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THE PRACTICAL MAGAZINE WITH THE PROFESSIONAL APPROACH
elttorglectroopcs
Supplement: a miscellany ofconstruction projects
EE JULY AUGUST 1988
SAGE HI-FI CLASS A POWER AMPLIFIERSTHE SUPER -SERIES
Linear High FidelityPure Class A
Power Amplifier Modules50 Watts to 500 Watts, four unique modules
A 'Quantum Leap' in sound design technology ....
.... with an unparalleled level of performance in all areas
Virtually zero distortionSuper fast slewrate
Continuous pure class A operationTotal reative load drive capability
Massive unrestricted current capacitySound colouration components eliminated
'Capacitor sound' eliminatedTop quality audiophile componentsSimple to mount, easy to connect
SPECIFICATIONS
I MODULE TYPE Sripenunp Sop . mos Uptown' 1 Suerses 2PARAMETER
HOWIOW
MOWISOR
KOWESA'
MP:ECW
POWER OLTPLTI OHMS4 OHMSSILISIC POWERI OHMSA OHMS
150WIS AV
ISOw2SITN WA'
SKNY7070:
MAX TRANSIENT P014 ER2 0 RAO 250a* WOW WV: UMWPEAK CURRENT 0'41 71A SSA SSA RSA
T HD AT RATED OPTHD AT LT2 CUP
OLCOWS
OIXOSI110:M%
0051%OD0021
Oesszt-sa,/e0.0:015
EatecematleINTERMODULATION DIST u1/41, AA] -MICE
I CROSSOVER DISTORTION Zac, Zen Zs. ZenSLEWR ATE .140Ym .23130,s, >2SW,, ,ISISY,FREQUENCY RESPONSE I DO -124H, SH1-200/1, Slit - PiCilit QUI,- MailRISE TIME I <2 Sri <1.75. <L7Sal sirs
' DAMPING FACTOR (SO 103 ICU MOSN RATIO T 1331, IX -eh IZSS I KIS,SENSIT IS ITV FOR FULL OP i 07750 0 TM 077S,, IV
INPUT IMPEDANCE I XL i Xe I Xe IsltMAX SPEAKER PHASE SHIFTDRIVE CAPABILITY IS 011+151 450 fi:P SO. SCP
SIZE ISM) ' 120175A50 112.75133 122073,3.0 2-KNICENK*WEIGHT (sm.) 0751 Cal& 0114 :La;
Ace,. woo at ahn, ft..Ncen- Distort en zocuturarrvts were uksa Iran to SA I MU oscillacs, the 0100 roduaries irazdaratera...4nark ref crexc signal KU= and 1.th the ansplifiaacally drisiag a haxlsgesker.
Uomesunable sears to disicatiOU lesCia below the SA L ie less than 0-000018% 10-1SplanL
AD iskdides are 100% toted arc% gnaranseeclao ores cc acted aD grannieis The Se en:vas 2 snodoles areaD issued with as inclisiassl signed =Ors= arperforransr coo:amity.
FEATURES TABLE
S.Pm..i' Sapernos Scum. I S.NNUIff. 2
I Acme CIss A OPr Casa= le. Vs ZEROMumma Gra .=)Lecanesi Fentvack &Lc* °mai Far&sta
tNevux1Con
T Warred Csr= )tarastOrpgs-4
Proecoon Cum.5
Aobosinle Compeer=1 Nts.3.1 Se...mi.:airsSOP F,-,nvr FtMiS100
,tIP7.obd Neavarkst liF Coroperosaars
Wepanslor Soma El=assood
t DC lissionnoat PSU Feed/wawa
Ripple Efiss-aexm
LED Amu Unfit& TaplisS.mor
These features art exclusive to the Sage Audio Super Series_
SageAudio's Super Series Power Amplifier Modules are built to thehighest quality audio grade components, including HOLCO resistorsand SMDs with minimal capacitor design and matched customsemiconductors. These modules could not have been conceivedwithout SMD. Since SMD is still in its infancy, however, Sage haveused a combination of standard components for high power levelsand SMD for critical areas, thus getting the benefits of bothtechnologies. In particular, the lower lead inductance of SMDresistors and small semiconductors has substantially improved theHF performance and the slew rate of the amplifiers as compared withconventional components.The Super Series Class A Power Amplifier Modules consist of Superamp - a low cost 100 W bipolar design with a perform-
ance in excess of all other MOSFET modules. Supermos - a 150 W MOSFET design with an unparalleled per-
formance, typically 10 times greater than all other modules. Supermos 1 - identical to the Supermos but uses Supermos 2
output devices and has totally reactive speaker drive capability. Supermos 2 - a totally new, 100 W to 500 W amplifier with
exemplary performance combined with 6 additional technicalsound quality improvements, eliminating the sound colourationsinherent in all conventional amplifiers.
The Supermos 1 modules are ideal for use with the 'Active Loud-speaker System published in the April 1988 issue of Elektor Elec-tronics and are reported to give superior performance to the Sanyomodules.Sage can also supply a high -quality power supply kit, incorporating'the smoothest d.c. output regulator in the world' for use with thepower amplifier modules or, indeed, any audio amplifier requiring thebest possible power supply. Also available are a variety of high-gradeaudio components not easily found in other catalogues.
The Supermos modules retail at £65; the Supermos 1 at £78; and theSupermos 2 at £140. The PSU kit is £98, but if ordered before 31August together with two of the above modules, it is offered at thespecial price of £62 post paid (UK only). Normal postage costs are£2.00 for a PSU kit and £1.50 per module, except Supermos 2 forwhich p&p amounts to £2.00. Overseas orders sent by airmail,charged at cost.
To receive an 8 -page glossy brochure, send a £1 cheque, PO, or coinplus a large SAE 126p1 (overseas: 6 IFICs).
SPIOE RICE ELECTRONICS
Manufacturers and Exporters of Precision High Fidelity Audio ElectronicsConstruction House Whitley Street Bingley I West Yorkshire BD16 4JH
Telephone (0274) 568647 Telex 517783 Fax (0274) 551065
2 SUPPLEMENT Please mention ELEKTOR ELECTRONICS when contacting advertisers
EE JULY AUGUST 1988
Audio & Hi-fi
16 Automatic volume control56 Background -noise suppressor57 D.C. detector26 Five -band stereo graphic equalizer59 Four -channel stereo switch23 Simple phono preamplifier19 Single -chip 150 W AF power amplifier58 Stepped volume control
5 Three-way tone control37 Wireless headphones (receiver)36 Wireless headphones (transmitter)
Car electronics14 Car interior light delay
8 Car tilt alarm46 Fast starting wiper delay28 Headlights indicator47 Power switch for cars35 Wiper delay
Computers48 48 MHz clock generator34 I/O extension for Amiga 50014 LCD for Z80 -driven computers42 Non -interlaced picture for Electron
_
30 Printer sharing box4 Prototyping board for computer extensions
17 Sample & hold for analogue signals
General Interest20 Auxiliary negative -voltage supply40 Driver for bipolar stepper motors50 Electronic sand -glass39 Fishing aid44 Fruit machine12 High -voltage BC54732 Programmable switching sequence28 Quiz timer13 Servo -pulse generator51 Stepper motor driver21 Timer29 Touch -sensitive light switch35 Universal SMD-to-DIL adaptors
Power supplies
25 Computer -driven power controller55 Discrete +5 V to -15 V converter22 Flashing light37 Lead -acid battery charger55 Over -voltage protection
7 Secondary power -on relay13 Self -switching power supply20 Single -chip solid state relay38 Step-up switching regulator
Radio & TV
22 Amplitude -modulated calibration generator31 OMA-2500 time standard receiver15 Polarotor control
6 RTTY filter for 170 Hz shift54 Video distribution amplifier28 Voltage -controlled SHF oscillator
Test & measurement
9 33/4 -digit DPM24 Alternating current source33 Burst generator10 Deflection detector49 Digital attenuator5 DMM as frequency meter
56 From altimeter to variometer18 Low -frequency LC oscillator58 Nostalgic sine -wave generator29 Power multivibrator16 Programmable voltage source11 Simple transistor tester46 Test -voltage supply45 Wideband level -independent trigger preamplifier40 Wideband RF signal tracer
SUPPLEMENT 3
EE JULY/AUGUST 1988
ono PROTOTYPING BOARD FORCOMPUTER EXTENSIONS
This printed circuit board is ideal forbuilding and testing experimental ex-tension circuits for a wide range of com-puters. The double -sided, but notthrough -plated, board has contactfingers that enable it to be accepted incommonly used slot connectors for ex-tension circuits in many types of com-puter, including those in the MSX andIBM PC series. In addition, the boardholds 3 general-purpose buffer chipswhich can be wired to requirement toensure correct and safe interfacing be-tween the computer and the extensioncircuit being developed. Supply tracksare provided in the buffer and prototyp-ing area on the board for ease of wiring.When required, a number of contactfingers can be cut off to suit a particularslot width, or to prevent the board beingfitted the wrong way around in the slot.Also, the contact fingers are relativelylong so that a section of this PCB areacan be cut off for use as an adaptor
together with a purchased slot connec-tor. It is also possible to fit a slot connec-tor at right angles at either side of thePCB as shown by the printed markers.The pin connections of the Type74HCT245 octal transceiver, and theType 74HCT541 octal three -state linebuffer are given here for reference.These chips are suggested for use asdatabus and addressbus buffers re-spectively, because they have inputsand outputs arranged at opposite sidesof the 20 -way DIL enclosure. The user is,however, left completely free to choosehis own bus buffers in accordance withthe interfacing requirements.Remember to ground unused inputs onHCT chips!
Note: the printed circuit board for this pro-ject is available ready-made through theReaders Services as order no. 884013 (seeReaders Services page).
016 0 1 0 6 0 a 11 0 DICI 0 II
li11111111O0000o000000000oo0000000000000000oo0000000000000001000000000000100000000000+
,eiv,o
00000000000T000000000000T00000000000000000000000000000000000000000000000
0
1
1000000000.0000000000000-0
0111
CI
`cc
DIABLE
a,
B3
'5j B4
Bs
B7
X188
Li 84
rw13-lo
a0aaaaadaaotd011114060ad0dda000a0
0000000000 0 00000000000000000000 0 0000000000
0000000000 0 0000000000 0 0000000000000000000 0 0000000000 0 000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000S000000000000000000000000000000 S000000000000000000000000000000000000000000000000000000000000
4 SUPPLEMENT
EE JULY/AUGUST 1988
THREE-WAY TONE CONTROL
Although tone control is not desirable ingood -quality audio equipment, thereare still instances, such as when playingwell -used records, when it is. Such anadd-on tone control should enable thefrequency response to be altered totaste, have no detrimental effect on theaudio equipment, and be fairly com-pact. The circuit proposed here meetsthese criteria.It is based on National Semiconduc-tors's LM833. This dual operationalamplifier has a very low noise factor(4.5 nV/i f (Hz)), a high gain -bandwidthproduct (15 MHz), and a slew rate of7 WLs.The tone control circuit consists of threeranges, so that a presence control ataround 1 kHz is possible.The opamp at the input, Al, is connec-ted as an inverting buffer. Its non -inverting input is connected to a 10 k re-sistor to equalize the direct currents atboth inputs (with respect to the bias cur-rents). This is necessary to keep the out-put of A: near enough at 0 V because ofthe d.c. coupling to A2.The second opamp has in its feedbackloop a simple three-way tone control,whose cross -over points are determinedby the value of the four capacitors.If desired, a capacitor may be added tothe output of A2, because the d.c. out-put of this opamp varies somewhat withthe setting of the potentiometers.
0 0
15V
15V
c1 R1
CLL
5mA
C7
C8
100n
100n
R3
IC1
A1,A2 = IC1 = LM833
The cross -over points of the low -frequency and high -frequency controlslie at about 200 Hz and 2 kHz respect-ively. The presence control operates ataround 1 kHz.Maximum attenuation is about 16 dB.
R5
1CM
88404
With all potentiometers at the centre oftheir travel, the signal-to-noise ratio isbetter than 90 dB at a bandwidth of1 MHz. The gain is 0 dB but can bealtered by changing the value of R2.
DMM AS FREQUENCY METER
By providing a high -input -resistancemultimeter (preferably of the digitaltype) with a frequency -to -voltage con-verter, it can be used to measure fre-quency.The range of the proposed device ex-tends from 10 Hz to 1 kHz on range Aand from 1 kHz to 100 kHz on range B.The sensitivity for frequency measure-ments up to about 10 kHz is of the orderof 35 mVpp, and for measurements from10 kHz to 100 kHz about 350 mVpp.The input signal is applied to Schmitttrigger IC3 via limiters Di and DzBistables FF, and FF2, and IC2 form amonostable. When the monostable istriggered, it generates a pulse whosewidth is accurately determined by a 12 -MHz crystal.The number of times the monostable istriggered per unit time depends on the
input signal.The pulse height depends on thesupply of the monostable. The supply isprovided by voltage regulator IC; and isabout 5 V.At the output of the monoflop, i.e., pin 13of FF2, there will thus be a train ofpulses, whose width and height are con-stant, but whose number and, therefore,the average voltage is directly pro-portional to the input frequency.The RC network at the output of FF2forms a low-pass filter, so that theaverage voltage of the pulses will ap-pear across C6.Potentiometers PI and P2 and resistorsR7 and R8 form a potential divider whichenables the frequency - to -voltageconversion factor to be adjusted.The voltage across C6 measured by theDMM is thus directly proportional to the
frequency of the input signal.In range A, a voltage of 10 mV cor-responds to 10 Hz, and 1 V to 1 kHz. Inrange B, 10 mV corresponds to 1 kHz,and 1 V to 100 kHz.For adjusting the meter. temporarilyconnect the junction of R7 and R8 to pin12 instead of to pin 13 of FF2. Thereshould be no input signal. Set the DMMto the 20 V range, and connect it acrossC6. Set S2 to position A, and adjust Pi un-til the meter reads 2.93 V. Then set themeter to the 2 V range, and S2 to positionB. Now adjust P2 until the meter reads1.875 V. Finally, reconnect the junctionof R7 and R8 to pin 13 of FFzThe meter may be powered by a 9-V PP3battery: the current consumptionamounts to only 10 mA.
SUPPLEMENT 5
EE JULY:AUGUST 1988
5V
C1
0-1115n
R1
R2
C2
R5
C3
2
113p
D1 D2 R3
1C3
TLC271
4
2V7
a
56p
6
-13 0
FF12
3 CLK 50-R
FF2
0_
2CLK
D4
1N4148
5V
2V7
12
S2
1 41
8
100p
11{1-R) OL OF1C2
74HC(T)406141 (t'a
11 10
C8
1111.3p
suom
131 , D2= 1N4148FF1 ,FF2=1C1= 4013
*multiturn
RTTY FILTER FOR 170 HZ SHIFT
Anyone interested in the reception ofradio teletype traffic will appreciate theprogrammable audio filter describedhere, which may be fitted at the input ofthe RTTY converter. It improves thesignal/ -to - noise ratio, particularly ofsignals in the crowded short-wavebands.The circuit is based on programmablefilter IC3-see Fig. 2. The special facetof this IC is that the resistors of the on-board RC filters are simulated bycapacitors. This little-known techniqueis described in the January 1981,October 1982, and February 1983 issuesof this magazine.The value of the capacitors, andtherefore the pass -band frequency ofthe filter, is determined by the fre-quency of the clock at pin 8 of IC3. Theclock frequency is made variable bypassing a 10 -MHz signal through a pro-grammable divider, IC,. The divisormay be set between 1 and 256 with theaid of switches S!a-Sih.Monostable IC2 converts the outputpulses from the divider into a near -symmetrical signal, which is sub-sequently used as the clock for IC3 (pin8).
1
0
0
- 10
- 20
-30
- 40
50
60
-70
-90
- 90
1 1 1 1
-fCLK 130kHz
15 2 25
ti(kHz)
3 35
884004-11
The filter characteristic is shaped by theresistors at the various pins of IC3 to avery -narrow pass -band as is requiredfor small RTTY shifts. The characteristicis shown in Fig. 1. The entire pass -bandmay be shifted with the aid of theswitches.In narrow -band RTTY (70 -170 Hz shift),one filter suffices, since both the highand low AFSK frequencies can bepassed by the filter. For broadbandRTTY signals (425 -850 Hz shift), it isprobably better to use separate filtersfor the high and low frequencies.The circuit draws a current not ex-ceeding 20 mA.
6 SUPPLEMENT
2EE JULY AUGUST 1988
O
0 0 0 0
R1
0
R5
10-2271kI 224,
R2 R6
22k
R3 R7
22k
R4 RS
0-1 2 2 k 22
4 6 7 10 11 12 13
JO J1 J2 J3 J4 J5 J6 J7 14SPE0 CL 101
10MHz 74H C40103 CO 15
R23
0ttp
C3
R17
13
o0 >o_
z
R15
R18i R161 R11
11 12
C7
moo10
ENE
8 0 C8 16 1,c1IC2 mum IC1
R9
*--1 3 k 9 1--
3 2
mim
R131 R121 R11
XcX
+T IC2
4047B
R101 R19
17 118 119 120
C > ZLa-J
0 0n_
(23-< 07
R20
2 4
"
8
R25
< < < <Z > -J
_J
00.7.. >
T;(I)
IC3
LTC1061
9 15 6 16
R22
R21
7 10
C5
47
C6
16 V
884004-10
SECONDARY POWER -ON DELAY
The circuit described here enablesshort-circuit protection and power -ondelay to be added to a power supply.Power supplies with a large reservoircapacitor may draw such large currentson switch -on that problems occur, evenat the primary of the mains transformer.Particularly when a toroidal mains trans-former is used, it may be necessary to fita much heavier primary fuse than isdesirable for normal protection.The current in the secondary is limitedby a resistor, R:. in series with the reser-voir capacitor, C:. A few seconds afterswitch -on. R: is short-circuited by arelay contact. Compared with switchingat the primary side, this method has theadvantage that no separate supply forthe relay is necessary and that this doesnot have to switch the 240 V mains.
