chromatheque 5000 - world radio history

CHROMATHEQUE 50005 CHANNEL LIGHTING EFFECTS SYSTEM

r,4c

4"" 4/1PLETEZITON..lb

£49, .616 + VAT!

A 100

cp.NO.

cvb

MP sint444<mixtemveinvb*"

CryiPLETE KIT-r16 .8=1i -it. MX .0.: : 0: :ik:

MEW 0 0 7 -tor. O+ VAT0

4 c 4gh dth,Apttrn deetoroiclal - Parts for power supply only

es, caps. E1 .60 o wit Jot, El 0.54,0 Ai reap

R A Pitt E VOCOrtSI LEtatIOD04YNtHESIZER

COMPLETE KITONLY

£172.00 + VAT!

PONIRTRAN

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TRANSCENDENT 2000 POWIRTM

ORDERING INFORMATIONAND MORE KITS ON PAGE 8

Boats Crossroads . ,327

electronics todayAPRIL 1979 VOt 8 NO 0 INTERNATIONAL

FEATURES

NEWS DIGEST 9 Did you knoyPOWER ...MVP/ 19 Power .0. PeOPIe

Grn REVS.ED 37 New Me foi an okl ideaDATA SHEET 52 IC swyey

READERS DESIGNS 54 Vow deSignE buthTEN 3080 CIRCUITS 70 It does more than you think

MICROFILE 80 A floppy petTECH TIPS 103 CitYuits from you to you

PROJECTSVIDEOGRAPH 27 Sound to fight on your telly

CLICK ELIMINATOR 41 Clean up your recordsAMBUSH 61 The new spa. game with a.m.

WIND SPEED INDICATOR 85 Gel the wind up this unitGUITAR EFFECTS UNIT 97 We think we've found a new one for you

PCB FOIL PATTERNS 110 All in one pia. now

INFORMATIONBOOK SERVICE 25 von name o we have a book on it

HOBBY ELECTRONICS PREVIEW 35 On as way to y.ETi PRINTS 49 or DIY PCB a

MARKET PLACE 58 Can von n.nne$. prices,ETI SPECIALS 69 Specially for you

COMPUTING 0000 83 On its own nowNEXT MONTH iry 90 What we ve got for May

25 27 Oxford Street 71117AVIrTVeTprgrOEINUr41 2 Tele 8811898

Mayby. Ian ...re 8

Teennly. IllustratorsVey Menton Vv.. Ed.,

Ste,,:re:riny?:at Pm, Development

Iterna7-=

Smt12":"*IYa=lt27-1=AdveMs.Y

ELECTRONICS TODAY INTERNATIONAL - APR, 1B/B

BOOKSBOOKS BY SABAN!

...

AND COMPONENTTRANSFORMERS

. .. . . ..,

SWITCHES

AUDIO LEADS

. ..

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FUSE HOLDERS ..-. AND FUSES..,,._, .....,...

::BOOKS BE NEWNES ,.......-IT"

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ANTALUIS CAPACITORS

NEATSINNS

SI

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ELEC, NIPS TODAY INTERNATIONAL - APRIL 197

SEMICONDUCTORSTRANSISTOR 74 SERIES TTL ICs

' 1

CMOS ICs

11 B13 H' 1L 11 11

1111

LINEAR ICs

'47', 3 I- 4,113 111.7

DIODES

!!!!

1 -PAN

QUARTZ LCDALARM 7 Function

£19 65

M5

HANIMEXElectronicLED Alarm Clock

£8.65

M13

QUARTZ LCD AlarmChronograph psi. DualTime Zone Facility

£27.65 MB

QUARTZ LCD AlarmChrono oillM1 front alarm

£29.65

QUARTZ LCDLadies B Function

M15

QUARTZ LCDALARM 6 Function

E16.65

M4

SOLAR QUARTZ LCD5 Function

9.95

MI2

1717fteC ELECTRONICS& TIME CENTRES

ELECTRONICS TODAY INTEPNATIoNAL -AP,1979

DIGITALCLOCK RADIO

.11g

019.95. .,

M17

DIGITAL CLOCKRADIO Portable LCD

DIGITAL CLOCK LCDTr.., --- -

coot,

,,,,

Digital Clock/Alarm/Calculator/Stopwatch

A0.1000

021.85 M20£19.95

M18765RADIO/CASSETTE4.13ancl/LIN-MW.SW.FIVI

RADIO/CASSETTE3-Bancl/LIN.MW-FM--,

£34.95

RADIO/CASSETTE2.13and/LWEEW

E29 95

RADIO/CASSETTE1-Band/MW

017 95M24

. .....

(38.95 M21M22TV GAMES

Atiltq1k.a

E13.95 ColourL5.95 BM' .26

TV GAME WITH GUN,

MAINS/DATTERVPortable Radio

AIRCRAFT RADIO

f9.95028

'k " 4.'/a.I tk

£19 95

M26

..:':.f19.135-'-'.-, M27

RESISTANCEDECADE UNIT(Exc.. to Mewl

S'

. .... i ........

(29.95

1029

METAL DETECTORc

Fn187'r

SHARP GE -1603MQuality Radio/Cassel

CAPACITANCEDECADE UNIT(Exclusive to Maud

.0

r 29 95

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£25.95

I

10....I

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ril M =tv.=W:.

CrliONICS TODAY INTERNATIONAL APPEL 1979

POWERTRANPS10002 STUDIO MODEL

FOR ELECTRONIC KITS OF DISTINCTION

COMPLETE KIT ONLY E1913.90 + VAT

READ THE REVIEWIN SOUND INTERNATIONAL DEC. 711

1.1m1 v -a 4JO 20W STEREO AMPL/PIER L33./0 4. VAT -

I EE

21111+2110 watt AMPlifIfil400VV rms continuous - 800VV peak!003% TH 0 at FULL power!PLUS all the following features too!

WIRELESS WORLD EPA TUNER ENE 20 4. VAT

LINSLEY NOOD CASSETTE DECN E79 60 + VAT

POWERT0AN SFMT TUNER E3S 90 VAT

WWII TUNER EE17 70 + VAT

OLIR CATALOGUE IS FREE. WRITE OR PHONENOW!

POWERTRAN ELECTRONICS

. APRIL 197

D9,770 digestLI [OR ANALYSIS

ELECTRONICS TOD, INTERNATION, - AP, 979

42S. ,, ,,,,

RIR

.... nnnnnn nnnnnnnn r.easmasssIces

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ELK, niCS TODAY INT DT.PTID , - APRIL 1979

f " - ," I-

rMIC110 CNimEsFROM THE INVENTORSOF MICROPROCESSOR

MUSICAL CHIMESNew price for the fioriginal

t-CHROMA-CHIME KIT24 tune model!

CuN the fantasticSuccess el the Prod .across Me World we are aMble to offer itat

Only £9.95 + MP IMPCornesCorriplete. POSOOOMerp Feihneepareiregg

Superticalainet Pa semponductorg

_r fulrydelaenenma.ual

TAAS 1000N -M111.002iA Microcomputer ch. available separaIefyreguded 24 tune spec devicesupplied.. data sheet and lull,guaranteed

New low price only £4.95 Inc.pap

A COMPLETE KIT FOR THE

NEW MICROCHIMEThis eas

OlIncludesMISIODOCuslom MPU ChinSoeco, Purpose cies,. casePretv drilled and mgenaed PCBMI transistors RehalOrs endCapacitors

n Full Wel mechanical gagsSrnan leave labelsIC SOCFelanOLOWspeaNerReally Low lance.

poly £8.95 + PSO pap

'P"."'","'PLAIP record,

.-_61;11101TIATF10111C:RONICS INTERNATIONAL - APRIL 1979

newsdigestOOMPH -UP n

OOPS AND ALL THAT ...1,1sco Lightshow - Dec

"r1

ra!ilgee"

Stage Dimmer March

STEVENSON imomas 7'sElectronic Components

SWITCHES

POTENTIOMETERS

KNOBS

MICROPROCESSORS

REGULATORS

THYRISTORS AND TRIACS

:gatatztoMad orders to STEVENSON IIloot ET,

236 High St, Bromley, Kent, BR11PO, England

news digestINFRARED EYES

ESE RAILWAY HOUSE, HARDHANI CROSSING. HOWL/ROUGH, SUSSEX

ELLC7RON. TODAY INTERNATIONAL - APRIL 1979

INTRODUCINGDUAL DRIVE MINIFLOPPY FOR PET!

INTERNAL MEMORYEXPANSION FOR PET!EXPANDAPEr

. VAT INV

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OHIO SCIENTIFICSUPERBOARD II

MI plus VAT

LOTUS SOUND, 4 MORGAN ST., LONDON E3 ASTel' 01-9613993 Telex 261026 Ann ,r

INTERNATIONAL -APRA I LA

NON -SUBSCRIBERSSTART HERE

D. I

Bridge StreetNerwel=eteerl

LECTRONICS TODAY INTERNATIONAL - APRIL 1979

AUDIO ANDTEST EQUIPMENT

CENTRE

LONDON S TEST GEAROPEN 6 DAYS A WEEK

5,^1- N srOCK MCP P t? 50 ea I

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NORMAN INSKIP;V:474:ay 10634) llllll 12 hnea/

FEATURE

POWER AMPSURVEYThe Americans would describe it as a 'crowded marketplace'. Power amplifiers appearalmost daily and the resulting choice can easily lead to confusion. Ron Harris attemptsall overview.

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what we have a ....der the two ampt I ars wh chd darr vela. the one on km

Our source for the I sten tests vas to he a SonyEL Elcaset machine wh ch gives reel to reel quaity of

ro.1=1.m"="yterrr'y 7anrCh7p=a1Odereo of equ pment such lona ous convenience is not

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T. rale ence arnpl e was a Lamson AP3 I

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The qua, ol construct,. was peewee), h Oh and muse Me ALI20s hare ra no trouble al all They drove therequired speakers Celest on KEF) reth nO apparentdress a. gave a see. )eehe ee, eeeeee) deem

Grimm CBIOSThere a not really a lot to say about Cr mson Elecir k thathes not .01 sa 0 a ready The r products aro wel

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FEATURE:Power Amps

TTI-A1616MTIIOT electronics truPs',2MZVOIT1111:7110"31111",nne,.ton th werb .ern TELEPHONE:01-W 370S

LOW POWER SCH0r11, and TTL CMOS BITS and PIECES

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:11.

ELEMIONICS 700a71,17EMPTIONAL - PPP, 1879

The latest kitinnovation!from

the quickest finingCLIP ON -capacitive dischargeelectronic ignitionin KIT FORM Smoother running // Instant alLaseaMor starting Coma:nal peak performance L y5,5il/battery /DMP .MS Irnproma accelaratioMtop speed OPSIIIIiIm fuel consumistiOn

BLOW THE af:F=Lne SOLD nipNASCOM I COMPUTER

1"1411;:12VATTACI:"E165 KITS IN STOCK:

BRITISH DESIGN.. HST SO...11

EXPANSION

SUPER -STRIPTHE UNIVERSAL BREADBOARD

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E ECIRIONICSTODAM1NTERNALIONAL - APRIL 1,79

ELECTRETAFOR A 0000 DEAL BETTER THAN MOST

ntett!IITT9=1.:,==ar

TWO DEPOTS TO SERVE YOU NOPTIII AND BOUT

ELECTRO I-VU LTD

PLEASE MENTION ETI

WHEN REPLYING

TO ADVERTS

-A Wilmslow-111 AudioTHE firm for speakers!

EyiFatt.::,":71Z

. .*. .

*AN,' -

WILMSLOW AUDIO Dept. ETI

PROJECT

VIDEOGRAPHTurn your colour television into a dual trace oscilloscope withthis UlIF colour modulator and video display generator.

Principle Of Operation

h line end a fixed.lengthhr4ght-up pulse

a twin trace. nd theSe

Zpectiwely 'U"rut::"triggered by a c pulse

generator. and .1 unher oemponents,enerate an eighaga Packg.andcolour change.

rcrer's7:17stZ"tape -recorders

Central, are provided for inven,^9

nd colour and swoching a

from William Stuart Systarn. Ltdwho Ned ie. PCB COPWng,,,at. produce a ready .11H/calomelThe heaw gauge anochsed facia plate

'"nkr;inatTdrs=entha id"..n

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e sy

nc)

to g

ive

anun

brok

en b

ackg

roun

d, a

nd a

djus

tR

V7

(fra

me

sync

) to

giv

e ve

rtic

alst

abili

ty. P

rovi

ded

that

the

TV

tuni

ngis

exa

ct th

e pi

ctur

e sh

ould

now

be

unifo

rmly

gre

en. I

f the

top

of th

epi

ctur

e is

red

then

adj

ust R

VB

(fra

me

puls

e w

idth

) fo

r be

stpo

sitio

n.A

djus

t RV

2 en

d R

V5

to g

ive

blue

and

oran

ge v

edic

al s

trip

es: t

hese

shou

ld a

ppea

r fr

om th

e le

ft as

the

I.

Inkg

;:rea

W7e

, iN

Mgr

Ale

fga

-rId

4,4

____

_

_

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y

la-

Fig

. 2 C

olou

r m

odul

ator

com

pone

nt o

verla

y.

