Man in5005000 Modem electron,. have made it easy ro operate Readout,a 7.tagn Juan/ay arrange


method which was later tried unsuccessfully in the1600's. At that time they lacked fast enough respondinglight sensors.) The AGA method could measure 20 kmdistances with only a few parts per million error.

After the Geodimeter came the Tellurometer. whichmade use of modulated UHF radio waves and could dobetter in range than the Geodimeter, with similarprecision.

What a GaasMore development ca me about in the 1960s,the notable addition being shorter distance rangingapparatus based upon the easily modulated galliumarsenide Ga-As solid-state infra -red diode. This devicewas suited for the surveyor's needs in building andsimilar size tasks.

Simultaneously came the development of automatictheodolite scale -reading electronics. Observing with asecond -of -arc scale instrument can prove tiring to theeyes, with the subsequent chance of a high error rate.

By 1970 electronic theodolites, as they becameknown, were being marketed by most of the largeestablished surveying instrument makers. It was thenjust a matter of time to extend the automatic reading ofscales to include straightforward conversion of anglesand slope -distances into the required geometricparameter. These calculations were first done withseparate electronic solid-state calculators; then thecalculators were incorporated into the housing of theinstrument itself. Today the latest machines use in-builtmicroprocessors.

When automation can reduce the labour requirementat a cost less than the labour alternative, there is a case

That is why, in cases where extensive surveying workis needed, electronic methods have been used. For thesame reason one instrument, that marketed by Hewlett-Packard, reduces the tolerances needed for initiallevelling of the -theodolite" system by incorporatingcompensation measurement of the out -of -level existingat the time of measurement

Let us now turn our attention to the detail of some ofthese developments.

UgttN1170.

Figure 3 Much simperierd schema!, of Georimatar model 6A distancemeter In tors design electrooptical methods are used

25

Ii1.1171ltONICN IN NIIIEVININGRangingMicrowave methods: A continuously generatedUHF signal, which is typically generated today by aGunn diode oscillator, is sent from a small reflector orhorn to a second unit placed at the other end of thedistance to be determined. Phase difference betweensent and returned signals provides a measure of distancein terms of the velocity of electromagnetic wavepropagation in free -air conditions.

Accuracy is limited in all EDM (electronic distancemeasurement) methods by the knowledge of the refrac-tive index of the air path. This limits all methods toaround a 2 parts per million error in determiningdistances which range from 100 m to 50 km.

The first systems required the operator to learn a quitecomplicated procedure of use. Today the latest modelsprovide digital readout, a voice channel to the person atthe other station and, in some cases, an outputcompatible with digital data storage and processingsystems. A modern microwave EDM unit is shown inFig. 2.

The design and construction of microwave systemsfollow established radio communication practice usingmixing techniques and special tone pattern generation.More detail on these methOds is available in the "furtherreading" list given at the end of this review.

Electro-optical modulation: In these an opticalcarrier beam is modulated by altering the intensity of thecarrier or its angle of optical polarization. The modulatedbeam is transmitted from a high -quality optical telescopeto the far station where it is reflected back to the senderby one or more corner -cube reflectors. Fig. 3 shows theschematic of a Geodimeter model 6A.

Various sources of radiation are used in the models

discharge lamp was employed. Later improvements torange were provided by the use of helium -neon C.W.laser sources. Lasers also provided better utility indaylight conditions. The Mekometer method uses apulsed Xenon gas source. The shorter distance modernunits usually use a laser -diode source of infra -redradiation.

The kind of electro-optical technology involved in themanufacture of an I -R ranger is seen from the schematicof the optical system of the Hewlett-Packard 3620A,provided here as Fig. 4

Moore 4. Electro-opt cal rangers legume sophistic . ^Moo, ac 1,44 1°extreme provisions. This schematic is or an h0 er Mode Instrument

26

Figure 5 TheWild OLIO

OR ranger thatfits on to aconventionaltheodolite

Tacheometry: Basically the angle subtendedbetween a fixed interval bar of scale unit is used todetermine range by redirecting the theodolite from endto end of the target interval. The alternative is to observethe interval of a graduated staff seen within the angledefined in the field of view of the telescope by twoparallel lines appearing in that field of view.

A variation is possible in which the optics of thetelescope are altered geometrically at the operator'scontrol.

This method of ranging is simple in principle, butneeds many geometric corrections in practice for thesubtended interval is rarely geometrically square andcentral with the telescope. Corrections are needed tochange slope to horizontal and vertical distances and toallow for the fact that the observed interval is nor squareto the observer.

Many of the new electronic methods are called'reducing tacheometers". These, it seems, are not truetacheometers in the traditional sense, but are in realityrangers to a point target.

Automatie angle measurementThe period 1950-65 was one in which extensivedevelopment of automatic angle measurement methodstook place as part of numerically -controlled machine -tooldevelopment. Many methods of producing an electronicsignal equivalent to angular rotation were invented.

Around 1960 several of the instrument designers inEurope began to apply these methods to surveyinginstruments so that the scales of a theodolite could beread automatically providing digital readout andautomatic data reading.

Angular encoders for this task must provide circlesubdivision to at least 21600 increments (1 arc minute)in a small diameter.

Of the wide range of angular encoder types invented,optical methods have been adopted in electronictheodolites. Optical encoders may be of the incrementalkind in which a pulse is produced and counted for eachminimum resolvable increment of angular movement,the pulse being added or subtracted for the appropriatesense of direction. The alternative is to use a disk on


which a digital code pattern is manufactured. This iscalled the absolute method, for there is no chance ofpulse loss or gain due to noise,power-supply failure doesnot destroy the value.

Incremental methods use simpler to make measuringgratings because they need only identical lines ruledradially. A much higher density of lines is possible bythis method than is economically available with theabsolute scale. The absolute scale is more costly to makeand read than the incremental version.

In practice experience has shown that a hybridsystem is the best to use, one in which an absoluteencoder disk scale provides the coarse -positioncomponent of the readout, a finer ruling incrementalscale providing the less significant digits, usually by wayof an analogue subdivisional method that interpolatesbetween the rulings.

The futureIn the world of large commercial manufacture. newideas are slower to reach the market place than they areto realise. Over the next decade a number of

Figure 6. The 2820A electronic TotalStation is an example or the mom sophisticatedelectronic surveying instruments. Like someothers, it contains a microprocessor that doesthe tedious calculations required, and the extracomputing power available is used to correctreadings for such variables as outoFvertical ofthe instrument

SLIT

ItUNATOR

improvements and alternatives should emerge.Study of the time taken to set up a theodolite or level

shows that the initial levelling procedure takes asignificant time to achieve. Hewlett-Packard haverecognised this and provided a partial solution to theuser. Using electro-optic sensing of a plane surface.defined by a mercury pool, two -axis correction signalsare produced that compensate for the not quite trulyvertical central axis. The operator needs only to level theinstrument within crude limits using a small circularbubbly level. The next stage must surely be to provideautomatic levelling servos that set the instrumentorientation regardless of gross misadjustment of thetripod top. This is straightforward to design - it is amatter of cost and time being available.

The next time-consuming task is to acquire the targetare' set the telescope fudicial mark on to it so that theangles can be read out. In many cases the target isidentified by a special mark or pattern to make it easier tofind. The next logical move is to have the theodolite orlevel automatically seek out the target, locking on to it.Once acquired, the scale values would be readautomatically.

Another development that may replace the theodolitein many applications is a technique called chronometricangle measurement. In this method a rapidly spinningmirror causes a photo -detector to see established targetsin sequence. The time between the sources is a measureof angle if the rate of rotation is known. Simplearithmetic establishes that the precision of timingavailable today is able to provide second of arc accuracy.There are no scales to read in the method. This conceptwas explored and an instrument built in Germany adecade ago. Perhaps the surveying instrument makershave a prototype ready to market now - suchinformation is hard to establishfield of sophisticated instrumentation. ETI

Further reading

':Surveying" by A. Bannister and S. Raymond. Pitman. 1977.amnionsu quite up-to-date chapter on electronic Methods. It doesmit. however. discuss such concepts us electronic theodolites and

ments having micro -processors in them."Electromagnetic Distance Measurement.' by C. D Burnside

Crosby. Lockwood Stapes. provides detail.Hewlett-Puckard Journal issues descnbe the theory, operation

nal construction of their Total -Station instrument in considerabledepth. Most companies marketing this kind of equipment are ableto provide reprints of papers describing the use of their products.

WAVg8rtitarA...

SINUSOIDAL1

778liiu Toe

ENCODER DISC

Figure 7 Cross -Section of reading heads that sENBae

sense the angle in the HP 3820A TotalStation.


7SENSOR

fSE15,ZEN'STO'R'S

C-) COE,

ROTZZNAL

LETTE_Rs Bzt7p7rkContributions to this page are invited from all our readers. If you wish tomake a point --this is the place to do it. All contributions to this sectionshould be intended for publication. Please mark your envelopes 'LETTERSPAGE'.

ANNUAL ENQUIRY

In an advert in one of your mag-azines there is one book 'Arc WeldersAnnual', I wonder if there is an ArcWelders Monthly magazine please letme know if there is and if your com-

pany publish it. If they don't wouldyou be so kind as to tell me theaddress of the company that doespublish it.

F.Q.Eire

Excuse me ... erm ... I don't knowhow to tell you this but that was acartoon i.e. a joke - mind you themagazine displayed beneath AmWelders would be sure of one readershould it ever appear.

BLOB BOARDSDear Readers,

If you are following the series 'Dig.ital Electronics by Experiment' inElectronics Today International, youwill have found the boards differentlylaid out to a ZB 81C. The author othe series used pre -production samplesof ZB SIC Blob Boards and these wereslightly different to the productionmodels.

The only difficulty that this shouldcause with the series is in the con-struction of the voltage stabilizer cir-

cuit, and we suggest the followingmodifications: -

USE bus -bar .1 for the regulatedsupply, linking to bars I and34.

USE bus -bar K for unregulatedinput and 0 for negativeline. Link 0 to 141.

USE line 151 in place of line N.USE line 161 in place of line M.For the remaining projects, use

the boards supplied with the letters ontop and the numbers down the lefthand side.

We regret the inconvenience causedand now hope that you can still enjoythe series of articles.

P. L. 11P.B. Electronics (Scotland) Ltd.,

AND THE SAMETO US_ ... ,Dear Sirs,

Can you imagine the chagrin yourpoor correspondents must feel at thenasty replies to their letters printedin the November issue? This letter isdirected at you, the staff of ETI, sothat you may share the experience.

You may be expert at plagiarisingand paraphrasing but you du notactually know any basic theory doyou? Original thoughts must be asscarce as butterflies at the ofticeS atETI. One should, of course, sufferfools gladly but the mendacity.jealousy and spire of the aspiringintellectual makes him hard to hear -and when he pours malicious scorn onthose only slightly more naive thanhimself a rebuke is in order. Howdifferent is the humble simplicity ofthe true scientist, whose virtue lies

in his readiness to admit that thereare things he doesn't know.

The copy you produce. redolentof third -form wit, parading knowledgelifted verbatim from the manufac.turers' handouts-the ponderous puns.the gaffes, the howlers, thc tnala.propistns, the spelling mistakes doesnothing to justify' the superiority youso obviously feel.

Ouch!

R.S.Piddlchinton

BLOOMING SPELLDear ETI.,

I see the little homepride menhave struck at the ET! offices!

You keep on spelling fluorescentas Fluorescent.... an ely dikshunarydon't agree!

D.J.Chelmsford

We've downgraded the typist for that.Cos graded brains make finer fluor!

POINTING OUTDear Sir,

Although full of admiration for theNovember cover, I feel there is morethan meets the eye behind the SpecialOffer.

There are in fact two points I

should like to see raised. however, asthis may he physically impossible.perhaps the offer could be moved toanother page?

W.T.W.I lednesford

Oh yeah? What size plastic mac do youeke then?

28 ELECTRONICS TODAY INTERNATIONAL -JANUARY 1978

HAMMER THROWAn exciting game of skill and luck that will help pass those long and

lonely winter evenings.

IF, LIKE MOST of the ET staff, youhave more brains than brawn, andwould not boast about the quality ofeither, it is likely that the mere thoughtof swinging a massive weight aroundyour cranium is enough to strain yourbodily systems. This probably means -and we are sorry if this camas as adisappointment - that your chancesof selection for the Olympic hammerthrowing team are, shall we say, nil.

Some may say that this is a pity asthe sheer thrill of an event such as thehammer throw is probably very stimu-lating to those chunky brutes that arelucky enough to be able to take part.This is where we come to the rescuewith our armchair version of the game.We think it has a number of distinctadvantages over the real thing. One ofthese is that anyone, from an anemicsparrow upwards, can play the game. Asecond being that it is nowhere near asmessy if, when playing in your lounge,you get things wrong.

The game, as can be seen from ourphotographs, has a front panel with acircle of sixteen LEDs together with aline of eight LEDs eta tangent to thecircle.

To play, after pressing reset, firmlypress the play button. The LEDs in thecircle will light one at a time simulatinga spot of light moving in a circle. Atthe same time a distinctive, not to say

loud, sound will be generated.The spot will et first travel slowly

round the circle, but will soon beginincreasing in speed until it is travellingquite fast

The object of the game is to releasethe play button at the instant that the'top' LED of the circle is lit If sucessfulthe line of LEDs will light to indicateyour more, the faster the spot wasmoving when you scored the more willbe your score. If you miss, the cirle ofLEDs will continue to rotate at thesame speed as they were when youplayed.

Big Ones And Little Ones.A game will consist of, say, eightrounds - the score from each beingadded to the last. At the end of a gamethe person who scored the most is thewinner. The skill comes in decidingwhether to go for a number of lowscores that are relatively easy to get, orfor a few big ones,

As befits the design of a project ofthis nature we were in convivial moodand pleasant surroundings when wefirst discussed the game. We producedthe first design sketch (well a few lineson a beer mat - yes in the pub again)which used digital devices. Upon seeingthis some likely person said that hethought most games featuring LEDsdesigned over the past few years should


generically be called "spot the 4017".Our initial reaction was to defend

our design but a moment's thoughtshowed that he had a point - the4017 CMOS counter is over -used whenit comm to games. At this stage wedecided to rise to the occasion andproduce the game using an all analogueapproach.

The result can be seen in the circuitdiagram. We are pleased with thiscircuit: It uses some unusual ICs andfeatures a number of interesting circuitblocks - and of course there is not a4017 in sight.

ConstructionConstruction of the game is greed),simplified if the PCBs are used. Threeboards are required. one for the powersupply, one for the display, and finallythe main control board. Begin bybuilding and testing the power supply.Take care to ensure that all componentsare mounted as shown in our overlay.

Next assemble the control anddisplay boards. These carry a largenumber of components and mistakesmade during assembly can be difficultto trace later so take care at thisstage. Do not insert the link betweenIC2/4 and IC9 at this stage.

It is best to test the boards beforemounting them in the case, as it is

difficult to get to some of the deviceswhen the boards are in their final

29

HAMMER THROWon

Eg

4A.

S

Ou Oyu SSO

0, ?Jo

positions. We used a sloping front Verobox to house our game and the generallayout adopted can be seen from ourphotographs.

Setting UpThere are five preset potentiometers onthe board and all must be correctly setup before the game can be played.

The first adjustment to be made is toRV4. To calibrate this conttol first pressthe reset button and then the playbutton for a few seconds. At this stage asound should be heard from the speakerand the game display LEDs should beseen flashing. Adjust RV4 until theLEDs produce a continuously rotatingspot of light. The speed at which thecircle of light rotates can be adjusted byRV I.

The next operation is to set up thescore display. To accomplish this, pressreset and then operate the play buttonuntil the spot of light is rotating atmaximum speed. Release the playbutton and enable the score display byapplying a positive pulse (front supply)to the junction of R29 and IC6. RV5should now be adjusted so that theseventh score LED is just extinguishedand the eighth lit

The final adjustments concern the'window' discriminator. To make thisadjustment R38 the end remote fromIC9) should be connected to the slider

BUY LINESSome of the ICs used in sir

rnay be unfamiliar but theyed by most of the lasso'stores. Some of the hid'may also prove illusivthey are not available o cclshop try the advertisers in this issue


of RV2. Adjustment of RV2 shouldilluminate successive LEDs of the gamedisplay. RV2 should be set to the pointat which the top LED just extinguishesand the LED to the left just lights.

Now connect the input of IC9 to theslider of RV3. Adjust this pot so thatthe top LED just extinguishes and theLED to the right is just on.

This cornpletes the adjustments andthe link omitted during construction,should now be fitted.