15V N'
8A
N
RI
0
'Cl78H12
12...15V
215,.
r. -Cl C21 PI --.-CI 1=3mum
22000y 100,1 2I5n25Y 25V
R2
12V2..
55-'4.32
SUPPLEMENT 7
EE JULY/AUGUST 1988
Operation is fairly simple. After switch -on, CI is charged slowly via RI. After afew seconds, the output voltage hasrisen sufficiently for the relay to be en-ergized, which causes Ri to be shorted.When the output of the supply is short-circuited, the output voltage drops to alevel where Re: is de -energized.Because Ri is then in circuit again, theshort-circuit current is limited and nor-
mally the voltage regulator does nothave to limit (less dissipation).Switch Si enables a choice to be madebetween a fixed output of 12 V and onevariable between 12 and 15 V.With heavy loads it may occur that theoutput voltage remains too low, becauseof R, to energize the relay. In that caseit will be necessary to remove the loadfrom the supply before this can switch
CAR TILT ALARM
Many cars are fitted with some sort ofalarm system as protection against pettycriminals and joy riders. Most of thesesystems rely on a door switch and oneunder the bonnet (to prevent inter-ference with the battery connections toimmobilize the alarm system). Suchsystems afford no protection whatsoeverto another criminal pest: those who jackup the car and remove expensive alu-minium sports wheels.
RI00
(!)A
reset CL10n
1_,S5
19Cl
The circuit described here is an add-onto an existing alarm and energizes thiswhen the position of the car is changed,for instance, by a jack being placedunder it.The position of the car is monitored byfour mercury switches which areplaced in such a way that when the caris horizontal they are open. Because acar is sometimes parked in an inclinedposition, which causes one or more of
16
*S1
0*S2.0 0
0*S3.10' 0
5
12
CLC
1D 01'Cl
2D4017502
3D Q313 Q4 15
0*S441r 0-0-
R2
* see text
R3
0R4
0R
IC2 1C3
on.The earth of the circuit is in a somewhatunusual place to enable IC: to bemounted on to the heat sink without aninsulating washer (IC ground is connec-ted to its case). For this reason, it is notpermissible to use the earth for externalground connection.
these switches to close, some additionalcircuitry is necessary.The four D -type bistables in IC, deter-mine the output state of the mercuryswitches. The outputs of ICI are con-nected to gates Ni to N4 which functionas inverters when the mercury switchesinitially are closed (so that there is a 1 atthe output of the relevant bistable). Thisresults in the outputs of the four gatesremaining 0 as long as the mercury
2
N1...N4 = IC2 = 4030N5 = 1/2 103 = 1/2 4072
11 12
9a0 10
11
12V
BC547
0884002.10
8 SUPPLEMENT
EE JULY AUGUST 1988
Parts list
Resistors (±5%):=100K
R2. . R5 incl. = 10KR6= 15K
Capacitors:C I;C2= 100n
Semiconductors:Ti =BC547IC1=HEF40175BP (Philips Components)IC2=CD4030CNIC3=MC14072BCP (Motorola)
Miscellaneous:St ...S4 incl.= mercury contact.S5= push -to -make button.PCB 884002 (not available ready-madethrough the Readers Services).
switches stay in that initial state.If only one of the mercury switcheschanges state, the output of N5 goeshigh and T1 switches on. This transistormay, for instance, be connected in paral-lel with the door switch.The output state of the bistables may bestored via R1 -C1 at the moment thesupply is switched on. All car alarmshave a certain delay after beingswitched on to give the occupants timeto get out of the car. If a signal isavailable that becomes 1 after this delay,it may also be used to store the outputstates in the bistables. Resistor RI andcapacitor Cl must then be discon-nected. This second method has the ad-vantage that if a mercury switch is justabout changing state, the closing of thecar doors will render it stable.The mercury switches are mounted onthe PCB together with the other compo-nents. One of the terminal wires of the
CIrleiCIOACtelD IC1
6-roA 99
9 t-tetrIntletn W +0
nITTIC3 00bb
OUGPOCIV 0
JO 0al- ILI
f6"t;
switches must be kept long enough toallow the switch to be slightly tilted withrespect to the board. The side of theswitch in contact with the board may
then be fixed into position with aralditeor a similar fixative. This arrangementensures that all switches are open whenthe car is horizontal.
33/4 -DIGIT DPM
Described is a digital panel meter-DPM-which is built around a specialmeter -IC, Type ADD3701, and may beused for the accurate measuring ofvoltage from a variety of sources.A highly stable reference voltage is pro-vided by an LM336. A ULN2003, IC4 isused to buffer the outputs of theADD3701, so that the common -cathodedisplays can be driven direct. TheADD3701 multiplexes the displays sothat the number of control lines is keptdown. The current through the displaysegments is limited by resistors Rs to R13incl.The oscillator that determines the con-version rate of the analogue -to -digitalconverter in ICI requires an extern RCnetwork (117 -CE). Because of the need ofadequate suppression of the mains fre-quency, the oscillator frequency mustbe exactly 400 Hz (it is very nearly equal
to 0.6R7Ce). A preset potentiometer maybe connected in series with 12.7 to adjustthe frequency accurately. At this oscil-lator frequency, there are about 3 con-versions per second.Another possibility of avoiding inter-ference from the mains frequency is touse the DPM for measuring positivevoltages only: LDs is then not required.The input voltage is applied to Vriri(pin 11) via a 100 kg resistor. Input ter-minals V(+) and V(-) are not used inthis case. Also, the oscillator frequencyneed not be exactly 400 Hz.The DPM is calibrated by short-circuiting the input and setting P2 to aposition where the display reads 0.000.Then apply a voltage of 1.900 V to the in-put and adjust P3 till the display reads3.800. An input voltage of 1.999 V willthen result in a display reading of 3.999.Take this into account if an input at -
tenuator is contemplated.The load presented by the input stage toa potential divider at the input is verysmall: typically, the input current is 1 nA(maximum 5 nA).The (unregulated) supply should beable to provide 8 to 12 V at a current of250 mA. The circuit, including the dis-plays, draws about 150 mA.
(National Semiconductor Application)
SUPPLEMENT 9
EE JULY/AUGUST 1988
L01= 7756LD2...LD5 = 7760 CC displays F.L.R15 = .5en
0250mA
IC27805
R16
R17
CICI2500pt6V
* see text
0
1=1C2
10V
0
DI
P1
105
*
LD1 LD2 L03 L04 LDS
I
1
1 L I: LI. L. leC
P
C 1 C
DP
15 14
b
9
13 12
1C4
ULN2003
R15
F15
R18
615
MEE
TFOn
151 16 17 18
Cs
10
19
H67
201 21 22 23 24 25 25 27 251
t20
r -t
vii of CC 1.11!
IC1
ADD 3701
s4Q t z <i n-s- e c- 4- ti 8 8 8 d
0
.
14 13 12 111 101 91 8' 7' 6 5
R19
770n
4 31 2
10p109
884011
DEFLECTION DETECTOR
Repairs to the e.h.t. section of a monitoror a television receiver always carry acertain amount of risk. It makes sense,therefore, particularly for the less ex-perienced technician, to seek a safeway of checking the extra high tension.In all television receivers and monitors,the e.h.t. is generated in the deflectioncircuits. These circuits operate at about16 kHz which generates a fairly strongmagnetic field via the line transformer.It may be safely assumed that as long asthe deflection circuits function cor-rectly, the e.h.t. will also be all right. Ad-mittedly, there is a possibility that adefect high-tension winding may be theculprit. But let's not be pessimistic....The proposed circuit enables 'wireless'monitoring of the e.h.t. section, since itpicks up all signals between about14 kHz and 45 kHz (and their harmonics)and converts them into audio signals.The frequency of oscillator ICI may bevaried with the aid of a potentiometer.The oscillator output is mixed with the
R4
CI
C4
R1
;5 C8
1000 Iy16V
I=M
C3 T1 R5
6F981
C2=In/2, On
C6
II47n
6
1C2
CA3130
R6
67
C7
884316
9V
10 SUPPLEMENT
detected deflection signal in T,. SinceIC2 is connected as a gyrator, filterLI - CI at the drain of Ti removes anaudio signal from the mixing product.The small audio signal is amplified in T2to a level sufficient to drive a small loud-speaker.The detector 'probe' is best made from
0 0
a short length of insulated equipmentwire, preferably, but not necessarily,connected to a small insulated metalplate. To test whether the deflection cir-cuits operate correctly, the monitor ortelevision receiver, as well as the testcircuit, must be switched on. Then theprobe should be placed in the vicinity
EE JULY/AUGUST 1988
of the line transformer and the poten-tiometer in the tester adjusted until aconstant whistle is audible from theloudspeaker. When the monitor (TV re-ceiver) is switched off, this whistleshould disappear. If this happens, thedeflection, and therefore almost cer-tainly the e.h.t., will be all right.
SIMPLE TRANSISTOR TESTER
While experimenting with electroniccircuits, it will often be necessary to rap-idly test bipolar transistors and FETsbefore they are fitted in the circuit, orwhen they have been removed from thecircuit when a malfunction is suspected.More specifically, constructors willneed to know whether a transistor ofknown type and make is sound or not,and also whether an unknown device isa particular type of FET, or a bipolartransistor (PNP or NPN).This tester can be built from parts foundin the junk -box. When the transistorunder test (TUT) is OK. and correctlyconnected, the circuit will oscillate dur-ing half the period time of the alter-nating supply voltage (50 or 60 Hz). RedLED Dz lights when the TUT is OK andof the NPN type. The function of greenLED Di is similar for PNP TUTS. TheTUT OK/not OK indication is obtainedwith S2 set to the centre position, and Siopened as shown in the circuit diagram.
1 R1
0D1 D2
green
0T1
BC560C
3 300
The LEDs will indicate that the oscilatoramplitude is significantly reduced, ornought, when St is closed with abipolar TUT mounted. Correctlyoperating FETs produce oscillation ir-respective of the position of Si. Only J-FETs and dual -gate MOSFETs produceoscillation when S2 is set to positions Aand C.The accompanying table should speakfor itself. Note that S3 must be openedand closed after each change in theposition of S2.Finally, the tester is preferably fed froma 6 VAC mains adapter.
R2
L1
L2
C3
100p _0S.-0
4mH7
00R4
1k
0B
ocoOA
0 G1
R6
C5 R5
100n
00 S3
6V
C4mim
100n
884015 - 10
SUPPLEMENT 11
EE JULY AUGUST 1988
Parts list
Resistors 5%):RI =330RR2;R3;R4=1K0Fls;Ra = 100KRS =4M7
Capacitors:
C3= 100pC4;C5 = 100n
Inductors:Lt =4mH7 radial choke, e.g. Toko Type
181 LY472 (Cirkit).L2=1mH5 radial choke. e.g. Toko Type
181LY152
Semiconductors:Di = green LED02= red LEDTi =BC560C1-2=BC5 50C
Miscellaneous:St = miniature SPST switch.S2= 3 -way rotary switch.6 off 4 -pin transistor sockets.PCB Type 884051 (see Readers Servicespage).
2
0
SWITCHTUT Si S2
B oA o
0 C
BIPOLAR0
c
J-FET x
o I
DG-MOSFET x 0 (U9.2 = 1/2 Ud) } (gi to 92)
ENHANCEMENT(MOS) FET
xo
= oscillation= no oscillation
x = irrelevant
o es#6
CRieeC\ALidl&
I
82
)
A C ,,c)2 ,,c310 0 o o ol4o 0(40T2
21 91 92 9 d
L2
9 9 s b c b e e
HIGH -VOLTAGE BC547
It is sometimes desired to use a BC547 atrather higher voltages than permittedaccording to the data book. Yet, it canbe done by connecting a number ofthem in series as shown in the ac-companying diagram.The set-up has a few, small, disadvan-tages: there is a constant leakage cur-rent through the series resistors and thesaturation voltage is rather higher.Where these disadvantages are of littleor no consequence, the circuit shownhere can be used with voltages up toabout 100 V.Assume that a voltage of 100 V has to beswitched and that the maximum currentis 2 mA. If the current amplification is
U
200, the base current will be 10 yA.Transistor T3 will then switch on as soonas the p.d. across is 0.68 V. The basecurrent of T2 also flows through R.:, sothat the drop across this resistor rises to1.36 V.The current that switches Ti flowsthrough R1. so that it does not cause anadditional p.d. across the potential div-ider. There is. of course, the usualsaturation voltage of about 0.2 V acrossT:. The total drop across the divider isthen 3(10-' x 68 x 103)+ 0.2 = 2.2 V.Increasing the resistor values to 270 kraises the saturation voltage to 8.3 V. Theleakage current is then much smaller.
12 SUPPLEMENT
0L I
EE JULY/AUGUST 1988
SERVO -PULSE GENERATOR
Circuits for the generation of controlpulses for servo apparatus remainpopular, which seems a good enoughreason to present another one.The popularity of servo control is en-hanced by the low price of servomotors, and the fact that they can beused for a variety of applications. Thepresent design is geared to stand-aloneuse of the servo.Simplicity of the circuit was the firstdesign consideration, and it seemedreasonable, therefore, to base it on thewell-known 555 IC. Unfortunately, thischip has the property, in its standardconfiguration, of producting pulsetrains with a duty factor* of 50% orgreater. This is so, because the chargingtime constant is always greater than thedischarge one, since during chargingthe discharge resistance is in serieswith the charge resistance.Servos, on the other hand, require pulsetrains with duty factors well below 50%.Ideally, the pulses should have a widthof 1-2 ms, and the pulse repetitionfrequency - prf- should be about 50 Hz.This gives a duty factor of 5 -10%.
0 I
*see text
This problem may be resolved by invert-ing the output signal of the 555 with theaid of a transistor and two resistors, butthis was considered extravagant. All itneeds is an extra diode and relocatingthe discharge resistance. The charging
time, and therefore the length of timethat the output is logic high, is now de-termined by Pi, RI, and the dischargetime through R2.The component values in the circuithave been chosen in a manner thatcauses the pulse width to change from1 ms to 2 ms when the resistance be-tween the positive line and the anode ofDi is increased from 2k7 to 5k4. This re-duction in resistance is brought aboutby a 75° shift of PI (normal joysticktravel), if this potentiometer has a valueof 10k. This potentiometer must be set toa position where its resistance is 4k1when the joystick is at centre position.Resistor Ri should then be replaced bya wire link.It is possible to use the normal 270'travel of the potentiometer, whichshould then have a value of 2k7. Resistor111 must then be used as shown.
'The duty factor of a pulse train is the ratio ofthe average pulse width to the average pulsespacing of pulses in the train.
SELF -SWITCHING POWER SUPPLY
The proposed power supply switchesitself off when no current is drawn bythe load. How this is done is shown inthe circuit diagram, Fig. 1.When a load current flows, the p.d.across DI is sufficient to cause D2 and T2to conduct. Ti is then switched on andthe relay is energized. When the loadcurrent ceases, T2 switches off. Thebase current of T1 will then charge C2 sothat after a few seconds the relay is de -energized. The relay contact, ref, willthen switch off the mains at the primary
FlTr1Tel B40C1500
Si
Ref
C1I=1
470...1500y 25V
40-
BC5478
of the transformer. The supply isswitched on again by reconnecting theload and pressing Si briefly.The output voltage depends on the re-sistance between A and B. A wire linkthere results in an output voltage ofabout 3.5 V. For each 100R increase, theoutput voltage will rise by about 1 V (thecurrent from the regulator to ground is anearly constant 10 mA). This makes itpossible to obtain a variable outputvoltage with the aid of some resistorsand a rotary switch as shown in Fig. 2.
."254.111°°"
1d7805 ;
-41
2x 1144001Di 02
NHR2
BC5578
0
The relay, Ref, should be of a type that issuitable for switching mains voltages.The a.c. rating of the secondary of Tr,must be about 1.5 times as high as thedesired d.c. output current. The outputcurrent should not exceed 1A; if thatmagnitude of current is drawn regularly,it is recommended to increase CI to1500 ELF.The delay in switch -off may be ex-tended by increasing the value of C2.The heat sink of IC, should be in ac-cordance with the output current.