PA

RT

S U

ST

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OD

ULA

TO

RR

ES

IST

OR

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ll U

MR

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24 3

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15.1

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13 1

4 17

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.31

22k

68k

CA

PA

CIT

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C7 C8

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este

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eram

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2 ce

ram

ic

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120p

C1C

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039

p pc

eram

ic

Cf3

880p

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330p

C15

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mic

C18

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yeer

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ed P

ox te

xt)

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ote

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ched

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rsIC

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018

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CE

LLA

NE

OU

SP

C13

10 p

enee

n, b

atte

ry d

ips

VH

F s

ocke

t

PRO

JEC

T: V

ideo

grap

h

Fig

. 3 1

/ideo

grap

h ge

nera

tor

circ

uit d

iagr

am

A ty

pica

l Vitl

eogr

aph

telly

pic

tum

Fig

. 5 G

ener

atin

g gr

aphi

cs w

ith th

e V

itlea

grap

h.

HO

W IT

WO

RK

S -

GE

NE

RA

TO

R

1(71

and

IC2

are

timer

s w

hich

gen

erat

efr

ame

and

line

sync

res

peC

tivel

y. 1

C3

coin

.bl

ocs

thes

e to

form

neg

allv

e S

YN

C a

ndpo

sitiv

e sy

nc T

. The

leng

th o

f the

fram

esy

nc p

ulse

I.ad

just

ed b

y te

st Il

iis is

nece

ssar

yIn

in th

e P

AI.

syst

em th

ere

mos

t be

an e

ven

num

ber

of w

hole

line

perio

ds In

a fr

ame

puls

e m

riocl

, oth

erw

ise

the

Ti'

sees

dei

..ode

r w

ill b

e ou

t of s

tep

at th

ean

of e

ach

pict

ure

scan

and

the

top

of th

esc

reen

will

tend

to b

e re

d `g

reen

rev

erse

d.A

udio

inpu

t sig

nals

for

the

right

han

dch

anne

l are

nor

mal

ly fe

d to

142

alte

rn.

ativ

ely,

if th

e "r

ight

Inve

rt"

switc

h is

oper

ated

, the

n si

gnal

s pa

ss te

nt th

roug

h Q

l.

Q2

driv

es :I

cla

mp

diod

e 1.

31vi

a C

h R

V2

(pre

set)

det

erni

ines

the

mea

n 1)

C v

olta

gew

hile

RV

3 (L

OC

AT

E c

ontr

ol)

glee

s a

fine

adju

stm

ent.

Gat

esI

tria

l 2 o

f IC

4 R

um a

mon

osta

ble

trig

gere

d by

pos

itive

syn

c pu

lse

Thu

s. th

esta

tt °t

each

line

the

outp

ut o

ffe

edba

ck lo

w. a

nd C

O p

rovi

des

posi

tive

pic!

. but

is c

lam

ped

Le a

n in

itial

valu

e of

say

3V

by

the

clam

p di

ode.

C9

now

char

ges

via

R9

until

gat

e I s

witc

hes

back

(et

appr

osam

attiy

4V

)and

the

mon

osta

ble

rese

tsits

eR N

ote

that

the

char

ging

is n

early

line

arov

er th

e ra

nge

3 to

4V

and

R9

can

be c

onsi

d.er

ed a

s a

cons

tant

cur

rent

sou

rce.

Sin

ce th

ein

itial

cla

mp

volta

ge is

mod

ulat

ed b

y th

e

udio

sig

nal.

the

nion

nsta

ble

perio

d q

also

linea

rly m

odul

ated

.A

t the

end

of t

he a

bove

per

iod

a se

cond

.fix

ed d

urat

ion

nnirc

ntab

le fo

rnm

d by

gat

es 3

and

4 is

trig

gere

d vi

a C

I I. T

his

prod

uces

pSiti

VP

pul

se w

hich

def

ines

the

osci

llosc

ope

trac

e. Q

4 is

an

emitt

er fo

llow

er w

hich

driv

esth

e M

odul

ator

with

Vid

eo (

brig

htne

ss)

and

colo

ur in

form

atuo

n. a

nd s

uppr

esse

s th

eha

ckgr

ound

by

pulli

ng 'X

' hig

h. L

ine

and

Fie

ld b

lank

ing

are

ensu

red

by R

I4, (

'13,

RII

and

C7

whi

ch e

xpan

d th

e lin

e an

d fr

ame

puls

es a

nd p

reve

nt tr

ace

gene

ratio

n w

hen

netv

sser

yT

he li

ft ha

nd c

hann

el is

iden

tical

, exc

ept

that

the

outp

ut d

rive

is to

a d

iffer

ent c

olou

r,an

d th

e im

ener

sta k

igna

gy is

ab,

ent.

QU

det

ects

pea

sls

(nn

Inc

right

han

dch

anne

l) pi

oyi

ded

thaz

,LO

UR

HO

LD b

asno

t bee

n se

le,te

dhy

se s

iana

l, m

e sa

mpl

edby

the

tram

, ..y

nc p

ulse

to m

oduc

era

nU o

m c

lock

oul

ve lo

t cw

t., IC

I,IC

gate

s th

ree

Cl t

he c

ount

er m

amas

with

the

trim

. sig

nal a

nd d

rivrs

the

Mod

ulat

orw

ith b

right

ness

(V

ideo

) an

d co

lour

Ito

b)st

ICS

is c

onne

cted

as

the

squa

re w

ave

gene

rato

r. p

hase

-lo

cked

to th

e pi

ctur

e sc

anby

the

nega

tive

fram

e sy

nc p

ulse

FS

.

Fin

. 4 T

win

cha

nnel

Vid

eogr

apM

1 au

dio

driv

er c

ircui

t.

SLUE

BEE

rite

SOUARE WAVE

ig. 6 Videograpb generator component overlay

Circuit boards completed andinWalled in the \Odeon,. chassis

No. its not something from outer space,

BUYLINESA complete kit of parts is availablefor this project from William StuartSystems Ltd, Dower House.Herongate. Brentwood, EssexCM 13 350. The PCBs remain theircopyright and will be available onlyfrom them. All components areavailable separately, and the PCBsare normally supplied as a "mini.kit' along with ICI -3 and readywound coils. See advert elsewherein this issue for prices.

pots are turned clockwise. Positionboth stripes centrally. then separatethem using the LOCATE controls. Atthis stage the line sync IFIV9) shouldbe fine.adjusted to give perfectcolour registration on the stripes.

IC7 may now be inserted (and thelink removed.) to give thebackground colour change function:the sequence being black, white,cyan. yellow, green. mauve, blue,red. ET

32 ELECTRONICS TODAY INTERNATIONAL - APRIL 1979

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ELECTRONICS TODAY INTERNATIONAL APRIL 197

Hobby 4t+0,244-4,4,,,4

Electronics

The May issue will be on sale on April 13th

ENTERPRISESRoom ET

POSTCODE .

""'""E' W'-=RONICS TODAY INTERNATIONAL - APPIL I SYS

FEATURE

Gm REVISITEDNothing to do with American car manufacturers Gm is in fact a throw -hack from the days of valves, now finding a new lease of life with up-to-date semiconductor devices. K. T. Wilson explains ....

Correct Generators

ELK-M.1[510D., tt-rEit tt,irttc, tot 1,,

not

d aoue wee C011ector and minertha, uStstor An equivalentcomponentS which

of way aS SOnte deviee

Ftg 2 li conStStS 0 aand .1

ro'neosk InT,Z,:n ".: - ao.ntne .oclne Stae et ',tea,. cur Zc::::=Vand Ina output restsi

Hoe sloes Ces nalp uall the I tme that en tve e

-seen se cometnea Os peeve sumer So. eseeSneF cel as sac se as ins earth line

owet supply there s a sm

for ACing the

load

tpritit ate COnCetnect theonnecled between collector and emitter

nto the aunts! nICIF.11. and the result IS Ftp3 ears e teroldress el seises Mose, corner OesCes 'coed es sere e, loss erc eeeoe e erne,

"''' iliRdEtE;1Simple Silicon

?iF11°.!.=s.'sntrs"::07'71:ttrVtftl:li;e'g:doa:I'm°::

=.'s=c'e'111=1=17i:ZITtn' lAonl°401r:'tnr:Irt rtne's1=leclk;!er*I'l '1%*: Vantldor

Vrl'olrestZ.=':C:178:elo=s7on'th:7hetqaTiZIa tra.s.sior amplifier iS 'oat GmR

11 il s as easy aS that why dOn 1 we see ,t Mai 1reM tYEIM

,on tran,siorA u nan,sto. forget a Im ol Me old 1 ormulae we once uSed in Calcudoesn hay. a constant yetue of On. ri " o..apt. rating the design al transistor amnhtiers The fact Mat

Gm is not conStant but vanes with the bias current ts

tr-Zevott

Os MieVer-atiVleediibeGAIXMOlood

Vleact ISTIIE STEADY MIAS,VOLTAGE ACROSS

Ebert Moll

A lew yea, hack though the Baer: Molt eq.ration was...teed You Ye never hmrd Vou nOt atone

eapia.n., Very briefly s an equation whiahImIcs the collector cnneni won the Vhe yalu%for a

'er'rnr :1'.otrergL"is'aVsnour=g tit?:,utt a, mathematreat sr.., You ma,' "'.. W."tre1we It repays close aliennon theogh OMaose most

'c'onTr.an't"Xg'Iwo'XinnetrnTarh:er:'7nu'cr6n7c:1them .S Ine Steady ems current IC a. the othet ist'^EMMt.re . hed.ons ternOere,". 'or the Ournoses ol the Elam Moll equation .$ rneaSured in the

around - 273 C Room tennOerahne7-erotOre around 2g3K In0 Pewees sign, the Kelvin

Gain

!urge outPut resis'an0".'"0

woe.° piaceol Gmllig 41 This makes thegamol

equa1ion is Ihe steady bias collector current a.SO 100 must De the steads OC voltage across rel. theload resistor Thts mak. selculattno the gon of pens..tor ampltf ter. with resteive was iNt new than fal/ingoll a log Pock value of volmge across theltaad testator

OV 40 and Ma, S OmMinn example we very ol ton design voltage amplilierS

sothal about 01thesuppre settage 00"MP. MtOM

arm you can eanect a voltage gain ol 40 ea 5=180trmes 010, helmee lt arm. elt Pg. amMests oa a

VOu don t or course expect to get a garn exact, ' 80

on load ,PS.S10., apart hOm anythum etSe but you re

anoMer stage of course Mai s another story You mayhave sel the gain ot Me first stage to 180 limes hut notB1101.16 oupui Signal en. uO usefully at the inpul of the

ELECTRONICS TODAY INTERNATIONAL - APRIL 1979

FEATURE:GM Revisited

Fig. 5. Calculatinghow much signal ispassed on to sub-sequent stages.

L

r(Ittk=,

next stage. Reason? The next stage has a rather lowinput resistance, and feeding signal from the collector ofone transistor into the base of another, even if they aredirectly connected, is rather like feeding signal through avoltage divider. There are, in fact, two ways of calcu-lating how much of the signal is passed on. One simpleway is to imagine a voltage divider (Fig 5) in which theload resistance of the first stage forms the upper resistorand the input resistance hie of the second stage. Thequantity h,, (on k ohms) is equal to h)))/G in, where h1, isthe current gain of the transistor, a quantity which doesvary between one transistor and another. For a transistorwithlh,-= 100, Gm set to 40 ft mA collector current) h.. is100 /40= 2 k5. If we feed this from a transistor with a4k7 load resistor. the amount of signal reaching thesecond transistor is

2.5352.5+4.7

of the signal at the output of the first This brings thegain of the first transistor stage down to 180 X .35 =- 63which is the sort of value we usually measure for onestage of a multi -stage amplifier.

With all this going for it, Gm, is coming back, folks.As Sam Goldwyn is supposed to have said, "sim plicateand add lightness- Let's hope we've 'added a bit oflightness today. Ell

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CLICK ELIMINATORPart two of the Click Eliminator article, presented here, is in fact a redesign of theproject leading to better performance and lower cost.

In the January issue of ETI wepresented a design for a clickeliminator unit. However, betweenthat issue and the time for theFebruary ETI - in which we were tocomplete the project we foundseveral disturbing inconsistencieswhich would have rendered thedesign's repeatability doubtful-toput it mildly.

These problems mainly concernedthe area around Q1, IC9 and ICI O.The biasing arrangement for 01, andits function within the circuit meansthat the adjustments are very verycritical indeed. Our prototypeoperated satisfactorily, especially inits breadboarded form, but was toodependent upon too many variablesfor us to be happy with the project.

Taking AimThe aim then, as now, was to presenta design for a unit which wouldremove the clicks and scratches fromdamaged LPs, without impairing themusic material contained therein.

Operation was to be indicated byan LED, and threshold of operationwas to be variable to make theEliminator flexible in use.

However, as we said, developmentwork has continued since initialpublication, and while we felt thatthere was nothing wrong with theaims of the project, our method ofrealising them left something to bedesired.

Change Of TrackAccordingly we are presenting herean alternative design, and

recommend our readers to constructthis in lieu of the design shown inPart One of the article. A comparisonbetween both circuits will show thisversion to be greatly simplified, andusing components which will makeconstruction cheaper.

For example the 570 has beenreplaced with a 4016, which isclosed to the signal for a short periodof time to blank the 'click' signal.