Now is the time to get in trainingand, if you're good enough, you mayyet make it to Moscow. ET

L

E;LOBt16 1

PARTS LIST

02

NN q

NN14

14

14

Fig. 2. Circuitdograrn of gameOisplaysection

LE

RESISTORS all IOW 5% unless stated C5 10u 25 V electrolyticC6 10n polyester

R1,5,17,26,42,48 100k C7,8 202 polyesterR2,13,15 10M KW 10% C9,10,12 100n polyester83,6,8,14,16,25, CI 1 100u 25 V electrolytic

30,37,38 1M04.40.55 4k7 SEMICONDUCTORSR7,18 2512 ICI 78L154R9,31 560k IC2,3 L513900510 4197 IC4,5,7,9 741R11,12,28,29 820k IC6 CD 4016820,21,34,36,39,41,43 IC8 555

45,47,49,51,52,54 10k IC10,11 UAA 170R22 220k of BC2I2LR23 150k 02 BC1841_R24 2k2 01,2,3,4-12 1N914027 120k LEDs 1-24 .2') type532,46,53 1k BRI 9 pin DIL TYPER33 56k 0.9 A 400 V (fromR35 1005 R. S. Stockists)R44,50 33k014 47k TRANSFORMER

T1 240 V - 15 V 6VA

POTENTIOMETERS LOUDSPEAKERLSI G.PQ Wee Mears

100k min hor trim10k min hor trim SWITCHES

P61,2 Push to makeSW1 SPST toggle

CAPACITORS

C1 10000 25 V electrolyticC2 220n polyesterC3 470n polyesterCA 1n polystyrene

CASE Vero type 65-2523

MISCELLANEOUSFlex, PCBs as patterns, LED mounting Clips, toccataholder to suit.


HAMMER THROW

ETI HAMMERTHROW PSU

0 roZis3MeF';;" s""P' 0""0"

Fig. 4. Component overlay of PSU mains earthis connected to TI by a solder tag under the

Nmounting bolt. The dans formera screen shouldalso be connected to earth.

32

Fig 5 Full size /160 x 110 mm) foil pattern of display board

Fig 6. Circuit diagram of the game's power sum, y

FS' 24 V/15Ve

ELECTRONICS TODAY INTERNATIONAL -JANUARY 1978

tj yrTh

.1114f1

i iC4119

89 8 The overlay for score board


Fp 7 Full s8e fool pattern of main control 60,060 x 110 rnm)

'7)

Fp 9 The overlay for the oontsol board

33

HAMMER TH W HOW IT WORKS

ONO -4

741

Fig. 10. Knouts for the integrated ',cilia usedin the hammer threw.

34

The circuit may be broken down into anumber of major blocks - viz the displaysections for both game and score. a voltagecontrolled oscillator, a ramp and holdcircuit whose output controls the oscillator,a 'window' discriminator, a sound generat-ing circuit and finally a power supply. Aswell as these major blocks there are also anumber of latches, buffers and switchesthat are necessary for circuit operation.

The block diagram shown in Fig 11 showsmost of the circuit blocks and, togetherwith the circuit diagram. should be read inconjunction with this how it works.

SYSTEM OPERATIONThe game display is based on a UAA 170 IC.This device is for driving LED displays andwhen connected to a line of sixteen LEDswill illuminate any one of these dependingon the magnitude of the analogue voltageapplied to its input. For the game displaywe need to produce the effect of a spot oflight moving in a circle. To achieve this wearranged the sixteen LEDs Ina circle andfeed a sawtooth waveform into the UAA170. A moments thought will show that thiswill produce the desired effect.

In order to make the display rotateslowly at first, but speed up as play pro-ceeds. we made the sawtooth generatorvoltage controlled. The control voltage isproduced by a ramp and hold circuit whichis reset to zero at the start of play, butbegins to ramp up, thus increasing thesawtooth's frequency as play continues.When the play button is released, thevoltage reached is held by the ramp andhold configuration until it is reset. Thisvoltage is used for score purposes as de-scribed below.

The game requires that if. at the instantof releasing the play button. the 'Top' LEDof the game display is lit, a score is indi-cated, the magnitude of the score beingcr p to the

mspeed at which the

irocle'orf LEDs was moving at the instant ofrelease. From the description of the gamedisplay it will be seen that in order to light aspecific LED the voltage input to the dis-play driver must lie within a specific vol-

., rage e, thus in order to detect whetheror not the 'top. LED is on we must look atthe output of the sawtooth generator (thisis input to UAA170) and decide whether itlies within the range that will light thespecific LED at the instant the play button

released. The circuit that accomplishesthis Is the 'window' discriminator.

This a formed from two voltage compa-rators together with two analogueswitches. Detailed action is described be-low, but briefly the circuit, when fed withthe sawtooth output, will provide an indi-cation whenever this waveform passesthrough an (adjustable) 'window' voltagerange.

At the instant that the play button isreleased a short pulse is produced from amonostable. If this pulse is coincident withan indication from the window circuit thatthe top LED is on we must arrange toindicate as core.

The score must be proportional to thespeed of the LED circle which is Inn tomproportional to the voltage level reached bythe ramp and hold circuit. Thus, to producea more, we feed the output from the rampand hold, via an analogue switch, to asecond (IAA 170. This second display con-s.. of eight LEDs in a line.

This completes a brief description ofcircuit action: we shall now deal with eachblock in more detail.

RESET CIRCUITRYThe buttonsi initiated by operauon of thereset (Pat). This zeros the ramp andhold circuit described below. as well assetting latch 1 1C2/3 and resetting latch 2IC3/1. Latch I enables the play buttonwhen its output is high (set) - latch 2enables the score display when low (reset).the game display when high (set)

Each latch is based on two of the am-plifiers of an LM 3900 Quad Norton am-plifier package. This device is unusual Mthat instead of amplifying the difference involtage applied to its input terminals. itamplifies the difference in input current.

The and - inputs of these Nortonamplifiers are both clamped to one Diode -Drop above ground and thus all inputvoltages must be converted to currents (byresistors) before being applied to the inputs_This is the basis for the current -Mode(Norton) type of operation.

In operation the current flowing into the+ input must equal that flowing into the -input, the difference between the currentdemanded and the current provided by anexternal source must flow in the

by

circuitry.Operation of both latches Is the same and

we shall only describe the action of latch I.Assuming that the latch output is low

(the latch is reset) the current injected intothe - input of 1C2,3 will ensure that theoutput remains low If now sufficieur-rent is injected into the + input the outpuvoltage will rise as the device attemp. toreduce the input current differential tozero. Positive feedback via R9 will enhancethis action and cause the amplifier to latchhigh. This is because the current injectedinto the + input via R9 in this case isgreater than that into the - input due to.R8. A positive pulse via It 11 to the - inputwill however once again bring the outputlow.

C5 and R4 ensure that when power is firstapplied the game is reset.RAMP AND HOLDThe ramp and hold action is provided byIC2/2 and IC2/4. A positive voltage via RS -

and DI causes the output to ramp downwhile a similar voltage via RIO causes theoutput to ramp up. The reset button causesthe downward ramp while play causes anupward ramp.

In any sample and hold application a verylow input bias current Is required if the holdperiatod is to be stable. The existence ofmched amplifiers within the LM3900allows one amplifier to bias another.

In operation the LM 3900 requires a biascurrent to be applied to its - terminal.IC2r4 has its + terminal grounded andfeedback applied via R15 and RIR Theoutput voltage of this device will attain alevel such that the current fed back viathese resistors is equal to the bias currentdemanded by the input. This same currentwill flow via R13 and R14 into the - inputof IC2/2 reducing the effective bias currentof this amplifier to almost zero. Dl isolatesthis bias current from the rest of the inputcircuitry.

If now a positivepurrent is injected intothe - terminal, the output voltage will fallas It attempts to feedback a current of thisvalue In order to reduce the input currentdifferential. This constant current acrossCO results in a Linear voltage ramp ap-pearing across Cl. Input to the + terminalcauses a positive going ramp. to the -terminal a negative going ramp.

The rate at which the voltage across C7changes is proportional to the value of the


constant current supplied which is in turnproportional to R5 and R10. As R5 is some40 times larger than RIO, the ramp down(reset) is far quicker than the ramp up.

The output from the ramp and holdcircuit is fed. via IC6/1 to the score displayand via IC3/2. a non -inverting scaler, to the IXsawtooth VCO.NON.INVERTING SCALER

The scaler is required because the outputfrom the ramp and hold configuration canvary over nearly the whole supply voltagewheres the VCO requires only small vol-tage swing to provide the required hg. I I. clock diagramfrequency change. of the hammer

The scaler is based on another Norton throw game.amplifier arranged as a non -inverting am -piffles feedback is applied via RVI and RI9and output is fed to a potential dividerformed by R22 and R23 and thence to the"CO.VOLTAGE CONTROLLED SAWTOOTHOSCILLATOR

The VCO Is formed by IC3/3 and IC3/4.Action of IC364 is much the same as that ofIC2,2 described above. The special inputbias circuitry is not required as there is nohold requirement.

IC3/3 acts as a comparator and circuitaction is as follows: while to output of1C3/4 is high and ramping down (input to- terminal) the current into the - input ofIC3/3 due to R26 is greater than that to its-1- terminal due to 1125 - its output is thuslow.

As the output of IC3/4 ramps low how-ever, there comes a point where this situ-ation is reversed. The output of IC3/3 goeshigh. This state being maintained bypositive feedback via R7 and injects a largecurrent into the + input of IC3/3 as R7 ismuch smaller than R25.

The output if IC3/4 thus goes high, res-toring current flow via R26 and starting thecycle again.

By varying the current injected via R22the time taken for the output of IC3/4 toramp down to the point at which the com-parator triggers is lessened. This results inan increase in the frequency of the saw.tooth.

The output from the VCO is fed to the

EnclIntpalgr=bRyIntahnedralnItTa.IC7 to the sound generator ICS.WINDOW DISCRIMINATORThe window diuriminator is formed by twocomparators IC4 and ICS and two of theanalogue switches in IC6.

Operation is as follows, If we assume thatthe output of the sawtooth is is high andramping down the voltage on the-input ofIC4 will be higher than that on the input(a reference level established by RV2) andits output will be low. The output of IC3 willbe high as the input tons + terminal ishigher than that to its -iput

As the voltage ramps down. a point willbe reached where the output of lm goeshigh as the voltage at its - input falls belowthat set by RV2 at its + terminal. At thisstage the out of both IC4 and 105 arehigh. as ICS has not switched. As thevoltage continues to ramp down, however,the voltage on ICS's input falls to a pointbelow that on -input and the output ofthis IC goes low.

Thus the outputs of both ICs wages highfor a small range odepot voltgs (thewindow) defined by the difference in vol-tage between the sliders of RV2 and RV3.

The outputs of these ICs are Adis theinputs of two analogue switches. positivevoltage applied to these switches turnsthem ..on'

Thus during the window a signal pathexists from the input of 106/4 to the outputof 106/2.MONOSTABLE

The monostable O formed by IC2/I thisproduces a short positive going pulse uponreceipt of a negative spike produced by therelease of the play button.

Current injected into the - terminal viaR3 will normally hold the output low,however a negative pulse applied via C4and RI will "rob" this current from theinput and causes the output to go high.

00 latches the gate in this state after thenegative pulse is removed. Al this stage C6beginscharging, feeding back an increasingamount of current to the - input as thevoltage at the junction of R6 and R3 rises.

There comes a point when this current isgreater than that fed back via 122i and theoutput returns low. Diode D2 rapidly dis-charges C6 to provide reliable re -triggering.

The leading edge of the output pulse iscoincident with the release of the playbutton. This pulse is used to tum on analo-g rememberedue switcht

voltagewindow at this point - switches IC6/4and IC6/2 will also be on. This allows thesupply voltage input to IC6/3 to set latch 2and thus initiate the required actions, ie,blank game display, enable score display,etc.

The monostable also resets latch I IC2/3to remove supply from the play button, thisprevents cheating.GAME DISPLAY

The output of the sawtooth VCO is fedvia an inverting fuffer, IC9, and a potentialdivider, 004, to the input of vice a UAA170.The input circuitry of this device consists ofa series of differential amplifiers with oneinput of each connected to the input Mminal (pin 11) via an emitter follower. Theother input of each is connected to a pointin a potential divider chain consisting ofequal value resistors. The differential am-plifiers thus opera. as analogue voltagecomparators and as the input exceeds thereference voltage of a particular compa-rator, the output of that comparator willchange state.

To reduce the package pin -out the LEDsof the display are not driven individuallybut are arranged in a four by four matrixoutput by the row and columnoutputs of the IJAA170 (A -D and E -F res-pectively). By enabling the appropriate rowand column output any one of the sixteenLEDs may be selected. The matrix outputsam controlled by the internal logic of theUAA170.

The resistor chain R42, R44 and R45 theup the reference voltage inputs of thedevice. The voltage on pin 12 establishes

the lowest voltage to which the CAA ,,will respond. If the input voltage is belowthis point the first LED of the displayremains lit As the voltage rises above this'level the first LED is turned off. the secondon - as the input rises the spot moves upthe chain, until the voltage reaches that seton pin 13. This is the maximum voltage towhich the display responds and if the inputis taken above this level the last LEDremains lit.

In addition to defining the indicationrange the voltage between pins 12 and 13determines the abruptness of transitionbetween any two LEDs. With this dif-ference set to 1V4 the light point glidessmoothly along the scale, with increasingvoltage difference the passage becomesmore abrupt until. 4V the light spot jumpsfrom one LED to the next. We have set thisvoltage to a point between the two ex-tremes.

resistors R46, an and 1247 controlthe brightness of the display. QI suppliespower to the display and is driven fromlatch I IC2/3. This you will recall. is reset,

its output is low, at the start of a game. Alow voltage applied to 01 via R4I turns thistransistor on and enables the display. Thelatch is returned high at the end of a game,this turns QI off and blanks the display.

SCORE DISPLAYThe score display is formed by a second

UAAI70 (1C10). Much of the circuitry is the.same as that of the game display exceptthat we only wish to display eight LEDs.The diodes from unused outputs to the+ VE supply act as 'dummy' LEDs, res-tricting the display to eight LEDs, youcould use LEDs for extended scoring - buta larger box is needed. This display ispowered by Q2 which is again fed from theoutput of latch I (C2/3. This tme, how-ever, the display isI blanked, Q2i off, whenthe latch is low and enabled, Q2 on, whenthe latch output is high.

SOUND GENERATORThe sound is generated by ICS an NE555

operated in its astable mode.The reset pin(4) is normally held low by

R32 and hence circuit action is inhibited. Aposit ive voltage applied from latch I via theplay button enables the sound during thegame.

The output is frequency modulated byapplying the output of the sawtooth VCO,via buffer IC7 to provide the necessary lowimpedance drive, to the voltage controlinput (pin 5) of ICA


RACE TRACK

WEBET YOU'LL HAVE FUN WITH THIS GA

THE DESIRE TO place bets tem'almost any event, from the outcome ofthe big race at Newmarket to the likely -hood of life on other planets, is a deepseated one in many of the inhabitants ofthese islands. That old joke about theguy who bet his friend a couple of quidthat he can give up gambling for a weekwould not be amusing. but for the factthat it were so near the truth.

Three Way Bet

Bets fall into a number of differentcategories. They may be made ondisagreements of fact 1'1 bet mine'sbigger than yours'l, about eventscapable of being modified by skill orlack of it CI bet I can get mine furtherthan yours'). or bets made upon randomevents IThe mind boggles!).

It :s this latter type of bet. the tossof a coin, cut of a card or spin of aroulette wheel, that is probably themost popular fonn of gambling amongstgroups of people, our race track gameprovides an exciting means of indulgingin this type of activity.

The game is really a development ofthe well known 'heads or tails' typeof game, but whereas most games ofthis sort are visually unexciting, the race

RaceTrack

0 s s'C, I

track game more than makes up for anyshortcomings in this area!

They're In The LEOWhen the game's reset button is preseedall the LEDs are off and the 'horses' lineup at the starting post. Now is the timeto choose a horse and place bets if youwish

sing the button starts the actionwith rho encl. or LEDs representingthe 'horses' starting to flash as first onehorse then the other takes the lead. Aseach horse completes a lap the approp-riate lap LED lights. The first horse tocross the finish line lights his 'win' LEDand halts the racing hors.. If lady luckdid not smile on you this time, pressingthe reset button give her, and you,another chance.

ConstructionMount all the components on the PCBas indicated in our oveday diagram. Werecommend that sockets are used forICs 1--6 as these are CMOS devices andshould not be placed in circuit until allconstructional work is complete. TheLEDs are hard wired to the PCB andthe interconnection information is givenin Tab'. 1 and 2. Note that LEDs 37and 38 have their cathodes taken to 0 Vvia R6 and R7 and not directly toground as the rest.

The value of Al sould be selected togNe the bett display on the race track.A value somewhere between 4M7 and10M should suit.

Now is the time to turn on, placeyour bets and probably loose yourshirt.


Fig I Mmout for 40,6 IC

The circui use two oscillato s each basedon two of the NORgatoaiote 4001 QuadNOR CMOS packing. One of these (IC1/3and ICl/4 runs at a high freq ency and itsoutput is ed to the Input of one half of a4013 Dua D type flip-flop. The device de -

de the utput of the high speed ouilletorby kwo a d provides two signals that are180 auto! phase at ils Q and 0 outputs.These signals enable either IC3 or ICS, theICs being enabled if their enable input isheld low.

The second oscillator based on ICl/1and IC1/2 runs at a lower speed and isarranged to provide a non -unity markspace ratio, in fools very short -high"output followed by a much longer "lose".