31/5
ES4056.2
88-1056 - 1
SUPPLEMENT 13
EE JULY/AUGUST 1988
LCD FOR Z80 -DRIVEN COMPUTERS
There is a growing tendency to useliquid -crystal displays (LCD) as thescreen of computer monitors. Such dis-plays may also be used where the nor-mal monitor is too large or draws toomuch current; they are readily available.An LCD is normally driven by a micro-processor: in the proposed circuit by aZ80.The display in the proposed circuit is aSharp Type LM16251: a full descriptionof this appeared in the May 1986 issue ofthis magazine. It is located in the I/Oregion, addresses 0 to 3, of the pro-cessor. This arrangement enables thecircuit also to be used in combinationwith the 32 -bit I/O and timer cartridgedescribed in the January 1987 issue ofthis magazine. This cartridge does notuse the lowest four addresses (chooseaddress 0 for the cartridge so that an ad-ditional I/O region of 0 to 15 is ob-tained).The address coding is effected by gatesNi to N4. When A2 to A7 are, and I0REQ becomes, low, the output of N3goes low. If MI is high (no interruptdemanded), N4 outputs a 1 and an en-able signal is given to the display.Depending on the logic levels at inputsR/W and RS, data is transmitted or re-ceived. The RD and WR outputs of theZ80 are not used, because the R/W andRS signals of the LM16251 must be stablenot later than 140 ns before the E inputgoes high. If the RD or WR signals of theprocessor were used, the E input of thedisplay would be accessed togetherwith the other signals and that is not per-mitted.By using an address line, the timing isarranged by that of the Z80, because theaddress bus must be stable not laterthan 320 ns (180 ns for Z80A) before anJO REQ signal is generated. Owners ofa Z80B-driven computer might havesome problems here because the timedelay is then only 110 ns. Note that MSXcomputers invariably use a Z80A.The negative voltage for the contrastsetting (Pt) of the display is provided by
0 I
137 ' D7
D6
05
D4
D3
D2
131
0--1-940 206 037D5 0
0 38 404
35 5Do 036 602 p.
33 7DI
DO
034p.
LM16251
RURs
vo
,k.7,/
USREO 0 10
ItTFTCO11
21 4 10A7 p'
22 5
DA6 0
31A5 11
32 12 10 2 DA4 0 CO29 13A3 sr
30A2
Al
027 10
AO
028 11
Mt 9042 Cl DI 1N4148
CLOCK 17, ED100n C2D2 MBE12P1
1N41480 0n 1k
45
47 1 13041
.43 14
mm.
10
C31 CaIC1,IC2
loon 100n
N6. Note that some types of displayneed a positive voltage for the contrastsetting. Wire link 'a provides a negativesupply, and 'b' a positive one. Link 'a' isrequired for the LM16251. If anothertype of display is used, make sure that
N1...N3= ICI = 74HCT4075N4...N7 =1C2= 74HCTOO
884066-10
the pin numbering is the same as shownin the diagram.Gate Ns serves to render the BUSDIRline low at an I/O read command in MSXsystems. In other systems, this gate is notrequired.
CAR INTERIOR LIGHT DELAY
It's dark and it's raining cats and dogs.You rush to your car, open the door andquickly close it behind you again. Thenyou sit there fumbling for the ignitionlock. Solution? Add the following cir-cuit, which will keep your car's interiorlight on for a little while after the door isclosed.The circuit is connected across theswitch in the door post. These switches
are removed quite easily.In the circuit diagram, Si is the switch inthe car's doorpost and LI is the interiorlight. As long as the door is open, Si isclosed and the light is on. When thedoor is closed, Si opens and the lightgoes out. The full 12 V from the car bat-tery is then present across the switch.The circuit detects when the voltageacross Si begins to rise. Transistor T3,
and consequently T1 and T2, is thenswitched on. This results in the voltageacross Si rising to about 1 V, after whichit can increase only very slowly. Thismeans that the interior light stays on,although its brightness will slowlydecrease.At a certain level of potential across Si,transistor T4 switches on, which resultsin the drive to T3 becoming zero, and T3,
14 SUPPLEMENT
EE JULY/AUGUST 1988
T2, and Ti switch off. The interior lightwill then go out very quickly.The delay in the light going out after thecar door is closed is preset by PI,although it is also affected by the valueof CI. The larger this value, the longerthe delay and the smaller the variation inthe brightness of L. After the light hasgone out, the circuit no longer drawscurrent.
884008 -10
POLAROTOR CONTROL
The polarization of satellite TV signals isdefined as horizontal (H) or vertical (V)with respect to the equator below thesubsatellite point, and not, as is oftenwrongly assumed, with respect to thehorizon on earth. Depending on the lo-cation of the receiving system on earthand the satellite's geosynchronous pos-ition, a horizontally polarized signal mayhave some offset with respect to thehorizon. As a rule of thumb, the lowerthe dish elevation for a particular satel-lite, the greater this polarization offsetangle. The difference between horizon-tal and vertical is, however, always 90°.Most commercially available polariza-tion rotation units (polarotors) used forselecting between horizontally and ver-tically polarized transponders on boarda TV satellite incorporate a small servomotor whose direction of travel is con-trolled automatically by the channelselection circuitry in the indoor unit, orsimply by a switch. The servo motorrotates an angled probe fitted in a PTFEbush in the waveguide flange that issecured onto the feed horn. This probecan be rotated over 90°, and re -transmitsthe received 11 GHz satellite signal bymeans of a 1/4). probe fitted vertically inthe waveguide that connects to the LNB.The polarotor assembly is fitted perma-nently between the feed horn and theLNB input, and is connected to the in-door unit via a length of 3 -wire cable,which runs in parallel with thedownlead coax. A polarization selectionswitch, S3, is provided on the IndoorUnit for Satellite TV Reception oi, butnot the accompanying driver circuit,which is given here.The polarotor control is an astablemultivibrator that determines the direc-tion of travel of the servo motor by sup-plying output pulses with a duration of1 ms (V) or 2 ms (H) (typical values).When horizontal/vertical (H/V) switchS3 is closed, Pi is short-circuited, so thatICI supplies pulses with a duration of1 ms. In the polarotor assembly, a com-
bination of a potentiometer coupled tothe motor spindle and an electronic cir-cuit is used for comparing the durationof the received control pulses with thatof the internally generated spindle posi-tioning pulses, and actuates the motoruntil the pulses are of equal duration.The microwave probe in the feed hornwaveguide is then positioned vertically.Similarly, when S3 is opened, Pi is in-cluded in the R -C timing circuit of ICI.Due to the higher total resistance, ICIsupplies pulses with a duration of about
2 ms, so that the waveguide probe isrotated over 90° for reception ofhorizontally polarized signals.The control circuit and the servo motorare powered from a regulated 5 Vsupply, which is simple to constructaround a Type 7805 3 -pin integratedregulator. In the case of the above men-tioned Indoor Unit, the input of the 7805can be connected to the input of IC7(Type 7812 on the vision/sound/PSUboard). Due care should be taken, how-ever, not to overload the mains trans-former, Trl, or optional series resistorRx, since the maximum current con-sumption of a blocked polarotor motoris typically about 300 mA. In somecases, it may be necessary to fit a rela-tively large electrolytic decoupling ca-pacitor direct across the supply ter-minals of the servo motor. The value ofthis capacitor depends on the actualcurrent consumption of the motor, but470 pF should work satisfactorily in mostcases. It is recommended to use fairlystout wire for connecting the polarotorto the control circuit.The circuit is simple to set up: connectan oscilloscope to the pulse output line,and adjust Pi and P2 for correct dur-ation of the rectangular output pulses(note that the settings interact). Openthe available polarotor to check that thetravel of the probe covers the full rangeof 90°. In the absence of an oscilloscope,PI and P2 are adjusted until the servomotor works reliably over the full rangein both directions of travel. Polarizationoffset correction can be achieved by ad-justing the presets accordingly. Con-tinuous adjustment of the probe pos-ition (skew) for satellite reception ex-periments can be achieved by usingpotentiometers instead of presets inpositions Pi and P2. Current consump-tion of the control circuit is about 7 mA.
(1) Indoor Unit for Satellite TV Recep-tion. Elektor Electronics October &November 1986, January 1987.
SUPPLEMENT 15
EE JULYIAUGUST 1988
PROGRAMMABLE VOLTAGE SOURCE
A number of appliances, such as anEPROM programmer, require a supplyvoltage that can be switched to a varietyof levels. The proposed circuit enablesthe user to do so between 5 V and 21 V.As soon as the switching transistor con-ducts, R3 is connected in parallel withR2. This lowers the total resistance be-tween the 'adj' pin of the LM317 andearth, and consequently the outputvoltage.It is possible to add a number ofswitching transistors and associatedresistors and capacitor to the circuit toincrease the number of available outputvoltage levels.The level of the output voltage dependson the ratio between RI and theresulting value of R2 in parallel with R3.The p.d. across RI is always 1.2 V. Thus,
Uo = [1+R2/RR3I volts
Capacitors CI and C3 serve to optimizethe switching behaviour of the circuit.The value of these components has tobe established with the aid of a square -wave generator and an oscilloscope.The effect of these capacitors on the
1
I
output voltage is shown in the photo-graph.An additional advantage of the use of anintegrated voltage regulator is that thisaffords a means of current limiting. If,for instance, the 'E type of this IC isused, current limiting starts at about100 mA. This magnitude of current willbe more than adequate for mostEPROMs.Finally, it is possible to replace T1 and R4by a high -voltage open -collector TTLgate, such as provided by the 7407.
AUTOMATIC VOLUME CONTROL
The proposed AVC gives weaker com-ponents of the input signal extra amplifi-cation while ensuring that this dynamiccompression is not disconcerting. Ittherefore eliminates those annoying dif-ferences in loudness between speechand music on radio and television.The principle of the circuit is fairlysimple. Field-effect transistor T1 is usedas a variable resistance. The value of thisresistance. rips(0.), can vary from infinityto about 150R. It is in parallel with R3and, in conjunction with R4, determinesthe gain of Al. Without the effect of theFET, the gain of Al is about 20 dB.Opamp A2 is connected as a straightfor-ward amplifier, whose gain may bevaried by PI. The negative part of theoutput signal of A2 is connected to thegate of T1 via a rectifier formed by Dt, C1,R7, and Rs. Resistor R8 ensures that theswitching of T1 happens gradually. Thismeans that it takes a short time before T1operates; in other words, momentarydifferences in input level do not affectthe overall gain. The reduction in gainalso takes place gradually, because CIhas to discharge via R7.Because the resistance of T1 is influ-enced by the drain -source voltage, UDS,
1
A1,A2 = ICI = TL0721C2 = TL071
BF245C
G 0
*1.1©x 13C H.see text
the signal level has to be kept as low aspossible (thanks to the use of opamps,there is no direct voltage across thedrain -source junction). An attenuator,R1 -R2, which gives an attenuation of40 dB, is therefore provided at the input.This enables signals of up to 1 V r.m.s. to
be processed with a distortion of notgreater than 0.6%. With an input of 1 Vr.m.s., the signal-to-noise ratio is about70 dB.The amplification in Al and A2 compen-sates the losses in the attenuator: thetotal gain of the circuit, with T1 switched
16 SUPPLEMENT
EE JULY/AUGUST 1988
Parts list
Resistors 1±5%1:fir;Rs= 10KR2= 100RR3;Rs = 11(5R4 = 15K116;138=100KR7 = 1 MOPt =100K multiturn preset
Capacitors:CI =100; 16VC2;C3=1p0; MKTC4 = 12nCs... Ca incl. =100n
Semiconductors:D1=1144148Ti =BF245CICt =TL072IC2=TL071
Miscellaneous:PCB Type 884023 (not available ready-madethrough the Readers Services).
3
0
2
0
-5
-15
-30
-25
40 -35 -10 15 -20 -15 -10 -5 0 5
Ujr, ;jig]17
o-o-0 -
off, is 0 dB.Network R9 -C4 is a high-pass filter whichensures that strong bass signals do notaffect the control function to much ex-tent. The cross -over point may bealtered to personal taste.Signals at a level below that set by Pi areamplified by a factor of up to 6.9(gain =17 dB). Fig. 2 shows the relationbetween input and output levels.The circuit needs a supply voltage of+15 V and draws a current of about6 mA.
wm, 9 9
CI
0 -7Z -010o 1 2ci
(1,tat WU to. 0.
a -P1 0.A.as a c°171°° 0+
0 0calloo 0-0-4179_ 0
6°1 Tr
R7R1RB
-o
-o
1SAMPLE & HOLDFOR ANALOGUE SIGNALS
Conventional analogue sample and holdcircuits are notorious for their tendencyto drift. a phenomenon unknown in digi-tal memories. It is, therefore, interestingto study the use of a digital memory el-ement for storing an analogue signal.The present circuit is based on in-termediate storage of digitizedanalogue information, and therefore re-quires an analogue -to -digital converter(ADC) at the input, and a digital -to -analogue converter (DAC) at the output.Unfortunately, DACs and ADCs aretypically expensive components, andthe present circuit is therefore set upwith a DAC only, driven by an up/downcounter-see Fig. 1. The counter is es-sentially an ADC, since the outputvoltage of the R -2R based DAC is con-tinuously compared to the input voltagewith the aid of a window comparator.The error signal produced by the com-parator arranges for the counter tocount up or down, depending on themagnitude of the difference betweenthe input and output voltage. Theup/down counter is corrected until theinput and output voltage are equal. Thedigitized result of the A -D conversion is
available at the counter outputs.The extensions for converting the basicset-up into a sample & hold circuit arerelatively simple. The current count is
1
hold
windowcomparator
retained by activating the HOLD input,which enables halting the U/D counter.Evidently, the counter state is not sub-ject to drift, so that the analogue output
osc
U
D
U/D-counter
u ref
D/AR -2R
87511-1
SUPPLEMENT 17
EE JULY/AUGUST 1988
signal is available unaffected for as longas the circuit is powered. The converterused here is the Type ZN435 ADC/DACfrom Ferranti. This chip containseverything shown in the dashed box ofFig. 1. With reference to the practicalcircuit diagram, Fig. 2, the internalvoltage reference and the oscillator areadjusted with Ri-C, and R2 -C2 respect-ively. The latter are dimensioned for400 kHz, i.e., nearly the maximum oscil-lator operating frequency. The internalcounter is controlled via inputs up,down and mode. The logic levelapplied to the mode input determineswhether the counter continues or haltsupon reaching state 0 or the maximumvalue, 255. In the present application,the counter is halted. Gates Ni and N2are added to enable blocking the U/Dcounter. Opamps Al -A2 form the win-dow comparator. Current source T1 -R7and R6 arrange for the toggle thresholdof Ai to be 20 mV higher than that of A2.This off -set creates the window, or inac-tive span, needed to suppress oscil-lation of the counter's LS bit, and to pre-vent unwanted effects arising from thecomparators' offset voltages. Decoup-ling capacitor C3 is fitted for sup-pressing spikes that occur during statechanges on the counter outputs. The
25V
40mA
Oar87
805578
0
hold
R5
RSn 8415
Al
A2
R3
131 15
14
15
MG!
IC1ZN435
12 um.f at
°refnode
2
3
4
5
7
15
Al ,A2= IC2 = IA1393NI , N2 = 1/2 IC3 = 74LSOO
I =digitalII = analogue
conversion time of this design is about640 ;is, as determined by the oscillatorfrequency (400 kHz), the resolution (8bits) and the input voltage change(2.55 Vpp max.). This corresponds to a
C2 Clolm 010
TINNO0o 220,3
A= Uref =2.55V
C3
57511-2
014580000 Wo ;
0O L.58
00n
0
slew rate of 4 mV/is at the input. Finally,bear in mind that the output impedance(IC,, pin 11) is relatively high at about4 kQ.
LOW -FREQUENCY LC OSCILLATOR
It is not always appreciated that LC cir-cuits may be used for generating lowfrequencies. The proposed circuit, pro-vided it uses good -quality components,can be used for frequencies down to150 Hz, and possibly even slightly lower.The oscillator proper consists of T1 andT2 with the LC circuit connected in thecollector circuit of T2. The amplificationis set with the aid of the current sourcearound Ts.The voltage across the tuned circuit istapped at high impedance andamplified by Ts. The output of this FETis buffered by T3 and then rectified byDI-D2. The resulting direct voltage isused for driving the current source.Since the rectified voltage still containsa ripple, a further buffer, T4, is added atthe output of the circuit.The circuit draws a current of about20 mA, which can rise to about 25 mA athigher frequencies. Its output im-pedance has been kept as low as poss-ible to render the bandwidth of the os-cillator as broad as possible.Fairly high values of inductance may beused, provided the Q is of a reasonablevalue. Capacitor values may go up to10 µF, but note that electrolytic typescan not be used.In the prototype, LI had a value of150 mH and CI was 6/18: the resultingfrequency was 150 Hz. The oscillatorgenerates pure sine waves up to 7 to
C9BE=moo
1p
*L1
0 R1
*C1
C2
100n
T5
C4
1:10n
T3
R5OR60 C=TMR4flON
T6
D1,D2 = 1N4148T1...T4 = BF199.T5 = BF256BT6 = BC550C
D1
10y
* see text
C6 R7
47p1011
Tant.
D2
10 - 25mA 05V
T4
C3 ::.1250mV
CS 0100n
1 0 0
#
884070 - 10
18 SUPPLEMENT
8 MHz and operates well up to about30 MHz; the waveshape is then nolonger a pure sine wave, however. Oper-ation at still higher frequencies is poss-
0 2
ible, but the output level then dropsfrom the nominal 250 mV.The circuit may be used to measureunknown capacitors or inductors, pro -
EE JULY/AUGUST 1988
vided the other component in the LCnetwork is known, with the aid of theformula f =1/2n1 LC.
1SINGLE -CHIP 150 W AFPOWER AMPLIFIER
The Type LM12 operational amplifierfrom National Semiconductor has atleast one remarkable characteristic: itshuge output current capability of about10 A. The chip is housed in a 4 -pin TO -3enclosure, can handle peak powers upto 800 W, and has extensive internal pro-tective circuits to prevent damage caus-ed by current and voltage overloading,or by overheating. Peak operating tem-perature of the on -chip power outputtransistors is measured for controlling alimiter that forms part of a so-calleddynamic safe area protection circuit.The power output stage is not connec-ted to the relevant pin until the supplyvoltage exceeds 14 V (±7 V). Outputdisconnection is automatic when thechip temperature rises above 150 °C. Itis possible to connect LMI2s in parallel,or in a bridge configuration, for veryhigh power applications (voltageregulators, automotive drivers, steppermotor or power servo controllers, etc.).The present application discusses theuse of the LM12 in a high -power AFamplifier.The circuit diagram shows two clamp-ing diodes at the chip output. Theseprevent the output voltage swing ex-ceeding the supply voltage when thepush-pull output stage in the chip isoverdriven, and the output load ismainly inductive. The diodes also pro-tect the chip when the output is short-circuited to the positive or negativesupply rail. The Type LM12CL or LM12Cmay be used with supplies up to ±30 Vor ±40 V respectively.