Fig 1. Basic block diagram for Click Eliminator Mk 2.

lx

ELECTRONICS TODAY INTERNATIONAL - APRIL 1979 41

PR

OJE

CT

: Clic

k E

limin

ator

ri1:-

,2',`

,7,',

1,60

Z7:

::,el

'7:,;

1,11

','Z

IT.::

::Trr

el'e

nd,V

:r "

no "

"'"'""

°

HO

W IT

WO

RK

S

The

full

circ

uit o

f the

rig

ht p

re -

amp

and

dela

y lin

e bl

ock

is s

how

n in

Fig

ure

2. th

ele

ft ch

anne

l circ

uit b

lock

is id

entic

al.

The

inpu

t sig

nal f

rom

the

pick

-up

is fe

dto

ICI a

. whi

ch is

wire

d as

a s

.10

inve

rtin

gam

plifi

er w

ith a

n in

put i

mpe

danc

e of

47k

.T

he o

utpu

t of t

his

stag

e is

fed

to th

e cl

ick

deltc

lote

tcut

laet

llcttl

hseh

tcht

sw

ired

as a

sec

ond

orde

r lo

w p

ass

But

ter-

wor

th fi

lter

with

a tu

rnov

er p

oint

of a

bout

10 k

Hz.

Thi

s st

age

also

has

a s

mal

lam

ount

of g

ain

in it

s pa

ss h

and.

The

out

put o

f the

But

terw

orth

fitte

r is

fed

into

inpu

t pin

-5

of 1

C2,

whi

ch is

a T

DA

1022

512

-st

age

char

ge -

coup

led

dela

y lin

e.T

he R

O-R

VI-

R11

-R12

and

RIO

net

wor

k at

the

inpu

t of t

he IC

eas

ed to

set

pin

-I3

at

abou

tI

volt

abov

e go

mnd

. to

ensu

rem

akm

nurn

dyn

amo:

. ran

ge o

n th

e de

lay

line

and

m N

esIn

to c

lass

A a

tm

inim

um li

stor

tinn

rhe

dela

y lin

e is

cloc

ked

to)

sym

met

rical

ant

i pha

sesi

gnal

s to

pin

, I a

nd 4

at s

few

hun

dred

kHz,

to p

rovi

de a

tota

l del

ay o

f abo

ut I

rnS

. yhcc

ttlyu

l of t

he d

elay

line

as

take

n. v

ia(4

. to

anot

her

seco

nd o

rder

But

terw

orth

filte

r 11

C3)

, whi

ch r

emov

es th

e un

wan

ted

high

freq

uenc

y cl

ock

sign

als

that

are

impo

sed

on th

e au

dio

sign

al b

y th

e de

lay

line,

and

the

clea

ned

-up

sign

als

are

then

pass

ed o

n to

the

clic

k bl

anki

ng c

ircui

t ,a

voln

me

cont

rol R

V2.

As

the

bloc

k di

agra

ms

of F

ig.

1

will

sho

w, t

he b

asic

rem

ains

unch

ange

d. T

he in

com

ing

audi

o is

del

ayed

by

a T

DA

102

2.lo

ng e

noug

h fo

r th

e ci

rcui

t to

dete

ctth

e cl

ick

and

gene

rate

a p

ulse

whi

chsh

uts

off t

he tr

ansm

issi

on g

ate

(401

6) a

s th

e 'c

lick'

arr

ives

.T

he w

avef

orm

s sh

own

in F

ig. 6

give

an

indi

catio

n of

the

timin

g of

the

circ

uit,

and

the

man

ner

in w

hich

the

blan

k pe

riod

is m

ade

to 's

trad

dle'

the

clic

k si

gnal

.

Circ

uits

and

Com

pone

nts

Fig

ures

2-6

sho

w th

e sc

hem

atic

for

the

Clic

k E

limin

ator

. Fig

ure

2 is

the

audi

o in

put a

nd d

elay

line

circ

uit.

Fig

ure

5 sh

ows

the

clic

k de

tect

ion

and

blan

king

pul

se g

ener

atio

nco

mpo

nent

s. In

puts

A a

nd B

com

efr

om p

oint

s A

and

B m

arke

d on

the

left

and

right

aud

io in

puts

resp

ectiv

ely.

Circ

uits

5 a

nd 7

are

the

outp

utbl

anki

ng (

and

bypa

ss)

and

syst

emcl

ock

resp

ectiv

ely.

The

latte

r is

refe

rred

in th

e au

dio

circ

uit s

impl

y as

()an

d Q

.

Con

stru

ctio

nT

he u

nit i

s as

sem

bled

ont

o a

sing

leP

CB

. and

so

cons

truc

tion

is r

eally

guile

str

aigh

tforw

ard.

Ass

embl

e th

ebo

ard

care

fully

, rem

embe

ring

to fi

tre

sist

ors

and

capa

cito

rs fi

rst,

and

ICs

last

. Soc

kets

are

bes

t use

d fo

r th

ese

devi

ces,

esp

ecia

lly th

e hi

gh c

ost

item

s. T

his

will

faci

litat

e ch

ecki

ngan

d se

rvic

ing

shou

ld th

is b

e ne

eded

.T

he e

asie

st p

lace

to m

ake

am

ista

ke is

in fi

tting

the

pola

rised

com

pone

nts

- el

ectr

olyt

ics,

dio

des.

ICs

etc

so c

heck

thes

e ca

refu

lly. I

t is

best

to b

uild

up

the

PS

U fi

rst a

ndch

eck

this

bef

ore

conn

ectin

g to

the

rest

of t

he c

ircui

t.

tOtW

o

Fig

3. C

ircui

t of t

he c

lick

dete

ctor

sec

tion

of th

e M

k 2

Clic

k E

limin

ator

. The

LE

D fl

ashe

sto

indi

cate

ope

ratio

n.

of

*r^

Ast

044.

0000

604.

0

Fig

4 (

a). A

bove

: the

wav

efor

m o

f the

Clic

kE

lillli

1101

0, b

lank

ing

puls

e st

radd

ling

the

clic

kw

avef

orm

, whi

ch in

clud

es s

ome

ringi

ng. F

ig4(

h). B

elow

: the

com

bine

d w

avef

orm

msh

owin

g th

e bl

ank

perio

d in

sert

ed in

to th

eus

ic. --0.

4040

0,11

0

HO

W IT

WO

RK

S

The

full

circ

uit d

iagr

am o

f the

clic

k de

-te

ctO

r bl

ock.

whi

ch in

corp

orat

es a

"cl

ick

iden

tifie

r,"

a th

resh

old

dete

ctor

. and

abl

anki

ng p

ulse

gen

erat

or, i

s sh

own

inF

igur

e 3.

A "

clic

k" o

r sc

ratc

h ha

s a

num

ber

ofun

ique

cha

ract

eris

tics.

It h

as fa

st a

ttack

and

deca

y tim

es, a

nd it

s ou

tis

con

se-

quen

tly r

ich

in h

igh

-fre

quen

cy c

om-

pone

nts.

Als

o, it

app

ears

to a

ste

reo

pick

up h

eed

as a

set

of r

ecor

ded

anti

-ph

ase

sign

als,

sin

ce it

cau

ses

pure

ly v

esU

ral d

ispl

acem

ent o

f the

sty

lus,

whe

reas

norm

al r

ecor

ded

sign

als

tend

to b

e in

phas

e an

d ca

use

pred

omin

antly

hot

izon

-ta

l mov

emen

t of t

he s

tylu

s. T

he E

TI C

lick

Elim

inat

or u

ses

thes

e un

ique

pha

se c

ha-

ract

eris

tics

to p

rovi

de it

s pr

imar

y m

eans

of c

lick

iden

tific

atio

n.In

the

circ

uit.

the

ampl

ified

pic

k-up

sign

als

are

take

n fr

om th

e ou

tput

s of

the

andc

hann

el p

ream

plifi

ers

(IC

la, F

ig 2

,ar

e pa

ssed

to o

ne o

r ot

her

of th

e tw

oin

put t

erm

inal

s of

IC4

in F

ig 3

IC4

isw

ired

as a

diff

eren

tial a

mpl

ifier

or

"sub

-tr

acto

r,. a

nd h

as a

gai

n of

abo

ut fi

ve o

n

each

inpu

t. T

he a

ctio

n of

this

IC is

suc

hth

at it

am

plifi

es th

e an

ti -p

hase

"cl

ick"

sign

als,

but

tend

s to

can

cel t

he p

re.

dom

inan

tly in

.pha

se r

ecor

ded

sign

als.

so

that

the

outp

ut o

f the

IC c

onsi

sts

of a

nau

dio

sign

al w

ith g

reat

ly e

mph

asis

ed"c

licks

." T

his

sign

al is

pas

sed

to th

resh

old

dete

ctor

IC5,

whi

ch is

wire

d as

an

open

-lo

op v

olta

ge c

ompa

rato

r, w

ith it

s ou

tput

norm

ally

at p

ositi

ve s

atur

atio

n.T

he "

thre

shol

d" le

vel o

f (C

5 ca

n be

adju

sted

via

pan

el -

mou

nted

con

trol

RV

3,so

that

the

outp

td o

f.the

IC ik

just

hel

dhi

gh th

roug

hout

the

pass

dge

of a

"cl

ean"

reco

rd T

hen,

eac

h tim

e th

at a

..cl

ick"

arriv

es, t

he o

utpu

t of I

CS

sw

itche

s hi

nega

tive

satu

ratio

n, to

pro

duce

a la

rge

nega

tive

-goi

ng p

ulse

. Thi

s pu

lse

is u

sed

totr

igge

r m

onos

tabl

e m

ulti

-vib

rato

r IC

S.

whi

ch h

as n

per

iod

of a

bout

5 m

S, a

ndw

hich

driv

es "

clic

k in

dica

tor"

LE

D I

onan

d dr

ives

out

put t

rans

isto

r Q

I so

satu

-ra

tion

for

the

dura

tion

of th

e 5

mS

pul

se.

The

out

put o

f Ql a

ppea

rs a

s a

blan

king

puls

e, a

nd is

fed

to th

e cl

ick

blan

king

circ

uit o

f Fig

4.

Lg?ral.o

71!

OV

Fig 5. Clink btaskieg niseait. ""'""'

HOW IT WORKSThe circuit of the click blanking block isshown in Figure 5. Circuit operation isfairly strMghtforwand. The output of eachchannel is taken from im volume control(Fig 2) and is fed through a times -teninverting amplifier (ICI or IC9). and isthen passed to one half of ICS, a4015 goadbilateral switch. In each channel. two ofthe internal ',witches.' of the 4016 arewired in series. and are normally held onby the high control signal from the col-lector of QI (Fig Q. but turn off for 5 mSwhen a blanking pulse arrives from theclick detector circuit, The output of eachchannel is then passed on to the outsideworld via a divide-hyten (sm..) MM.nuator network.'

Thus, dining "cleari" parts or the recordthe output signal from the delay line ispassed through the click blanking circuitof Fig 5 via the two series -connected on

The power supply is a straightforwarddesign based on a pair of threeterrninalIC regulators. which provide plus orminus twelve volt outputs. LED 2 is apanelmounted component, which indimess the power on state.

Next assemble and check theaudio circuitry. Make sure a signal ispresent at the level control RV2a andRV2b, Normally IC8 gates will be'open' and so an audio output shouldbe present at the phone sockets if allis well.

If no output is present, check theaudio through to RV2. and if a signalis present here, the fault probably lieswith IC6 and QI . Disconnecting thebase of 0.1 will restore output if thisis the case.

Over the ThresholdIn use the unit is connected betweenthe output of a record player pick-up

44

switches of ICS with negligible loss orgain, but in the presence of a ',lick" thetwo series -connected switches of IC8open I mS before the arrival of the clickand remain open for about 5 ins, thusreplacing the click with an imperceptible

Note in the circuit that the inputs of IC8are biased at half -supply volts to enable

the IC to pass signals with a minimum ofdistortion when operated trots a single -ended power supply. The 4018 IC suffersfrom a certain amount of control -signalbreakthrough; by using a times -tenamplifier before the input and a divide,by- ten attenuator after the output of theIC. this breakthrough is reduced to in.significant levels relative to those of thebasic audio signal.

V011,

Fig 6. Power supply fort. unit. aiDand the input of a stereo amplifier.Volume control RV2 should beadjusted so that no perceptibledifference occurs in audio soundlevels when the bypass switch isswitched in and out Pre-sets RV1and RVI 01 should be adjusted forminimum distortion on the Right andLeft channels respectively. Thresholdcontrol RV3 should be adjusted inuse so that LED 1 just operates in thepresence of a 'click'.

It should be noted that the relativeamplitude of a 'click- is proportionalto the velocity of the record track pastthe pick-up head. and decreases asthe head moves towards the centre ofthe disc: the threshold control may

ONO

consequently need o casionalreadjustment as the ecordprogresses through i s play.

There is no equali ation circuitrywithin our design, and so it cannotbe used in place of the preamp inyour system, it must be used in frontof n instead.

When playing damaged LP'ssimply advance the Thresholdcontrol. RV3 from its minimumsetting until the click is removed.This is the correct setting.

LED 1 will indicate the unitoperation, and it it flashes on musicalpeaks, chances are you have thethreshold control set too high and areremoving some of the signal as well.