HOW IT WORKS

The photograph of the game shownleft shows the general method ofconstruction used in the prototype.Connecoon details for the wiresbetween the board and front panelare shown in Tables I and 2.

This non -unity mark space ratio is achievedby the inclusion of DI in the oscillator'stiming network. This second oscillator canbe gated on and off by signals to be des-cribed below.

Circuit action is as follows. PSI isclosed and this resets an the countess toearn as well as inhibiting the slow runningoscillator. Upon releasing PRI, 1C3 or IC5will be clucked as the first positive pulse isgenerated by ICl/1 and ICl/2. Whichcounter is incremented will depend uponrho -slots of IC2's outputs.

In general hr the two oscillators ate outof phase the counters will appear to beclocked in a random manner. A furtherrandom element is introduced because

while a 401 7 is normally clocked withpositive going pulses at the clock inputwith enable held low, it is possible for it tobe clocked with a negative going pulse atenable while clock is high. Thus occasionallyIC2 will act as a clock.

At the 004 01 a lap a pulse is generatedfrom the carry out (CO) output of eitherIC3 or 105 and is used to advance the lapcounters (IC4 and ICE).

The game ends ton the ninth lap whenthe '9' output of either lap counter goeshigh. This turns on either 01 or Q2 and intom lights the appropriate win LED. Thesignal from either '9' output is ()Red by

' diodes and this signal used to halt the gameby disabling the slow running oscillator.

'TRACK.

LEOS 1-10 LEOS 21-2

EDS 11-2

cc

5

LEDS 29 36C6

62

ESTE TEXT


OV

on

Fog. 2. Full °,00m(Magram of the racetrack game, Note theunused sections ofIC2 are tied high as isgood practice withCMOS ICs

37

TABLE 1CONNECTIONS TO IC3 (5) PARTS UST

RESISTORS Inc tow 5%) SEMICONDUCTORSPIN LED (ANODE)

RIR2 ;07 t"'

ICI 4001IC2 4013IC3-6 4017

6 116)21

112)(11) R3,4 100k P1,2 BC108

3 113)R5R6,7

270k270R

D1-3 1N914LEDI38 TIL208 red7

8118)4

(In(14) SWITCHES

910

9119)5 (15)

CAPACITORS P81 Push to make typeSW1 SPST toggle

10 (20) C1C2 1n7nel',..trer MISCELLANEOUS

Battery clip, flex, PCB as pattern, case to suit.TABLE 2

CONNECTIONS TO IC4 (6)

PIN LEO (ANODE)

25 133)21 129/

626 (34)27135)

9

13 131/28 (36)

10 24 (321

BUY LINES.There should be no problem gettingany of the components for this pro-ject. The (Cs should be available frompeople like Lynx, Maplin, Watfordand Marshal's. The main thing is to tryand get a quantity discount on thethirty-eight LEDs needed.

38

Fig. 3 Full site (115 x 020, loel pattern


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is can be a nuisance can't it, going Isom newsagent to newsagent,"Sorry squire, don't have it - next one should be out soon."

AlMough ETI is monthly. it, 5510 'arc to find ...NWaafter the fMt week. If it is available, the new.gent, going to besure to cut his order for the next issue - but we're glad to say itdoesn't happen very often.

Do yourself, your newagent and us a favour. Place a regularorder for ETI) your newsagent will almost certainly be delight..If not, you can take out a postal subscription so Mere, nothingfor you to remember - we'll do it for you.

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ELECTRONICS 70DAY INTERNATIONAL - JANUARY 1978

You may think your conversation is private but

WALLSHAVE EARS

There appears to be little control in Britain over the manufacture and sale of buggingdevices. ETI has been investigating the current situation.

IT WILL COME as a big surprise tomost readers that bugging is not initself a criminal offence. Plant an RFbug in an office during working hours,listen in on highly confidentialdiscussions and the worst that you'llbe got for - if you're caught - isoperating a transmitter without alicence. Technically you could also behad for listening to 'an unauthorisedtransmission' but we know of no suchprosecutions.

6.7r51t,WIFE:45,171'

The Younger Committee onPrivacy which reported in 1972 quiterightly recommended that bugging inany form should be an offence, initself, but it has not yet been actedupon.

How serious is bugging?In researching this feature wefound ourselves continually comingup against stony silence - few peopleare prepared to discuss the subjectand none would agree to having theircomments personally attributed. Try

wo.

to talk to a company that's advertisingbugs and ten -to -one he'll tell you he'snow stopped, but he will supply youwith equipment to 'sweep' your office(the technical term for finding otherpeople's bugs).

It is possible to get some idea ofthe scale of things however. There areabout ten companies in Britain openlyadvertising bugs - most of themappear to be very small. Even so thisindicates that sales are unlikely to beworth less than £100,000 a year andsince bugs are cheap, literallythousands are sold every year.

Most technical publications (thisincludes ETI) refuse to acceptadvertisements for these devices on

OD

Arrangement of an infinitytransmater used to eaves-drop on unds in roomthousandsso of miles awayusing the telephone es themicrophone.

Exploded view of the USGreet Seal presented to theAmerican Embassy inMoscow in 1945. This in-genious dewse was passivein operation and could notbe detected by moat of to.day's anti -bugging equip-

sf..ben You appreciatethat this was devised 33yebigo it makes onewantler how sophisticatedmodernday intelligenceequipment must be.


the grounds that they are undesirable,not because we are not allowed to.

Where are these bugs used then?We suspect that the overwhelmingnumber are bought as toys and not forany devious purpose but this stillleaves probably several hundred thatare bought for their stated purpose: oflistening in on other people'sbusiness.

MS./ABLER SUPER SALE. Our famous Code-Brosicorworks with ell wenn." MO tunes ell Kral, frequenckoSonly NM. CO. 1601 M.., ..> lo.

The vast majority of businesses areoperated decently and honestly but inevery sphere it is very useful to know

- -about your competitor's business.There are seve al ways of finding thisout. the commonest is to head -hunt asenior employee but his information isquickly out-of-date once he has left.Even knowing what's going on inR&D has serious limitations sinceeven the staff in these departmentsdon't know if their work willeventually get into production.

Bribery has been tried but you runthe very serious risk of meeting one ofthe 95% of employees who wouldreport it to their boss.

Bugging is anonymous. Even if thebug Is found, it's almost impossible tofind out who planted it and since the

41

WALLS NAVE EARS

This telephone insert looks pretty Marto,. Infact it contains an FM radio transmitter with arange of several hundred metres.

risks to a company initiating buggingare enormous, middlemen are almostalways used.

rio""Ina kka. essayl

SweepingMany, if not most of the companiesailing bugs will also supply sweeping

equipment - after all a radio signal iseasier for someone close to thetransmitter to pick up than it is foromeone a hundred metres away - or

frit? First you don't know whatequency it's operating on. It could in

heory be from 50 kHz (though theantenna would be a problem) up toseveral hundred megahertz. OK, usen untuned circuit but then what do

you do about regular radio and TV

broadcasts? If you set the frequencyof the bug close to that of a powerfulFM station it's difficult to sort out thetwo.

The makers of `the equipment arehighly secretive about theirtechniques and not one would discusstechnicalities; they claimed, perhapswith some justification, that if youknow how the sweeping is done, its allhe easier to use a technique which

won't be picked up. We believe manyof them employ a howl -roundtechnique - put a receiver near a bugand you'll set up an audio/RF loopwhich will go into oscillation.

1'4=

International EspionageAlthough companies will normallykeep quiet about attempts to bugthem, Governments delight inexposing the failed attempts.

The American Embassy in Moscowrecently announced that they werebeing subjected to extremely high

a vu'e't''7n''aMT to have range or necresAitra50 -hour battery life, it retails for under t40

The sire &Mist', can,. fudged hoar the PP3battery plug. It is claimed to have an output of300 mW which the makers claim is good for 5milks and can as supplied with any frequency inthe mega 84-150 MHz. We have no way orverifying these claims; price is about C16

power, high frequency radio signals.It was of such a magnitude that it waseven suggested that it was an attemptdeliberately to make the staff ill. It is

now thought far more likely that theRF signals were being used torecharge batteries in bugs within thebuilding.

In 1945, as a gesture of good will,the Russians presented the USEmbassy in Moscow with a beautifulwooden carving of the US Great Seal.After several years it was discoveredthat that this had built into it awonderfully simple bug. Inside theseal was a copper cavity coupled to anantenna; one end of the cavity wascovered by a thin metal diaphragm.

The bug was activated by anexternal RF signal (in fact 330 MHz)this made the cavity resonate but thediaphragm caused the reradiatedsignal to be modulated and this torelay conversations near the Seal.This could still have been in operation

DISSECTING A BUGTHE RF BUG shown in thephotograph is a home-brew one thatcame into ETI's possession. Thecircuit was openly published in aBritish book a few years ago - weshow the circuit as well although wehave not, nor will we, provide anycomponent values (Since there areseveral variables we do not suggestyou 'suck -it -and -see'.)

Although a DIY circuit, it wouldseem that virtually all the smaller orsimpler bugs are of similar complexityor even similar circuitry.

This bug operates anywhere in the87 MHz -108 MHz range and despitethe. simplicity and low battery drain(only a few milliamps) it will transmit afair quality signal for several hundredmetres in most areas and at least 30metres even in heavily built-up areas

with steel -frame buildings like citycentres.

The microphone will pick upnormal speech at 10 metres quiteeasily. The performance, frankly, isworrying - because of theeffectiveness - and the unit can bebuilt for about E31

comp/era Of a VHFbug vvikch can be both foronly is few pounds


if some British technicians had notstumbled across the signal byaccident. A thorough subsequent'sweep' of the US Embassy broughtto light no less than 60 other devices,

It is hardly surprising that BritishIntelligence Services are involved aswell. The Russian Embassy in Londonmoved a year or so ago and whenaccess to the building becamepossible it could be seen the lengthsto which the Russians went to preventeavesdropping, even to having built aroom within a mom. Various bits ofinformation have leaked out thatIntelligence Services were directing alow power laser at the window glassthis would then have been slightlymodulated by the sound inside theroom and the reflection picked upcould detect this.

MICRO MINI MIKElI,ELESS POICROPNONE

One of the techniques which hasrecently come to light is that of 'RFflooding' of a telephone. Even whenthe phone is on the hook, the RF can'jump' the contacts. This is thenmodulated by the microphone andcan be picked up. As beused with single lines. a switch -boarddefeats this technique.

The other phone tappingtechnique, the 'infinity transmitter' isalso made useless with a switch-board. Many company executives usedirect lines for security whereas theswitch -board itself is a pretty gooddefence against some techniques.

IllgVigrIntj iaigt.1;641:TeggrWfilLBANtrldetieraleoF.

imra.Equipment AvailableLaws in many countries have failedto keep pace with technology but it isironic that most of the reallysophisticated equipment being madeoriginates in the US - the very place

ARE YOUBEING

BUGGED?THE BIGGEST PROBLEM facingsomeone wishing to bug another isgaining access Breaking and entering Hobviously criminal but a bug can beinstalled literally in one mniute if somensk of the device being discovered isacceptable. Unless the villains haveaccess to a building during building ordecorating work. problems in siting thebug are real - well.concealed hidingplaces are usually bad for picking upsound. Favourite sites reported to us arein low pressure air.conditioning ventsand behind radiators - another one is onsticky pads under a desk. somewherewhich would not be noticed for years.

simple search Is best and most bugswill be discovered unless& true expert hasbeen employed.

The extent of telephone bugging isunlikely to be high - access is so difficultthat only the Intelligence sery,ices will beable to handle this. In any east electronictelephone scramblers can overcome this.

If you regard yoursetf ass candldateforbugging, check the credentials of PostOffice engineers if you haven't calledthem in yourself. But don't be fooled bythe novelists who seers to inset that 'twoominous clicks' after the telephone islifted is a certain indication that therean unwanted listener on the line.

with the strictest laws againstbugging and phone tapping. Thiscould be because the problem there isgreater but no amount of legislation isgoing to prevent the availability ofequipment - the profits are too great.

UNSCRAMBLE COMO MESSAGES Own B ire meMaimal Charm. same ern service. SMMIEVIBB Bum,

The range of equipment is sovaried and the interest so keen that inthe Spring of 1977 a full scaleexhibition of both bugging and anti -bugging devices was held in WestGermany - a country which

At liver sirLeanit has everything incorporated

afapieiltd will put out a signal over 100 metres forthree days on eve sets, batteries


A real spykit advertised for Ineprolessione. A6 -channel transmitter operating on VHF preheatwave is supplied - there is a matchingisceivea Also included is a cassette recorder

mains operation facilities

incidentally bans sales ... except if itis marked as 'Export Only'. It'ssurprising how many retail outletsregard themselves in this field!

The FutureHowever superior anti -buggingequipment becomes, the number ofwaysof eavesdroppingelectronicallyisso varied and the techniquesdeveloped for keeping the devicesundiscovered so ingenious, it seemsthat bugs and bugging are not likelyto become any less of a problem.

Legislation may not stop buggingbut it can raise the risk factor to such alevel that those practising it will thinkcarefully. ETI

&ETU

47'7'

"'"&t,tArLIZT.'

ETI is not prepared to answer anyq cries, for whatever reason, onthe circuit components or as to theavailability of the equipmentshown in this feature.

43

electronicstOyWhat to look for in the February issue: On sale J r nuary 6th

IB MetalLocatorMk 2

The photo shows our Mk. 1. publisheda year ago but we've taken this design astage further.

The Mk. 1 was one of the most popu.lar projects ever published, probablybecause the early builders were able todemonstrate the exceptional perfor-mance to others.

We've looked at every aspect of thedesign and have Come up with an im-proved version which we are sure isgoing to be of interest to practicallyeveryone.

LIGHTNINGflask of lightning

nctte more1 '11:power is immense. The

current hundredsach tensor evert orthousands of amps and

poten about IC or 10volts: no wonderFrankenseinsmonster ai ,

How lisghtunping occum and what

u'

h= Oralp

f:1", M ntgyo dinenk.

Taleste'rUniversity explains

ttst how dangerous if

Electronics &your water supply

/Sounds dull? Not a bit of n. As in most field_electronicmeasurement of all sorts of pademilers is ems widespread. Dr Sydenh,mscribes how transducers ensure that ou

drinking water is monitored.

OP ,

Following Tim Ores very popular serieson Active Filters. we've twisted his armtr, cover OP.Amps in the same way. Thefeature will not only give the theory butwill be heavily spired with usableM.o.PS

44

wETI

goes technicolour!The next issue of ETI will haveseveral pages in 4 -colour. Atthis stage it's only an experi-ment but you can be sure that ifil's in the electronics or pu-blishing field. ET! is way ahead

of the competition.

UltrasonicSwitch

This project describes both turn,matufreceiver and unlike most can be modulated.The basic project in the February issueenables you to control a relay remotely froma very small transmitter - and no licensingproblem,

ETI Cover PriceSorry, folks - up we go to 45p from theFebruary issue. We hope you'll still considerus worth it. You may have noticed that

ent iss have been 100 pagesalthoughtough many are accounted fur bi heeditorial pages have increased kit uu

AccentuatedMetronomeNot (us( ygr lick, lick, tick but a tick, tick,Lock. Don't follow, Well, musical tunes (eg3.4 time) are more complex than the regularmetronome can cope with - next month'sproject explains.

Articles mentioned here are in an advancedstateof preparation but circumstances mayaffect the host contents.


If they've time to invent Such damn' uselesstrinkets int' mills time, Mr Ackroid, then

you're not working 'em hard enough!


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PUZZLE OF THEDRU\ <E\ SALO

THE MODEL REPRES NTS a sl-Cpwhich has our navigation lights on theport (left) ide and four n the s rboard frigh l side. Unfortunatela drunken ailor install° 4 green ightsin the sock is on the port side a fourred lights o the starboard side - which,as everybo y knows, is t e wron wayround. Eve ybody know tooth th t youdon't have our navigati n lights oneach side - but never mi d that, this isa puzzle.

And the puzzle is t .get all thegreen lights on to the st rboard side,and all the red lights on o the port side- where they belong. T at would beeasy if you just unplug them and swop

t em around, but the r les of the gameare that -

only one lamp can b moved at atime'a lamp can be move only along theblack line and must e put into avacant socket at the nd of the move,a lamp can be moved as far as desiredon a y move, includ ng going roundCOM r;

dl a lamp cannot jump ver anotherlamp

Well hat's the puzzl . If you thinkit's easy - try it. Just d aw the lines ona sheet f paper, use do s for thesockets and use 4 hc an 4 2c coins aslamps.

Circuit diagram Fig 1: The aloe of current limi ingresistor R should be found by trial to keep totebattery drain to about 100 ma.

J1 J2

12 Sockets

J11 J12

R

8.2 ohms

T -

A tually that's all you really need forthe puzzle, but to make it more attract-ive a d electronic we sed red and greenLED which light up i the sockets.

Construction

The circuit of course is simple - just12 audio sockets connected in parallel,a 3 volt battery, a current limitingresistor, a switch and 8 LEDs which canbe plugged in.