Parts list
Resistors (±5%):RI ;R3= 10KR2=220KR4 = 2R2; 4 W
Capacitors:CI =1p0; MKTC2 = 6p8C3;C4=100p; 40 V
Semiconductors:131;D2=BY229ICI =LM12 (National Semiconductor)
Miscellaneous:Large heat -sink for ICI °C).Insulating material for ICI.PCB Type 884080 (see Readers Servicespage).
Input bias currents are compensatedbecause the circuit is laid out for virtu-ally equal impedance at the invertingand non -inverting input of the opamp.Input offset is 20 mV maximum. If this isconsidered too high, it can be cancell-ed completely by applying an appro-priate offset compensation voltage toone of the inputs (use a well-decoupledpotential divider). Output offset voltagein a number of prototypes without com-pensation circuitry was between 100and 200 mV.Half -power (-3 dB) bandwidth of theamplifier is 16 Hz to 40 kHz; distortion isapproximately 0.02% at P0=1 W andRL=2 C.2 or 4 Q. At full drive, distortionincreases to 0.05% (//b= ±30 V; Ri=4 Q).Maximum current is supplied to a 2 Qload, but distortion then increases to0.1%.Quiescent current of the amplifier is be-tween 65 and 100 mA. Inductor Lt iswound as 40 turns of 1 mm dia. enam-elled copper wire on power resistor R4.It serves mainly to ensure correct oper-ation of the feedback amplifier withcapacitive loads, such as large voicecoils and loudspeaker cross -over filters.It will be clear that the supply for theamplifier must be capable of handlingthe peak current requirement of theLM12. For the LM12CL, it is rec-ommended to use a toroid mains trans-former with a 2 x 22 V secondarywinding (150 W can then be supplied toa 2 Q load only). Depending on the ap-plication and the output power re-quired, the transformer's secondary
0E10088 S cl 3 a
*Stt tt2t
mow
01.02.= BY229ICI = I.M12
should be rated between 7 and about12 A. Smoothing capacitors in the sym-metrical supply should be not smallerthan 20,000 pF on each rail.Finally, IC: should be bolted on to alarge heat -sink, from which it is elec-trically insulated.
'011111111111.,
r1
SUPPLEMENT 19
EE JULY/AUGUST 1988
0 2 AUXILIARY NEGATIVE -VOLTAGE SOURCE
Many circuits require, apart from theusual positive voltage source, a negativesupply from which only a small currentis drawn. In such cases, a mains trans-former with twin secondary windingwould be a rather too costly solution.The circuit proposed here generates anegative potential from a positivesupply. This supply may provide be-tween 5 and 15 V. If the current drawnfrom this supply is smaller than 1 mA,the level of the negative voltagegenerated lies about 1.5 V below that ofthe supply voltage. Thus, if the supply is5 V, the negative potential is -3.5 V.When a current of 2 mA is drawn fromthe supply, the difference between thetwo voltages increases to about 2.5 V.Operation of the circuit is fairly simple.Gate Ni, in conjunction with parallel -
01
connected gates N2 to N6 incl., functionsas a square -wave generator with buf-fered output. The peak -to -peak valueof the square -wave voltage is, due to theuse of CMOS gates, very nearly equal tothe supply voltage. Rectifier D,-D2 en-sures that the alternating voltage is con-vened into a steady negative one.If a clock frequency between 10 and50 kHz is available, this can be appliedto the input of Ni. Capacitor Ci and RIare then not required.
(Intersil application)
1C1 =
CD4009
D1,D2= 162148
10y105/
884012
SINGLE -CHIP SOLID-STATE RELAY
Light -duty (25 to 600 W) solid-state relayshave recently been introduced on themarket by Sharp. These small and com-pact devices switch accurately at thezero -crossing and provide the requiredelectrical separation. The photographshows clearly that switching occursexactly at the zero -crossing. Thisprevents switch -on currents of lampsbecoming large and so extends the lifeof the lamp.The breakdown voltage of the triac sec-tion is 2 kV and the pins are on a 0.1 ingrid.The relay requires an energizing cur-rent of 10 mA at 1.4 V, but with inductiveloads about 25 mA is necessary.The additional components shown inthe diagram make the relay moreuniversally usable. Diode Di preventsthe IC being damaged if the input isconnected incorrectly. Transistor Tisets the trigger current to precisely10 mA. The RC network at the outputprotects the triac from sharp voltagepeaks.The IC may be used without heat sink toswitch currents up to 1 A. For switchinglarger currents, up to a maximum of 3 A,a 2mm thick 100 x100 mm heat sinkshould be used.
1
131
G:..0S
C1100n630V
884074
20 SUPPLEMENT
EE JULY/AUGUST 1988
0 2TIMER
This timer can be set to count a maxi-mum of 60 hours. It also allows an inter-val to be set. When this interval isreached, a buzzer sounds.The larger part of the circuit is con-tained in an Intersil Type ICM7217 four -digit CMOS up/down counter and dis-play.Circuit IC3 is the clock that generates asquare wave with a period of 1 s. Theclock signal is available at pin 3 (Q13).The clock signal may be divided by 60in IC4 if it is required to time more than1 hour.When Ss is closed, the supply isswitched on and IC, is reset via R9 andCs The position of S4 determineswhether minutes or seconds arecounted: maximum 59 h 59 min (pos 2)or 59 min 59 sec (pos 1).
5V
0
2
CLR
5 IC4 -APEp, CO: 7C
7 13'143
12
13 CD40103
CLCE ax
0
C1I
16
161
0
SPE
1C3 MRCD4060
RTC RS
R7 0
32Jaklez FJ
C10
T°0p TODD
C121
PB2720
MI=
017
I1N4148
If, for instance, a total time of 35 min withan interval at 20 min is to be counted, S4is set to position 1. Thumb wheelswitches S7 to Sio are then set for a dis-play reading of 20.00. Briefly pressing S3
stores this setting in the memory of ICI.Then S7 to Sio are set for a displayreading of 35.00. During these settings,Si should be open. Pressing S2 causesthe ICM7217C to count down from 35.00.When display reading 18.00 is reached,the buzzer briefly sounds (energized viaN3 and N4). The timer may then bestopped by closing Si. When Si isopened again, the timer restarts thedown count to 00.00. When that readingis reached, the buzzer sounds brieflyagain. Note that at any time during thecount down the timer may be stoppedby closing Si.
N1...N4 = IC2 = CD74HC(T)132D1...D16 = 1N4148
5V
C4
mrt0On
14 RESETEl
S3ts4SET
ALARM
11201 24DC et.FL'OFF
START
* ,,ee teat
-a
=
e
-E
IC1
0450)134
1:13
D2
(LSD) DI
ICM
7217C
TFP0EQUAL
0-'s
65
STOPS Ut)9 19 10
M..50
LDI
23
27 7
25 3
28 2
22 1
26 10
15
IS
17
18
The timer is reset with S5; when that hap-pens, the buzzer sounds briefly and thedisplay reads 00.00. The set count downperiod of 35 min is, however, retained inthe memory until a new period is pro-grammed.The current drawn by the timer, includ-ing the displays, is about 100 mA. If abattery supply is used, it is possible toswitch off the displays when the timer iscounting by adding a switch (with singlebreak contact) between points A and B.This switch enables the display to beread briefly. With the displays switchedoff, the current drawn is of the order ofonly 4 mA.Do not set the thumb wheel switches toreadings greater than 59.59, becausethe timer will then no longer count cor-rectly.
LD1...LD4 = 4x TFK0300PKH
LSD
LD2 LD3 LD4
0000 00 000
0 O'O 0 0 0000
o o 0 0 0 0
LSD
SUPPLEMENT 21
EE JULY/AUGUST 1988
L
FLASHING LIGHT
This is a rather unusual application ofthe Type 317 voltage regulator. Withonly a handful of external components,it can be used for flashing a small 12 Vlamp. The output voltage is not stabiliz-ed by the circuit: it is simply a few voltslower than the input voltage. The 317 iscapable of delivering more than 1 A.The circuit automatically limits theswitch -on current, so that lamp life isconsiderably extended. The waveformsat the four major points in the circuit areshown in the accompanying photo-graph.The component values given result in aflash frequency of about 4 Hz. Flashingcan be stopped by driving Ti with avoltage of more than +1 V.
Source: Lambda Power Supply Hand-book
0
IC1 LM317
i AMPLITUDE CALIBRATIONGENERATOR
A calibration generator is used forquickly checking receiver operation.The design shown here generates RFsignals (markers) at I MHz intervals overa frequency extending up to about 2GHz. These signals can be amplitude -modulated by driving T4 with a sinewave generator.A stable 2 MHz oscillator is set uparound XI and Ti MOSFET T2 functionsas a digital buffer for clockingbistable/divider FF1. Pulses at the out-put of FF2 have a frequency of 1 MHzand a width of only 12 ns, which is ob-tained by FF2 clearing itself after outputQ has gone low. The pulses drive T3into saturation. This SHF transistorconsequently produces a wide spec-trum of harmonics, and its class C set-ting causes it to function as a frequencymultiplier. The collector current can bemodulated via series transistor T4. Sincethe two sidebands generated in the pro-cess of amplitude modulation are offsetfrom the carrier by the modulation fre-quency, AM can be used to generatesignals at frequencies in between themarkers. Example: modulating the cali-bration generator with a 204 kHz sinewave gives two additional frequenciesadjacent to the marker at, say, 1120 MHz:1120 -0.204=1119.796 MHz and 1120 +0.204 =1120.204 MHz. Hence, a con-tinuous tuning range from 1 MHz to
2 GHz is obtained when the sine wavegenerator output frequency is adjust-able between 500 kHz and 1 MHz.The measured amplitudes of fourmarkers produced by the calibrationgenerator show that available outputlevels fall with increasing frequency:
f=100 MHz: Po= -25 dBmf= 400 MHz: Po= -45 dBm1=1.0 GHz: Po= -55 dBm1=1.8 GHz: Po= -70 dBm
Note: 0 dBm =1 mW in 50 Q.Construction of the calibration gener-ator is straightforward even for thosewith limited experience in building RFcircuits. It is essential that close -tolerance (2.5 or 5%) polystyrenecapacitors be used in positions CI, C2and C4. Inductor Li is wound as 3 turns0.2 or 0.3 mm dia. enamelled copperwire through a small (3 to 5 mm long) fer-rite bead. Be careful to avoid short-circuits between the windings as theenamel coating may be damaged whenthe wire is pulled through the hole inthe bead.The calibration generator is poweredfrom a 6 V battery pack so that it can beused as a portable test instrument. Cur-rent consumption is less than 201nA.
B
Parts list
Resistors (±5%):1:11=2K2R2= 33KR3 = 47KR4 = 1K0 Fi5;Rs;R7=22KRe= 56R
Capacitors:CI =470pC2=22pC3 = 40pfoil trimmerC4=1n0C5= 180pC6= 22nC7= 4p7Cs=390pC9=4):7; 16 Vcio=10n ceramic
Polystyrene (Siemens Styroflex); tolerance55%.
Inductor:Li = see text.
Semiconductors:Di =1N4148ICs =74HCT74Ti = BF494T2= BF981 or BF982T3=BFG65 (Philips/Muliard)Ta=BC550B
Miscellaneous:Xt = 2 MHz quartz crystal; 30pF parallel
resonance.PCB Type 884054 (see Readers Services
page).
22 SUPPLEMENT
1
EE JULY/AUGUST 1988
2
X1
2MHz
Cl
* see text
C222pC4
-F7op
R1
180p
D1 C10min
n
1N4148
C6
IC1
13 10R S
- CLK 0
FF1
12S
BF981
22n
S
aLk a
FF2
aR
R6
T4
BC550B
uli*1
0 C) 6V<20mA
0
I 0 00AC411716V
C8
BF T35 0 00T3C7
1_11 04p7
R5
FF1, FF2 =IC1= 74HCT74
50-11L40
orifi3s_+0
cc cc
91 se I
is-5 b6. d-a -
C9
390p
R8 C
884054-10
C3
00
uo
a
LI
0 ®
bT3e e 0 I
K:10CB
00O
0 J.
SIMPLE PHONO PREAMPLIFIER
This circuit shows that a preamplifier formagneto -dynamic cartridges can berelatively simple without seriously com-promising compliance to the IEC stan-dard in respect of frequency response.Compared to the RIAA standard, theIEC frequency curve has an additionalroll -off point at 20 Hz-see Fig. 1.The circuit diagram of Fig. 3 shows thatinput and output of the preamplifierbased around the Type TL071 oper-ational amplifier are direct coupled,making it possible to accurately definethe previously mentioned roll -off bymeans of network Ra-C3. Output offset
of the preamplifier is about 3 mV. Outputcapacitor C; can be fitted if this offsetvoltage can not be handled by the inputof the line or power amplifier.For optimum compliance with the IECfrequency curve it is recommended touse close tolerance polystyrene(Siemens Styroflex) capacitors in pos-itions CI and C2, and an MKT capacitorin position C3. Resistors are preferablyhigh -stability metal film types from theE48 or E96 series, although less expens-ive and commonly available types fromthe E12 series may also be used withreasonable results when selected for
the required resistance with the aid of adigital ohmmeter. It was with this inmind that Rz has been dimensioned at5K62 (E12: 5K6). This value gives a roll -off at 18.9 Hz instead of the required20.0 Hz, so that the low -frequencyresponse (up to 50 Hz) of the preampli-fier deviates slightly from the IEC curve.The deviation, J, of the amplificationwith respect to the values set by the IECis shown as a function of frequency inFig. 2.A prototype of the preamplifier builtwith the component values given in thecircuit diagram gave the following test
A
SUPPLEMENT 23
CS
EE JULY/AUGUST 1988
1
2
CI
c2
0
S O aa
2
10 aii ate Ste
114 me Sea A
A IA 222 00.
SC2
AMA- 22
220k
ttelMOW -
3
results: voltage gain 39 dB at 1 kHz;signal-to-noise ratio greater than 70 dBat 1 kHz and 100 mV output signal (up to80 Hz: greater than 60 dB). The inputwas connected to a test generator whichsupplied 1 mVrrns at an output im-pedance of 1 kQ.The circuit should be fed from a well-regulated symmetrical supply(preferably +15 V, but +12 V or ±8 Vshould also work). A suitable supply issimple to build around two integratedregulators such as the 78Lxx and 79Lxxtypes, which can step down supplyvoltages already available in the line orpower amplifier. Current consumptionof the preamplifier is only 2 mA.
ALTERNATING CURRENT SOURCE
One of the less known properties offield effect transistors is that some ofthese are electrically symmetrical,which means that the drain and sourcemay be interchanged under certain con-ditions. This circuit is based on thisphenonemenon, and feeds a constantalternating current through P2 whenconnected to an alternating voltagesource.The operation is best explained withreference to the curves of Fig. 2, and byassuming that a sinusoidal voltage is ap-plied to terminals A and B.When the drain of T1 is negative withrespect to the source, DI blocks, andforms a resistance that is considerablyhigher than that of RI. This has virtuallyno voltage on it, so that Vcs= 0 V. Thismeans that ID is constant at about 19 mAwhen Vcs>8 V (see Fig. 2a). It shouldbe noted that the curves and values ofID and Vos are typical, and may deviatedepending on the FET used (A, B or Csuffix). When the drain of Ti is positivewith respect to the source, Di conducts.Provided Pt is adjusted such that thevoltage on it equals VD, there is, again,
no voltage difference between the gateand the source, so that the FET functionsas a current source as shown above.The constant alternating current sup-plied by the circuit can be defined byfitting small resistors in the drain andsource lines, so that Vcs is set to valuesother than 0 V. The input voltage rangeof the current source is 6 Vrnis to 18 Vrrns.
2
1
! t_t- Ilit;in,. valuesr7, = 2S °C r..,
.
I- r .
7'.
1- - - .
" : . ,
(0 cos (VI .-
884041.11
B 884041 - 10
24 SUPPLEMENT
EE JULY/AUGUST 1988
VOLTAGE -CONTROLLEDSHF OSCILLATOR
This oscillator supplies an output levelbetween -10 dBm and +3 dBm, andcan be tuned between 1250 MHz and1800 MHz simply by varying the supplyvoltage. Operation of the circuit isbased on the fact that the transition fre-quency, fr, of the BFG65 is reducedwhen the collector current rises above10 mA. The oscillation frequency is alsodetermined by the physical layout of in-ductor L3, which is a strip line madefrom two parallel running lengths of1 mm dia. silver plated wire. The lengthis established experimentally, startingfrom 13 mm. Chokes Li and L2 are 3turns of thin enamelled copper wire(dia. 0.2 or 0.3 mm) through a small(3 mm) ferrite bead. Capacitors C2 andCa are leadiess ceramic types (rec-tangular or disc).The SHF test oscillator is ideal forquickly finding the maximum usable in-put frequency of, for instance, a fre-quency meter specified to reach up to1.2 GHz. In addition, it can be used fortesting RF input sections in indoor unitsfor satellite TV reception.