PROJECT: Click Eliminator

ff=:1 1=111=1 1=1

6e as

C1,',

n :

BUYLINES

Being composed mainly of'standard' components, theEliminator should pose most com-ponent shops no problems. The LF356 is available from Watford incase of difficulty.

CD=1=

<7.7>

CD

<7",:, 4=3,ir-o-er

1=1,ni FROM

CDT,

CZ,1:711 4=/f==/ 1=1.

= C=11=11=3

Fig 7. Component overlay for th Click Eliminator unit. Note thatall the components bar the potentiorn mount on this PCP.The operation LEO is also best front panel mounted.

PARTS LIST

RESISTORS (at VeMr 5%)POTENTIOMETERS SEMICONDUCTORS

29.45 47kR2 470k

RV1RV2

dk7 preset100k log twin gang

ICI TL083IC2 TDA1022

114, 17, 23, 25,33.37, 39.44 10)

RV3 5k Lin 1C3. 5 LF 3581C4, 7 9 741

135, 6. 30, 3135, 36, 41 42 15k

106 555co1 4016

07, 10. 14.15. 16. 20,

ICI 0 4011IC11 4013

22, 23 34,43 100k CAPACITORS

IC12 780 2IC13 79112

RB 56k0.9 257

01. 2, 1503, 4. 9,

330P Pc941414"4 Ell BC 10901,04 19 4001 ,

Rif 6k8R12,27. 28 , 10, 16 -

C5T IO-On polyester.56p ceramic

"Coal. 2 TIL 220

R18. 24 4k7 co 1.00p ceramic

021, 26, 32 226038. 40 1k8 k2

C7CO

lOn polyester202 polyester

R46 1C1I-14C17. 18

4u7 25V electrolytic MISCELLANEOUS1000u 25V electrolyte240/12.12 trenslorrner 1100mA). rum

55RH channel i6etical

1s-tors

101-118 Mr C19. 20 410n polyester (34) end holder, case to sot. SPOT mains

ear -18 C21 22 47u 25V elecoolytm switch control knobs. PCB


PROJECT: Click EliminatorTHE SINCLAIR PONT Digital riluitiineter

Figs Clock generator ChM,.

HOW IT WORKSPins& and of the TDA 1022 delay line IC each channel via a buffer stage (IC10d ,Jrmust be presented with symmetrical ICI0c) and a D -type RIP -flop (ICI la oranti -phase clock signals for correct ICI1b), which provides the required anti -operation. The basic clock signal of a (ew phase drive signals (from the Q and Qhundred kHz is generated by a CMOS outputs) for the delay line The cluck

'astable muluvibrator formed by !Ma generator has SF decoupling provided hiseth cob. The clock signal is taken to CIA. which is mounted close to the supply

pins of ICIO and ICII.

%%Ma=

.stivaz,

Close up of theSocket wiring forthe Cock Elimina-tor. Keep... asclose to the boardsas possible, anduse sc eeeee dloads if this is M.possible, earthingonly one end of theSLAP..

46

Fig 9. Sometaldeal waveformswhich illustratethe timing of Mecircuitry withinthe general blockof the ClickEliminatorBlanking pulsewidth is fixed.

SINCLAIR DM235

SINCLAIR DM3500 DM450

KRAMER & CO

H & S ELECTRONICS

TRAINAMThe exciting new

TRITONPersonal Computer

EXPANSION BOARDS

:7;i:Or=intr'e:11=oIrv.00.11: .ode vOu o ' '^`

COMPUTER PRODUCTSNEW LOW PRICES

MICROPROCESSORS

VERO

TRAIN

Triton Kit Ene

Full dem. Ca;i4ue 30, SAE

MEMORY 9 SUPPORT

HOME COMPUTING

, TN a 1 oN o ON ow poo

.Am =NTS a.LOMB NWIia 402 OM

12 CUM STRUT

P.FI OOP AMMER

pmicRopion-Aupm,parl4110

weihi

MICRODIGITAL LTD.,2.?,,BEWORfigOITJREETTel' 051 218 0707

TIONAL - APRIl 979

ETIPRINTS are a last new aid for pro- ETIPRINTS are made from our originaldiming high quality printed circuit artwork ensuring a neat and accurateboards. Each ETIPRINTS sheet con- board. We thought ETIPRINTS weretains a set of elCh resistant Mb down such a good Idea that we havetransfers of the printed circuit board patented the system (patent numbersdesigns for several of our projects. 1445171 and 1445172).

LISTEarlier earners re available.

I1,

WORKSLey ilown the 'TIMM, andrub over with son pencil

:IT =7: 7;:board. Peelof,. flocking sheet

you'. been bit careless

b..s!

SUS LINOSORDER TOD.

75p INC P IL P49

NO DISCO SYSTEM ISCOMPLETE WITHOUT...

Mega=ELFLTRONICS '004Y INTERNADONAL - 1979

116

,,,,,,,,, ,:,1:. i ,,,* .. ......,,---

S IlDUSJDWg! --i_

data sheet

Operational Amplifiers pp Amps]

Audio AmpIdlers

Multipliers

Oscillators

CHART I OP AMP - ABRIDGED PERFORMANCE

U., eat

Comments

TM T 3. `t. 0 25 50 a 03 50 5

997 2 70 NPN 1 0 25 100 +18 90 5 60.03401mercenms0b00

991 2 70 NPN 10 0 5 100 +18 90 5

741 2 80 NPN 1 0 6 106 +18 90

748 t 120 NPN 10 0 5 103 222 90 5 0 00000,000.010.1001

300 2 1 5 NPN 3

° 9 'iitri:=Z;177:Ze70.00319 3 150 NPN 15 50 106 +20 100 5

707 2 80 NPN 1 0.5 106 +113 90 0 6000006,0.1.0000001498 80 NPN / 0.8 103 +18 90 04136 0 5 00 PNP 3 1.0 110 +18 100 039809001

Curreniinputs

30 Currentsinks

2.5 0.5 70 +18 - 0 belen.in,rnaiw

924 2 06 PNP 1 0.5 100 +30 7°

9409 2 150 PNP 1 1 2 100 +38 9" )

FDA1 30 Nell 1 0 5 103 SIB 90 0 I

52 ELECTRONICS TODAY IN7.19.109111. - APRIL 1979

NEWS

"777 rz.zrx...z=

'117 zr..4=::::-

'1'1311

11=

1,7

zgn

i11

' -°"

EGG Or PAIS - MGM PRINIMMANC6

FfL,Comments

RG7S9 2 4D PNP 3 1 110 +18 100 °

G739 t 300 NPN 10 1 86 +18 90 0

. +20

applicable WOG.WIG 8 0.005 IN (WET 15 10 110 +16 90 ,r,157,76;62,FFiz....t.

C0140 8 0.010 N1OSFET 4.5 9 100 +36 90 :74=7'4=4 66C96169 6 0.005 MOSFET a lo als so e t=1;,..7,6;=,6.6';:,,REMRC4521

2 400 NPN 10 35 96 822 100 5

CP3080 0 4 NPN 2 50 8- 18 110 S

C0.6094 0 48.00 N N

30 50 1"RAN 15 0.4 JFET 3 13 83 4113 70 S ,., me

71.0111 15 0 4 JFET 3 13 83 -P 18 '° Z4= 741" F.77992 15 0 4 JFET 3 13 83 8-18 70 8 1123

0 4 3 13 83 70 P

11014 0 4 J'F'E'TT 3 13 83 -.118 70 320


TELEPHONE CALL TIMER Submitted by Mr A. M. Tucker el Dorchester.

ia

P.a.. t. Call 'timer circuit.

This new feature is open to all our readers. Itexists as a showcase for projects YOU have des-igned and built. We pay full ETI page rates for

any designs we publish. We must stress thatthese designs must have been built by you. Tofurther this end, we are giving preference tothose which arrive at our offices with photo-graphs, or which can be photographed by us.

Initially a simple draft outlining theidea behind the project and what the unit

can do is all that is required.> Photographs should be included at

this stage.

J

Write to'Readers De-signs,' ETIOffices, 25-27Oxford Street,London, W1 R1 RF.


(A DIVISION OF GOTHIC ELECTRONIC COMPONENTS LTD)

PO Box 2908 Hampton Street

TELEPHONE:MAIL

ORDERELECTRON/CS Birmingham B19 3JR 021.233.2400 ONLY

ALL PRICES IN PENCE EACH UNLESS OTHERWISE STATED

LLECTF N CS TODAY INTER,TIONAL - APRIL 1979

ACCESS FREEPOST ON ORDERS GMT ELECTRONICS BARCLAYCARD VAT INCLUSIVE PRICES Freepost CASH ADD 30p P&P Birmingham B19 1BR CHEOUE 24 HR TELEPHONE ANSWERING SERVICE z_

CLOCRADIO

111.="MD

£20.50

LADIES DIGITALLCD WATCH ALARM

£9.95vox 1

fia,...,,

£8.95--v. of VAT on0 Ponagel

immT4iLVi- AlrDIGITAL ALARMALARM MK2 CNRONO LCD

LCDCOMORO

£12.95 £10.50 E27.95

010117.1. ALARM CLOCK MI12 1.

ftvc,-nr-

ELEUROMCSTODAYINTERNATIONAL-Ain

Put Fluketo the TestA Digital Multimeter on 14 days approval

'FLUKE'

1!!!!!MAiiii

E3 =

L _J

PROJECT

AMBUSH! is bound to rate as the most fascinating, exciting, and addictive space gameof the year. It gives visual and sound effects of a space battle. and is loaded withrealism. Impress your friends land enemies) by building this unique and fascinatinggame.

AMBUSH. soacegarne

rvKZZnZI':=rni'o'rZt$:=45eh:hv a fleet of Surto. craf t The craft

=c:O=tk:e7:C1':[17:aVan:

tOtvOPMeen nOMOilt and hve seconds

tenet ...one el low [ref btolion1

fare

2rta'-o'kt:;:-"''."111;11VE1=

:==ca:Wer:17:t2Te"sn't:rM. of game chosen A Of It gan.

gz.741417,1==.1

sound And Light

ELEC-rtOVCS TODAY orrf Pa lots. - APRIL 1479

101 volumerho ef loos are also quite

impress.. The attacks are 00,4n by

form of a croM wth at.e Of var.,Wr,s The of.. arm representsthe 10tward Mack quad.. at.

...range S Thelower arm reOresenis Ole aft allat.

,F0 s the portant! starboard...5eact,CO.O.s. so yeffew LED s .the centre onne voss ,arl LED

Science ProjectAmbush! is a CMOS based design ofconsiderable technical interest, andshould make an excellent educationalproject for schools and colleges. Ituses seventeen IC's plus a couple oftransistors. The IC types range fromsimple NAND and NOR gates tocomplete decade counter -decoderchips, and include flip-flops. datalatches. 12 -stage ripple counters.and multiplexers.

Playing The GameGame Stan. The game starts assoon as power is applied to itscircuits. A game can be restarted bypressing the RESET switch.

Attacks:(1), The game can be set for playagainst either ten (a DEM or ahundred (a CENT) attacks.

(2). Attacks come at randominterval, variable between noughtand approximately five seconds.

(3). The quadrant of each attack israndomly selected. except for thefirst attack of the game, which always

ETI ir.,,a4vaii

111

comes from the aft quadrant(41 The speed of attack can be

pre-set by the player to suit skilllevels. A 'respectable' attack speed isequal to about 50 mS per LEDdivision on the quadrant attackindicator.

(5) At 'respectable' attack speeds.the player has approximately 250mS of attack warning on the forwardquadrant, 300 mS on the port and

*0 0

ID a IDnwo ooo ir:**

.......

starboard quadrants, and 350 mS onthe aft quadrant

(6) Attacks on the aft quadrantare accompanied by a full volumestaccato sound. Port and starboardattacks are at reduced volume. andthose from the forward quadrant aresilent

(7) The accumulated number ofattacks is registered on a 2 -digitdisplay throughout the game

HOW IT WORKSSIMPLIFIED BLOCK DIAGRAM OFTHE AMBUSH GAME

The heart of the unit is the 'DisplayMatrix Driver and Logic' block. which inreality takes the form of a 4017 decadecounter with ten decoded outputs Out.puts Ito 7 of the counter ale fed to theLED display matrix. and outputs 6 to it areselectively fed via a multiplexer to theGAME LOST indicator block and to theCI.00K DISABLE pin of the 4017. Theinput of the 4017 Is derived from s clackgenerator via a gate. which to turn iscontrolled by a simple START -STOP(Reset .Set)blotable.

The operating sequence of the abovesix blocks is fairly simple. Initially. theblstable Is in the STOP mode the gate Isclosed. the 4017 Ole the RESET state. andall LED's in the display mama are off. Atseine randomly determined timeSTART pulse 0 fed to the listable thegate opens. clock pulses start so reach the4017. and LED's are oequentially switchedon in one of the arms of the displaymatrix. If the gate remains open. one ofthe selectively chosen 6.7.S outputs of theIC eventually goes high and operates theGAME LOST.indicator and disables theclock input line of the 4017

Alternatively. the bistable can be set tothe STOP mode before the game term.,ales by operating the appropnate FIREswitch. In this case the bauble closes theclock pte. and the 4017 resets to the zerostate A- new sequence of operations startowhen another random START pulse fed

to the Input of the tastable. Nate thatoutput I of the 4017 is fed to the ATTACKCOUNTER. so that the counter advancesby one count each time the clock genera

fit

Figs. to and b. Sim-phfied mock diagramof the Ambush game.