The prototype was constructed in aplastic box measuring 140 x 100 x 75mm with an aluminium panel. Any boxabout that size would do; constructionis not Critical.

PARTS LIST -RESISTOR8R2 % W Mee text)

LEDS4 R.4 Green

MIL 209 or similar)MIL 209 or similar)

MISCELLANEOUS2.5mm jack socket 112 off)2.5mm jack plugs 112 off) Is. text)On/Off switch May type)Hoolpup wireBox to suitBattery 13 VI


The lamps are 4 red and 4 green LEDssoldered straight on to the terminals of2.5 mm audio plugs. Care must be takenthat all LEDs are soldered in the plugsthe same way round, so that the positiveside of each LED is connected to thecentre contact of the plug. There areavailable several lengths of 2.5 mm plugbut the best for this project has a'handle' measuring 22 mm and a hole inthe top which is just right fora LED.The plugs should have colours to matchthe LEDs if possible - red and green -or at any rate red and black. Take careto get all LEDs protruding by the sameamunt.

The sockets mounted in the panel _must all be wired the same way roundtoo so that in every one the positivewire is connected to the contact whichmeets the centre contact of the plug.In this way any LED will light up in anysocket.

The resistor R in the prototype waschosen to limit the current drain on thebattery to a reasonable value - 100 mA,and still give adequate brightness to theLEDs.

The battery comprised two D cellssoldered together in series and to thewiring on the panel. They were held inthe box with suitable packing, but a clip

Photo 1. The finished puzzle

could be made instead.The black line on the panel was made

by cutting a strip from a sheet of blackcontact which was on hand. Scotchcal,paint or drawing ink would do instead.

Well, there you are, that's the puzzle

and nothing else need be said about itsconstruction.

Its solution is another matter. Theanswer will be published next month.Suffice it to say for the present that it_requires several moves! ETI

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WHAT THE CMS

ARNOLD SKULFINGTONI built the timer, the moresCoedlist, the buzz game and thetemperature alarm - all using thesame PCB design. I really liked thepictures of the ETI staff, I've cutthem out and Muck them on mybedroom wall (wherethe dartboardused to be). I want to learn moreelectronics so I can build a robot likeR2, the internal pictures of the StarWars robots are really good in JimPerry's big feature on Star Wars. Iasked my uncle Coget me one ofthose futuristic calculators thatHalvor Moorshead talks about, buthe said that they won't be inventedfora couple of years yet!

'

),)

41147,SJACK VVURTFANGLER 11.4PPRon Harris's report from the Proie, mENArG

fue twu r rd he 'a 's givene yrne7p inn; 'fit'? C 4°2'my hill system - but 1 "".0.4udio.disagree with his viewson valves, surely valveswill never be replaced! I

After reading Angus / r?Df/se.Robertson's feature 1 STAR .Doeon the future ofvideo I'mthinking of installinga video complex in withmy hi-fi - which is based onthe system shown in the audio section.

S'AYABOUT

MISFUN NEW SPECIAL- Apologies to Roy Pullen for messing wound wah his

ieCtonespurgetedyersions in Electronics

cartoons, you can see the lull gloroous,

Tomorrow.

Punks' P

ELECTRONICS

TOMORROWOn sale now at yourfriendly newsagent or directfrom ETI for 1 inclusive of p&p.Send cheque or postal order(payable to Electronics TodayInternational) to ElectronicsTomorrow, ETI Magazine, 25-27Oxford Street, London W1R 1 RF

48

JASPER OATSWhen I convert my TV to a display -

for my computer (as described inthis far-out special edition), whatwill I do with all the print-out I'vegot lying around? If Gary Evans is

right with his predictions aboutM PUs, I'll be able to build my own

Star Wars robot in about a year'stime. With the tips I picked up fromClive Sinclair wasn't it good of ETI

to send Steve Braidwood and HalvorMoorshead to interview him for us),I'll take on the Yanks and Japs with

my own robot company - OatsRobotics.

GERRYLE WIN K LE

I don'tknow when

I'll find time toI build the CMOSI switched amp,

but I've alreadystarted on thePower supply- my old one

just blewup! The cartoons

by Roy Pullen aregreat, and all those

gadgets for buildingprojects (the ones

Jim Perry talksabout) are going

to make electronics alot more fun.


tIOUSitStiOttP"1fl

estrocsio

ti

Inside Star Wars - The inside story fromthe most successful film ever made. Notdue for release until later this month, ETIstaff travelled to Canada to preview it forElectronics Tomorrow readers. Plus R2 -D2and fellow robots exposed - detailedinternal shots show how they were made.

Electronics Tomorrow is the latestfun-packed special from ETI ma-gazine. Available at your newsagent -or direct from ETI. Here are just someof the features, for more details seewhat the critics say on the oppositepage.

ETI Types - Graphically portrayed by Roy(you name it. Ili draw it) Pullen, this dee-m -cheek feature takes a look at thebeginner, project builder, audio man andthe MPU addict.

The ETI Story - In Me beginning there wasno ET! and there was a great wailing fromthe electronics enthusiasts of the world.Then Modern Magazines Let there beETI. and Mere was great rejoicing - readabout the history of ETI and seethe staff inaction (downing pints) with aseicotiaefrom our scrapbook.

Calculators Of The Future - In the last 5years prices have dropped and complexityhas risen, we don't think prices will dropmuch further - but the facilities offeredwill become mind boggling! HalvorMoorehead designs a new model for 1.79and talks about the generation to follow -some manufacturers may think we've beenat their research files!

-L7,817,21' The Sinclair Story - Steve braidvvood andHalvor Moorehead went off (tape recorderat the ready) to get Clive Sinclair's true lifeconfessions - exclusively for ElectronicsTomorrow readers. The man who broughtyou the world's smallest television talksabout his past failures (and succ sssss andthe possibilities for the future - grippingstuff!


50

wireless 'Wireless Show' at the Victoria and Albert Museum until

collection of British radio receivers from a periodwhich could loosely be called the 'valve era' is the most

December 11. The show, which consists of a fine

THE NOSTALGIA TRIP of 1977 is undoubtedly the

comprehensive survey of historical radio receiving setsever compiled.

showPete Scott, our visiting Australian hi-fi

editor, took a wander through thehallowed halls of the Victoria and Albert

Museum to cast his eyes over thevintage radios displayed therein and

bring us this report on the ancestors ofthe `trannie.

111111111111111=11111111111111111111111111Decca Deccette 1953 A antalve battery portable, upng nthsaturevalves of superb, design and voth (detachabla)marns eliminator base.

ScopeThe 130 classic receivers have been chosen as arepresentative selection of equipment producedbetween the early 1920s - when regular publicbroadcasts commenced in Britain - to 1956, when theera could be said to have ended with the introduction ofthe first British transistorised portable radio.

The show is necessarily restricted in scope by theavailable space and so does not attempt to give acompletely balanced view of the thirty years it covers.Items such as the combined radio -gramophone, or thelarger combined radio -TV, are not included. It is alsoobvious that the exhibits of the larger floor -standingconsoles have been limited to allow a greater overalldiversity.

Table -standing valve sets - every home used to haveone - form the dominant section of the shoW, but oldervisitors will have their memories stirred by the earlierunits with their free-standing horn speakers.

BackgroundThe choice of 1922 as the starting point is notrandom, even though a great number of the majorinnovations in the wireless field had already taken placeby that time. Marconi had filed his first world patent in1896, transmitted over the Atlantic in 1901, andspeech had been broadcast by Fessenden in 1903.

The first broadcast of speech across the Atlantic hadbeen achieved in 1916, using a transmitter comprisingsome 300 valves, and the first practical use of superhettechniques for speech broadcast across the Atlantic wasmade M 1921.

About this time wireless was being used only byexperimenters and enthusiasts, who tended to constructtheir own receivers, although it was estimated that therewer some 500 companies manufacturing componentsin Britain alone.

[pry Ekco model SH25 from 1932, and on the doh( the UAVY78. five yea. older Led to cant A 1948 GEC a 114arconononePersonal (would voo beneath sethl 047, no,


An photographs Crown Comm*, Our ro the Victoria and Arbor Museum forpermission to reproduce them here.

Wireless at this stage was not used for 'passiveentertainment' in Britain, although America was beingserved by several hundred transmitters - largelyunregulated. However, with the formation of the BritishBroadcasting Company, set up in 1922 to organiseregular entertainment programmes through a network ofeight transmitting stations, wireless began to have a lessesoteric appeal.

So the starting point for the Wireless Show representsthe -time at which radio started to become a popularcommodity. The growth rate in the industry from thistime was extremely rapid, as was public acceptance.

The Technical SideFor those interested in the changing technology theshow is an interesting aid to tracing technicaldevelopments through the thirty years precedingBritain's first transistor radio.

Immediately obvious features include the rapidimprovement in tuning facilities, the fight for higherselectivity as the number of transmitters escalated, andthe move from battery operated sets (or combinedbattery /an) to ac only as more houses were wired up, andand then the move back to battery power as portabilitybecame a desirable feature.

Even the gimmicks and convenience features, such asthe 'magic eye', introduced as technological advancesslowed in the late thirties, prove fascinating.

StylisticallyThe main purpose of the exhibition at the Victoria and

Albert. however, is to show the changing styles in thepresentation and appearance of radio receivers throughthe chosen period. Styles that moved from the ornate -almost ornamental - crystal sets of the very early days.through to the receivers with intricate wooden cabinets,and then to the architect -designed, sculpted -plastic'creations' which eventually proved too much for thewoodworking craftsmen, but which were dropped inpost-war austerity.

The show, produced by the V-8aA in association withthe British Vintage Wireless Society, is well worth a visitby anybody who ever built a crystal set It will revivemany memories for older visitors and gives a fascinatinginsight into the background and formative years of radioin this country. En

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Super., from 1932 and Ekco. 3 freely?, could be ben., ere

n3r, 11. aee ,9113 and e 1950,9e190 Arlarconiphone 1932 model 42 on the left of the PyeMr Lawrence &Mho

ELECTRONICS TODAY INTERNATIONAL -JANUARY 1978'

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25.27 °Mord Street,LOnclon WI R .F.


ETI DATA SHEET-TL080 Family Bitet Op Amps Texas

The T1080 family of BIFET operationalamplIfiers, provides an ideal combination ofhigh -impedance JFET inputs withlow -distortion bipolar output arc.. Qualityperformance in the TL080 family is achievedwithout complex circuitry.

TL080 family circuit description

The following sections should be read incontunction with Fig 1, the basic schematic forone channel.

Bias circuits

0011016. eerier 02 trensistors CO r C115 a.resistor R6 esteblish the bias currents for theinput differential amplifier and the second gainstage Epitaxial FET 016 provides a fixedcurrent to D2 establishing 5 2V on the base of015 The resulting 31 7uA collector current of015 Ilows through 014 and sets the currentlevels in CP and 09

Resistor RI causes 196iJA current in altha: is divided between the input stage JFETs02 and 03 The secondigainistage biascurrent about 60004 r gene. from E9

Input circuit

Input JFETs Q2 and 03 operate Into theactive load circuit consisting of Q4, Q6. and07. Current imbalance and input offsetvoltages may be adjusted on the TI.081 and11083 through connectors to the emitters of05 and 07. External offset controls for the111080 connect to the collector of Q6 and07 The CI compensation capacitor is internalon the TW80. T1082 and TL083 and Tk084.For the 110080 connections for externalcompensation are provided which Mow useradjustment of AC characteriocs

Ion -implanted input devices provide veryhigh input impedance controlled pinchioffvoltage for maximum commonimode inputrange, and matched characteristics for controlof the input offset voltage JFET inputs alsoallow adequate dove to the second stageresulting in maximum output peak.to-peakcapability and wide power band widths

Output stage

Q10 and 011 provide Class AB Ops to theoutput transistors 012 and 013 This allowsnear zero crossover distortion and produces alow total harmonic distortion at the output.The orriplicity of the output circuit results inrranirman silicon area requirements keepingmanufacturing cost gown nitiiie maintainingquality performance 82 R3 and Re form theoutput shorticircun protection network

Fly, I Schematic diagram for 10000 lannly.

Second stage

Drive from the input stage is single -ended fromthe collector of 07 DI provides a clampingaction across 515 and 08 preventing saturation

of Q8 and excessive current in Q5 05 and 08form the high -gain second stage. The secondstage output, collector of 08, drives the outputstage consisting of bias transistor 010 andQ11, and output drivers Q12 and 013

Icy Road Warning Indicator

ADJUSTFORLEDON AT32 F


Ve.i, -12V

THERMISTOR 15K

-,125

470

53

L080 exas

Peak Detector

H

RESET

11111

Tone Control

so

HIGH INPUT ILOW OUTPUTLOW DRIFT

2/AS

1HH

FEATURES

grol=1:7T

HIGH SLEW RATE

2N929

(-4 *I,/ 00.1.i 100k 003.IF

EM

DOM

L1Hpi

ADVANTAGES

Minimum loading effects allow eff Arent usewith high impedance transducers.

Provides the desired response characteristicsrequired in audio frequency active filters anciquality sou. systems.Minimaed crossover distortion yields very

e LOW DISTORTION low total harmonic distortion for maximumPerformance in critical music systems.

CONTINUOUS SHORT No damage resulting from so dotal shoosCIRCUIT PROTECTION or operation into low impedance loads

GLOW POWER Only 2 8 rnA per operational amplifier Less

CONSUMPTIONsystem power required and battery operationis practicable

absolute maximum ratingsTLO8_C

Tb08_ACTI.08_13C

Supply voltage, Vcc (see Note II 18 V

Su.* T.°42er VCC Isee Note II -18 V

Differential In voltage (see Nom 2) 130 V

Input voltage (see Notes I and 3) .5 VDuration of output short circuit see Note 41 Unlimited

Continuous total dissipation SOS)C free -sir

temperature

4,36.5) or P Package 668205.

L Package

Operating freeoh temperature ranee 010 70.0

PIN OUTS

non

TL081

:1,2122:1111GL

The TL082

The TL083 The TLOB4

_ s

NOTES: All voltage values. except differential voltages. are vv.. espect to toe zero reletence aver larmin41 Of Me SUM", VOitage1 whereMe zero reference level IS the midpoint between and Vce .

2. Differential voltages are at Me noninverting mnut tertnina with respect to the inverting input ter.nel.3. The magnitude of the input voltage must never exceed th /noon.. of the supply voltage or 1.5 volts. whichever is less.

4. The OU(PUt may be shorted to ground cr e.cr supply. Temperature and/or supply voltages must be limited to ensure that Me

diSSiPatiOn raring is 110L e1COOded.

54ELECTRONICS TODAY INTERNATIONAL - JANUARY 1978

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NAME

AllORES


SOFTWADE

GAMESThese games for the Sinclair

Programmable were submitted by Mr PCornea of Crewe in Cheshire. A flow

chart is given with each listing. so thatowners of different machines have a

head start in producing a program fortheir machines.

O

INFORMATION OUTPUT

DATA TO BE INPUT

GO IF NEG

OPERATIONS

MEMORY EXCHANGE

PROGRAM ENTRY POINTFOR A OR M

ENO

ACCULATORMISUMPLAY)

56

Object -

1.

3.

4.

To simulate a show jumping course in such away that:-The player enters a guess as to how manystrides of acceleration he thinks will be requiredby a horse to clear a fence H feet high.The player is given an indication of right andwrong guesses.The players total score is made available to himat the end of the game.The players score is made dependent on thevalue of his guesses and on his successfullyclearing the fences.

Execution -0/4Ato/.0eAvigoto/0/0/input H fence 1/RUN/input strides/RUN/right-wronginput H fence 2/RUN/input stridesfRUNdight.wronginput last H/RUN/input strides/RUNiright.wrongA./Rd/score.

The biggest problem with this program was trying tofind a realistic relationship between the number of acceler.acing strides input and the height that these strides wouldenable a horse to jump. The following curve shows the sortof relationship that is required.

HEIGHT

FEET

NUMBER OF STRIDES

As you can see from the curve the extra height that thehorse can jump decreases as the number of strides increases,such that after a certain point no increase in height is

gained by increasing the number of strides. This is the sortof curve you would expect in realise. I have simulated thiscurve by using the arcten function. The tan of an angle cantake any value between eero and infinity so the erctan ofany number between zero and infinity has a radian valuebetween 0 and 1.57 and you will find that taking thearctan of any number greater than about twenty givesapproximately 1.57 as an answer. The only thing to bedone now is to scale the arcten values up to give a reason-able range of heights, to do this we multiply by five.

Looking at the plan of the course you will see the pathconnecting the fifteen fences together. The number along.side each fence is its height Oil and the numbers on thepaths between the fences are the distances in strides toeach fence. If you input these numbers as your guesses


LS 9461 1,11411NIVI- - 1990LLV91131N1 6000.15011108.10313

1.10.041.000

WOO 0 elatlYTIO

0040 1.1011171=

3.00000/0.