R2
COMPUTER -DRIVENPOWER CONTROLLER
Th's circuit enables a computer to con-tro the power supplied to a mains oper-ated device (lamp, heater, drill, etc.) in255 steps. Variation of power is achievedby controlling the voltage supplied tothe load (RL in the circuit diagram ofFig. 2). A conventional power regulatoris used here, composed of a triac and asimple associated circuit to control thephase angle at which the triac is trig-gered.The power supply and mains trigger cir-cuitry are shown in Fig. 1. The circuitaround Ti...T4 incl. and ICI is a zero -crossing detector which produces anactive high pulse every time the mainsvoltage is zero. Opto-coupler ICI in-sulates the rest of the circuit from themains.With reference to Fig. 2, Schmitt -triggerNi inverts the zero -crossing pulses,causing 8 -bit binary down counter IC2to load the 8 -bit word applied to counterpreset (jam) inputs JO. J7. The counteris decremented one count by eachclock pulse supplied by oscillator N2.When counter state nought is reached,output ZD goes low, and N3 inhibitsfurther clocking of IC2. Simultaneously,N4 produces an output pulse, so that T5conducts and fires the triac.As the triac is only fired when IC2counts to zero, the instant at which thishappens depends on the value of the 8-
1
0
DI D2
03 04
11111111'11111111
10 20 30
CS C70 =MN
IC 57805
TO0070n
Di ..D5 = 1N4001- -
L._
16V
CSCI710p
'I6V
05
C9
mow1001,16V
13
Ti, T4 .= BC5578T2, T3 = BC5478
R7 R9
R8
0 T4
0
* see text
RIO
5V
0
R11
1WIL160H2
IC 1
2 I 4
TIL125I .--(D
584981 - io
SUPPLEMENT 25
EE JULY/AUGUST 1988
bit control word received from a com-puter. Hence, the time that lapses be-tween the zero crossing instant and thetriac firing instant is a function of themagnitude of the control word. Thegreater the 8 -bit word, the greater thephase angle, and the less power isdelivered to the load.Inductor Li suppresses RF interferencecaused by the triac, and should be ableto carry at least 5 A. The triac in this cir-cuit can be a TIC206D (4 A) or a TIC216D(5 A). Other types may be used if theseare known to trigger at a gate current ofless than 10 mA. The value of R12 is de-termined empirically, and should be ashigh as possible without causing thedisappearance, on point A, of pulseswith an amplitude of 5 VF.The only adjustment required is that ofP. If complete switching off of the loadis required, this preset is adjusted for0 V indicated by an AC voltmeter con-nected instead of the load, with dataFFH (2551o) written to the power con-troller. If regulation from 0 V onwards isnot desired, Pi is adjusted so that themeter reads the required minimumvoltage. When writing programmes forthe power controller, it should beremembered that the power deliveredto the load is an inverse function of thevalue written into the computer's outputport.
Safety precautions:The shaded parts in the circuit diagramsare operated at mains potential, andmust never be touched while the unit isbeing powered. Great attention shouldbe paid to proper insulation in theselecting and mounting of the partswithin the shaded areas. It is stronglyrecommended to bend the pins of theoptocoupler away from the package toensure an insulation distance of at least6 mm.
2
DO 0131 0D2 0D3 0D'0dvP
1350D60D70
G1100-;=
1
C5
2
4
5
7
10
11
12
13
CLR (Cr., SPE
ZD
IS
11
12IC 2
14
15 4010316
17
CLK
L1*
630V
R12
R2
5V
3
T6
BC5475
22._441LHz
C3 =1141
20o
N1..144 = IC 3 = 4093B
T6S7n30V
+T
5
BC547B
R5
Finally, it should be noted that the cir-cuit may not operate correctly withloads below about 40 W, and thatwriting 00ii to the data input has the
FIVE -BAND STEREOGRAPHIC EQUALIZER
This design of a stereo equalizer is fairlyunusual because it is based on induc-tive feedback. In theory, the feedbackcircuit around opamp Al would provide15 dB amplification or attenuation ofeach frequency range, but in practiceonly about 13 dB is attainable owing tolosses in the inductors. A virtually flatfrequency response is obtained whenall five potentiometers Pi to Ps are set tothe centre position (0 dB). Total controlrange of the unit is about 33 dB.The TL072 dual opamp in each channelis a trade-off between cost and perform-ance in respect of noise and distortion.Set to 0 dB gain, a prototype of theequalizer produced 0.04% distortion atan input signal of 1 kHz; 1 V, and 0.13%at 5 and 10 kHz. Distortion is highestwhen the test frequency lies within oneband that is fully attenuated while the
t.
1
41 2
TIL125nim
_ 551501 - 11
5V
0
0 C4moo
IC 3 mim100n0
<3 100Hz
0
same result as FFH, namely minimumvoltage applied to the load. Regulationefectively starts with data 01H.
other four are set to maximum gain. Inthis condition, test measurementsresulted in a maximum distortion of1.5%, which is certainly tolerable giventhe simplicity of the circuit. Signal-to-noise ratio is greater than 90 dB at an in-put amplitude of 1 V.The frequency response curves wereobtained with the following settings:
- curve 1: all controls set to maximum;.ru----;" curve 2: 4 controls set to 0 dB, and 1 to
' maximum;curve 3: 4 controls set to 0 dB, and 1 tominimum;curve 4: all controls set to minimum.Due attention should be paid to the DCresistance of the inductors. The total re-sistance of the inductor and seriesresistors in each feedback networkshould remain 680 Q, so that R3 to R:2incl. may have to be dimensioned dif-
26 SUPPLEMENT
EE JULY:AUGUST 1988
RSA, SCE,E
1e012102:1,E I'S
o
-21-51.0iCOE
1534013k
r.rx ,ra-ijeNitl
CI.
_
23n
W1417046 SPEED 200 = I MEER SPEEDc-mkiCEP -vs)
EMI
ICI
Ca
15V Icon 0
At,A2 =ICI =11.072
CI CI EZEIlJ = CI '
PA ,
-I-
ailisaip __ _ itmmmmmmm mm m I mmmmmmmmmSO
REVERS I'VE T.
Parts list
Resistors ( x 5%):R1;111' = 47KR2;R2';R13;R13' = 3K3R 14;R14' = 100RPt ... PS incl. = 1 K0 stereo linear poten-tiometer for PCB mounting. The following values are given asguidance only !see text):
R3;R3'=470RRe;R4'=4K7Re;115';R6;Re'=1K0137;R7';Fi1 t;R l'= 680RRe;Re'=12Kli9;R9'=390RRto;lito' = 3K9Fit2;R12.=27K
Capacitors:CI;Cl';C3;C3' = lir0 MKTC2;C2 = 6u8; bead tantalumC4;C4' = 220nC5;C5'=47nce;c6' = 22nC7;C7 ;Ca;C8' = 100n
Inductors:L.1;Ll'=1 H, e.g. Toko Type 293LY-105ICirkit stock no. 34-10513).
L2;L2' =680 mH, e.g. Toko Type 293LY 684(Cirkit stock no. 34-68413).
L3;L3'=150 mH, e.g. Toko Type 293LY-154(Cirkit stock no. 34-15413).
L4;L4' =68 mH, e.g. Toko Type 181LY-683(Cirkit stock no. 34-68302).
Ls;Ls' = 10 mH, e.g. Toko Type 181LY-103(Cirkit stock no. 34-10302).
Semiconductors:1C1;ICI'=TL072
Miscellaneous:PCB Type 884049 (see Readers Services
page).
a
lkr
-V'L_ a © 6 -ItC)
Ci
i;) kJ iJC8 C7
a
OC2 C2
29 St
Earl akaEra a aa Oa a
0<>1C 3
L2
C1.°43 0 -CH3 C 4
L2
ferently than shown in the circuitdiagram. Always measure the resistanceof the inductors used, and thencalculate the value of the resistor re-quired to obtain a total of 680 Q.Example: a Type 239LY-154 150 mH in-ductor from Toko was found to have aDC resistance of 37 Q, requiring a seriesresistor of 680-37=643 Q. This value is
20k
- It
A 6
(inn&I C 1
LIU UC7
C22 C5 CS C6100
L3 Let
ra
ECM
Type
a a
C6LS
approximated with the aid of a 680 Qand 12 k.c.? resistor in parallel (117 -Its inthe circuit diagram). Ferrite -encapsulated inductors are rec-ommended to reduce magnetic coup-ling, and to keep crosstalk at relativelyhigh frequencies down to an acceptablelevel (< -60 dB at 10 kHz).
SUPPLEMENT 27
EE JULY/AUGUST 1988
0 3QUIZ TIMER
Here is a simple `who's the first' circuitthat can be used in quiz games with upto eight participants or groups of par-ticipants. The circuit indicates the firstone to press his key by a glowing LEDagainst his number or any other identifi-cation used in the quiz or game. At thesame time, the circuit gives an audibleindication that some key has beenpressed. The RESET key enables the quizmaster to restore the circuit's originalstate before updating the score and pro-ceeding with the next question orassignment.After RESET has been pressed, the eightR -S bistables in ICI and IC2 are reset.The Q outputs all go logic low and,consequently, the output of IC3 goeslogic high. The circuit is now ready tobe operated. For example, if Si ispressed first, the first bistable is set andoutput 01 goes high. The output of IC3pulls the common line of keys Si...S-3incl. logic low to prevent more bistablesbeing set. Hence, Q1 is the only outputthat is logic high. This condition is indi-cated by LED Di. Simultaneously, Ti isbiased and switches on the buzzer to at-tract the attention of the quiz master.Capacitors CI to Cs incl. prevent thebistables being set permanently if a keyis kept pressed for a long time. Finally,Ss is pressed to reset the circuit. Thiscauses all Q outputs to be made logiclow, and the common key line high,returning the circuit to its original con -
0 3
SaY
Rt 82 RIR R ININ49 R. RI. RIZ
ooa0000
I
IC411__,L4
csi1400n
C6I,00.,
SIN 09
) 1"014 I LTRIMEl
1111
14
ICI40438
RIT
11
ICt e,ci)
IC240438
dition.The circuit is not critical in respect ofsupply voltage, which is preferably theworking voltage of the active piezo-buzzer (6 V or 12 V). Current consump-tion in the de -activated state is less than
D 04 DS CS Or DE
131-86 = LED
00VY
R19
a- . DC
IC340788
0OLE,Z31
1 mA. while less than 25 mA is drawnwhen one of the LEDs is illuminated.The supply voltage need not beregulated, making it possible to use aninexpensive mains adapter of the DCtype.
HEADLIGHTS INDICATOR
It is never advisable to leave a car'sheadlights on for long periods when theengine is not running. Yet, especiallyduring the winter months, many of us in-advertently do this. The indicator de-scribed here helps to prevent you suf-fering the consequent and inevitable flatbattery.In its simplest form, the indicator con-sists of a d.c. buzzer and a diode asshown in Fig. la. With the headlights on(S3 closed), the interior light (Lt) doesnot come on until one of the front doorsis opened (when either SI or S2 closes).At the same time, the buzzer is ener-gized and sounds. Either closing thedoor or switching off the headlights (S3)turns the buzzer off.The diode in series with the buzzer isnecessary because B is normally at+12 V via L1 and A at ground via theheadlights (L2-only one shown here).
la
la
5
8:1 125DI A
111N4001
02
1N5401
E.S.CIE 11
The buzzer should then not sound, ofcourse.A slight modification to the circuit, en-abling it to operate only on the switch inthe driver's door, is shown in Fig. lb(where it is assumed that Si is the rel-evant switch).The buzzer draws a current of onlyabout 10 mA when energized.
28 SUPPLEMENT
EE JULY/AUGUST 1988
0 3POWER MULTIVIBRATOR
This simple multivibrator circuit isremarkable for its high efficiency andability to drive relatively heavy loads.The circuit supplies a symmetrical rec-tangular signal that floats with respect tothe supply voltage. An astablemultivibrator is formed by T5, Ts, RI, R2,Ci and C2. The collector currents of Tsand T6 drive T1 and T2 respectively,while the emitter currents drive T3 andTi respectively. Current limiting may bedimensioned to requirement by chang-ing R. It should be noted, however, thatthe transistors may carry relatively highcurrents. Their current amplification,her, is, therefore, fairly low, so that thecurrent limit point can be approximatedwith In-Emax,(Ub -1.4)/111. With Ri=68 Qas shown in the circuit diagram, themultivibrator can be used for switchingloads up to about 3 A.Output frequency of the oscillator isapproximated by 0.7/(R2C), and isabout 53 Hz with R2=68 kQ,C=C1=C2=220 nF and Ub=12 V (14 V:50 Hz). One of the many applications of
3
T I T2 =1313244C
T3, T4 = 8D2t3CT5 . T6 = 5D679
the power multivibrator is a battery -operated mains converter. Its outputsare then connected to the low -voltagesecondary winding of a mains trans-former. A prototype of the multivibratorwas dimensioned for relatively high out-put current at 50 Hz by fitting R1=33 Q;R2=2 x68 kQ in parallel, andC=2 x 220 nF in parallel. Connected to a9.5 V; 5 A mains transformer, it powereda 40 W mains bulb with a rectangularvoltage of nearly 240 Vrms. Supplyvoltage and current consumption were14 V and 6 A respectively, yielding anacceptable efficiency of about 40%.Quiescent current consumption of thecircuit is determined by RI, and was0.3 A in the test set-up.When the multivibrator is used for driv-ing an inductive load, as in the above ap-plication, each output transistor must beprotected from inductive voltage peaksby two fast high -current diodes fitted inreverse across the collector and emitterterminals.
TOUCH SENSITIVE LIGHT SWITCH
This low-cost circuit enables turningroom lights on and off simply bytouching a round metal sensor. The lightis turned on by briefly touching thesensor, and off again by touching itslightly longer. With reference to thecircuit diagram, when the sensor isbriefly touched, hum and noise inducedon the body are amplified by cascadedgates NI, N2 and N3. A pulse train with aswing of nearly the supply voltage(4.7 V) and a frequency equal to that ofthe mains voltage (50 or 60 Hz) is ap-plied to a bistable set up around N4 andNs. C2 is charged via D2, and thebistable latches in a high output state.Triac Trig is triggered via driver Ti, sothat the lamp lights.When the sensor is touched for about2 seconds or longer, the pulse traincharges CI via Rs and D. Inverter N6pulls the input of Ni low when thevoltage on Ci is sufficiently high.Bistable N4 -Ns toggles and Ti breaksthe gate current for the triac, so that thelamp is turned off. The circuit alsoworks in a relatively noise -free environ-ment. When the user forms a relativelylow resistance to ground, the input ofNI is effectively pulled low by RI -R2,whose total resistance is low relative to
1 Rs -R4. The effect of this on the bistableand triac circuit is similar to that outlin-ed above.A suggested construction of the sensorand LED is shown in the accompanyingdrawing. The LED is fitted in a plasticholder, and in the dark indicates the lo-cation of the light switch. The LEDholder (C) is secured in the side or toppanel (A) of the ABS enclosure thathouses the light switch circuit. The LEDis located in a thin aluminium or brasswasher (B), which is connected to RI,and glued onto the outside surface ofthe plate. In the interest of safety, it isrecommended to observe a minimumdistance of 7 mm between the LED andRI. In this context, constructors areurgently advised not to use a metal ormetallized LED holder as the sensor.Also, never replace RI and R2 with asingle 4M7 resistor.Since this circuit is connected direct tothe mains, it must be fitted in a safe andsound ABS enclosure that is impossibleto open without it being deliberatelydamaged. Once more we advise thatthe presence of the mains voltage is aserious source of danger, so that theFirst and foremost concern of every con-structor should be absolute safety.
SUPPLEMENT 29
R11
EE JULY/AUGUST 1988
2
R2
0
R3 R4
IOM 1OM
12 t1 10
TIC206D BC550B
...eAl
A2
3
9 b
R6
R5
D1
10p35V
1N4148
C2
C5
470n40 DV
A 1N4007
BC550B
R10
77p16V
A2
Fl
OLa0
Tint
TICAl 206D
N1...N6 = IC1 = 4069BE 884050 -10
PRINTER SHARING BOX
This simple circuit makes it possible toconnect two computers to a singleprinter. Toggle switch S2 selects the rel-evant computer by applying the appro-priate logic level to the enable inputs,G, of octal bus transceivers Type74LS641 (ICI. . IC4 incl.). The directioninput, DIR, of these is hard -wired to +5V, so that the data direction is from An toBn. When G is logic high, the buffersare switched to the high impedancestate, so that chip outputs can be con-nected to form a bus structure. With thisin mind it is relatively simple to see thatthe circuit is the electronic equivalent ofa 16 -way toggle switch.
Parts list
Resistors (±5%):RI;R2;115;Ra = 10KFi3;R4;116;R7.= 8 -way SIL resistor network
10KRs= 1K01Capacitors:C);C2;C3= 22n
Semiconductors:ICt incl.= 74LS641
Miscellaneous:Si = miniature toggle switch.52= miniature toggle switch.KI;K2;K3= 36 -way terminal strip block.PCB Type 884030 (not available ready-madethrough the Readers Services).