H

Fig. ,

-a

for gate opens, fhe game ends shortlyafter the attack counter reaches its full let10 or 1001 state, at which point the GAMEWON indicator circuits come into opera.non.

The START signal to the listable isderived from the random delay generator.which zo integral with the FIRE switchcircuit,. In each attack, the appropriateoe of the four FIRE switches is selecfinely coupled the STOP side of thc

ELECTRON:CS TODAY INTEPherlOhe:_ - APRIL 1979

PROJECT:Ambush

(debt) This boardcarries LED displaymatrix drivers,multiplexers andlogic, plus audioand powerconnections.

Defence

(a). The player has four FIRE buttonsfor defence. The buttons are markedF (forward). P (port), S (starboard).and A (aft). To stop an attack. theplayer must press the FIRE buttonappropriate to the prevailing attackquadrant. before the attacking vesselreaches its target (the red LED at thecentre of the display) A correct firingis accompanied by a rasping sound

(left) ICs 2 and5-11 mounted

an Ambushacs.

No sound is produced if the wrongbutton is pressed.

(b). The ship has sufficientammunition to fight off attacks only ifeach FIRE duration is limited to about100 rnS or less. Thus, there issufficient ammunition for about onesecond of continuous fire in the DEKgame, and ten seconds of fire in theCENT game. The ammunition state isshown on a register throughout thegame

(c). When the correct FIRE buttonis pressed, the rate of ammunitionusage is directly proportional to thetotal number of FIRE buttons that arepressed at that time. Thus, if all thefire buttons are pressed at once, theammunition supply will exhaust in0.25 seconds in the DEK game or2.5 seconds in the CENT game. Theaudio frequency of the FIRE sound isproportional to the rate ofammunition usage. When theammunition store is exhausted, theplayer has no defence, and loses thegame after the next attack.

Game Lost. The player loses thegame by having his starship hit by anattacking suicide craft. When thegame is lost the red LED at the centreof the attack quadrant indicator turnsoff, and simultaneously a louddroning noise is generated and a redGAME LOST LED flashes on thecontrol panel.

Game Won. The player wins thegame by defeating all attacks. AtGAME WON a green LED illuminateson the control panel. and a coarsebeating or throbbing sound Isgenerated

!listable On a multiplexer and a qmulated

activates the correct switch: thefrequency of thetfire' cooed is determinedby the FIRE RATE SELECTOR circuit.and Is proportional to the 50151 number ofFIRE snitches preeed at any given mnMen(

The output of the fire sound generatorurea to Mite the ammunition register.

which counts and gives a visual readoutof the total number of cycles generated.The sound it also used to generatelatched random 'select' code for the fourmulltplexers that are used in the game.These multiplexers are used for FIRE


switch selection, for LED Display Matrixline and line length selection, and todetermine the audio levels bf theATTACK tarot

The ATTACK. FIRE, WIN and LOSEsound signals are all ted to a simpletwo -transistor audio amplifier whichdrives a 40 ohm output speaker,

63

HOW IT WORKSRANDOM DELAY and 'FIRE SOUNDGENERATOR, plus 'FIRE' RATESELECTOR and FIRE SWITCH MULTI.PLIDCER

THIS IS probably the most complexMock' in the entire game, because mostof Its individual sections are interdepen-dent. Fig 2 shows the circuit diagram ofNis major 'block'.

THE TIRE' SOUND GENERATORLet's deal first with the 'FIRE SOUND

GENERATOR. IC2 d one half of a 4052dual 4 -channel multiplexer. This connectsouselected one of its four inputs to its

tput. depending on the 'a - b' binarycode signal that is fed to its 'select' (pins 9and 10) terminals. Thus, when the appro./Mate one of the four FIRE switches ispressed. a logic -1 signal appears at outputpin -3 of the multiplexer. This signal isiebounced' by R6 -C6 and R7. and ispassed to the signal input of the INHIBITGATE formed by IC3,3 and IC3i4.

It passes signals only when itsGALE input is at logic -0: pin -1 is the 'G'terminal of this particular gate, and is tied

grefafid vie RS but can be driven highby the outputs of the LOSE and OUT OFAMMOdetectors. The gate thus passes onthe FIRE switch signals only when die

game is not lost and the ammunition store

Theis not exhausted.

output of the inhibit gate is used toactivate a gated TIRE' sound oscillatordesigned around IC5,3 and IC5:4. Themain timing components of thisosultator are C2 and RI2 to RI5. Thesetiming resistors are connected via ICI,which is a 4016 quad bilateral switch.which has each of its four internal

witches' activated by one of the fourFIRE switches: these internal switchesaxe Connally open. and close when theirappropriate FIRE switch is closed.

Thus. the complete action of the 'FIRE'and generator is such that a and is

produced only when the 'correct: FIREswitch is pressed, and only when thegame is not lost or the ammunitionexhausted. The frequency of the sound isproportional to the total number of FIREs,vitches pressed and varies from about800 Hz for one switch, to about 320 He forformeitcn-4 h

output of the 'FIRE' oscillatoris low in the normal quiescent state, andits signals are passed to the input of anaudio amplifier for sound effects, and alsoto the inputs of the ammunition registerand the Random Delay generator. Aninverted output (normally high) is alsotaken from the pin 3 output of theoscillator and is fed to the WIN LOGICcircuitry. Note that the gate Input signalof the oscillator is also fed to the STOP

side of the bistable and to the RESET pinof the display matrix driver. so that IC12is reset each time the correct FIRE switchis pressed.

THE RANDOM DELAY GENERATORThe heart of the random delay genera.

tor is IC4, a 4017 decade counter with tendecoded outputs (numbered 0 to 9): the 'Poutput of the counter is coupled to theSTART side of the bistable vianormallyON inhibit gate The clock inputto the counter is derived from a slow(about 2 14z) oscillator (ICS- I and IC5/2)and from the 'FIRE' oscillator output viaan OR gate formed by DI -132 and R3.

Whenever the correct FIRE button ispressed during an attack a logiml signal isfed to the '0' (pin 131 terminal of theinhibit gate, which bums off and blocksthe signals from the 4017 counter.Simultaneously. fast clock signals are fedinto the counter from the 'FIRE' soundgenerator. Consequently. when the FIREsynch is released and the inhibit gatereturns to the ON state the counter is anunknown or random number of stepsfrom the 9' count (which is the one thatprovides the START signal to the hist-able). Clock signals are th fed to thecounter from the slow oscillator onlyuntil. after a delay that is infinitely vari-able from zero to about five seconds, thecounter reaches the '9' stale and feeds a.START command to the bistable.

Fig. Z. Circuit diagram of random de-lay, fire sound generator, fire rateselector and fire switch multiplexer.

HOW IT WORKSTHE HISTABLE, CLOCK GENERATOR.'ATTACK' SOUND MULTIPLEXER.AND 'GAME Lost INDICATORSTHE BISTABLE is a simple R -S type,made from a pair of NOR gatm(1C9/1 and1C9,2). Its 'START' input is derived fromthe random delay generator via C4, and'STOP' inputs are obtained from the'FIRE logic or theGAME LOST detectorcircuitry via the Dl.D7-R30 diode ORgate. The rift output of the bistable isnmally. high, but goes low in the"START mode. and is fed to one input ofthe IC10,3 NOR gate, which provides theclock Input signal to IC12 (the display.matris counter -driver). Theother input ofthe NOR gate Is obtained from the

variable.speed CLOCK GENERATOR(IC10/I and ICIO.,2) or from the WINDETECTOR circuitry via the D4.D5-R28diode OR gate.

Thus, input pin -6 of the NOR gate isnormally high, and its output is lockedlow, so it is unable to pass clock signals.When a 'START' signal is fed to theMstahle from the random delay genera.tor. input pin.6 of the gate is driven low.and it does pass clock signals. The gate isturned off again when a 'STOP. signal isfed to the histable from the 'FIRE' logiccircuitry. Note that the gate gets lockedNo the off state if a logic." signal is fed toits pin.5 input from the 'WIN' detector

134). or if a logic -I 'GAME LOST'

signal is fed to the 'STOP side of thebistable via D6.

The IC10/I and ICI 0/2 clock generatordetermines the speed of any attack, andIts frequency is variable via RVI. Theclock signal appearing at the pin -II out-put of the IC10,3 NOR gate provides thebasic 'ATTACK' sound of the game. Theamplitude of this sound is determined bymultiplexer IC212 and resistors R31 andR32. Attacks from the aft quadrant are atfull volume, those from port or starboardare at reduced volume, and those from theforward quadrant are silent.

The 'GAME LOST indicators use fourNANO and one NOR gates: their basicinput signals are obtained from pin -13 ofIC12. which is normally low but goes highunder the game lost condition. 103,3 uwired as a simple inverter, and drives the

LI, NIC.- 100,- URN,: 1-L- AFFIL 1

PROJECT:Ambush

Fig. 3 Circuit diagram of ammo register, tendon, muniplex codegenerator and latch with the reset line control.

THE AMMO REGISTER. RANDOMMULTIPLEX CODE GENERATOR ANDLATCH. AND RESET LINE CONTROLTHIS BLOCK is relatively simple in itstheory of operation. IC7 is a 404012 -stageripple counter, and takes its clock inputfrom the output of the 'FIRE' soundgenerator. ICS Is a 1013 dual D flip-flop,which iserired as a dual data latch with Itsclock signal taken from the output of thebistable and its data taken from the 51 (2) and Q2 (04) outputs of IC7. Thus.whenever a FIRE button is pressed andthen released 1C7 sets randomly deter.mined states on the data inputs of 1C8, thenext time that the output of the bistablegoes high (as an attack begins, on receiptof the bistable START command) thesestates are latched Into the 4013 and are

HOW IT WORKSpressed on to the games multiplexers as a2 -bit ornery code.

IC8 h yet another 1017 decade counterwith ten decoded outputs. It has its out-puts fed to a vertical line of ten LED's,which act as the ammunition register.The '0' output of the 4017 sues to the top(FULL level) of then.. and the '9' outputgoes to the bottom (EMPTY level) of thehne. The '9' output also goes to the inhibitgate controlling the 'EIRE' oscillator.preventing the oscillator from workingunder the 'ammo exhausted' condition. Atthe start of each game the counter is resetto zero. so that the line of LED's indicatethe FULL state.

The clock input of the counter Is takenfrom one of the outputs of the IC7 ripplecounter via SW2a. When SW2 is set for a

red LED at the centre of the games maindisplay matrix. This LED is normally on.beet` oes off when the game lost.

(CI 1, I and ICI 1/2 are wired as amedium -speed gated astable. which pro.vides the 'GAME LOST' sound output viaDO and 934. and 1C11,3 and 1C11,4 are

wired as low -speed gated astable. whichdrives a red 'GAME LOST' LED. Bothpstables are normally off. with their out-

uts low. Under the 'GAME LOST con-dition both astables operate, the'LOSE' sound is generated and the 'LOSE'LED flashes on and off.

Fdte", (;:ZAIVITTArITZ:.tor.Fig. 5. (right) Bistable, clock gen.,'ATTACK' sound multiplexer and'GAME LOST' indicators.

DEK (ten attack) Same the Q7 (. 1191output is fed to the clock input of ICEgiving a clock signal of about 6.2 Hz whena single FIRE button is operated, and thuscausing the register to empty in about 1.5seconds When 5W2 is set for a CENT(hundred attack) game the 510 (0 10211output Is fed to ICS. giving a clockfrequency of about 0.8 Hz from a AngleFIRE button, and causing the register toempty In about 11.2 seconds. Thus. to win

DER ame the avera FIRE durationmust beg limited belowge 150 mS in eachattack, and in the CENT game it must belimited below 112 mS.

The games main reset line is activatedautomatically at switch -on via C8 Theline can be operated manually at any timevia RESET button PBS.


1111.11111111

Fig 6c Audio amplifier.

LED DISPLAY MARTIX DRIVERS.MULTIPLEXERS. AND LOGIC, PLUSAUDIO AMPLIFIER AND POWER SUP-PLY CONNECTIONS

THE MAIN PART of the LED displaymatrix is made up of four lines of LED's.arranged in the forrn of a cross. The upper(Forward) line is five LED's long. thelower (Aft) line is seven LED's long, andthe other two lines are each six LED'slong. The individual LED's in each hoe areselected by IC12. a 4017 decade counterwith ten decoded outputs. and the linesare selected by multiplexer IC13/1. Notethat diodes 015 to D25 are used toeliminate sneak paths in the matrix, andensure that only a single selected LED

HOW IT WORKSturns on at any one time. Eigure6b showsthe positions of the LED's in the actualdisplay. Note that LED t t, at the centre ofthe display, is normally on and representsthe players own vessel.

Prior to the start of each attack IC13 isin the RESET state, so all LED's in thematrix (except LED II) are off. As soonas an attack starts.IC13/1 selects a line oflength 'a' in the display matrix. and

connects the 'tie l' output of ICI3to its own pin.I3 'clock disable' terminal.Thus. when an attack starts the LED's inthe selected line turn on sequentially andrun towards the centre of the cross' if aRESET signal is fed to pin15 of IC12 fromthe 'FIRE' logic circuitry before the 'n I'state is reached the attack is defeated if

6b. Line selection.