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0310013 301.3f 110i on- anlon

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umo 1noA $048010 sisp pue sea., asp to s146iasi alp a6uessa os muesli aiduns a si 41 assns. sitis mssesu noA uaq

'1.006 se 'sal to U01 pue pa,punt, aU0 to WOOS e Jannisoa pinosis

noA lnq .4.Asouns s0 asoas e issys. pua noA wins S. 1.11.r. osn1.!... .41 in 0011al Olaha map noh p

0731181 mot 0041 01041 Limon pow' noA painieribsip aq 0l sias

sapisuoa moils nos, .1.10 sou op noA aqua/ 0080 104 mood auisi Asieuad e Emippe Aq pue asm00 asis puno,

sassonli 100A pe 6u1ie4e9 Aq nominal. si asoas 1no,o UMOLIS 11010 sar0.02

seal w sown 044 lo soul map os airossod si is 1841 Nis AIM noA 1nq saanas aiss leap o1 paawean6 am noA uato

I

31A11/9 9N1d1A111r 3SHOH

UNIVERSAL RANDOM NUMBER

digit can take any value from N to M.

Object - To generate a random number of any requiredlength up to eight digits in such a way that each

OR generate single randOm numbers with valuesfrom K to L.OR play an ESP game such that the player hasthe opportunity of entering a single digit numberbefore the calculator generates a random nu m-bar, both digits being displayed at the end of therun for comparison and statistical purposes.

Execution 1 -Any number between 0 and1/A./Sto/4,/./goto/0/0/'/ce/RUN/random digit/ if you require a two digitrandom number then press RUN again and asecond random digit will be displayed alongsidethe first. a three digit random number, pressRUN a third time etcWhen you have a random number of the requiredlength and wish to generate another numberpress the clear button followed by RUN/random.digit/ etc....

Exeurnon 2 -Any number between 0 and1/4./Sto/A'194,./goto/0/6/e/ce/RUN/random number/RUN/random number/RUN/random number/ etc ....

Execution 3 -Any number between 0 and1/4v/Stoiev/ev/goto/0/0/c/./Your guess/RUN/random number and your guessYour guess/RUN/random number and your guessYour

With the program as it stands the variables take the follow.ing values:-

N K = 1

M = L 6Obviously with these values the program can be used tosimulate the throwing of dice with executions 1 or 2.

When you come to change the variables you should do itin the following way:-Executions 1 and 3

Chose a value for N between 0 and 10 (integer).Chose a value for N and 9 (integer).Replace lines 9 and 10 with the value of M - N.Replace lines 29 to 31 with the value of N - 1

(including sign).Run as per execution instructions.

Execution 2Chose a value K between 0 and 10 (integer).Chose a value L between K and K .99 (integer).Replace lines 9 and 10 with L - K.Replace lines 29 to 31 with K - 1 (includingsign).

Run as per execution instructions.With a moments thought you will see that there are one

hundred and one uses for this program, a few of these aregiven below.

Slot Machine

Use execution t with N = 1 and M = 4 and score wiaccording to the foll owing table.

GAMESGEDN0E.,RATOR -FORWin

111 10

222 10

333 10444 10221 6

331 5441 5

11- 42

With the values of win shown, the program gives a 954.pay -out.

RaceUse execution 2 with K = 1 and L = number of players(say four). Run the program and each time a number comesup enter a one in the table shown. in the next emptysquare down, underneath the number displayed. Thefirst player to fill the column below his number is thewinner.

SageUse execution 3 with N = 0 and M = 5. Each player takesit in turn to enter his own number lone to five) and runthe program. When the display appears subtract the smallerdigit from the larger and then add the larger digit to thisanswer. The player with the highest number at the endof the round wins the round. The first player to win fiverounds wins the game.

ELECTRONICS TODAY INTERN," C'.'

ATOMIC DECAY GAMEObject - To sin nil ate the decay of B grams of a radioactivematerial with a hal }.life of D seconds in such a way that:

1. The player has the opportunity of guessing how muchof the material (plus or minus C grams) is left aftereach second.

2. The player is given indications of right and wrong (hit -and miss) guesses.

3. A running total of the player's score a displayed aftereach guess.

Execution --1 ANCPAY'stod.% v/goto 10/0/0/R UN score (0) IYour guess/RUN/Hit-Miss/RUN/ score/Your guess/RUNILlitiMissIRUNrscore/ etc ...

With the program listing and execution sequences giventhe variables take the following value: -

B 100 grams. D = 10 seconds. C - 1 gram.

Should you wish to change the variables (When you getused to Playing the game) then:

To change B- Put the new value in place of the 100at the beginning of the executionsequence.

To change C - Change hoes 21 and 22 in the programto your new value (any 2 key -strokenumber between .1 and 09)

To change 0 - Thb variable is the most difficult of thethree to change as it requires calculationthus: -2i vfln 0,' i.iNew Diti //e'Itif =If the answer is Was than one, thenreplace lines 08 to 10 with the threemost significant digits after the decimalPoint. If the answer o greater than onethen replace lines 07 to 10 with thefour most significant keystrokes.e.g. If answer is 0.9330114 then put933 into lines 08 to 10.

START

FINISH

Abe e the score sheet for thebattle game and left are the lisonyand flowchart for the overall gams

ELECTRONICS TODAY INTERNATIONAL JANUARY 1978

N.B. The only way the answer to thissequence can be gmatei than one is

if your value for D is -ve in which caseyou are no longer working with a

radioactive decay curve but with anexponential growth crave.

V

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CUTS quipDesigned by John Miller -Kirkpatrick

LAST MONTH WE completed thedescription of the System 68 TTYcard and described a simple cassetteinterface circuit that could be used inconjunction with this card. This monthwe begin describing what is probablythe most popular means of encodingdata in a form suitable for storageon magnetic recording tape - theCURS format. CUTS stands forComputer Users Tape System and is alsosometimes referred to as Kansas CityFormat.CUT Above The RestFigure 1 shows the basic specificat-ion of the CUTS system. From this itcan be seen that a serial data stream ofeight bits has a number of control bitsadded to it, muchcontrol information added to its output.The reason for these additional controlswere dealt with in the first part of theTTY interface published in Novemberlast year.

Figure 1 also shows that the CUTS

DATAON TAPE

specification palls tera logic '1' to berecorded as eight cycles of a 2 400 Hztone and a logic '0' as four cycles of1 200 Hz. These tones have been select-ed as being suitable for recording onmost tape systems and are also easilyderived from the master 4 800 Hz clockpresent in standard UART systems.

The circuit diagrams of the decoderare shown in Figs. 2 and 3_ These ewecircuit blocks replace the equivalentsections of the TTY interface circuitryto provide a complete CUTS encoder/decoder, all memory decoding andUART configuration being identical tothat of the TTY card.

Next month we shall deal with theconstruction of the CUTS card as wellas dealing with the necessary software.We shall also deal with means of provid-ing additional RAM and PROM for theSystem 68.

Before winding up this month how-mayer we go on to discuss an in-

teresting area of software.

0

o BITS = I CHARACTER tIME-

8 BITS = I BYTE

DATA ON BUS 1 0 1 0 0 1 0

DATA BYTE HEY AS DECIMAL 165


Assemblers and Disassemblers.

An assembler is a program which allowsinstructions to be entered in a codedform which are converted by the pro-gram into a machine code form. Largeprograms canot be written without anassembler ors similar program to helpwith address and branch decoding. Adisassembler works the other wayround, if you feed it with a machinecode program it will attempt to convertthis back into the coded form used bythe assembler. This is useful for docu-menting programs which have beenwritten originally in machine code.

Mr. G. L. Evans of South London(not our G. Evans) has sent us anexample of a routine written InAssembler for use in a disassembler.We hope that Mr. Evans will send usfurther details of his Disassembler asit progresses. If anybody has a smallAssembler we would be very interestedin that as well.

Fig hoe shertboabbo of theCUTS s ',stem co, fora logos tobe ted as etontsecles o/2 400 SA, and a log. 0' as /OurC,C.S Of 1200 Hr

61

CUTS CARD

Much of the circuitry of the CUTS encoderis exactly the same as that used for theTTY interface described in the November1977 copy of ETI.

The CUTS format calls for a byte ofdata to be recorded as a START bit (logic1E1 followed by eight dam bits with theend of a word being signified by two STOPbits (logic '1'). The setting up of theUART's control registers to conform tothis specification was dealt with in theDecember issue of ETI.

With a data rate of 300 baud each bittime will be equal to sixteen pulse timesof the DART transmit clock (4 800 Hz).We require that a logic '1' be recorded aseight pulses of 2 400 Hz and a logic '0'be recorded at four pulses of I 200 Hz.

ENCODER

The circuit of the encoder is shown inFig. 2. As mentioned above. this circuitryreplaces the circuitry associated with theSO output of the UART shown in the111' interface.

The 4 800 liz. TCP clock is input toone half of the 74C74 Dual D Hip -flop

tic J

aT

HOW IT WORKS

Fig 2 Circuit diagram of the CUTSencoder. This circuit encodes theoutput from the UART SO output

where it is divided by two to provide a2 400 Hz signal with a 50% duty cycle.

This simial is fed to the dock input ofthe second half of the 74C74 and, via CIto the input of IC2/2 a 74002 NOR gate.

Circuit action is as follows. When SOis low and we require a 1 200 Hz signal,the inverted SO output is fed to IC2/2. Aglance at the truth table for a NOR gatewill show that the output from this gatemust then be low. This output is invertedby 102/3 and the resultant high applied to

CLR input. This input is active lowand the clear is thus disabled. This meansthat ICI /2 will act as a divide by twoelement producing the required waveform.

If now SO goes high, a low is inputto IC2/2 after inversion. Reference shouldbe made to Fig. 4 to make the followingdescription easier to follow.

The signal at the CI /RI junction consistsof a series of negative spikes coducidentwith the trailing edge of the 2 400 Hzsignal at ICI/1's Q output. With a lowapplied via the inverter, to the other inputof IC2/2, the output of this gate will be a

series of short positive going pulses, whichafter inversion, are used to reset ICI /2.

As the 74C74 clocks on the positive edge

m0 ICIa 1-7

12001, 2400Hz

Fig. 4, Diagrams showing the various waveforms presentencoding circuit

of the clock input from ICl/I's Q outputbut is reset on the negitive edge of the samesignal, the output of this IC becomes therequired 2 400 Hz signal.

The 2 400 Hz or 1 200 Hz output fromIC1/2 is fed via a filter formed by R2 andC2 to the AUX output and via an atten-uate, R3 and R4, to the MIC output.

The filter is necessary to convert thesquare wave logic signal to a waveform moresuiMble for recording on tape.

DECODERFigure 3 shows the circuit of the decoder,which again, is used to replace the equiva-lent circuit block on the TTY card.

The output of the recorder is squared upand brought to TTL levels by Q1 and 102/4.It is then applied to IC3/1, one half of a74123 dual reniggerable monosMble. Thisdevice has its astable period set to a limethat is longer than the period oftl 2 400 Hzsignal, about 550 uS is the best.

If we now assume that the signal fromthe tape is of 2 400 Hz, when the first pulsereaches the 74123 its output goes high for550 uS. As the input is 2 400 Hz however,after some 417 uS, the device is rotriggered.Therefore with m input of 2 400 Hz the Qoutput will remain high.

If, however, the signal is replaced by a1 200 Hz output from the recorder, the Qoutput will still go high for 550 uS, but asretriggering will not take place for at least830 uS, the Q output will consist of 550 uS,logic I' pulses with logic '0' pulses in-between.

The output from the monostable is inputas data to the D flip-flop 104/2. The clocksignal for this device is the I 200 Hz or2 400 Hz input to the 74123. The D Hira-no!, is triggered from the low to hightransition of this waveform and thus if thesignal is 2 400 Hz implying that the Q out-put of IC3/1 is at the ouput of 1C4/2will also be at logic 'I'. If however theinput is at 1 200 Hz, at the moment ofclocking, the Q output of IC3/1 will be.low, thus the Q output of IC4/2 is also low.The waveforms shown in Fig. X help explainthis action.

The Q output of IC4/2 is fed to the SIinput of the CART thus completing therecovery of dam.

62ELECTRONICS TODAY INTERNATIONAL - JANUARY 1 978

Fig 3 Circuit diagram of the CUTS decoder thiscircuit decodes a CUTS encoded signal andpasses this to the UART's SI input.

ONG

123/1A

Fig. 5 Diagram showing the various waveforms present in thedecoding circuit

SYSTEM CLOCKS

The receive clock pulse RCP used in thedecoding operation is the same as that usedin the transmit mode (TCP). In order tojustify the use of the same clock for bothojetritlictioutt,uvie 11:.eiddoto,ost.u.dy.trahige

straightforwardarithmetic. (Fora full explanation of theterms used below see the FART data sheetpublished in November 77's ETD.

Figure 6 shows the timing of the TARTin receive mode, the data presented la theUART by the CUTS decoder is shown as St.If we assume that the UART in looking for aSTART bit then it will recognise the trans-ition of SI from high to low as a possible

START bit. It now wails for eight pulses ofits 4 800 Hz clock and then samples the SIline at what should be the mid -point of theSTART bit. If SI is high at this time thenthe START bit logic is reset and the UARTwail for another high to low transition ofSI. If SI is low at the sample time then theCART accepts this as a valid START bit andprocedes to sample the SI line every sixteenpulses of the 4 800 Hz clock. After inputt-ing the correct number of data bits theUART looks for a valid STOP bit (logic 1)at which time it transfers the data and anyerror conditions to the output registers andsignals DAV (Data Available) to the MPU.The MPU accepts the data and status wordsand resets the DAV line to indicate accept -

arm to the FART which by now is lookingfor the next valid START bit.

The ideal sampling pulse is shown as Fig.6A, two worst cases are shown as Figs. 6Band 6C. In these worst case conditions it isassumed that the 4 800 Hz clock used asTCP it also being used as RCP and thusthe only variations possible are phasechange and frequency change. The phasechange problem is oveKome inside theHART and thus does not concern us here.The frequency change can only be due tochanges tapc speed between recordingand playback at the 555 timer used as a4 800 Hz oscillator is independent ofvoltage variations in the power supply. Ifwe examine sample pulse train B we can Seethat the date is being input at a faster ratethan expected and as a result the samplepulses end up very close to the end of databit seven time. As the sample pulse is setduring the START bit as being the eighthpulse and in data bitven is during thefifteenth pulse time ofse the input data itmust change by seven pulses in eight bits

x(8 6 pulses). This can be worked out to anerror variation of: -

7-g7T 100 percent

= 5.46%On a tape recorder of a reasonable

specification this level of tape speed toler-ance will not occur and thus the 4 800 HzTCP can also be used as the RCP clock.

r .

1 START [ BITO B121 BIT 2 BIT 3 1 BIT/. BIT 5 j BIT 6 BITJ i j

g="21 1 1 1 1

I I I I I

I I I I I I I I I

STOP1 STOP 2 I START

1 1 1

I I 1

I I 1

Fig.6 Diagram showing the effect on the sampling pulses generated by the UART with a difference between TCP and RCP. A'shows the 0.1 sampling pulse (MP = RCP), shows TCP < RCP while 'C' shows TCP > RCP.


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66ELECTRONICS TODAY INTERNATIONAL -- JANUARY 1978

1171' RICId71911/11

IN THIS PART of our series we shalllook into sequential logic by using the7400 IC.

Set the IC up on the board to make acircuit using two of the logic gates asshown in Fig. 1. The gate with its out-put taken to the LED should have itsspare input marked R, while the spareinput to the other gate should bemarked S.

Fig. 1. Cross -coupled NAND gates forming anR -S hip -flop.

This circuit is a flip-flop, as you mayhave guessed from the cross-section ofinputs and outputs. Complete the tableshown in Fig. 2, and note that the out-put for R = 1, S = 1 is not the same ineach case.

Sequential Logic

The R -S flip-flop, as this is called, is anexample of a sequential logic circuit, inwhich the output depends on the se-quence of signals at the input - in otherwords, the state of the output dependson the previous signals as well as thepresent ones. Strictly speaking this cir-cuit is more of a larch, a circuit whichtemporarily stores an output while bothinputs are high. Note that in normaluse, we want two outputs 0 and CI to becomplementary ID is always the inverseof 0) so that the input R = 0, S = 0must not be used, since this givesQ = Q = 1.

In logic circuits, clocked flip-flopsare much more common. A clockedflip-flop changes state only when a

0

Fig. 1 Part rush t Pie for R -S flop -top. Whenyou complet the able, talon readings hamyour blob -board circuit he sure to work througheach state in sequence

timing, or clock pulse is received. Thisis done by combining the flip-flopaction with gating so that the signal in-puts have no effect until the gating(clock) pulse arrives.

One type of clocked flip-flop is the1) -type, and a typical truth table isshown in Fig. 3. In this type of circuitthe signal (0 or 1) which is present atthe D (for Data) terminal is transferredto the output at the clock pulse, andremains unchanged until the datachanges and the clock pulse arrives,

Clocked Flip -FlopThe type of flip-flop chosen for thisboard is the J -K flip-flop. This is a

more versatile device which combinesclocking with gating to achieve a widerange of actions. On the type we havechosen, the SN7476, the action is thetype known as "Master -Slave", whichmeans that the input signals are accept-ed on the leading edge of the clockpulse, but the outputs do not changeuntil the trailing edge comes along.This avoids problems which wouldoccur if outputs were connected back tothe inputs, as we shall see later.