Input BUSY of the non -used computer isheld logic high to prevent this machineattempting to send data when the othercomputer is accessing the printer. The74LS641 was chosen because it hasopen -collector outputs - the reason forthis should be clear when it isremembered that the Centronics stan-dard dictates the presence of pull-upresistors in the printer. The 74LS641s, ofcourse, need pull-up resistors at thecomputer side also, and these areformed by resistor networks R3, R4, REand R7.A RESET switch, SI, is provided to clearthe printer buffer by means of an
1Q50 19
INPUT -PRIME pulse should theuser find out that the wrong file is beingprinted. This reset option is definitelyneater than switching off the printercompletely to correct the error.The circuit is conveniently poweredfrom the 5 V supply in the printer. Inmost cases, this supply voltage isavailable on pin 18 of the 36 -way Cen-tronics input connector, but this wouldhave to be ascertained by measuringand reference to the printer manual. It isrecommended to connect +5 V to non -used pins 15 and 34 also to distribute thecurrent over several wires in the Cen-tronics cable. Once again, check the
000000000000000000000000000000000000
Ar/3618
0-1R 9 1-0 0-1R B 1001 RE 1-0a./
4ir
000 00noncleirionein arictrinnemineIC2
1C,131JVCItJtJUUU 11;11./0;11:0LPJKit)T
01
191
R3
KI000000000000000000000000000000000000
CdR1 14`)
3618
r.
R8
19
0
00
K2
1 R7
00000000 00000000000000000 00000000000GIR2 143
3618
30 SUPPLEMENT
R1
5V
K1
5V
R2 [:1
I :12
2324
25
2627
28
2930
00OO
0O
R3
8.10k
00a 2 3 4
5V
5_64J9
3 Dia4 02a 4
5 03a 5
6 D4a 67 D5a 7
160 019 -
0 0-2021
22
2324
25
2627
28
2930
8 D6a 8
g D7a
0000
10 ACKa00 0 11 BUSYa
0 0 12 PER
5VR5
Al
A5A6
A7
A8
5V
TDIR
B1
ICI
74LS641
6
B3
6687as
18 DO
17 DI6 D2
15 03 ,;(/:14 04
13 D5
Eal18
19
12 DS
11 7
19
13117 8216
O 00 0O 00 0
32 ERFla31 Via14 AFa
1 STFLRa
2 3 4 5 6 7 8
R4
8.10kCentronics
COMP. 1
13
K2
0000
5V
5V
11
R6
8.10k
2 DM3 0164 02b
15
6
83
AS8 A79 -1--- A8
6
IC2
74LS
641
DIR
AlA2A3
A4
B6
7
88
ACKBUSY -7"PE /
5V
5V
ERR
4 %'13
12
AF
STRB
11
1
52110
COMP. 2
5 D3b 5
DIR
A2 IC3rx3
0 6 , 6
7 050 7
16 0 0-819 020
0- 9O
076
0000 0
DES
5V
10 ACKb
RB
AS
A7
8
74
LS641
G
B1
B2
B3
84
B5
B6
B7
83
18
17
16
15
14
13
12
It
D2
D3 /D4
D5./VD6
137 %.",
0 Km18
19
ISO
000 00 00 00 00 0
11 BUSYb 17
12 PEb 16
32 ERRS 15
31 INS
AFb
STRBb
2
R7
8.10kCentronicsCOMP. 2
3 4
91
B3
6
IC4
74
7 LS8A7 6419
6 71.,8 91ABD1R
5V
5V
AlA2A3
A4
96
7
63
ACK
K3
CentronicsPRINTER
DO
01 3-0D2
3 BUSY
PE
ERR
14 W4
3 AF
12 STAB
5 06 07-08
0-00 0
O
0
Ad( 12-0 0"0 0
PE 12-0ERR 32-0AF 10
STRB
BUSY
11
1 o
31
884030
6
19
2021
22
23
24
26227
2930
RESET
1OMA-2500 TIMESTANDARD RECEIVER
OMA-2500 is a 1 kW time standard trans-mitter on 2500 kHz. The station islocated in Liblice, Czechoslovakia, andis operated by the Astronomical Insti-tute of the Chechoslovak Academy ofSciences.Contrary to time standard transmitters inthe VLF band (DCF77, HBF), modulationis pure AM instead of a Combination ofAM and PSK or FSK. This means that theseconds pips transmitted by OMA-2500are free from phase noise, which is a
must for some types of PLL, particularlyin communications equipment, wherethe 2500 kHz signal supplied by a timestandard receiver is used for generatingor deriving other frequencies of equalstability.Transistor Ti is configured as aregenerative buffer which acts as an ac-tive filter with an effective Q (quality)factor of about 1,000 at a 3 dB bandwidthof 2.5 kHz. The received signal is furtherraised in amplifier T2 -T3 before it is ap-
EE JULY1AUGUST 1988
printer manual to see whether thesepins are actually available for this pur-pose.The printer sharing box will generallybe located close to the printer. PCB con-nectors K1, IC2 and K3 are 36 -way straightheaders. Three cables are required forconnecting the completed PCB be-tween the computers and the printer.Two 10-15 cm long adaptor cables aremade from flatcable with IDC (press -on)connectors at either end. One end is ter-minated in a 36 -way IDC socket for plug-ging onto the PCB header, the other in afemale IDC Centronics socket (blue rib-bon type) for receiving the printercable.The short printer output cable is com-posed of a female 36 -way IDC socket asabove, and a 36 -way male Centronicsplug.Current consumption of the printerswitch is about 200 mA.
plied to active crystal filter T4 -XI whichensures a 3 dB bandwidth of about500 Hz. Output amplitude of the re-ceiver is sufficient for driving almostany type of simple PLL. The receiver ispowered via the downlead cable at theoutput to enable it to be mounted in anoise -free environment.Inductor Li is wound as 2 turns(primary) and 50 turns (secondary) of0.3 mm dia. enamelled copper wire on aType T50-2 core. Quartz crystal Xi is a
SUPPLEMENT 31
EE JULY/AUGUST 1988
R7L2WI I= MO
c,
560p
ZOn
C2 C5
1130pC3
mmiIn
R1
BF256B
TI
R2
R5
BF494
T2
R6
T4
T3
C41BF494
R4
111
R3 C7 R8
mmm
11
68n
1500
X1
101
1mH
25 00kHz
BF451
C8
C0
2500 kHz type for series resonance.Construction of the receiver shouldfollow the standard rules for RF circuits:keep all connections as short as poss-ible, and use ample screening anddecoupling.Adjustment: set a function generator to2.5 MHz at U0=10 mV. Connect the out-put to CI. Connect an AC -coupled os-cilloscope to the source of Ti, and peakC2. It may be necessary to reduce or in-crease the number of windings of thesecondary of Lt to obtain resonance at
0 3
6p8R9
Tlp16V
01
BF451
8V2
R10
T5
2.5 MHz. Reduce the signal amplitudeand redo the adjustment of the trimmer.Disconnect the function generator, andconnect the aerial. Connect the scopeto the output of the circuit. Peak Cs foroptimum amplitude of the AM signal,but make sure that this is not greaterthan 500 mV. Remember that Ti is aregenerative stage, so that the settingsof C2 and Cs interact. If necessary, re-adjust the trimmers to ensure that thesignal at the collector of T3 is stable,and not clipped during night-time
R11 C10
47n
0
*see text
O
100...500mV
BF256B
G 11DS
884079-10
reception, when OMA-2500 is receivedwith high field strength throughoutEurope. Daytime reception in westernand northern Europe will mostly rangefrom poor to just usable, depending onpropagation conditions and location ofthe receiver.The circuit is fed from 12 V, and con-sumes about 10 mA. Finally, bear inmind that a good aerial (long wire orrhombic quad) is imperative for reliablereception.
PROGRAMMABLESWITCHING SEQUENCE
The proposed control circuit is shownin the diagram as containing two relays,but this number may be increased ifnecessary. The switching sequence isdetermined by the time delay of an RCnetwork at the input of a gate that isused to energize a relay via a darlingtontransistor.When S: is connected to the supplyvoltage (as shown in the diagram), theinput capacitor, CI, C2, . , begins tocharge via a resistor, Rii, Ri2,..., and di-ode Di. After a given time, dependingon the time constant of the relevant RCcombination, the voltage across the ca-pacitor has reached a value sufficient totoggle the gate. The relevant transistor isthen switched on, and the relay is ener-gized.By giving the input of each gate a differ-ent time constant, the sequence ofswitching is determined.When Si is switched to ground, the op-posite happens. Diode Di is reverse -biased and the capacitors, CI, C2,...,
0BC516
1N4001 CIM
toN
N1 N2 = 4584
32 SUPPLEMENT
EA 5Y 414 13 12 11 10 9 8
CD i
4584
117F c ,55
1 2 3 4 5 6 7I Y 23 2Y 3A 3Y
discharge via resistors Rol, Roz,..., anddiode Dz. The discharge time constantdetermines how fast the capacitors candischarge and retoggle the gates. So,here again the switching sequence isdetermined by time constants. The gatewith the shortest time constant willalways toggle first.The supply voltage may lie between 5 Vand 15 V, but must, of course, be equalto the operating voltage of the relays.Furthermore, the BC516s must notswitch more than 400 mA, and this againinfluences the choice of relay. A good,
BURST GENERATOR
A burst generator is indispensable fortesting the dynamic response ofloudspeakers, and, in some cases, AFamplifiers. The fact that a number ofcycles of a sinewave are applied to theloudspeaker under test, and not a con-tinuous signal, eliminates the adverseeffects of reverberation, reflection andechoes which are otherwise caused bythe test room, and are almost inevitablypicked up by the test microphone. Inaddition, the burst provides a good indi-cation of the loudspeaker's perform-ance in respect of voice coil transientresponse, resonance, and ringing.The test signal provided by an externalsinewave generator is switched on andoff at or around the zero crossing, de-pending on the setting of phase controlPi. The pause amplitude can be set byP2, while controls P3 and P4 are used foradjusting the duration of the pause andthe burst respectively. It should benoted that the settings of these poten-tiometers interact, so that an oscillo-scope is required for correct alignment.The duration of pause and burst is notrelated to the input signal. This meansthat the number of cycles supplied bythe generator increases with the fre-quency of the sinewave applied to theinput, unless, of course, P3 and P; arere -adjusted.Comparator ICI converts the sinewaveat the input into a rectangular signal.The switching takes place at a specificinstantaneous amplitude of thesinewave, set by Pi. The timing of theswitching instant is arranged by astablemulitivibrator IC2, and is copied inbistable IC3 on the first positive edge ofthe sinewave, since this corresponds tothe rising edge of the clock signal. Out-put Q goes high, so that the pole of elec-tronic toggle switch IC4 is connected topin 12, and hence carries the attenuatedsinewave burst.The burst generator is not critical inrespect of supply voltage, as long as thisremains between +5 V and ±9 V. Donot exceed ±9 V on penalty of damag-ing IC4.
O
EE JULY'AUGUST 1988
practical energizing current for therelays is 200 mA.The values of resistors Ri and Ro may liebetween 1 kg and 10 Mg; the value ofcapacitors CI, C2,..., between 10 pFand 100 pF. Time constants exceeding1,000 seconds create problems in prac-tice, because the leakage current of theelectrolytic capacitors then becomescomparable with the charging current.In general, choose the time constants sothat two consecutive ones always differby at least 0.1 s.
R2
P3
tO
4
IC2555
C2I5
I0On
16
1306
IC4
4053
12
EN
14
9V 11mA
0
Sync.
7412
IC1DI
01
4
3C -IS
IC3
4013
0
'3
11
9V 3mA
a 0SI6343
SUPPLEMENT 33
EE JULY/AUGUST 1988
0 3I/O EXTENSION FOR AMIGA 500
The Commodore Amiga is claimed tobe a computer with plenty of facilitiesfor extension circuits. The model 500,for instance, comes with no fewer thantwelve connectors and sockets. Thereare, however, awkward constraints tothe practical use of all these extensionfacilities. The SERIAL CONNECTOR iscumbersome to use with TTL circuitsbecause of the +12 V logic levels on it.The use of the 86-PIN CONNECTOR on themachine is complex and risky becauseof the unbuffered connection to manyinternal signals. The one remaining op-tion is the PARALLEL CONNECTOR, whichcan be extended to a maximum of 56I/O lines as shown here, with the possi-bility to realize a bidirectional port.The circuit was designed and built forthe Amiga 500 computer. It is likely towork equally well on models 1000 and2000, but this has not been tested inpractice.
Output lines BUSY, P -OUT and SEL onthe PARALLEL CONNECTOR can be pro-grammed to supply a 3 -bit addressselection code which is applied tobinary decoder ICI. Octal bus bufferIC2 is the input port at address 2, latchIC; the output port at address 3, andtransceiver 103 the bidirectional port ataddresses 0 (read) and 1 (write). The re-maining 3 addresses (lines E4, E5 andE6) can be used for 3 x 8=24 additionalI/O lines. Line 7 on ICI may not be usedfor selecting an input of output port, andis used instead for driving READY LEDDI when none of the ports on the I/Oextension is being selected. It shouldbe noted that IC3 is not a latch, whichmeans that it can only output data for aslong as it is written to by the micropro-cessor. Output port IC; does have a lat-ching function, so that datawords arekept stable on the outputs until overwrit-ten by the microprocessor.The accompanying listing is intended asa guide to writing software for the I/Oextension. As an example of the practi-cal use of the subroutines, instruction
a =1:n=123:GOSUB Wr <CR>
sends dataword 123io to 103, which thenfunctions as an output port. Conversely,instruction
a=2:GOSUB Rd:PRINT n <CR>
reads the dataword applied to IC3, andprints it on screen.Subroutine Init need only be calledonce at the beginning of the program-ming session. Input ports must not bewritten to. The I/O extension should befed from a separate 5 V supply.
Pcut
K1
0 12 II
13 1
17
D7
2
2
1 119
El
IC2
E2
74LS244
2
4
8
11
13
15
17
BC5578
74LSOB
0130140,5016017
/ 7/ 7/7/7/
2
19
E
IC374HCT245
Init:
POKE 12571136&,199POKE 12570624&,255POKE 12575489&,0
RETURN
Rd:
POKE 12575489&,o
POKE 12570624&,248+an=PEEK(12574977&)POKE 12570624&,255
RETURN
Wr:
POKE 12570624&,248+a
POKE 12575489&,255
POKE 12574977&,nPOKE 12570624&,255
RETURN
a 080
15
7 08116 062
)
4083 hik
13 0852 086
084 Ni-lor
' 08?
5V / 100mA
O
11
DO 3 AlAl 61 fl00
01 452 82
02 7.--3001
A3 IC4 6303
,s1,03As 74 as
04 13'-003
HCTDS AG 374 5_00504
A7 B7D7
."-.1:705",007A8 B8
ICI IC2 IC3 IC4444'call once after power -on
'BUSY, P -OUT and SEL = output bits
'select address 7 (light READY LED)
'set port to input
ICS
0000000
'load contents of address a in variable n
'set port to input
'select address a
'read value
'light READY 17g1)
'store variable n in address a
'select address a
'set port to output
'write value
'light READY LED
34 SUPPLEMENT
EE JULY AUGUST 19880'mUNIVERSAL SMDTO-DIL ADAPTORS
An increasing number of electroniccomponents, and in particular inte-grated circuits, is now only available assurface -mount devices (SMDs). Circuitdesign on the basis of these leadless,tiny, components invariably poses prob-lems to many because there is no way togo round making a printed circuit boardfor building and testing prototypes.Making PCBs for SMD based designs iscumbersome and time-consuming. Inmany cases it will, therefore, bedesirable to develop the circuit as itwould have been done using ICs andcomponents of standard size. The PCBadaptors introduced here make thispossible. With the exception of thegeneral-purpose type, they are slightlylarger than ICs of normal size, but still fitin the generally adopted 0.1 in. raster.The adaptor PCBs effectively enable arange of SMD ICs to be handled just astheir normal -size equivalents, and soalleviate the plight of designing and et-ching a new PCB for every experimentor minor change to the circuit.SMD ICs with 8, 14 or 16 pins are usuallyhoused in a 'narrow' enclosure, and 16,
4
" ffirMSITTEN:4rorral42\- \- ../13002.:: 4 fp ,c00 -42 sloeEPS.8134025
Note: the printed circuit board shown here isavailable ready-made through the ReadersServices under order no. 884025.
20, 24 and 28 pin types in a 'wide' en-closure.The printed circuit board shown hereallows making multiple adaptors thatcan be used for fitting:
Narrow SMD ICs with a maximum of16 pins. For 8 and 14 pin types, thePCB can be cut to the required
length. Wide SMD ICs with a maximum of 28
pins. PCB sections are cut off to therequired length as above.
SMA transistors, capacitors andresistors. These are arranged in a DIL
configuration on a general-purposeadaptor to enable fitting networks andcircuit sections as complete modules ona standard prototyping board. The sizeof this adaptor does not exceed that of astandard 16 -pin integrated circuit.
Suitable lengths of terminal strip arepushed through the holes at the under-side of the boards to create pins for fit-ting the modules in standard IC sockets.
7'W
WIPER DELAY
This two -key wiper delay circuit isremarkable for its simplicity and ease ofuse. The wipe is started by pressing thes-F.T. switch, which also serves to adjustthe length of the wipe interval. The cir-cuit is turned off by pressing the RESETbutton.The wiper delay shown in Fig. 1 consistsof three opamps and a monostablemultivibrator (MMV). Opamp AI is setup as a triangular wave generator, con-trolled by the output of the MMV. Whenthis is low, a slowly rising sawtoothvoltage appears at the output of Ai. Therise time of the sawtooth depends onR2 -C3. Opamp A3 compares the voltageacross C4 to the instantaneous sawtoothamplitude. The output of A3 drops from8 V to 0 V when the sawtooth voltage ex-ceeds U[C41. This change in the outputvoltage of A3 is delayed by Re-Ce andpassed to A2, so that the MMV is trig-gered somewhat later. The wipers areswitched on via Ti and Re when pin 3on the 555 goes high. Also, C3 is rapidlydischarged via D! and RI, while D2prevents the voltage across C3 becom-ing positive. When the MMV outputgoes low, Ai generates a new sawtoothperiod.