Fig. 6d. Panel LEO displa,

the attack is not defeated. pin.I3 of IC12 isdriven high as the counter reaches the'n I' state. and all further clock signalsare inhibited and all GAME LOST indica-tors are activated.

All sound effects signals that ar.egenerated in the game are digital in form,and are fed via gate diodes andamplitude.determining resistors to thesimple QI.Q2 audio amplifier stage. which

The amplifier directly drives a908 speaker. which has transient limitingprovided by Olt

The game is powered by a 12 V batterysupply. and typically consumes 50 mA to150mA of current, depending on the stateof play. Readers can. if they wish. powerthe game via a Ample mains adaptor.

RIR253. 8 9. 10. 11. 31. 40. 48R4R5. 26. 28. 29, 30. 39Re. 16-25, 36. 37. 47R7, 12,13.14.15R27R32R33R34, 41.42. 46R36R38R43R44,45R49.62

PARTS LIST66113 SEMICONDUCTOR390k ICI22k IC2, 1310M 1C3, 9, 10414 IC4. 6. 12IS IC5, 17. 111006 IC]330k ICEI, 16648 IC14, 15680k10k2M2270833R11454708

POTENTIOMETERRV1 IMO

CAPACITORSCl. 5,6 7.8.11, )4.15C2. 3, 4, 10. 12, 13C9

100010n150n

401640524001401740i1434040264013

NOTE All CMOS &summate B Series.

01 BC10902 8FY50014 184001All Other diodes are 184148LED 1-37 are standard 0 2in dmLED 7 segment displays are commoncatnocle 0.3in

MISCELLANEOUSL.51 21n 4OR5 olISPST push buttons1 oft SPST latching ono button1 off DPDT min. toggleEl off oPt12 on 4 section battery holderscase tO SAllt

BUYLINES

The case we used for theAmbush project is availablefrom Boss Industries. Fulldetails next month. Sincepanel layout is not critical,inventive ETI readers may beable to come up with theirown hardware designs. Allthe ICs are common types,available from most com-ponent mail order firms.

If you think you are likelyto spend every waking hourzapping the starfleet, it'sworthwhile investing in amains adaptor, availablefrom your local Tranny shop.

ELECTRONICS TODAY INTERNATIONAL - 1979

PROJECT:Ambush

THE ATTACK COUNTER AND GAMEwon detector and indicators

THE 'r OUTPUT of 1C12 (the displayrnatnx driver) briefly goes high at thestart of each attack. This 'I' signal pro.vides the clock signal to the 1C11 -1C15ATTACK COUNTER. These two IC's are4026 decade counteis with decoded out.puts suitable for directly driving commoncathode 7 -segment LED displays at lowpower levels. The two counters arecascaded. to give 00 to 99 indications'

HOW IT WORKSleading zero suppression is not used in theCOLIMA,

The 'GAME WON' detector is designedaround IC16. a 4013 dual D flip.flop. endICIOol, a NOR gate. IC16/I is connectedas a bistable divider stage. and is clockedvia one or other of the attack counteroutputs. The action is such that its Qoutput is normally high, but switches lowat the stan of the 10th attack in a DEKgamor the 100th attack in a CENT game.The Q output is fed to one of the inputs ofthe IC10/4 NOR gate, which has its other

Fig. 7 (left) Circuit diagram of display drivers. inultiplers and logicwith audio and power connections.

Fig. 8 (below) Attackcounter and 'GAMEWON' detector and int,cators.

input provided from the normally -highoutput of the IC5 'FIRE' sound generator.The output of the NOR gate is fed to theSET (pin8) terminal of 1C16.'2. which Wwired as an R'S flip-flop. Both bistablesare reset at the start of each game.

The action of the complete 'GAMEWON' detector is such that 'FIRE' signalsare fed to one input of the NOR gate eachtime a 'FIRE' signal is generated. but areunable to reach IC16/2 until ICIO/1changes state after the start of the 10th(m a DEK game) or 100th (in a CENTgame) attack. at which point the Q Outputof IC16/2 goes low and drives green 'WIN'LED 37 'ON' via 1C9o1. and the Q outputgoes high and activates the 'WIN' soundgenertor.

The 'WIN' sound generator is designedaround IC17.and consists of two virtuallyidentical inediumfreguency gated ast-able multivibratorg which am operated inparallel and have their outputs fed to theaudio amplifier via the D26.D27.R46diode OR gate. Because of inevitableslight differences in timing componentvalues. these two eatables oscillate atslightly different frequencies. and pro-duce a coarse 'beating' or 'throbbing'sound when they are activated by the'WIN' detector.

I=I

Next month we conclude the project with fullconstructional details and component overlays. Inaddition we'll show you the act of inspired heroismwhich led to the saving of the starship Eatyeighand the designing of this project! For those who toget started the Parts List and circuit diagramsgiven here are complete.


new books onELECTRONiCS

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ELECTRONICS 100,1 INTERNATIONAL - 107

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CIRCUITS

No2

ORDER FROMSnook. Mo... Ltd 25.27 Word Street London WIR I lir

from ETIELECTRONICS 700,19 191,9,10 - 9,1111 19,,

3080 CIRCUITSThe 3080 is not a run of the mill op amp. These ten circuits from Tim Orr showyou why.

The CA3080 is known as an operational transconduct-ance amplifier. (OTA). This is a type of op amp, the gainof which can be varied by use of a control current, (1A8c).The device has a differential input, a control input known

Voltage Controlled AmplifierThe CA3080 can be used as a gain controlling device. The inputsignal is attenuated by 51. 52 such 'het 20 mVIIIP m... Ioapplied to the input terminals. If this voltage is much largerg, thensignificant distortion will occur at the output. In fact. .isdistortion is put to good use in the trlangle-to-oinewave con-vener. The gain of the circuit is controlled by the magnitude ofthe current lase This current flows into the CA9080 at pin 5.which is held at one diode voltage drop above the -Vcc rail.If you connect pin 5 to 0 V. then this diode will get zapped, (and

Vibwill the ICII The maximum value of Mc permitted is I ma ande device is linear' over 4 decades of this current. That is, the

gain of the CA3080 is 'linearly' proportional to the magnitude ofthe Ion current over a range of 0.1 on to I mA. Thus, bycontrolling losc, we can control the signal level at the output.The output is a current output which has to be 'dumped. intoresistive load (115) to produce a voltage output. The outputimpedance seen at IC1 pin 6 is 10k IRS), but this is 'unloaded' bythe voltage follower {IC2) to produce a low output impedance.The circuit around IC3 is a precision voltage-tomurrent convenerand this tan be used to generate 1.4 When Vin (control) ispositive, it linearly controls the gaM of the circuit. When it isnegative, loeC is zero and so the gain is zero.

This type of circuit is known by several names. It is a voltagecontrolled amplifier. (VCA), or an amplitude modulator, or a two

70

as the -Amplifier bias input- and a current output. Itdiffers in many respects from conventional op amps andit is these differences that can be used to realize manyuseful circuit blocks.

SIGNALINPUT

- Vcc

V

C/OnNTROL /Ns' ov

OUTPUT 14 VP. itt0 00

quadrant multiplier.One problem that occurs with the CA3080 is that of the 'Input

off set voltage'. This is a small voltage offset between its inputterminals. When there is no signal input and the control input isvaried a voltage similar to the control input will appear at theoutput. By adjusting R VI its possible to null out most of thiscontrol breakthrough.


FEATURE

Triangle To Sinewave ConverterBy overloading Me input of a CA3080 it is possible to produce a'sinusoidal' transfer function. That is. if a triangle waveform ofthe correct magnitude is applied to the CA3080 input, the outputwill he distorted in such a way as to produce einewaveapproximation. In the circuit shown, Obi Is adjusted so that theoutput waveform resembles sinewave. I tested this circuitusing an alitanlatiC distortion analyser and found the sinews.distortion Be be only 1.8%. mostly third harmonic distortion,which. for such a simple arrangemeM, seems very reasonableindeed. This could be used to produce a elnewave output from atriangle/square wave oscillator.

Vin

POWER FROM± 12V

CA3080

R210k

;ABC

PROTECTIONd, RESISTORAl10k

V HYST tVin

V HYST -

V OUT

OUT

Schmitt TriggerMost Schmitt trigger circuits prove to be very complicated whenit comes to calculating Me hveterysie levels. However, by usingthe CA 3080 these calculations are rendered trivial plus there isthe added bonus of fast operation. The hysterysis !eve. arecalculated from the simple equation,

St v (IPBC X 112)

The output squareweve level is in fact equal in magnitude to thehysterysis levels. The circuit operation is as follows.

Imagine the output voltage is high. The output voltage willthen be equal to (R2 len) which we will call + VMS, If VWbecomes more positive than WM, the output will start tomove in a negative direction, which will increase the voltagebetween Me input terminals which will further accelerate thespeed of the output movement. This is known as regenerativefeedback sods responsibb for the schinitt trigger action. Theoutput snaps into a negative ttttt . at a voltage equal to - (R2 xImc) which is designated as -Mir.. Only when Vie becomesmore negative than - VFW. will the output change base to the+VaVST state.

The Schmitt trigger b very useful building block for

detecting two demrete voltage levels end finds many uses incircuit designs.

+ Sour

+ Vin

I. T/STUMM

LIWITZ1141.".172r


Voltage Controlled OscillatorBy using two CA2080, end some op amps it is possible to makean oscillator, the frequency of which is voltage controllable. Thisunit finds any applications in the field of electronic musicproduction and test equipment. The cirollit has been giveo alogarithmic control law, that is, the frequency of operationdoubles for every volt increase in the control voltage. This makesit ideal for musical applications where linear control voltagesneed to be converted into musical intervals (which are logarith-mically spaced) and also for audio testing where frequencies aregenerally "mred as logarithmic functions.easu

IC2 is an integrator. The Iwo cur eeeee that drives this IC is usedto either charge or discharge C1. This produces triangularwaveforms which are buffered by 1C3, which then drives theSchmin trigger IC4. The hysterysis levels for this device erefixed at - 1.5V, being determined by RC R7.

The output of the schmin is fed back in such a way as tocontrol the direction of motion of the integrator's output. If theSchmitt output is high, Men the integrator will ramp upwards andvice verso Imagine that the integrator is ramping upwards.When the integrators output reaches the positive hysterysislevel. the Schmitt will flip into its low . end the integratorwill start to ramp downwards. When it reaches the lowhysterysis level the Schmitt will flip back into its high state. Thusthe integrator ramps up and down in between the two hysterysislevels. The speed at which it does this, and hence the oscillatingfrequency is determined by the value of laic into IC2. The largerthe current, the faster the capacitor is charged and discharged.Two outputs are produced, a triangle wave (buffered) from IC3and a squarewave (unbuffered) from IC4. If the squarewaveoutput is loaded then the oscillator frequency will change.

The log law generator is composed of . 2, 3 and ICI.Transistors Q1 and 02 should be matched so that their baseeminer voltages (VW) are the same for the same emitter current,(SINAI. Matching thaw devices to within 5 mV issatisfactory, although unmatched pairs could be used. Whenmatching transistors take care not to touch thorn with yourfingers. This will beat them up and produce erroneous measure-ments. Transistor 02 is used to produce a reference voltage ofabout -Ova which is connected to ICI pin 3. This op amp and

72

rue.EDS AVIVER

SE

.5

03 -07

al

VOLTS 0

-mpuENCY

101-0 100Hr lkOo 10101.

-2

-4 --5 -

-Vc LOG CONTROL LAW

03 is u ad to keep 01 emitter in tlas same voltage of -MM.The inp t cOntral college is attenuated by RI, R2 such that a +1Vin ert, se at the input produces a change of only +18 mV at thebase of 01. However the emitter of 01 is fixed at -WM, sothe cur ern through Of doubles. (It is a property of transistorsthat dr collector current doubles for every 18 mV increase inVW).

The twiner current of 01 flows through 03 and into IC2 thuscontroll'ng the oscillator frequency. It is possible to get a controlrange of over 1000 to 1 using Mis circuit. With the valuesshown, operation from 10 In to 10 Mir is achieved. ReducingCI to I n will inc eeeee the maximum frequency to 100 kHz.although the waveform quality may be somewhat degraded.

Changing CI to Sul (non -polarized) soil givefrequency of 0.1 11..


FEATURE: 3080 Circuits

TONE BURST GENERATOR

Fast ComparatorThe high slew rem of the CA3080 make it an excellene feetvoltage comparator. when pin 2, ICI is rnore positive then VrefMe output of IC1 goes negative and vice versa. Vref can bemoved around so that the point at which the output changes canbe varied. As long as the input sinewave level is quite large Vsay) then the output can be made to move at very fast aaaaaindeed. However, care must be taken to avoid overloading theinputs. If the differential input voltage exceeds 5 V. then theinput stage Meeks down and may cause an undesired output tooccur.