The J -K flip-flop has five inputs andtwo outputs. The inputs are labelled J,K, Clock, Set and Reset (the Reset issometimes called dear, and the Seterrninal is sometimes called prese 1.The outputs are Q and 5, with it always

the inverse of Q. We shall check theaction of the J -K flip-flop using signalsgenerated on the board.

From previous work you shouldhave available one section of the 7414connected es a low speed oscillator. Thisprovides an ideal slow clock pulse, andyou should already have an LED con-nected to the output of the 7414 tomonitor this pulse.

SET(PRESET)

RESET(CLEAR)

Fig. A J -K {lip -flapsymbol

Double Flip -FlopsThe connection diagram of the 7476 isshown in Fig. 5. From this you will seethat the 7476 contains two J -K flip-flops which are completely indepen-dent. For the first series of practicalexercises we shall use only one half.

Solder connections from pin 13 ofthe 7476 to earth, and from pin 5 tothe +5 V line. Now solder an insulatedwire connection from the clock oscil-lator output to pin 1 of the 7476, sothat flip-flop number 1 is activated.

Connect pins 4 and 16 to earth sothat J = 0 and K 0, and connectswitches so that the reset pin (pin 3)and the set pin (pin 2) can be connectedmomentarily to earth as needed. The

D SIGNAL 0 BEFORE CLOCK 0 AFTER CLOCK0 0 00 1 01 0 1

1 1

Fig J. D -type np-Flop end truth table. Note that, tad. the R -S flip-flop. changes take p ace onlywhen the clock pulse arrives.


? 77'77 ? ?

71171RIFIRITTIFIEIfth,

E ET

LI I2J LI LI LI LICK1 SET1 siert +Ve CK2

Fig 5 Pinout of the SN7476 dual master -slave .14( fhp-llop

circuit is now as Fig. 6, and the appear-ance of the board is shown in Fig. 7.

Now connect a resistor from pin 15(0) to a spare pad, and an LED fromthe spare pad to earth. This LED willindicate the state of the output fromthe flip-flop at Q.

Switch on, and look at the LED.Using the SET switch, set the output togive logic 1 (This happens when theSET switch is returned to 0, whateverthe dock pulse is doing at the time).When the switch is changed back again,does the output change at once? Orwhen a clock pulse arrives?

These changes and others to followmay be easier to observe if the clockpulse is very slow, and a 1 000 uF, orgreater, capacitor may be used in theoscillator circuit. Later, a "debounced"switch will be used.

Complete the sequential truth table,in which On., is the value of Q justbefore the clock pulse arrives, and Qnis the value of Q just after the endof the clock pulse (the 1 to 0 change).Can you decide when the change, if any,occurs? is it On the leading or the trail-ing edge of the clock pulse?

Now switch off, and disconnect oneend of the link between K pin (pin 161and earth, so allowing K to float to 1.Now we have J = 0 and K = 1. Switch

Fig 6 Circuit for checking J.K action, see textfor details.

68

1_7j 112 j

sitnc3ct

on and observe the output. Change theoutput by using a switch (which onewill you use SET or RESET?). Does theclock pulse affect the output after theswitch has been returned to normal?

la)

(b)

, or 0101,,,BE,ORE CLOCK PutsE

STME OF 0 le OR RAVI-ER ,ncx PULSE

Fig 7. (a) The layout on the board. with the LEOin position(b) Form of part faith table.

Switch off again and reverse theconnections so that J = 1 and K = 0, andrepeat your readings. Enter all the read-ings on the sequential truth table ofFig. 8.

J.0K.1

Qn-1 On

.1=1

K=0

From these exercises you will havefound that the action of the J -K flip-flop can be controlled by the J and Kinputs, which act to force the outputto either 1 or 0 when the clock pulsearrives. The SET and RESET pins actindependently of the clock, making theoutput go to &or 1, and holding it thereuntil the reset or set voltage rises to 1again, when the next clock pulse willcause whatever output is forced by theJ and K voltages.

TogglingWith the power off, disconnect thewires from both J (pin 4) and K (pin16). Switch on again, and observe boththe output and the clock LEDs. Nowcomplete the truth table of Fig. 8 (c). Inthis arrangement the J -K flip-flop is act-ing as a divide -by -two stage, for there isone complete output pulse for each twocomplete input pulses - we say that theflip-flop is toggling. At any time duringthis action, the ouput may be forcedto 1 or 0 by the action of the SET orRESET pins, but it will revert to thetoggling action when the SET or RESETis released.

Try applying a clock pulse obtainedfrom a switch, as in Fig. 9 (a). Wire theswitch to the board and replace theconnection between the 7414 clockgenerator and the flip-flop with a con-nection from the switch output to theflip-flop clock input. Turn on the 5 Vsupply, and use the switch as a slowclock generator. You will probablyfind that the output is erratic, some-times seeming not to change the out-put when the switch is operated.

This is caused by switch contactbounce.

De -Bounce De SwitchWith power off, rewire the switch with aresistor and a capacitor to one of thespare sections of the 7414, as shown inFig. 9 (b). This is a simple de -bouncingcircuit.

Solder a resistor and an LED to theoutput of the 7414 in the usual way toshow the state of the clock pulse, andconnect the output also to the clockinput of the 7476. You should find thatthe action is perfect, and the very slowclocking which is now possible willshow that the changes which take placeat the output do so when the clockpulse goes low, that is, from 1 to 0.

On-t Do

Fog 8. Remaining tru h tables for .14( action.

J-1K=1

Qn


PUSH BUTTONSVIIITCH

Fig 9 (al Using a bush.button switches a clockpulse CUPPlIF

debouncerl switch circuit.

Note that other flip-flop types may nothave the same sequence of actions.Some, for example, are edge triggered,meaning that all the flip-flop actiontakes place On the leading edge of theclock.

When you are using flip-flop circuits,you must be careful to use the sametype of fli -flop as that specified, sincecircuits which suit one type may notsuit anot er. In particular, the 7476"Master-SI ye" type of flip-flop has aparticular' complex action.

In esse ce, the action is that on theleading ed e of the clock, the infor-mation wh oh is present 11 or 0) at theJ and K i puts is stored and once theclock pulse has reached its 1 value,these inputs are locked out, meaningthat chang s in J and K will now haveno effect. At the trailing edge of theclock pule , the flip-flop action takesplace to change the output. The reasonfor this construction is that severaltypes of ircuits, some of which weshall build in this series, use feedbackconnection between the output of theflip-flop and its J or K inputs.

If all the action of the flip-flop,

Fig. 10 Truth table for 7.1(

(a Complete truth table.

J-K FLIP-FLOP

happened at the leading edge of theclock, such feedback would causeindeterminate action - any change in

would cause a change in J or K,which might cancel the effect on CI,and the flip-flop would probablyoscillate at the high frequency. Becauseof the Master -Slave action, this does nothappen - the changes in Q happen atthe trailing edge of the clock pulse, bywhich time the J and K inputs arelocked out and their voltages cannotaffect the action until the leading edgeof the next clock pulse.

InvestigationYou should already have one sectionof the 7414 set up as a high frequencyoscillator with earphones, or similar, todetect the output note. What is theeffect of leading the output of the 7414oscillator to the clock terminal of the7476 with J = 1 and K = 1? Listen tothe output wave from Q and compareit with the signal from the oscillator.

Can you now design an "octave"oscillator? This circuit will use a singleoscillator, but its output will be alter-nately at oscillator frequency, then athalf oscillator frequency (one musicaloctave below) according to the input tothe gate. The gate input could then beobtained from another slow oscillator.

Finally, Fig. 10 (a) shows the aim.plate truth table for the 7476. Fig. 10lb) shows a changes truth table, inwhich the settings of J and K to pro-duce certain changes (or non -changes)are listed. In the last table, X means"don't care", signifying that the valuemay be 1 or 0, and the action will bethe same. Check that this last tableagrees with the full table of Fig. 10 (a).

You may want to copy these tables,since we shall refer to them severaltimes in Part 5 of this series. MIREADERS FOLLOWING THIS SERIESSHOULD REFER TO THIS MONTHS LET-TERS PAGE FOR DETAILS OF SOME AP-PARENT CHANGES TO THE BOARDUSED IN THESE ARTICLES. WEAPOLOGISE FOR ANY CONFUSION THISMAY HAVE CAUSED.

To be continued.

Shortened truth table for than es onl

INPUTS OUTPUT OUTPUTJ K Q BEFORE CLOCK 0 AFTER CLOCK0 0 0 00 0 1 1

0 1 0 0o 1 1 01 0 0 1

1 0 1 1

1 1 0 1

1 1 1 _ 0

K Qsfl OnXx

x 0


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HIf you have any problems relating o hi-fi, choosing equipment, compa 'bi "ty between units, weirdoccurances etc. we might be able to help. Audiophile is to have its own reade s queries service, for whichthere will be no charge just an SAE please and mark the envelope 'AUDIOPHILE' so that it gets to

where it should be.

A RECENT heated discussion between several hi-fi enthus-iasts here brought to light several interesting points. Thefirst was the number of similarities which exist between thefairer sex and hi-fi equipment!

Think we're joking eh? Well consider: both tend todominate the room they're situated in. Both are capable ofgenerating very high sound levels, but will stay absolutleysilent if turned off or ambient conditions are not favourableto smooth operation. Upkeep on both is horrendouslyexpensive, and requires constant purchase of software(wear) and cleaning materials.

In fact the only major difference detectable occurs whenthe specimen blows a fuse. One variety refuses to make asound, while the other demonstrates incredible slew -rateand reaches 200 dBA in a Microsecond.

Class E Birds?Be that as it may, our German edition has sent us newsof the missing E amplifier configuration. We shall assumehere that you've all read the article on class G in the lastissue. If you haven't ... go directly to jail, do not pass GO,do not collect E200. As you now know then Hitachi

dm 2A serene. andds ovelentpulsewidthmodulatedstmarewava Ina class E poweramp Ma wouldhopefully inducethe output Stagesto reproduce theSinewave

70

attempted to call their Dynaharmony circuit class E whenit first appeared, but found that classification alreadyreserved.

And now we know who by; Arcus. Their DPA 320,shown in Fig 1. is a 200 W RMS per channel poweramplifier-class E. Basically this configuration would appearto be a digital system, using pulse width modulation tocontrol the output transistors.

A 100 kHz square wave is generated within the amplifierby means of a crystal -locked oscillator, and integrated toproduce a triangular wave.

This Wave is then superimposed on to the incomingmusic signal, this being put through a very fast A -Dconvertor, the end result of all the logic circuitry producinga pulsewidth modulated square wave. Fig 2 shows a ine

wave with the square wave produced by the logic alongside.The square wave is now used to switch the output tran-sistors on and off very rapidly, the on time depending onthe widths of the incoming pulses.

In this manner the music signal is reproduced, buttheoretically without the inherent faults of the transistorsaffectin? it. Using the output stage like a switch is not new- Quads 405 current dumper does this , but in a differentmanner.

Fog I The Amos DPA 320 power erneProducing some 200 Int tmr channel this Sara,design is claimed to be tote/he free of crossoverdammed Pa and all other Mpolar amp vdes,

Pg 3 Themddle trace Atoe mengleProduced by

/00Flo.:egror col the

,puOrewave-,anal within theDPA 320 Thisrodngle is thensuperimposed onthemusic signal tocontrol thepower switchoutput pan


To keep operation symmetrical the transistors are notpushed totally into saturation and this allows 'recovery'from each switching operation to occur more rapidly.Contrast this to class D switching amps which operate bycompletely saturating the output pair in turn. Class E is10 times faster to 'recover'.

Those interested in further details can look up thepatent on the process (No 1444201) or contact Arcusdirect in Germany (Don't mention the war!) at:-Elektroakustik GmbH, Teltower Damm 283, 1 Berlin 37,Postfach 370 370.

Don't Wear It - Spray It!

An interesting spin-off from the space programme is tobe marketed in Britain by Pyser Ltd. Called Sound.Guardthe product is a spray preservative for LPs. (Just aroundthis point in the proceedings all the usual spectres ofganged -up records and glue -ridden styli ploughing throughseas of dust attracting substances should leap into theenthusiast's mind. They don't? .... Sorry!)

The compond was originally produced by NASA as a drylubricant for use in conditions of hard vacuum and hightemperatures. Development has now taken it into the formof a liquid spray.

This is applied to the LP surface, and immediatelyPolished up. A coating five millionths of an inch thick isapparently formed across the record and groove walls. Thebasic property of Sound -Guard is that it will not bond toitself, so that once applied a buildup on the surface is justnot possible, thus alleviating the horrors associated withsuch an occurance.

Benefits claimed are a cancellation of increase in har-monic distortion due to wear, reduction of surface noisegenerated by stylus weatand a preservation of high fre-quency response by protection of the delicate groovemodulations for those frequencies.

To The Test

To test these assertions, we decided to set up an A-13comparison on a Sound -Guard treated LP. This was achiev-ed by purchasing from our local record emporium two(different) LPs in as good a condition as could be managed


Spray now, play later - SoundGuard rakes your highs to a nyeold age

(after several return trips to dispose of copies with extraradial grooving) and recording these at 15 ips.

One LP was then treated with the fluid, simply byspraying on and rubbing well in with the pad provided. Notrouble here - once buffed up properly no audibledeterioration could be detected, and certainly the noiselevel was not affected. Nothing appeared round thestylus either!

So far, so good.Both records now went into the collection as normal,

and were played over a period of about a month, no specialcare being taken to differentiate them from any other LPother than noting when each was put under the needle.

The test was called to halt when we ran out of time onthis report. Things were evened up so that the test side ofeach had been played the same number of times, thirty-onein fact. Yes we do playa lot of records.

Masterful ComparisonEach could now be compared with the master tape madeat the time of purchase, and the by now obligatory listeningpanel was assembled to haggle over results. This timehowever no haggling was necessary, and the results could beunanimously agreed. The Sound -Guard treated LP haddefinitely 'held' the high frequencies better than theuntreated record.

On direct comparison with the tape, there was no doubtwhatsoever that the treatment had preserved the frequencyresponse to a clearly audible degree. Most people do notrealise how quickly extreme high frequencies are worn offan LP, even at low tracking weights. Our tests were con-ducted at 1.2 g. and so heavier weights would presum-ably show benefits earlier and to a greater extent.

For The Record

No conclusions could be drawn, however, as to whetherSound.Guard had achieved a favourable result with regardto surface noise-both LPs were still in excellent condition.As it is, we have no hesitation in recommending Sound -Guard as a worthwhile addition to the audiophile'sarmoury. it's worth its cost if it only prolongs the life oftwo LPs after all, and one bottle does 25.Price: Full kit (see photo) E4.99. Refill E3.25 (inc. VAT).Pyser Ltd., Fircroft Way, Edenbridge, Kent

7

Aiwa The LadsAnd so to our main news this month, a cassette deckwith several important differences. Recent models fromsuch noteworthy manufacturers as Nakimichi, Sony,Technics and Aiwa have shown a search for somethingother than that last few kilohertz at the top of the range.And now Aiwa have come out with the AD 6900, whichthey themselves consider "as far as one can go withcassettes," and have equipped the machine with thefacilities to let you know just how far that is!

Bias Your OpinionsWith all the various tape formulations on the markettoday. the age old compromise inherent in not optimisinga particular machine's bias for a particular brand isbecoming ever more irksome. While being fairlysatisfactory in general there is no flexibility in this systemat all, and no user control since such adjustment hasalways had to be done by a dealer. All the user could dowas to set a single three position switch to 'Fe-Cr','Cr02' or 'LH'.

What has been needed, and Aiwa have now provided(else we would not be rambling on about it) is somesimple user controlled system to set up the machine forany brand of tape desired, and obtain the maximumfidelity from it. Let's face it at 4.8 cm /sec and lain widewe need all the help we can get. Too high a bias currentresults in high frequency roll -off and increaseddistortion, and a balance has to be achieved.

On the 6800 the facilities to optimise bias are: built-inoscillator, test head, switched meters with filter, azimuthadjustment and two three -position switches for bias andequalisation, backed up by the three 'fine adjust' biascontrols. All this must add a considerable amount to the

shows how seriously Aiwa takethe cassette. (Wonder if they'll come up with an Elcaset?)

Self Satisfied UnitBefore we move on to show how the bias adjustmentsare made, and what effect they have on performance,let's consider the rest of what the AD -6800 has to offer.The finish is superb, and the controls are smooth andpositive. Everything about it looks - and probably is -very expensive.

The meters are a revelation in themselves. Twoneedles, peak and VU reading, are provided for eachchannel with excellent ballistics. The, peak readingfacility really is peak reading, not some cheapapproximation, and is switchable from peak reading topeak hold, or even to off if you feel like.

The hold facility makes setting up to record very easy.Just lock the hold on, and advance the record level untilthe needles move onto the level you want to set at. Nogetting eye -jump trying to watch cavorting little needlesavoiding 0 VU, and much improved recording as result.