1
a
04
os
T
RS
RESET
ILS2
SET
IC1
8V
O
®Bv
CS
1,00n
ELM
T
ED 135
Si 12V
0
D1 , D2 =1U4148114-08 =1114148
A 1, A 2 .1C 1.747A3 =IC2 =3140
57452 -
SUPPLEMENT 35
EE JULY/AUGUST 1988
When the circuit is first switched on, C4is discharged, and the output of Ai isslightly higher than 0 V due to Vic -ei ofthe internal output transistor. Thiscauses the outputs of A3 and A2 to re-main low, so that the wiper relay re-mains energized initially. When RESET ispressed, C4 is charged via Rs, causingthe the output of A3 to go high, and theMMV to be stopped. The delay circuitaround A2 is necessary to prevent C;being discharged completely afterpressing the SET button.The relay contacts should be wiredsuch that the dashboard switch is by-passed when the relay is energized, andthat the hold switch, H, for the wipermotor is opened-see Fig. 2. Due atten-tion should be given to the correct con-nection of the hold switch on penalty ofshort-circuiting the car battery.
0 4
2
31ff
53.0' 0'53b
o 1(4 o 4:;
Sa S b
15
0
0'31 b 31
87482 -
WIRELESS HEADPHONES(TRANSMITTER)
A circuit for the transmission, with goodquality, of the sound output of a TV re-ceiver over a couple of metres.The input signal for the circuit is takenfrom the headphone or video recorderoutput of the TV receiver. If these arenot available, NEVER ATTEMPT TO FITONE YOURSELF: THE CHASSIS OF THETV SET MAY BE AT A LETHAL HIGHVOLTAGE.The audio signal is amplified by ICI,which has been given some extra`body' by the addition of an outputbuffer, Ti. Capacitor C4 has a potentialthat is equal to half the supply voltage(via R3 -R4), on to which the amplifiedaudio signal is superimposed. Theresulting varying direct voltage is usedas the supply voltage for emit transistorT2 via the primary of L2. The carrier os-cillator, also formed by T2, can oscillatebetween 1,750 kHz and 3,500 kHz. Theconsequent amplitude -modulatedsignal across the secondary of L2 isstrong enough to span a few metres. Aferrite rod is used as transmit antenna.Diode D serves two functions: it in-dicates that the transmitter is `on' and itstabilizes the direct voltage (about 1.5 V)for the oscillator. The supply voltage forthe oscillator is thus independent of the12-18 V line.The inductors are easily made. A T50-2toroid with 80 turns of 0.2 mm dia. enam-elled copper wire is used for Li. A fer-
Rt
(16V390p
71
(1)11313241
LI*
rite rod of 10 to 20 cm is needed for L2:L2A consists of three turns of 0.6 mmdia. enamelled copper wire and shouldbe wound at the ground side of L2B. Thissecondary winding consists of 30 turns
A
L2
*see te.t
C6Ulm
760p
RS
0R7 12...18V
<150mA
0
'4417 red
©6611067- 0
16V
0.5 mm dia. enamelled copper wire.It is recommended to power the circuitfrom a mains adaptor, because a currentof up to 150 mA may be drawn.
36 SUPPLEMENT
EE JULY/AUGUST 1988
WIRELESS HEADPHONES(RECEIVER)
To arrive at a suitable headphone re-ceiver that meets the requirements ofbeing light, battery -powered, and offer-ing good -quality reproduction, a Ferran-ti ZN415 was chosen.This IC contains a complete AM detec-tor, an output amplifier, and operatesfrom a single 1.5 V battery.The circuit shows the ZN415 in its stan-dard application as a medium wave re-ceiver. Circuit Ci-Li is, however, tunedto a frequency above the medium waveband. The output stage drives a high-
impedance headphone without anyproblems. The circuit draws a currentnot greater than 5 mA, which ensures agood battery life.The tuned circuit, CI-LI, receives thesignal from the transmitter described inthe preceding article. The inductor con-sists of 40 turns 0.2 mm dia. enamelledcopper wire close -wound on a 20 mmdia. ferrite rod. For optimum reception,CI must be adjusted with a non-metalscrewdriver. Note that the transmit fre-quency lies somewhere between 1,700and 3,400 kHz.
0 4
6
L1I C1
80p
* see text
IC1
ZN415
CIL
3V
C3
100n
C2 C4=SE
7n 700n
2 4
C5
1n
1,5V
<5mA
640
0 ®884068 - 10
LEAD -ACID -BATTERY CHARGER
Modern sealed lead -acid batteries aresimplicity itself in use. In contrast toNiCd batteries, they may be charged byconnecting them to a constant voltage(at the correct level). The charging cur-rent then gives a pretty good indicationof the state of charge.These batteries may also be charged ata rapid rate, as long as the charging cur-rent is limited at the onset of the charg-ing process. Dependent on the make, acharging current of several times onetenth of the capacity in Ah is permiss-ible. For instance, a 5 Ah battery may becharged with an onset charging currentof 1 A. The charging voltage may thenbe 2.45 V per cell. At such a (relatively)high voltage, the current has to belimited, otherwise the onset chargingcurrent through a flat battery may be ashigh as 10 A.The proposed charger, whose circuit isshown in Fig. 1, incorporates a 'stan-dard' voltage regulator, IC1, and a vari-able current limiter consisting of Ti, Ri,and R4. As soon as the current throughRI becomes too large, T1 switches onand the output voltage drops. The out-put voltage is given by: 1.2(PI +R2 ± R3)/R3 IVOltSj.The current limiter becomes operative
1
++®
9.. 40V1A
IC 1
317
C1 _
MN =NI10001.1 220n40V
BC140
adj-
MIM
at a current of 0.6/R1 !amperes'.The charging voltage for a 6-V batterythat is required to be charged rapidly is3 x 2.45=7.35 V. The total effective valueof R2 + Pl should then be 585 ohms. Inpractice, this value may be slightly dif-ferent.For charging 12-V batteries, the value ofR2 + PI needs to be about 1290 ohms.
R1
00565W
884019-10
317
/ I \adj i -Cr
The input voltage should be not lessthan 3 V higher than the output voltage.The LM317 needs a heat sink, notbecause it is easily damaged, butbecause it cannot deliver its full outputcurrent at high temperatures.It is, of course, possible to use the pro-posed circuit as a common supply unit.
SUPPLEMENT 37
EE JULY/AUGUST 1988
Parts fist
Resistors 1±.5%):Rt =0R56; 5 WR2= 470RR3= 120RR4= 100RPt = 220R preset
Capacitors:CI = 1000p; 40 VC2;C3=220n; MKT
Semiconductors:T1=BC141IC1=LM317
Miscellaneous:Heat -sink for ICt.PCB Type 884019 (not available through the
Readers Services).
2 -6
I
CN-i 1=11 H°
iO4t;44 14)R2.-
1C317
STEP-UP SWITCHING REGULATOR
Maxim Integrated Products have re-cently introduced a series of integratedstep-up switching regulators designedfor simple, minimum component countDC -DC converters. All control andstabilization functions are contained inan 8 -pin DIP package: a bandgap volt-age reference, oscillator, voltage com-parator, catch diode, and an N -channelmedium power MOSFET. In addition,the ICs have a built-in low -battery (LB)detection circuit.One of these new chips is the TypeMAX641, which is of particular interestfor no -break 5 V supplies in computers.In the application shown here, the out-put current of the step-up regulator isboosted by an external bipolar powertransistor, Ti. The low -battery detectorcompares the voltage at input LB1 withthe internal +1.31 V bandgap reference.Output LBO goes low when the voltageat pin 1 drops below 1.31 V. The low -battery threshold voltage, Ms, is deter-mined by potential divider Ri-R2 as
LAB =1.31(RI/R2+1) [111
R2 is typically 100 kg. In the applicationcircuit shown here, LED Di at the LBOoutput lights when the input voltagedrops below 2.62 V.It is possible to make the output voltageadjustable by connecting input VFB to apotential divider R3 -R4 instead ofground. This option is shown inset in thecircuit diagram. The output voltage, U.,then becomes
Uo =1.31(R3/R4+ 1) rvi
Rt is, again, typically 100 kg. Cx is100 pF. Remember to observe thevoltage rating of C3.Maximum output current of the circuit is1 A. The input voltage should remainbelow 5 V. Maximum conversion ef-ficiency is about 80%.As to components: the minimum valuefor Lt, Lmm, is expressed by
3V
lc,R1
467,y
1
R5
D1
2
L1MI XI =I/Neve,160p
6
R2
00
LBOLB1
MAX
641
G N D
EXT
%tit 5
comp.VFB
3 7
BD131
IN 4937
D2
5V
IC2 C3=470p700p
*see text
Uird(2fo/roa4
Irnax depends on the current rating ofthe inductor and external power transis-tor. Factor fo is the converter oscillationfrequency, 45 kHz. The available outputpower can be increased by either rais-
0
884086-10
ing the input voltage or lowering the in-ductance. This causes the current to riseat a faster rate, and results in a higherpeak current at the end of each cycle.The available output power increasessince it is proportional to the square ofthe inductor current. The calculation of
38 SUPPLEMENT
the maximum inductance of Li is, unfor-tunately, relatively complex, and fallsoutside the scope of this introduction tothe MAX641. The inductor should beable to handle the required peak cur-rents whilst having acceptable series re-sistance and core losses. The inductorin this application circuit should berated at 2.5 A minimum.Due account should be taken of the rela-
0 4
tively high ripple amplitude at the out-put of the converter. The ripple voltageis composed of high (45 kHz) and low-
frequency components, and is practi-cally impossible to suppress further.Finally, D2 should be a fast Schottky di-ode. Alternatives to the type shown inthe circuit diagram are the Types1N5817 (1 A), 1N5821 (3 A), or the BYV27(2 A). General purpose rectifiers from
EE JULY/AUGUST 1988the 1N400x series are not rec-ommended because their slow turn -ontime results in excessive losses andpoor efficiency.
Source: Fixed Output 10 Watt CMOSStep -Up Switching Regulators. MaximIntegrated Products.
FISHING AID
This circuit provides audible and visiblewarning when a fish is nibbling the bait.Although this event is fairly easy tosignal with electronic means, the circuitis relatively extensive to ensure that itcan be powered from a 9 V battery.The circuit is based on a slotted opto-coupler Type CNY37, and a home madenotched wheel. Unfortunately, the cur-rent amplification of slotted opto-couplers is very low (0.02 min.), requir-ing considerable current to be fedthrough the LED before a usable collec-tor current flows in the phototransistor.To avoid rapidly exhausting the battery,MMV1 pulses the LED at about 250 Hzand a duty factor of 0.05. MMV2 detectsthe presence of these pulses. When aFish pulls at the bait, the notched wheelrevolves in the slot, and intermittentpulse bursts are received at the triggerinput of MMV2. Green LED Di lights,buzzer Bz sounds, and bistable N3 -N4 isset, so that red LED D2 flashes at a 1.5 Hzrate. Di and the buzzer are turned offwhen the fish gets off after nibbling thebait, but D2 continues to flash. The cir-cuit around Ni, T2 and C3 then serves tokeep the current consumption as low aspossible. The circuit can be reset bypressing St.Preset PI enables adjusting the fre-quency of the buzzer oscillator between600 and 2500 Hz. When several fishing -rods are being used, each can be as-signed a particular signal tone. Thebuzzer can be switched off by means ofS2.
A suggested construction of the lightbarrier and the notched wheel is shownin Fig. 2. A small shaft is used in combi-nation with a reel around which thefishing line revolves. The slots cut intothe detection wheel should not be toowide: 1 mm is a good starting value. Thedetection sensitivity is determined bythe number of slots in combination withthe reel diameter. The light barriershould be screened from daylight.In the stand-by condition, the circuitconsumes no more than 4 mA, whichgoes mainly on account of the LED inthe opto-coupler. In the actuated state,the current consumption rises to about12 mA.
1
0
2
CNY 37
R4
CNY 37
53
E ID
32
RS
4
252/6V314
TR
MMV2lo
0
O
78L05
R6
U
T1
BC 547
R7
01
2
RB
C7
IC378 L 05
TOOn
CRmim
9V
MEI
N 1...N 4 =IC 1 =4093MMV 1. MMV 2 = IC 2 = 4528
r±3
5,Reset
CO- CO
C31=1
77bi,E0e3
BC 516
02
57424 - 1
SUPPLEMENT 39
EE JULY/AUGUST 1988
Wideband RF signal tracer
This simple and versatile circuit can aidin troubleshooting defective RF ampli-fier circuits. The usable frequencyrange of the tracer is about 100 kHz to30 MHz. Measured signals (0.5 mV to500 mV) are amplified, detected andmade audible with the aid of a smallloudspeaker.MOSFET Ti functions as an amplifierwith a high input impedance to avoidloading the signal source. TransistorsT2, T3 and T4 form a high -gainlogarithmic amplifier that drives AMdemodulator Ts Ds. A single chip AFpower amplifier, IC!, is included tomake detected signals audible. Testingof RF equipment is carried out simplyby "probing around" at suitable lo-cations in the circuit and listening to thedetected signal, whose relative ampli-tude can provide an indication of poss-ible sources of malfunction. The tracer'slogarithmic amplifier obviates the needfor frequent re -adjustment of the volumecontrol, Pi. The unit is so sensitive that itproduces audible output when the in-put is only held near the circuit sectionunder test.As to construction of the tracer, this isbest fitted in a short length of ABS tub-ing to make a probe with three connect-ing wires for the supply voltage and theloudspeaker. Constructors are advisedto strive for ample RF decoupling andshort connections in view of the rela-tively large bandwidth. Current con-sumption of the tracer is about 100 mAfrom a regulated 6 V supply.
r10 4
BEM
BF494
U
c 103E
BF451
C 16E
ICI ,Lt 386 cioir 1
ii Coop3 47i
R14 I°V101/
3&045. 10
DRIVER FOR BIPOLARSTEPPER MOTORS
For some applications, the Universalcontrol for stepper motors (see 111) maybe considered too extensive a circuit.Many small motors with limited speedrange can be equally well controlled bya relatively simple circuit, based on, forinstance, the Type SAA1027 or TEA1012121. Most commercially available con-trollers are, however, intended for driv-ing unipolar stepper motors, which arenow gradually superseded by bipolartypes of similar size. In practice, the lat-ter can provide a larger torque, but re-quire a different type of controller.The recently introduced Type MC3479Pfrom Motorola requires a minimum ofexternal components for controlling abipolar stepper motor. The maximumquiescent stator current, Is, depends onthe value of resistor R between pin 6and ground:
h.(Ub-0.7)/0.86R [mA]
where R is given in Id?. The above rela-tion between Is and R is valid as long asthe output transistors are not operatedin the saturated area. The saturationpoint is reached sooner at low levels ofthe supply voltage, or when the ohmicresistance of the stator winding is fairlyhigh. The manufacturers state a maxi-mum current of 350 mA per stator.The supply voltage for the motor (pin 16)depends on the ohmic resistance of thestator windings, and is allowed to varybetween 7.2 and 16.5 V. When a highsupply voltage is used, it must beremembered that the output transistorswill not operate in the saturated area toprevent exceeding the set stator cur-rent, Is. The current control used hereallows a fairly high step rate at the cost
of an increase in the dissipation of thedriver IC, particularly when the motor isheld stationary. If necessary, theMC3479P can be cooled by connectingthe 4 central ground terminals to a rela-tively large copper surface on the PCB.The integrated controller has 4 TTL andCMOS compatible inputs (see Fig. 1):
CLK (pin 7): every rising edge of theclock signal causes the motor to revolveone full or one half step, depending onthe level at pin 9. The maximum steprate and the minimum pulse width are50 kHz and 10 ps respectively.CW/CCW (pin 10): the logic level ap-plied here determines the motor'sdirection of travel.F/H step (pin 9): this input allows selec-tion between full (0) or half step (1)operation-see Fig. 3.
40 SUPPLEMENT
1 uB0 7Y2...16V5EE JULY/AUGUST 1988
R5 7V2...16V2
MU 0R4
16
CW/CCWa100
FM step
1)0CLK
0output
impedance
stand by
90
70
90
Vm
IC 1MC 3479 P
CW/CC_frW 14'
frFiH step
CLK
OIC
O
R3
Phase A
Logic
-of Driver
Driver
VD
LI 3
L2 2
BiasiSet CND
41) IA 13?
a
4
CM (pin 8): this output impedance selec-tion input is only effective in the halfstep mode. It determines whether thestator winding is effectively discon-nected from the driver (0), or connectedto the positive supply at both ends (1).The latter option improves the dampingof the motor in the half step mode, andwill prove useful at relatively low steprates.Pin 11 of the driver IC is an open-collector output with a current capacityof 8 mA, activated during period A inFig. 3. A LED connected to this outputwill flash rhytmically when the motor isrunning.Transistor Ti was added to obtain areset function. No stator current flows,and the logic circuitry in the driver isreset, when the stand by input is drivenlow. When a logic 1 is applied, themotor is energized starting from state A.The addition of R2 makes it possible toswitch the driver to the power -downstate, rather than the reset state. Thestator current is reduced to the value setwith R2, as shown in the above formula.The motor driver is probably best con-trolled by a computer output port. Thecircuit in Fig. 2 is intended for stand-alone applications. It is composed of asupply, Rs -D3, an oscillator, N1 -C3 -R9-1:12,and a re-triggerable monostable multivi-brator, N2 -C2 -Rio -D2. When Si is opened,the oscillator is enabled, and the motor
3
D3
4V7400mW
087504-IN1 N2= 1/21C 2 =4093
R8
R9
-0 C3IN=St` om47n
RIO
D2
1N4148
8.as Set
c7R ccwnase A'
11
12
L3
L4
Phase AOutput
Wilt
//II/
R7E R600
C2
-17)On
O
CW/CCW
00FM step
00CLK
00
004V7
stand by
OUTPUT SEQUENCE
67504-2
C
uui
WI/.