One use of a feet comparator is in a tone burst generator. Thisdevice produces bursts of sinewaves, the bursts tarting andfinishing on axis crossings of the sinusoid. The comparator is

outputdetect these axis crossings and to produce a square wave

output which then drives a binary divider (IC3). The dividerproduces a 'divide by sixteen' output which is high for eightsinewave cycles end then low for Me next eight . This signal isthen used to gets ON and OFF the sinewave. The gate mechan-ism is a pair of transistor. which shoo Me sinewave to groundwhen the divider output is high and let it pass when the divideroutput is Mid. The resulting output is a toneburst. However, if

compa ttttt is not very feet, then there will be a delay ingenerating the gene and so the tone burst will not sten or finishon axis crossings. Using the circuit shown, operation up to 20kHz is obtainable.

Vin

Vref


Vie

LESS THAN4V WRT

V ter

UV/mac

73

POPIRRED FROM IRV

Slew LimiterThe current output of a CA3080 can be used to produce acontrolled slew limiter. By connecting the output curreM to acapacitor, the output voltage cannot move faster than a rategiven by

slew rate Icalc Volts per sec.

Note that Isec determines the slew rate and as Owe is avariable then so is the slew rate. The output voltage is bufferedby a voltage follower, IC2. This is a MOSFET op amp which has avery high input impedance, which is necessary to minimise theMarling on Cl.

When an input signal is applied to ICI the output tries to movetowards this voltage but its speed is limited by the slew rate.Thus the output produces a linear ramp which stops when itreaches the input signal level.

FASTESTR2 Cl SLEW RATE

150k 100n 1.5V/mSec150k 10n 15V/mSec

SLEW LINFOLOOOTRLIT 150k 100 0.15V/m5001M5 100 15V/Sec

Sample And Hold

The slew limiter can be modified so that it becomes a sample andhold unit. In this circuit Mac is either hard ON_ (sample) orcompletely OFF (hold). In the sample Med.. the output yob..quickly adjusts itself so Mat it equals the input voltage. This

74

flIguTT.r.zr-to

enables a short samp. period to be used. In the HOLD mode,IssC is zero a. so the voltage on CI should remain f ixed. Thecircuit is in fact an analogue memory. It is used in musicsynthesisers (to remember the pitch). in analogue to digitalconverters and many other circuits.



MANFRED FilfAt L 12V

NOUL

4 Quadrant MultiplierThe CA3080 is a two quadrant multiplier but. with the additionof a few extra bits of electronics. it can be made into a fourquadrent circuit. A two quadrant multiplier has two inputs,one can accept bipolar signals (the inverting or non inveninginput) and one can only accept a unipolar signal, (the Nomcurrent). However, a four quadrant multiplier can accept bipolarsignals on both of its inputs which enables it te PerfOrmfrequency doubling and ring modulation.

The circuit is fairly similar to thst of Me two quadrantmultiplier described earlier except for two differences. IC3 isused to generate lalIC in such a way that the Y input can go bothpositive and negative, thus the Y input is bipolar, when is at 0 V

KINN MOSS LATLON

and there is a signal on Me X input the desired ootpor(oo V)should be zero. This is achieved by adjusting RV, so that thesignal via ICI (this is inverted) is exactly cancelled out by that vieR3. Now. when is inc aaaaa d positively. a non -inverted value ofX is produced at the output and, when Y is increased negatively,an inverted value of X is produced. When I' a sem so le theoutput. This a known sometimes as ring modulation. if aspeech signal is connected to the X input and a variablefrequency oscillator to the Y input the resulting sound isthat of adalek.. Alm. if a sinewave is connected to both the X andinputs, the XY product is a sinewave of twice the frequency.This is known ace frequency doubler, but it will only work withsinewaves.

Single Pole FilterA singlepole lowpass filter can be constructed using a CA3080as a current controlled resistor. The filter is, in fact, just a simpleRC low pass section where the R. which is controllable, isconstructed out of ICI. RA 115. Varying Issc changes theamount of current drive to CI . This would normally make thecircuit a slew limiter, but because the signal level that ICI (pins 2

PONES. f ROM, In

and 3) handles is so small. the CA3080 works in ma linear modeThis enebles it to look like a variable resistor. When Mrs resistorIS varied. the break 'frequency of the f Met also raniaa Srapplying some positive feedback around the filter Re. C2 npossible to produce a peaky filter response Themcreases with frequency 'making the circuit useful a guitar

WM Wah unit.

ELECTRONICS TODAY INTERNATIONAL - APRIL 1979-0


Voltage Controlled Filter

A tandard dual integrator filter can be constructed using a fewCA3080.s. By varying Ines the resonant frequency can be swept

o r a 1000 to 1 range. ICI, 3 are two current controlledi rygretors. IC2, 4 are voltage followers which serve to buffer

rs

FIRFOLIE

the high impedance output of the integrators. A third CA3080(ICS) is used to control the CI factor of the filter. °factors as ighas SO can be obtained. The resonant frequency of the filter islinearly proportional to Icac and hence this unit is very useful inelectronic music production. There are two outputs produc d. alow pass and a band pass response. ETI

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ELECTRONICS TODAY INTERNATIONAL -APRIL 1979

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LECTRON.S. TODAY INTERN,IONAL - APRIL 1979

iftegkrElit,

microfileGary Evans looks at PET add-ons, a Simon that's not simple and has news ansuperboasd

has to date heon nor', s.spporn,the PET

numPer ol companies have stepped into the voidcaused hv ma of commodore periPherMs evervthirM homRS232 interfaces to PE I compatahm floppy drives are

about iocnange

PFSem hut f II outtule sg;ol'tne21===!nt"i71:1:" 111 allow 360K 13two standar:5,in Disk driverVu'q':751/'370r;Vs'is.accomplished without msortinq to double uaciung ordouble density This is achieved line re not told exactly

'fiZen'orZeXTC's=r1r2F140"4 a" 65°2 - a"may be used 38 tracks with a constant density recordingr,:ach track provide 171820 bytes for user stamp per

The 2.0 requites only one connection to dm VET anintertatecord connect, ele mut to PET s IEEE port

'cea'fcluu ''' 4,"="rtn: ;Kfs:Ters.sientcropc?sms or Tne 81('2001 8 m mom ro mave room lor,thelarge, keyboard Me intepralcasscm oem, nes o,enoz,t%

anct a seP ..... deck wdl nave ic ee ov.mvet

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.1'hasF7t1r.nat:ed'11:12%171"0'Pes'latFin:'tnnhe:gis:al'in'asn'i:Farrn'Sam''

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NEWS

Toying WilM1 MPUs

Super Ohio

ET1

Back numbersNatoaback. sssss of ETI Iwo available Inc.are not than well The table below ehcoPI. coo be obtoMod Nom ourcosts 60p Inc pOp and m

1976 /977 1976 1975 1970 1973 1972No! Not Nol No!Nol o!

alarch No! NW No,. o! NoI NW NW

Yo.roVe "W No! rPrgl rPtJuN Nol No! NolAug Not Nol No! No! NolSept No, NW Not No! No!Oct No, NoI Nol NW No,N. NW NO NO NW NW NWDeo NW NO NW NW NW NW

Photocopies of any artiale Nam arty one issue are

ALL INVOICES, ENQUIRIES, ETC., TO

OUR TEMPORARY ADDRESS OF

cmia.-irmiziik Ell LTDNORWOOD ROAD

READING

TELEPHONE NO. READING 65916

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WHAT'S IN THE APRIL ISSUE

COMPUTERSURVEYThe number ol small systems on

Vet [IC Vs't7eian Znet7n1Peot a machnte to suit your appliedtion.The April issue at ComputingToday surveys some ol the more

's7fori===.7sdslir:;

NASCOMADD ONST. NASOOM I computer hasbeen one ol the most success.ol the MY computer kits on Memarket recently IVASCOM ;nerdduced number ol extras Metallow the basic ...es poten-tial to be °onside.. enhancedWe take a look at the expansion

PLVD:offering.

EXPANDA PETT. commodore PET has beenwin, us Mr over year now butperipherals Mr the computer hambmn slow to appear. One ot theessential devices in many ...-no. is a floppy disk to pr.. asystem ol mass storege thattaster in operation .n the Wmsystem of the star.. inwhine

'Otnp :I= Is7 dr;:e's7;mon operatMg system thee wMProg straight,. your PET

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AMBUSH GAMEThe April issue of our six. that will .now those of you whomagazine, ETI, carries project don't dabble in electronics Mpleycalled Ambush. Ambush is an Ambush on your computer

CONSUMERSHOWThe recent Winter ConsumerElectronic Show in Las Vegas saw

MITZ:rro"d ugs TnfChew challenger Mat talksGerald Chevin was Mere lot Com.pitting Today and his reportappears in the April lassie.

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PROJECT

WIND METERHere is the project all you amateur meteorologists have been waiting for. When thismeter gets the wind up you'll know how fast and where it's coming from.

TRADITIONALLY, THE FOURprimary elements are fire, earth,water and air. At ETI, we'vedesigned projects concerned with thefirst three (temperature meters. soilmoisture indicators, rain alarms). butnot much for the last. The majorproperty of the air, apart from thefact that it is necessary to supportlife, is the movement of the air -wind. Light winds generally aren't ofterribly much significance except tometeorologists, but stronger windscan be useful as a source of power:for traditional milling, for electricitygeneration or as a means ofpropulsion for sailing yachts.Stronger winds such as hurricanes,can be destructive, causing damageto life or property.

So for all the private pilots,yachtsmen, amateur meteorologistsand general weather watchers whoread ET!. here is a device which willtell you the wind's speed anddirection, with a remote indication ofboth quantities. Our design is, we'dlike to think, both stylish andunusual, but there are simplermethods of mechanical constructionwhich you can follow if you wish.

The HeadThe drawings along with the photoswill give the general design that weused. The actual dimensions have tobe left to the individual constructoras components such as the ball racesand light bulbs may vary in size.

While we used a single head forboth speed and direction, it may besimpler to use separate heads.

The discs we used were 1.5mmthick clear plastic with a piece ofphotographic film glued onto it. Itmay be easier to make it out of thinaluminium and cut out the slots. Forthe speed disc simply drilling holeswill suffice.

The most important part of thedesign, apart from ensuring that thediscs rotate with a minimum offriction, is the shielding of the lightand preventing light scatter striking a

A/11\113 METER0

transistor which should be dark. Ascan be seen from the photos anddiagram the bulbs and transistors areembedded in aluminium blocks withsmall holes providing a passage forthe light beam.

The wiring of the head is shown infig. 3. Note that the base lead is notused and can be cut off close to thebody. Insulate the joints onto thetransistors to ensure that they do notshort on the aluminium blocks. Thebulbs may touch the block with theirouter connection but this is the 0 voltline and does no harm. In fact itprovides some electrical shielding farthe leads. The bulbs we used were12V but they were bright enough on6V giving a much longer life.

Design FeaturesWhen we started design on thisproject it was to have a digital


readout of wind direction with aresolution of either one or twodegrees. This would also make ituseful in a sailing boat to tell thewind direction relative to theheading

Difficulties however soon becameapparent. The first of these was thesensor head. The only accuratemethod is a digital head, probablyoptical. Two methods could havebeen used, one using a disc with asingle optical track of 360 slots andan updown counter and the secondusing eight or nine tracks in a greycode. The first is simpler in headdesign but the second is less proneto error. The problem, and thereason for rejecting both, is that withsuch resolution, the reading wouldmove around so much when thewind is gusty to be unreadable. Whatis needed is an averaging circuitwhich unfortunately becomes

85

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Fig. 1. Complete circuit diagram of the ETI Wind Mom

difficult when the wind is changingfrom just west of north to just east ofnorth. i.e. 355 to 005. How do youaverage these (use amicroprocessor?)_

As this was intended to be asimple project we relaxed ouroriginal speification, deleting the usein a boat (we may get back to this.problem. A four track 'Grey scaleallows the wind to be given to within11. of its true heading, without thecomplexity of a nine track one, andthe use of LEDs to give directionsolves the problem of averaging asthe variations can be seen andaveraged by the brain.

86

d I

15

ConstructionThe electronics is relatively simpleprovided the PCB described is used.Due to a height limitation C1 shouldbe mounted an the rear of the board.The LEDs should be mounted about7mm from the board with care beingtaken not to damage them as theleads have to be bent out slightly.The regulator also has to lie down togive clearance.

We mounted the unit behind analuminium front panel with the LEDsprotruding through holes. If this is tobe done it is preferable not to solderthe LEDs until after alignment with

6060

ovov

the front panel.The head is more difficult as some

mechanical ability is necessary toensure good results. Therequirements are basically simple Adisc is to be allowed to rotate. eithercontinuously with the wind oraligning it to the wind, with a bulbon one side and phototransistors onthe other.

The method used by us is shownin fig 4 with the aluminium blocksproviding the shielding necessary togive accurate results. As the unit willbe exposed to the weather it must bemade waterproof otherwise the ballraces will corrode. The races used


PROJECT: Wind Meter

HOW ITWORKS

Wind DirectionWind direction is indicated bye series of 16equally spaced LEDs around a circle. Theserepresent the main points on the compass.These are controlled by ICI and whichare in barn controlled by the directionsensor head.