Even loading this animal is different. In short youdon't - it does it itself. Press the open key and the doorswings up and over in an almost seductively dampedmanner. Facing you now is the cassette carrier. Put thetape in and give it a gentle push (or close the door) andthe machine jumps to life, takes the carrier out of yourhand and locates the cassette itself, all with a mechanicalwhirr of efficiency. Now I know it's only a little motor setto activate upon movement of the carrier, and I know it'ssilly and probably a gimmick - but it's still beautiful!

When the 6800 arrived here for review it was hours

72

Feg The tom needles meters show clearly the laeak Moth, es onhere, end the reading is thus of the heg hest level winch passed throughthe circuit on Me lest segment.

before we could actually play anything on it, since theentire office staff from receptionist to technician insistedon having a play with the loader. On a practical note, theauto -load does mean that the tape itself is less liable tobe mishandled, and the drive mechanism can bemounted further into the case with all the attendantadvantages of dust avoidance. A conveniently placedhead cover makes cleaning easy.

Reviewing ReviewAnother very useful facility is the "review/cue- mode.With the 'FWD' key depressed, operating rewindreverses the tape direction as normal, but leaves thehead in contact with the tape so that an audio signal, atreduced level, appears at the output. Very handy forlocating the end of tracks on recordings. The fast 'FWD"keys work in a similar manner to allow you to 'CUE' upquickly to the end of a piece. If used continually no doubthead wear would be accelerated. but Aiwa contend thatfor the amount of use the facility will see in terms ofplaying time such additional wear will be negligible andwell worth the facility. In our opinion a fully justifiedcontention.

Finding Your TypeUsing the bias tuning is simplicity itself. Let the machineload a cassette (don't fight it - use it) put it into therecord mode, with input selector at Test and Dolby off.


Fig. 2 The azimuth adjust control within the cassette compartmentThis is used in conjunction with the Skye °scone's,' and the right handmeter in obtaining maximum level end hence correct alignment

This allows the internal oscillator to put its signal ontothe cassette. Both meters now deflect. The right channelmeter indicates 8 kHz level, and the left 400 Hz. The testhead itself is aligned by adjusting the slider inside thecassette compartment for maximum 8 kHz level.

To optimise the bias sat the coarse control to thecorrect formulation, and adjust the fine control until bothmeters read as equal as possible It takes longer todescribe all this than it does to do it, and just to make iteven easier, the fine control you should be using isilluminated as soon as the coarse bias is set. CrO,switching is automatic.

Aiwa intend all this to be used to obtain a flat'response by setting equal levels at 400 Hz and

8kHz. Of course, if the tape type in use sounds a little'dead' at the top end, you can always leave a few dBextra on that meter....

We tried the 6800 on a whole range of cassette typesfrom TDK SA to BASF LH Super, taking in Cr02 andFeCr on the way. Results with all tape types were firstclass, but even using the fine tuning, the 6800 seems todisplay a preference for TDK Super Avilyn. Results withthis tape were the best we have ever heard from acassette deck, the sound displaying a clear and opennature with little of the usual stricture associated withthe medium.

Ferry Chrome Carried?With FeCr tape it was necessary to 'tune' considerablyfrom brand to brand, but once achieved the correctsetting delivered a very good recorded performance, Theresults with Cr02 tapes were frankly disappointing. Thesound never approached that of the SA recordings. andsome difficulty was experienced in following through thesetting -up procedure. We feel this is a minor drawbackhowever, in view of the outstanding qualities displayedwith both FeCr and Super Avilyn, and the excellent LHresults.

Without doubt, the bias controls of the AD6800added considerably to the unit's versatility. and allowedwide variety of cassette tapes to give of their best. Thevariation in sound quality with 'tuned' settings is surelyto be expected, after all some tapes are better thanothers! If you are looking for a machine that takescassettes seriously, and are pr'epared to pay for it (in the


10 3 lose,' of the clever bite Above the general input controls canbe seen the bias fine adjust control which allow tuning up for each typeformulation available. The control ito be used is illuminated once theinputis set to 'Test'.

region of £400) then this unit merits top place on theshopping list. It costs a great deal of money, but hasmuch to offer in return.

Manual LabourIn conclusion this month, one parting shot across thebows of the Japanese giants - Aiwa included. Thestandard of the instruction manual with the AD 6800 istypical of such publications - abominable! Productionand layout are nicely done, but the English - oh theEnglish! It's been said before, and now we've said itagain. Please please please someone somewhere con-vince the powers that be and get the instructions up tothe unimpeachable standards of the hardware.

Freese.

SN Ratio,

Wow & I lull.:

Tape Speed:Rex ind time:

Bias Frequency'Motor:Tape Head:D100111011:Input levels:

Output levels:

Power Consumption:Dimensions:Weight:

SPECIFICATIONETI

Rmponse. According to DIN 45 500LII tape: 25-15,000 1IzCrOz tape: 25 17.000 Hzlc-Cr tape: 25-18,000110Aueording to DIN 45 501164 dB (Fe -Cr tape DOLBY NR ON)Aecordim, to DIN 45 5000.1%4.8 em/sec (1-7/8 Ms)90 scc. (C 60)90 see. (C-60)Ice kHz38 pulse FG Servo MotorFerrite Guard Head (FGH)0.9',L, (400 Hz. 0 VU, Fe ..Cr tape)Microphone: sensitivity: 0.25 my

-zodirgiokLine, sensitivity: 50 my

impedence: oven 50 kDIN: sensitivity: 0.1 mVik

impedance: 3 kLine: 0.775 V (0 VT/uptimatload impedance, over 50 kDIN: 0.775 V (0 VU)optimal load impedance: over 50 k

Headphones:load impedance: 8R to 1505

20 Watts450 W.162 1-1, 335 D. (mm)10 kg

73

This month Gary Evans takes the hard work out of finding a way of producingcheap hard copy, at some new educational items from Heathkit and how to nobble

your AGC which can give trouble with digital signals.

May 1 begin this month by asking you a question? Yes?- No, hold on, that was not the question that comesnext.

Heath CUTSIf I were to ask you if you would be interested in animpact printer that produced copy with a thirty-sixalpha -numeric character set on eight -inch -wide paperwith sixty characters per line and five lines per inch forless than a hundred pounds, what would be youranswer? If it's No then suppose I threw in a keyboardwhich was capable of generating seven bit ASCII codeswith parity? Still No? Well, let's also throw in a UARTmaking the terminal TTY or CUTS compatible. If you'renot yet sold on this device what about reducing the priceto less than ninety pounds? If having read this far andstill not become very interested in the specificationevolving I can only assume that you mistook this columnfor news about a new item for your tool -box (shades ofneedle file?).

Why have I dreamt up this machine that wouldanswer most micro users' prayers? Well, the answer isthat it is no dream. I have been sent details of just such adevice, the DTS 77 data terminal. I shall try to get holdof one of these beauties and tell you all about it when Ido. In the meantime further details may be obtainedfrom: -Heath E & M,26 Broad Street,Lyme Regis,Dorset.

Heath KitsA few months ago I mentioned that Heathkit hadlaunched the H8, a personal computing system, in theUS. This interesting piece of hardware is yet to make itacross the great divide but rumours have it that themiddle of next year should see its UK launch. Micro-processors do. however, have a foothold in the range ofkits that Heath offer on the UK market. The micro-processor flag is being waved (set) by Heath's micro-processor course and computer Trainer package (Heathreferences EE -3401 and ET -3400 respectively).

These follow the lines of their, by now familiar toconnoisseurs of the Heath range, continuing EducationSeries. The format of these courses follows the samebasic pattern of providing a 'learning program' which isa comprehensive set of notes dealing with the theory ofthe subject to be covered - in addition practical experi-ments are described in the text. These experiments canbe carried out with the "trainer" that is designed tocomplement each learning program. These trainersincorporate a breadboard area together with all thecomponents necessary to carry out the experimentsdescribed.

At the end of each section a self -evaluation quizallows one to assess the progress that one has madeduring each unit of study. Until recently the coursescovered basic AC and DC theory plus SemiconductorPrinciples and a Digital Techniques course.

The MPU course H the latest addition to the rangeand looks as if it could bee good way of getting to gripswith Micros. I have not yet managed to get my hands onone, but from the photos and description shown in thenew Heath catalogue, it looks good.

Based on the good old 6800 supported by a 1KROM monitor, with 256 byte RAM plus other com-ponents and breadboard area, Heath say it should provea valuable teaching aid. It should provide a means ofgaining familiarity with machine language program-ming, hardware I/O interfacing, micro theory, anddesign applications.

With data input via a hex keyboard. and display ofdata plus address on seven segment LEDs, to use thetrainer is easy. It is an expensive item and has limitedapplications - in that it cannot be easily expanded toform part of a larger system. It was not designed for thislatter role however, and should together with thelearning program provide very valuable hands-on ex-perience. For further details of these new items fromHeath see their new catalogue. Fora copy of this contactHeath at:-Heath (Glees) LtdGloucesterG L2 6EE

A Corrupting InfluenceReferring to a past microfile last month I mentioned theSERT MPU lectures at Kent University during lateSeptember. Lack of space last month prevented me fromsaying much about it - and it looks as if much the samething has happened this month) So just another titbitfrom the event.

The idea came from R. A. Smith of Essex Universityand concerns the use of low-cost cassette recorders

IC1/1 IC1/2 IC1/3

Fig. f. Circuit of oscillator to produce aigne/ uitetle/or disabling AGC

74ELECTRONICS TODAY INTERNATIONAL - JANUARY 1978

110, 0

when recording data output from a micro system. It is atechnique to overcome one of the problems oftenassociated with this type of recorder - namely un-wanted action of AGC circuits.

In the less costly recorders these AGC circuits, idealfor recording speech, often cannot be switched out ofthe signal path. When recording any form of digital datathe action of such a circuit will be to corrupt it. Considerfor example a gap in the recording. The AGC will in-crease the gain of the input signal, thus increasing thelikelihood of noise or transients upsetting the recording.

Now we get to the clever bit, by superimposing acontinuous HF signal on the, usually, LF data signal theaction of the AGC can be nullified. How? Well, wearrange for the HF signal to be outside the response ofthe tape, usually not much more than a few KHz on thecheaper machines, but within the response range of theAGC processor.

Thus the AGC circuits 'think' that there is a continuous high level present at the input, and keep therecorders gain constant.

A simple CMOS oscillator can provide the requiredbias signal, and be mixed with the data just before beingfed to the recorder.A simple idea that should improve the performance ofthese low-cost storage systems. ET1

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BECTRORICSTOMORROW

by John Miller -Kirkpatrick

JUST A COUPLE of weeks to Christmas and you haven'tyet thought what you would like Father Christmas tobring you in your stocking this year? Its time to leaveextra large hints lying around, if you feel like dabblingwith your TV games unit try leaving this article in a placewhere 'Father Christmas' is sure to find ill

Christmas Colouring Kit.If you have one of the black and white TV gamesbased on the GIAY-3-8500 TV games chip you can nowupgrade it to colour. Watford Electronics have a kit toupgrade this type of unit to give effects such as a greencourt, red boundary and score yellow left bat and blueright bat. The kit includes a UHF modulator so that youcan plug the game into the aerial socket of your TV. Ifyour game was built from a kit which never quite workedthen this add-on might be lust the excuse to dig it out ofthe 'not quite completed' projects pile. If you still don'tfeel like trusting your ability to build such a unit you willbe pleased to hear that Watford can supply it built,tested and even installed in your own game. For detailssee their advertisement.

Other Upgrades and add-onsAnother way to improve your TV games unit is to changethe chip for the AY -3-8550 which gives additionalhorizontal bat control together with a few otherimprovements. The chip is pin compatible with theAY -3-8500 and requires only an additionalpotentiometer in each hand control to complete themodification.

Alternatively you could st art almost from scratch withthe AY -3-8600 chip which gives a total of eight gamesincluding Gridball, Hockey and Basketball. The AY -3-8550, AY -3-8600 and PCBs, kits, etc are available fromTelecraft, for further details see their advertisement.

Add-on Music.If you already have enough of the above modifications orthink that they will only cover Christmas day and you arelooking for something to occupy you on Boxing Day thenhow about making out a list of components for 'FatherChristmas' to enable you to experiment with this idea,

The TV games chips described use something like a2MHz oscillator to generate ail of the timing signalsincluding sync. If this oscillator were also divided by


about 4 and gated so that it was enabled only inside theourt' or visible signal time of a TV game then it should

be possible to divide up the court into several horizontalsections. If the sync signals are counted (and resetduring court) then the court can be similarly broken upinto several vertical sections. A little additional logic willallow you to display several 1in. or so squares on yourTV screen. With your colour modulator kit you can alsodefine the colours of the squares and define how thecolours are allowed to change.

Now all you need is an audio signal, a bit of filtering. afew BC109s and suddenly you have your own multi -option fourth TV channel. For additional mind -bendingexperiences try adding the TV games signals and yourgenerated 'music' signals to give a multicoloured court!

19761978 will bring some pleasant surprises in the TV gamesbusiness, with some cassette or cartridge units alreadyavailable. At first there will be a great divide in themarket between GRAPHICS games such as those al-ready available and BASIC games played in questionand answer form. Eventually these will become com-bined in some really interesting TV games units - staytuned to ETI for more information,

Software Made SimpleI have been involved in writing a lot of software forvarious applications over the past few months and I

thought that some of the techniques I use might be ofinterest.

First of all get yourself a hardback or loose-leafnotebook of a reasonable size to write down all of yourattempts - there is nothing worse than having to rewritea routine from scratch because you have lost thecigarette packet which had the original notes on theback.

Decide roughly what the routine will do, a roughflowchart plus an idea of any fixed stack assignments,sub -routines, etc. Convert this to a first draft machinecode listing with notes and labels but leave plenty ofroom for additional, insertions and changes. Looking atsome of my roughs and comparing them to the finishedproduct it seems that nearly every other line hasalterations.

Having decided what you think the machine codeshould be sit down at your MPU and try it. For mostsub -routines you will probably have to set up a callingroutine to test it, this routine simply sets up anyparameters used by the sub -routine and then calls theroutine. Do not bother to enter more than about 10instructions at a time because the likelihood of having toshift them all is very high. At a convenient point enter aninstruction to generate a Software Interrupt so that theMPU will perform the code entered so far and thenreturn to a routine which will allow the results so far tobe checked, in most 6 800 systems this will be a '3F'instruction.

If the results so far are those expected then another10 instructions can be entered and another '3F'instruction inserted. etc, etc. Any changes to the originalcoding should be made to your original notesimmediately after the change has been verified on theMPU.

Branches to parts of the routine which a not yetcoded are easily handled by branching tore a '3'Frinstruction or back into a loop until the conditionchanges, this allows one side of the branch to be codedbefore attempting to do the other. ETI

77

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.9 dig.' multimeter used tomean an expensive, bulky piece ofequipment.

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fhe Sinclair PDM35 gives youall the benefits of an ordinary digitalmultimeter -quick clear readings,high accuracy and resolution, highinput impedence. Yet at L29.95

VAT, it costs less than you'dexpect to pay for an analogue meter!

The Sinclair PDAI 35 is tailor-made for anyone who needs to makerapid measurements. Developmentengineers, field sendoo engineers,lab technicians, computer specialists,radio and electronic hobbyists willfind it ideal.

With its nagged constructionand battery operation, the PDA135 isperfectly suited for hand work in thefield, while its angled display andoptional AC power facility make itjust as useful on the bench. -

What you get with a PDM353'. digit resolution.Sharp, bright, easily read LEDdisplay, nailing to ,1,999.Automatic polarity selection.Resolution of I ml' and 0.1 nA0.00111tlA.

Direct reading of semiconductorforward voltages at 5 different currents.Resistance measured up to 20 .5111.190 of reading accuracy.

Operation from replaceable batteryor AC adaptor.Industry. standard 10 Ali t inputimpedance.Compare it with enanalogue meter!

The PDAI 355 Pe of readingcornpares with 3ke of full scale for acomparable analogue meter. Thatmakes it around 5 times moreaccurate on average.

The PIP1135 will resolve I mVagainst around 10 mV for acomparable analogue meter - andresolution tan current is over 1000times greater.

fhe PDA,135X DC inputimpedance of10 i t is 50 timeshigher than a 20 ki tevult analoguemeter on the 10 V range.

'Ihe PDA135 gives precisedigital readings. So there's no need tointerpret ambiguous scales, noparallax errors. There's nu need to

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78 ELECTRONICS TODAY INTERNATIONAL JANUAR y 978

Digital Echo UnitJ. A. Murdie

The Digital Echo Unit described belowmay be constructed on standard Euro-card PCBs with 31 way connectors,and utilizes the cheap 2102 1K staticRAM, of which from any amount from(say) 32-64K may be used to achieve a(continuously variable) delay of up to asecond. The delay time is of coursedirectly proportional to the amount ofmemory used. There are three PCBdesigns used: Fig. 1: Input/Clock board11 off), Fig. 2: Output/Control board(1 off), Fig. 3: 8K Memory Board (max.8 off).

Dealing with the input board first,it may be seen that the 555, 7476 and7408 constitute a non,overlapPio9 twophase clock whose outputs are 'EnableRead' (ER), and 'Enable Write' IEWI.During the write phase a bit is takenfrom the digitized input and fed to the'Data Write' (DW) line. The AD con-vertor used is the FX209 which wasfeatured in the ETI June 1976 DataSheet. The bits created are placed in the.memory location addressed by the 12bit counter ('Bit Address'). on thisboard and the 4 bit counter on theOutput/Control board ('Block Add-res').

When the ER line goes high a bit istaken from the memory address pointedto by the counters with the 4 bit valueproduced by the Hexadecimal Priorityencoder (Delay Switches) being addedto the block address. Thus the 'distance'between the write and read 'heads' maybe altered to place them any number ofblocks apart, and thus create a choice of16 basic delay lengths. The bit read is

placed on the DR line and is then con-verted to an analog value by the DAconvertor. Note that some of the outputmay be fed back to the input ('Regen')to create multiple echo effects.

After this sequence of a write and aread cycle the bit/black address is in.cremented by one so a succession ofbits may be placed in memory by input,and read from the memory by the out.put. The rate at which this sequenceoccurs is controlled by the clock rateof the 555 astable, and thus this notonly controls the delay time as do thedelay switches, but also the quality ofthe sound reproduced as this indepen-dent on the number of samples taken.

per second in the digitizing process. The bits/second - which is quite adequatedevi. may be set up to digitize the for (say) an electric guitar which re -analog input at a maximum of 125 K quires a bandwidth of some 10 KHz.

Fig 3 81, Mem, 8..1

En is prepared to co er circuital,' ideas submitted by readers for this pinte A,. nem._used will be paid for Drawings should be as clear as possible and the test should preferablybe typed Circuit. must not be subject to copyright. Items oxfordsideratron should be sentro an tleetroniCs Tetley International, 25,7 St., London W1R 1RIF.


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ELECTRONICS TODAY NTERNATION AL - JANUARY 1978

Dec-ed OutD. F. Tranter

When using S-Decs to test circuits,one often finds that several groups ofthe Dec contacts are taken up for onecommon connection, particularly thecontacts which run to the batteryconections.

In order to extend the capacity ofa single &Dec I fit a row of socketsalong each of the two Dec sides whichhave lugs for connecting to otherOecs, using the lugs as end fixing points.

If the sockets are bent and a strip ofinsulating tape used to anchor the lower

D FITS BEHIND LUG

101.

ETS ALoNG LARGEST SIDE

TS11141:3 TAPE

PINS BENT UNDR WITSOCKETS HELD I EN SITUH

STS AT SIDE

ends, one gets a reasonably robust fitt- The lug recesses along the other twoing which greatly extends the capacity sides can also be used for attachingof the Dec. more rows of sockets.

The Multi-zenerR. N. Soar

This is an application of zener diodesbased on the binary system. In theexample shown three zener diodes areused 3 V, 6 V and 12 V tie. 3.0 V,6.2 V and 12 VI plus three S.P.S.T.switches. In the on position of aswitch the diode is short circuit. In the'off' position the diode is in circuit.Thus the effective diode by suitable

operation of the switches is 3, 3+6, series 24 V and another S.P.S.T. switch3+12 etc. ie. 3,6,9,12,15,18,21 volts the range is 3,6,9,12,15,18.21,24,27,By the addition of the next in the 30,33,36,39,42,45 volts.

0 L4 14 1.412V 6V av

-o." "O

EFFECTIVE 2ENER

0

Cheapo Vc0A. J. Richardson

This circuit provides a cheap solution toa non precision voltage controlledoscillator. C1 charges towards the volt-age set on VR1 until inverter 1 outputgoes low whereupon the output ofinverter 3 goes low and discharges CI

is D and R4. Inverters 2 and 3 form aSchmitt trigger circuit with positivefeedback supplied by R3. Inverter 4forms a linear amplifier with its gain

set by the ratio of R5 to R6 whichsquares up the signal appearing oninverter 1 output. The signal is furthersquared up by the Schmitt trigger actionof inverters 5 and 6 to provide a squarewave of approximately 50% duty cycleat the output of inverter 6. With thevalues shown a frequency range of atleast 100 Hz to 15 kHz is guaranteedwith VR1 but other ranges can becovered with suitable values of RI andC1. The circuit works well at lowersupply voltages but the frequencyrange covered for a given set of com-


ponents may be slightly less. If a squarewave is not required a negative pulse ofpproximately 200 nS is available athe output of inverter 3 thus enablingwo VCOs to be built with one chip.

81

15-240 Watts!HY5Preamplifier

HY3015 Watts into 80

HY5025 Watts into 80

H Y 1 2060 Watts into so

SPO E.S.F..0.3PEOPEO,PF .4 IF 213,A PON o

NOSE AATC .113 FPE(..CE PFSPONSE 10X.1310, -3. S.,-

A.1:1:13t 0 N

EPECOICA,ONS

Po3. 22 F 653 VAI PAP AF

HY200120 Watts into BO :,=o,,,

HY400240 Watts into 40 r'ATT,'

SPECIFICATIONS

POWER

SUPPLIES

I.L.P. Electronics LtdCrossland HouseNackington, CanterburyKent CT4 7ADTel (0221) 63218

,FARS GC A,10 CL ON ALL OF OCR PRODUCTS

Please 50111,10Solid PI vvtose Price.

Eno /v:0 Cheoue 7 Postal Orders 71 Mone y Order

P,ease debn !II, Access acco,ni -:Account numberName A. Address

Sioature

Phaser ModM. Headey

I constructed a simple variable gain opamp inverter and connected it betweenthe output and the input.

When the feedback amp was switch.ed into circuit the effect was dramatic.The phaser sounded much deeper.

The modification is simple enoughand though can Ire adjusted to feedback(audio) level, sounds very good if thegain is kept down.

The circuit as shown gives very goodresults although you may be able tosuggest some component value changes.

Programmable GateP. Mead

The Programmable Gate is a gate whichconverts an AND gate to an OR gate byapplying a logic '1' on the functioninput.

The logic design uses 8 x 2 inputNAND gates. The number of gates maybe reduced by replacing the 5 NANDgates enclosed by the dotted line, witha 2 input exclusive OR, such as theTTL 7486.

5mS Delay UnitC. S. Rushton

The circuit shown will produce a delayof 5 mS from input to output with goodcorrelation between amplitudes over adynamic range of approximately 40 dB.

The circuit consists of four mainsections: an input buffer, a dampedresonant RLC circuit, a non -invertingamplifier and a clamping circuit.

The delay can be modified withinreasonable limits by adjustment of theRLC network.

FROM PHASEROUTPUT

INPUTS

TO PHASERINPUT

ELECTRONICS TODAY INTERNATIONAL JANUARY 1978

SECOND GENERATION

METALDETECTOR

KITDESIGNED SPECIALLYFOR THE HOME -

CONSTRUCTOR 4411.,11

EASYTO

BUILD

Ls:Tpdrore":,r,::,'.".1".270,°,:',1'07:"'"

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* Checking aid timber for nails before calling.

KIT - COMPLETE WITH PRE -ASSEMBLED SEARCH COILS

£16.50Plus El 01148, Plus Lt -32 VAT

ASSEMBLED & TESTED

£22.50Plus Le-ooaaa Plus L1-80 VAT

Communication Measurement Ltd15 MALLINSON OVAL, LIARROGATEVORNS.

TV GAMES IN FULL COLOUR

NEW COMPONENT SERVICE

3p Mt M2

22 rip212a2t.Elemelveies-SOW 42

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ma 19...93,37, Sp 10035I Sp. 220 220. Sp.27,;,,,e,g0p0mIlip.S.morS*400.,E24

AA INS TRA/GFORMERS

aotIlr.r.".,77,.50,...,1,.,0 "2_1,15 20 23.10V 23 SS IS 5 3vi 33 53

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PRINTED CIRCUIT MATERIALSso o ,-. p. 40p

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M O, ' 7.'n'aelT; '

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NEW NEW NEW

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Suitable for use with AY3-8500 orAV -3-12550 (110F920St91 a. vertical batMovement) a. above modulator. Potsand switches not supplied.

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Save on Calculators

Mil NEW FROM SINCLAIRA 36 Step

Programmable £13.76Scientific

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84ELECTRONICS TODAY INTERNATIONAL -JANUARY 1978

BACK IN STOCK -CREED 7B TELEPRINTERSTHE CHEAPEST WAY OF GETTING A FUL ALPHA , NUMERIC PRINTOU FROM YOUR MICRO

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ry `16OCONER

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Now _ FOR THE MICRO -PROCESSOR USERA LINE PRINTER YOU CAN AFFORD

THE I.C.L. 667 BARREL PRINTER

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Plays TV games withplug in cartridges

Fully Pal ColourCompatible - justplugs into your aerialsocket

No batteries -runs from mainssupply

Automaticon -screen scoring &time -keeping

Hold buttonfree:es play actionindefinitely

Play action speedcontrol

Time limit selection

Electronic soundeffects

Optional cartridges

This system can play a variety of different video gamesavailable on OPTIONAL VIDEOCART cartridges.

Up to 4 different games on each Videocraft.Two built-in games: Tennis/ Hockey (no cartridgesrequired)

Games available NOWCartridge 1: Noughts & crosses/Shooting

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AVAILABLE SOON: Backgammon, Magic Nos.. Maths Qua, Drag Strip,Maze. Baseball,

all at 817.75 Inc VAT& P&P each or 870 asa set of cartridges 1-5EACH .871.1.1)0F1

Price Only 8180.00 inclusive of VAT. Postage. Packing and Insurance.

Demonstrations available at: Videocraft, Assets House, Elverson StreetLondon SW1P 2QR. Tel: 01-828 2731 /2/3

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For a merry musical'rp Christmas an electronicS musical door chime whichPin can play 24 different tunes!

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8 NO prev.ous mcrocoinputer expenence neces., MI proprammno permanently relamed Ps on chip PO*Can be eupli .n about ]moors. *19*e*r da*.**12**9.Runs. PP3type baltenes orlfeintieseukoftkaeT4 Fully Guaranteed Sou, ftegad,..xmal ft.e

the Chrome,Cn..em iheroorl.firmelecuoncm..., 4 4,6,6.9,..4881888919111.1.8118581811,11OWaT11`...c.c.^89.'

ro generale tunes inst.. Wrwrgoid buues r

Jon9s.,e0vOmi Chi.e..n.r 'Anyone, ,tx 24 ...now.

s.acannol play the notes out 011uneThe und hascomprehenSive Ou.11..n<onlrols ao you A

can nol only »led lunaol e. I

!env° anclenve.edecar raleto change...sound 1 1,898

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Every kit is a hsolutely complete down to kwg, -

the last nut and bolt.'Ehe guiltily is the best.And each kit has an easy to follow instructionmanual that explains exally what to Soar flirob ,ezgh step.

So you enjoy assembling your kit and Yonfinish with first -glass equipment every time.

That's why I leal hkil are .stincessful.And that's why the range is rho biggest in the [anon I lefullkic taco!, ro to.1So 110ti FRETmaid.

II's all in the new edition of the free Heathk,catalogue. Everything from the simplest to themost sophisticated. Alang,digital clocks.testers.trinsceivers and lots more...even thetools are there!

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El ELTRONICS TODAY INTERNATIONAL - JANUARY 1978

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y Man With full Pree.X.rog lebUreelreee ("0oneSliel <hem,. required)

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RAMAR CONSTRUCTORSERVICES

MASONS ROADSTRATFORD-ON-AVONWARWICKS. Tel. 4878

MEMORIES!MEMORIES!

* INTEL 2102 SRAM . 179p* INTEL 1702A EPROM 770p* Texas TIL311 Hex Display (0-

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THE BRITISH AMATEUR ELEC.TRONICS CLUB for all interested M elec-tronics. Four Newsletters year with help andspecial offers for members. Major projectssponsored by the B.A. E.C.designed andmade by members. currently the B.A.E.C.LBO Computer. Membership lee for 1978

3.60 U.K.overseas E4.50 surface andE 5 50 airmail payable in sterling. S kE fordetails and application form to the Hon. Sec.J. G. Mergetts, 42 Old Vicarage Green,Keynehem, Bristol.

SPECIAL OFFER 741100 20p) 2102 (BOONE)El 50. TIL209 )BED) 9p: TBABI OS asp:91.1F3055 sop.

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PCB 41/2" x 2" contain/no 2 a 24V. 115V4 pale miniature relay, diode capacitor.ale 30p1A2/ p p 100

PCB 41/2" r 2" containing 24V, 140V, 4pole miniature relay, diode, capacitors.etc. 20p all boards (A31 P/P 1011

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P.C.B.sStandard or 'FR-Glapex' fibreglass P.C.R'sfor ETI projects supplied tinned and drilled.,E.T.I. 541 68p 568 ETV 193p.

E.T.I. 549 .. 77p 3 Channel tone con -568 VDUs (Mod) trot 63p

255p Digital Therm 112p568 VDU b (Mod) Clock A 97p

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81p New Monitor 89p568 CPU 226p Freezer alarm 46PPLUS Special Ofeeri now valid till Doc. 1, .77.Item 1: Full set SSE pcla (VDU A b, PSU,Micelle CA75 per mit.Item 3: ETI 904 TV Owe, 0.00 eachlom 3: ETI 0.80 a ORO PERE C1.90 per pair

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CARBON FILM RESISTORS 5% Ell Senes1/ BW, I /4W, 1/2W. Mixed to your choice.100 for Sop Electrolytics 50/15v 7p. MI-CROPROCESSORS SC/ MP £12.70. IntrokitEll, Keyboard kit E74, MM13800 E20. 7190E25. No extras. P&P 15p. CANDAR, 9Galloway Close, Denbigh Hell, Bletchley.

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SOFTWARE FOR SYSTEM 88. -TheScelbr 5900 Cookbook') includes routines forfloating point arithmetic. Input/Output andmuch more. El 0 post paid or SAE for detailsand new list which includes a 6800Assembler K. Roche, 20 Sleeker Close,Basingstoke. Monis

PROMS PROGRAMMED bon, your hexlisting. 55204A - E25 From papemmag-neve tape E21. Other types Svailablerequest. Our "Guide to SC 'MP prograrnm.in - introduction. techniques and manyexamples over 50 pages, E3.50 KernitronElectronics. 65 Warren Rise. Frinuey,Camberley. Surrey 0276 26192

MICRO -BITS. 1702A Proms E4 ea. Erasingand Progremming facilities available P&P15p DIDS 402.20 VDUs ASCII. No controlurat required E130 Manual amiable Carrby arrangement. LM309 five volt regulators90p P&P 12p Many cheap items alwaysOp

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AD-INDEX

Ace 93Ambit IAudio Electrons 92Bomber 47!Winne ..... 99Barclay Electronics 95Baron 91Benin 24Bilak 4 5Bynod 6

Camrbidge Learning 12Chillmead 85Chromalrenics 88

Communications Measuremeel 84Crimson 92D& D Power Supply 98ELM 7

Electrovalus 91Fothery.Willls 89Greenbank 92.94Greenwald 7lienkit 89EP 8 13 82Kramer 40, AO, B4, 87. 93Lewis 95Moulin ISOMarshall's ELIMega 80Melee 10Minikils Electrons 40Mountaindene 40. 69E R. Nicholls ............ .. 93

P.B. Electronics 90Powerlran 76Precision Petite 9Progressive Radio 92R.F. Equipment 87Science of Cambridge 23.66Sinclair 908155105 78SWIM 45H. L. Smith 98C. N. Stevenson 89Stuart Bruges 84Surefire 39Swanley .... .............. R4

TechnomaticTelecraft

6 91

14Tempos 94T.N. Electronics'hones

9B

80Vero 9

VideocraltWilford . .............76.

....86, 93

2

Wilmslow 87


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Still soldering on?You may be that rare person who gets his

circuit designs right first time, everytime.But it's much more likely that you

experiment to see what works, and what doesn't.In which case you ought to know about

Bandridge Decs.Bandridge Decs enable you to try almost

any number of possible circuits, without having touse your soldering iron.

You simply push the wires of your circuitcomponents into the holes in the Dec to make aperfect solderless contact.

Which means that you can use thecomponents over and over again.

And, of course, we don't have totell you how much time it will save you.

There are four Decs available

suet

to suit every possible circuitry requirement.From simple discrete work to 2xDIL or

4xTO5 Station work.And for larger or more complex circuits

you can use any number of Dew linked together.Eventually of course, you'll need that

soldering iron to make up the permanent versionof your circuit design.

And when you do you'll probably wantto use one of the matching Bandridge Blobboards, to make your job that much easier.

But until then we suggest you put yoursoldering iron aside and get yourself aBandridge Dec.

Bandridge Decs - Available at all goodcomponent stockists, where you see theBandridge sign.

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sst ccerocs DondiSsiges Ltd.,80c Borlessos Rise.: Ancon SW; I SERTels 01.228922]_

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SYNTHESISERThe International 4600 Synthesiser. A verycomprehensive unit. Over 400 sold. We stockall the pints coaling less then E500 includingfully punched and printed metalwork and a

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