The sensor head. which is described infig. 3. consists of a disc which has fouroptical tracks and four bulbs and photo -transistors. The phototransistors senseeither a clear disc (logical ..1.) or a blackdisc (logical '11") and thus control IC2 andICC. The code used n special in that onlyone bit is changed at each locationLing gross errors which occur with thebinary code if the heads are not perfectlyaligned. An example of this is going fromlocation i (MI I) to location g (WOO). It thisis not done simultaneously almost anylocation can be specified. With the greycode the same change 15 from 01W to I WO.Here there can be no ambiguity as only onebit is changed. Remember these bits are notweighted similarly to binary and a lookuptable must be used to decide what number(decimal) a particular code in.

The decoder, CO. is an eight outputanalogue demukiplexer with the commonline joined to the +5V line. When a parti.cuiar 3 bit code is presented to its controlinputs one of the eight outputs will bejoined to the .h6V line. The fourth outputfrom the sensor head controlsgives two. inverted. outputs to drive eitherbank of LEDs. The complete four hit cod,therefore specifies a particular LEO to belit. By placing the LEDs correct, aroundthe circle the grey code is decoded.

Wind SpeedThis is a simple frequency counter mea swing pulses from the sensor head. Thehead consists of a disc with eight holeswhichbreaksa light beam to its associatedphototrarisistor. The output of this photo.transistor is squared nob,: a schmitt triggerformed by IC5c. and ICS&

The counting is done by IC,. and IChb(adual decade counter, with 1(16 and IC'providing the store and LEI, driversnecessary to diler the seven segmentplay TiMe base Is provided by IC3 whichgives a 7 rnS wide negative pulse aboutevery one second We say about as it isadjustable by RV: as individual heads willhave different responses and calibrationwill be necessary.

This negative pulse opens the store toallow the number reached by the countersto be displayed while simultaneously stop-ping any further counting by disabling thewhinitt nigger. On the completion of the7mb pulse IC5a. and IC5b generate a 5000wide pumlse which resets the counter ICs torecomence the sequence.

Power SupplyThis is imply' a full wave rectified supplywith ICI giving a regulated +6V outputThis regulation is needed to ensure that thetime base (1C3lrernains accurate.

The finished unit in use

ELECTRONICS TLOT,'.AL-APRIL IS%9

toI'

TO TRANSFORMER

ACAC I I I CT

RS b 1

LED9=D- cui

TO 01 4h0,020 LE'l

LEDO

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0

16

Fig. 2. Component overlay for the Wind Meter

PARTS LIST

TO Q3

TO Q2-44 1 111-TO 04

9--

OSP 1

RESISTORS all 466 544. SEMICONDUCTORS81.4,8.9 10k CI 78061166,13-26 6800 IC? 405107,10.12 100k IC3 555R11 470k 1C4 5 4011

IC6 7 4511IC8 4518

/POTENTIOMETER

01-05 2057701.2 104004

901 1M Ihrnmmor LED TIL 209 or Streliar0141112111.2Common cathodeseven segment (high

CAPACITORS bughtness1C1 1000u 16VC2.6 10u 25V MISCELLANEOUSC3 tu 25V Four rernorture 12V bulbs. PC8L 240V!C4.5 8206 ceramic 18.1 transformer box head assembly

88

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Fig. 3, Connection to the bead. Note(' -4.that transistor bases are not used.


If

PROJECT: Wind Meter

[hemmed in the sensor head -1.5 mm thick, clear plastic with photographicfilm glued on.

Fig. 4. Mechanical construction of thesensor head.


will normally have to be washed outto give low enough friction with alight spray of WD40 or similar togive some protection.

While our housing is a littleornate, it did work but the moreusual half ping pong balls may bemore suitable.

CalibrationWind Speed.The easiest method for wind speedcalibration is to provide the unit witha DC supply (via the common andone of the AC inputs) and to take adrive in the car with the unitsupported above the vehicle.Providing there is no wind thepotentiometer should be adjusteduntil the reading corresponds to thespeedo.

Direction alignment is simply amatter of aligning the vertical rod sothat it gives the correct results.

EnBUYLINES

The metalwork for this project wemust leave to our readers, as this willbe fabricated to suit individualrequirements. The displays can beany type no's really, lust observe

Similarly with the LEDs. Thephotodarlingtons can be supplied byMarshalls.

as

'7421r

Now It Works -AM/FM

DOUBLEDICE

Zsrav7aunvo've7r211=3;doling,swihable odds to allow

tZle'llard'crotnrrtrIV:gn.mek:;lite easier and overall we think its anice on,

See what you think next month.

Atte.

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PROJECT

GUITAREFFECTS

UNITOur guitar effects unit isn't just a fuzz box. Use it to give you a new sound to playwith.

BUYLINES

The only component that may bedifficult to find ,s the .56 iEt

aupply this IC

ect A depth cont. allows

bypass sw.tch

Smashing sound

The luridarnentatency ol the input is NH waveed but the numerous hamonics

ult. sounds raffia/ like

.we don 0 vou no doubt Findmany mom musical uses tor thisele than we could

Swct itching between Fuzz enet suuzz

llin:vpt'c'hulon.s purpme

PARTS LIST

RESISTORS All 516 'ASV)

6602R2 686R3 27OR84.6.10. 11, 12 104AS: 383Al 100kRS 39kMS 820R813 14 lB

POTENTIOMETERSRVIIMOCAPACITORS

1110 elactroptsc5600 Pol18Vmne

SEMICONDUCTORSBC1097415358

01.2 1144148

SWITCHESSW1 SPOT SomswachSW2 SPOTSW2 DPDT

MISCELLANEOUS

Two Sm. mono lack socketsPCBVerocase MN

98

RV1

Fig.1. (above) PCB component ave.,'

(Above right) Completed PCB

Fig.2. (Below) Circuit diagram

ELECTRONICS TODAY INTERNATIONAL - APHIL 1979

PROJECT:Struzz

HOW IT WORKS

CALCULATORS

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HIT COMPLETE WITH PREASSEMBLED SEARCH COILS

£16.50ASSEMBLED 8 TESTED

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rfXrrn*"ntsov ow/ x9rov"'MTr102

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STOCIaRTVC=110 2170N ICS 0055 INTPRATiONAL - APRIL I Y

Readers' Circuits

Gentle Clock Alarm

I. Hill -Smith

RINGI RING! BUZZ! This is D LTCLANG! PIP PIP PIP!

There are gentler ways to wake up.This circuit provides an alarm whichbuilds up from being inaudible to loudover about one minute. As a result youare always woken by the minimumvolume required to wake you: a farmore comfortable experience than theusual trauma. The three multivibra-tors in cascade provide a signal likethe sound of a warbler telephone. AsC slowly charges through If a largerfraction of the signal is amplified bythe op amp producing a louder out-put.

Calculator Radio Alarm

T Corringham

This very simple circuit, used with aSinclair Cambridge Programmablecalculator. enables a transistor radioto be turned on after a predeterminedtime. (within the range of a fewseconds to five months).

None of the components are criti-cal. but the SCR should have a suf-

ficiently high voltage and currentrating for the radio used.

Ha transistor radio is used the SCRis connected in series with the battery,but if a cassette recorder/player isused it can be connected to theremote socket.

The LDR is placed above the lefthand three digits of the display. RV1 isadjusted so that the circuit is triggeredby '888' being displayed, but not bythe background light only.

Using the program given. the time

00010203

080607080910

in minutes of the required delay is putin and /RUN/ pressed to start thetiming period.

To stop the program prematurely/+/c/ CE/ is pressed.

The calculator should be used witha mains adaptor.

The timing is accurate to withinfive minutes in eight hours.

If a buzzer or similar alarm is usedthe same circuit can be used to givean audible indication of the termina-tion of long programs.

ELECTRONICS TODAY

prepare circuits or ideas submitted by readers or this page AO itemsused will be paid... Drawings should be as dear as possible and the text should p eeeeee sentrte typed. CirCuitS Meal not be subplot M copyright. Items for consideration should beto PTI.TECN-TIPS. Electronics Today I eeeeeee 25-27 Oxford St. London W111 .1R1F

103

TARGET ELECT S

TRANSISTOR SPEAKERS

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Semiconductor Guides.

Keyboard/display sound con-verterK G Reid

This circuit can be used in severalmodes: It can provide quantizedfeedback (a distinct improvementover the normal singie 'bleep') fromthe key actions made on a calculator -type keyboard It can be used to give a'sound' translation of a digital display,or completely replace the displaywhen sound would be a better com-munication medium.

The keyboard or display informa-tion (a maximum of 16 bits with one16 -line 74150 multiplexer) is trans-lated into a series of 16 high or lowfrequency tone pulses, correspondingto the 'high' or 'low' logic state of the16 bits.

The circuit illustrated was used inconjunction with a digital mulumeter,requiring three 4 -bit words for thedigits and three additional bits forover -range, negative and decimalpoint. Thus, 15 lines only were req-uired, the 16th being used for reset-ting

The 15 bits are latched on to theinputs of the 74150 multiplexer. Pre-sentation of the enable pulse results ina logic '1' appearing at the output ofgate 13, allowing clock pulses to passvia gates A and Fl to the 7493counter. Gates B, E, D and C form alatch which remains 'set' until all 15bits have been sampled. As each bit issampled, the inverse state appears atthe multiplexer output, opening gate

Readers' Circuits

J or K and thus operating one of thetwo reed relays. Asa count of 1111appears from the counter, the outputof F drops low, resetting the latch andcounter. The operation of either relayresults in a tone appearing at theloudspeaker (or earpiece), the tonefrequencies being set (1 2 kHz maxi-mum) by the 1 megohrn pots. Thetone pulse length is governed by theclock rate.

Digital Pulse Compressor

N C Hall

Whilst constructing a digitalfrequency meter the author found itnecessary to be able to accurately Fri m

.the width of a gate pulse. The circuit,shown uses only two ICs and can:reduce the width of a pulse applied atits input by up to a few milliseconds.The table shows the reductionachieved by using different values ofCl.


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a digitizer adds another dimension

Readers'Circuits

Darlington Drivers for a fewpence

C. J. Ramey

This circuit offers a very efficient wayof driving a pair of transistors in Dar-lington configuration from CMOS.The circuit in Fig 1 shows how twoloads of up to 1A may be driven froma single 14007 chip with no externalresistors. Using a 2N3055 in place of

will enable loads of up to3A to be driven at voltages limitedonly by the Vceo of the transistors(WO.

Fig_ 2 shows the internal circuit ofone section of the 14007. A high on

pin 6 switches the lower CMOS tran-sistor on, holding Q2 off and sinkingthe leakage current of Ql. A low onpin 6 drives Q1 and switches thelower CMOS transistor off and theupper CMOS transistor on.

The result is fast switch off at lowcost and efficient switch on.

A bonus is the Inverter betweenpins 10 and 12 Note, Vcc should be5-6V to prevent excessive currentbeing drawn from the CMOS chip.

Precision Rectifying with theLM3900

A. Winsor

The LM3900 is different from mostop -amps in that it is current differen-cing and operates from a single sup-ply rail, which mean that the inputsbias at one base -emitter voltage aboveground. Hence standard techniquesare not applicable as the diode wouldalways be forward -biased. Two feed -

NOTE.back paths are therefore provided:-R3 for DC stability, and R4 for the AC EF,441"`"°'signal after C2 and R5 have filteredout the DC bias. When R2 , 2 X R3 made very much smaller than R3. Cl ments.point A will be at Vcc/ 2, allowing the and C3 are DC blocking capacitors _This circuit has obvious potential,diode to be reversed at will. For large and determine the low frequency roll- especially in portable equipmentpositive input returned to ground. off. Component values quoted are where the 4 amps. in one packageInput impedance equals R1, and vol- those used on the prototype and may and single supply rail yield a more,tape gain equals - R4/ R1 since R4 is be altered to suit individual require- compact. mote convenient L9,


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PCB FOIL PATTERNSGATHERED HERE are all the PCBs for this month's symbol, the designer retains that Copyright to himself soprojects. From now on the boards will be grouped his company, and that particular board may not betogether like this in order to facilitate their use by those produced on a commercial basisreaders wishing to produce their own PCBs from these These pages form the basis of our ETI PR INT sheetspatterns. which are etch resistant transfers of the loll panerns

All are shown foil side Lip, and full size. Companies designed to simplify one-off PCB production See the adwishing to produce these for sale as ready made PCBs on page 49 for further detailsshould note that where the board carries a copyright

110 ELECTRONICS TODAY INTERNATIONAL - APRIL 1979

PCB Foil Patterns

Below left: Wind Speed Indicator PCBBelow right: Click Eliminator Mk 2 boardRight: Struzz effects unitAll are shown full size and will form the basis of ETIPII INTsheet 023 which will be available shortly

ELECTRONICS TODAY INTERNATIONAL- APRIL 1979

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DISK SYSTEM as shownMICROPOLIS 5100 disks - 315 K bytes per driveDrive 1 (includes S100 controller.Micropolis M DOS and BASIC software) £649Additional 315 K bytes drives (up to 4 per controller) £349Cables and regulators for 2 disk system £41

ADDITIONAL SOFTWARE FORSORCERER PLUS DISK SYSTEMCPIM operating system £145CPIM with C BASIC (Compiler/Interpreter) £235

FORTRAN 80 £350

COBOL 80 £490

PRINTER as shown MICROPOLIS STOCK CONTROL (INVENTORY)

ANADEX DP11000BASIC PAYROLL £99

80 columns. 112 char/sec 5 e 7 dot metric headPACKAGES ACCOUNTS RECEIVABLE eachFROM

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