B C B P
(al Full Step Mode
I MEr HSOic
= High Impedance= Logic '0'= Don t Care
:A: 8 C11 Fa= -7312g741
L2 FD2 .F7777771
L3 i/E414 fr7/7/
D:E A B C
1/////,.4
t777771
;lb) Half Step Mode
ALI
L2 CA13 0L4
Phase AOutput
77777, z Hrgh ImpedanceCW CM= Logic ' 0'VHS = OIC = Logic
F ; B C
(c) Half Step Mode
CV: CCW = Logic 0F HS = Logic "I"OIC = Logic -1"
87504-3
0
SUPPLEMENT 41
EE JULY/AUGUST 1988
will start running. The clock frequency,i.e., the step rate, is adjustable with P2.The monostable will remain set via D2,and Ti will conduct, as long as clockpulses are applied to the motor driver.The amount of ever reversing stator cur-rent is limited by the stator inductance,but can still be increased with the aid ofP. When the motor stops, Ti is turned
off, and the stationary stator current isreduced to the value set with R2. Theabove arangement keeps the dissi-pation of the motor and the driver withinreasonable limits.The current consumption of the com-plete circuit is practically that of themotor alone (700 mA max.). The motordriver IC consumes about 70 mA.
References:
[ii Universal control for stepper motors.Elektor Eelectronics, January 1987.[2] Stepper motor control. Elektor Elec-tronics, July/August 1986.
01 NON -INTERLACEDPICTURE FOR ELECTRON
Owners of the Acorn Electron homecomputer may well object to its interlac-ed, and therefore slightly instable, pic-ture. There is a trace of display flicker innon-moving areas on the screen, andthis is mainly due to the internal videoprocesing circuitry operating on thebasis of interlacing, a technique used inconventional TV transmission forsmoothing the appearance of movingpicture areas. Arguably, interlacing isnot very useful in computers, sincethese work with text in most appli-cations. Special displays with a rela-tively long afterglow time are noremedy for this awkward problem, andthat is why the present circuit was de-signed. It effectively switches off the in-terlace function. and so ensures a restfuldisplay, albeit that the individual linesthat make up the characters becomeslightly more prominent.Figure 1 shows that a TV picture is com-posed of 625 lines divided between 2rasters of 312.5 lines each. In an inter-laced picture, these rasters are vertical-ly shifted by one line. This is done bystarting the second raster x and a halftime later than the first raster. Inter-lacing can thus be rendered ineffectiveby starting the second raster half a lineperiod earlier (i.e., after 312 lines ratherthan 312.5). To retain the normal numberof lines (625), the second raster is ar-ranged to comprise 313 lines.The ULA chip (Uncommitted Logic Ar-ray) in the Electron computer provides ahorizontal and a composite synchroniz-ation signal, which are shown in Figs. 3a(HS) and 3b (CSYNC) respectively. Withreference to Fig. 3c, and the circuitdiagram in Fig. 2, MMV! forms a newvertical synchronization pulse, VS, withthe aid of the CSYNC signal. The periodof pulse VS is different for the first andsecond raster, so that MMV2 is neededto make VSYNC equally long in both.MMV2 is triggered on the first linepulse (HS) that occurs when VS is active,and is retriggered when VS goes low-see Fig. 3d. The length of the VSYNCpulse so made is about 160 us, or about2.5 times the line time (64 us). The HSand the new VS signal are combined inXOR gate N2 for driving the videomodulator. Gate N: serves to buffer theHS output of the ULA.The final results obtained with the cir-cuit depend mainly on the type of TV
1
2
firstraster
- flyback- -= = = (blanked)
secondraster
14
B
CSYNC
Or,
HS
r)o
O
MMV1
CLR
13
R
7
C2
27n
9-0
0
A
MMV2
CLR
11
MMV 1, MMV 2= IC 1= 74 HCT 123N1...N4 =IC2=74LS86
2
0b
C.
ig3
13
5V
IC2 IC1
0 0VSYNC
I
CSYNC
I
HSYNC
0Qo
MEM
8-7485.3
42 SUPPLEMENT
3
a) ULA HS
b)
c)
d)
e)
4
{ firstULA raster
CSYNC second Iiraster
VSYNCOi first raster
MMV1 VSYNCsecondraster L t1
111
Q/MMV2
4/N2 CSYNC
. , .
L.tla Lt.
IC,
r
ULA
MOO,
Cu
cur_
Cal NC
ti = period of MMV 1t2 = period of MMV 2
RII
4 12
7 C,1 -7-
C;1: (1 ..4*. C. : a''..SSE'.1
.1. -.........iri.1- I-DIF-1-kr, I
4=1 D.,.
"-lg.-11CM':.-I=4-19,--4
a-aa IOriMal a
-17.,r, .-1=1 _LUC .... ., [...,
a Is : at ssvo H,
css 1. 41.-0la KICC ' 1 1-a ars 1 vs?
-"s" mg, 7
..... -...._c
-,.. Elf., t. C.a., aw. ITV",..,..,.,
--mc Slo , 14: 4.2
lCr 0 -
.... __ti."
I....
.... _A,..,....-,.. !CIS 17; -I .. IC,
-es21:7
Co-}
1.31
PI[
fv
a ta
ssa 6,..ea
asa trio.
'> a`4* Cs.-47.
Se
S. 0-
.1/.5 tt
i=aal.
'" ,I. 1,3 .S. a- C=F
S
041.S
s.-4--.. r.
CCI...
IT:1
0.. a .. ..... ,
,4 ac
,...:Sid0--Saa
1:1. 31?) Z . ,,,- --:-. trt 7CP,122, 1:,...-C3
a. at
../..... 0.
..... ._ c,0.
alli. 41. ,.... SS:Sia. I =13C. .CL--E= 11-,.....,---- I
tc.It. :. -11-
.ss: c....
::,
IC,S
;)1V.FIS.1
a.XL
3.1.4 LJ-s. .s.1=..
"1""1:13%la% ...I.
ca.cus >I!..4;324 ILLSCC
IR
Cat
:1E10,-4SCIL act Kt at
Main PCB Circuit Diagram
EE JULY/AUGUST 1988
set or display used, and may not be opti-mum when the TV is driven via its RF in-put. On an older type monochrome set,the central area of the picture wasstable, but the upper and lower areasgave a less favourable look. Goodresults were obtained, however, fromthe use of Type TX chassis, which arecurrently the basis of TV sets sold undermany different names and licenses.Even better performance can be ex-pected from a video monitor, whose(TTL compatible) H and V synchroniz-ation inputs can be driven by N4 and N3respectively. The polarity of the syncsignals can be selected with the aid ofwire jumpers. Connections c and c'result VSYNC and HSYNC. Thechoice between jumper a or b dependson the type of display used. Preset P: isadjusted until the picture appears ver-tically synchronized: the adjustment isfairly critical when jumper a is used.The final results obtained with the cir-cuit can be judged from looking at a fewcharacters in the upper and lower areaof the screen. The modest current con-sumption of the circuit, 10 mA, makes itpossible to power it direct from theElectron computer.
CSYNC
O MMV1/1CSYNC
N2/6
HS0 N1/1
87485-4
SUPPLEMENT 43
EE JULYIAUGUST 1988
0 5FRUIT MACHINE
This is one of the very few 'one-armedbandits' to which the maxim the soleway to win is not to gamble is not ap-plicable. In other words, this circuitdoes not have a slot for inserting coins:every play is free.Actuation and release of the 'PLAY' but-ton, Si, causes the circuit to becomeoperative. Series regulator Ti is driveninto saturation by Tz, which is con-trolled by N2 -N7. The outputs of N2, Nu,and ND) go high in succession, anddisable counters ICs, IC4 and 103,which are all clocked by oscillator Niz-Ns, and reset by the pulse at their Q3output. The 3 LEDs driven by each of thecounters, therefore, lights cyclically.When a counter is disabled by the highlevel at its CE input, one of the LEDs inthe 3 groups remains illuminated. The
1
= IC 1 = 40106N7...N12 = IC 2 = 40106N13...N15 = IC6 = 4073
-0-0 0-0-
BC557T1
A R130mA
1 R2Cl R4
BC547
i.411715Y
N72O
R7
output state of the counters is notpredictable because of the inconstantdelay between the disable instants.NAND gates N13-N1s detect the winningcombinations, i.e., LED D2 lights, and Bz:is sounded, when 3 identical counteroutputs are activated. Note that diodesD3 -Ds form a 3 -input OR gate, and thatthe buzzer also produces sound whenthe LEDs are flashing, since the pulsesat output Q2 of 102 enable the oscillatorintermittently.The play is ended when the voltageacross C3 is high enough for gate N7 tochange state. T2 is turned off, and Ti nolonger powers the circuit. An on/offswitch is not required for the fruitmachine, thanks to its very low currentconsumption in the de -activated state.
R5
C2
4117116V
8 8 C7IC1 IC3 C9 CSIC2 IC4 - innIC6 IC5 3. 10n
100n R100 0
R6
N48
R15
Parts list
Resistors (±5%):RI;R3:R4;R5:R8;Fi1o= 10KR2 =4K7Rs = 220KR7=1M5R9 = 470KR11 =3M3R12:R14 =33KR13= 100KRis= 1K0R16=330R
Capacitors:C1;C3=4,17; 16 V; axialC2:C5:C6= 10nC4 =1/i; 16 V; axialC7;C8;C9= 100n
1 R14
LEI 13 0" " 1 10"02
C6
10n
N1
3x 1N4148 os10i 9
15
RCLK
7
03Co
IC 3
401701
CE 02
15 7
R Q3CLK 00
IC 401
4017
CE 02
151 7
N13
51 4 3
03
6
N14 I I N15
2 8 13 11 12
B
N6 N5
R12
R13
114-4
06
Bz 1
4
4
R 03CLK
IC 5
4017
CE
CO
01
02
D6...D8 = LED139...D11 =LED012...014 = LED
4
mff
09 ff
!,21
f
44
010 ff
013
4+
H08 f f
01
014
R16
87476
PB2720
44 SUPPLEMENT
EE JULY/AUGUST 1988
2
0
Semiconductors:DI;D3;D4;De=1N4148D2;136;D2;D8= LED (red)De;D to;Dit= LED (yellow)D12;D13;1314=LED (green)ICOC2=40106IC3;IC4;IC5= 4017ICe=4073Ti=BC557T2=BC547
Miscellaneous:Si = momentary action push button.Bz= PB2720 buzzer (Cirkit stock no.43-27201).
PCB Type 87476 (available through theReaders services).
5 WIDEBAND LEVEL -INDEPENDENTTRIGGER PREAMPLIFIER
This circuit eliminates the difficulty inre -adjusting the trigger level of an os-cilloscope or frequency meter any timethe amplitude of the input signalchanges. The block diagram shows thatthe trigger pulses are supplied by a fastcomparator that compares the instan-taneous input signal amplitude with areference voltage deduced from the dif-ference between the peak amplitude ofthe positive and negative half cycles ofthe rectified input signal. The circuit isfast enough to handle input signals witha frequency of up to 100 MHz, and has asensitivity of 100 mVpp.With reference to the circuit diagram,the input signal is raised in a widebandpreamplifier based around a UHF dual -gate MOSFET, Ti, fed by constant cur-rent source T2. Presets Pi and P2 definethe potential at the source of Ti, andhence form the fine and coarse offsetcompensation adjustments for the
ze. o c.
;5
o cv
6
© cu
18
0 . cc
P : cr CO ,-,,.'452 ch'*c cr@7... 7- T. 7° 1 7-7 -,
direct -coupled chain of opampsIC2-IC3. The signal rectifier and directvoltage amplifier are formed by D:-D2-Rt-C7 and IC2. The relatively weaksignal is raised further in direct -coupledopamps ICs and IC4 for comparisonwith the amplified measuring signal inopamp ICs. Schmitt-trigger/inverter ICecleans the trigger signal before it is ap-plied to the test instrument. The triggersensitivity is set by potentiometer P4.Choke Li is wound as 4 turns of 0.2 mm
13F981 .5F932
SF2568
ii.sfe test
IG
1:11-D3=AA11904 = 1114148
dia. enamelled copper wire through asmall ferrite bead. MOSFET Ti may bereplaced by a Type BF991 or BF966 ifeither of these is easier to obtain locally.The circuit should be constructed withdue attention paid to the relatively highfrequencies it can handle. In this con-text, it is recommended to use a largecopper area as an effective groundplane onto which the parts are fitted.The shortest possible connections, am-ple screening, and effective decoupling
SUPPLEMENT 45
EE JULY/AUGUST 1988
of the supply voltage at various point inthe circuit are also a must to ensure cor-rect operation.Optimum sensitivity is achieved by ad -
0 5
justing PI, P2 and P3 for lowest offsetmeasured at the output of IC3. Theseadjustments are carried out after awarming -up period of a few minutes,
and with the input of the preamplifiertemporarily short-circuited.
FAST STARTING WIPER DELAY
A wiper delay is essentially a bistablemultivibrator whose off -time is adjust-able with a potentiometer. Many wiperdelay circuits are based on the Type 555timer in its standard application circuit,which has the disadvantage of introduc-ing a delay of about 1.6 times the set in-terval before the first wiper action takesplace. This is especially annoying whenan interval of, say, ten or more secondshas been set. This circuit is also 555based, but is unique in that it arrangesfor the wipers to be activated immedi-ately at power -on.The circuit diagram of Fig. 1 shows theinternal organization of the 555 timer toaid in clarifying the operation of thepresent circuit. When Si is cl3sed, pin 6is immediately pulled to +12 V becauseCI is discharged as yet (see also Fig.2b). The bistable in the 555 is reset, theoutput goes low, and Re, is energized.This forms the basic difference with thestandard application of the 555, whereCI, connected as shown in Fig. 2a,delays the relay action until charged to2/3 of the supply voltage. Returning toFig. 1, Ci is charged via R2 and the 555'sinternal transistor when the output is ac-tivated. The bistable is reset when thevoltage at pin 2 drops below V3Vcc,causing the relay to be de -energized,and Ci to be discharged via RI -PI. Thedischarge time, and hence the wipe in-terval, is defined by the setting of P1.When this is set to the shortest delay, thewiper motor is constantly powered viaRef, since C1 is not charged via PI -R2only, but effectively via voltage divider131-121-R2 also. The wiper delay is fedfrom the 12 V car battery, and its currentconsumption is practically that of the
siI2V 0
P1
C2
mom100p16V
R
1M16V
6:
..L
L
R
0reSet
ICI555
relay alone. Note that the coil currentmay not exceed 200 mA.
E75ClZas
dis-har;e
threshold
87508-1
£200mA
D1 Re1
1N I EZI4001
43
575C5.20
1 = GND2 = trigger3 = out4 = reset5 = control voltage6 = threshold7 = discharge8 = V00
TEST -VOLTAGE SUPPLY
For testing zener diodes, base -emitterbreakdown, diacs, and so on, a fairlyhigh voltage is needed. The usual typeof laboratory power supply is notsuitable, because its output is normallyof the order of only about 30 V. If the re-quired current does not exceed 10 to15 mA. it is possible to make a short-circuit -proof power supply with vari-
able output voltage from 0 to 50 V froma handful of components as shown in theaccompanying diagram.Circuit ICI amplifies a direct voltage setby P2 by a factor of about 6. Its outputvoltage should be about 25 V withrespect to junction C1 -C2. This voltageis inverted by IC2, whose output is thus-25 V. There is then available either a
symmetrical ±25 V potential withrespect to junction C1 -C2, or 50 V asym-metrical across the outputs of the ICs.The actual value of the voltage is setwith P.The maximum current is limited by theICs to about 20 mA, so that thelikelihood of damage to a componentunder test is very small. The output is
46 SUPPLEMENT
EE JULYIAUGUST 1988
*see text
D1...D4 =1N4148
DI
D4
D2
R1
Cl C3=mo min100p 47p40V 16V
D6
5V6
PI
25kP2 C4
min100n50k
R3
C2D3
100P40V
R2
7
5V6
Eel
IC1
741
R4
mim100n
6
max. 50V15mA
100k
R5
100k
R6
100k
IC1
741
C6 D5NM=mimA
100n
0
1N4148
short -circuit -proof for an indefiniteperiod.To avoid common -mode problems, andalso to make it possible to vary the out-put voltage to 0, the supply voltages toIC: and IC2 overlap to some extent,which is arranged by Dr and Di. ZenerDs also functions as the voltage refer-ence. The supply to ICI must bedecoupled separately by a 100 n capaci-
tor; that to IC2 is decoupled adequatelyby C2 and C3.The mains transformer may con-veniently (and inexpensively) consist oftwo 18 V types, otherwise a single 36 Vunit is required. The secondary must beable to provide a current of 20 to 30 mA.If two transformers in series are used,make sure that they are in phase.Before inserting the ICs into their
884063 -10
sockets, check the voltage at pins 4 and7: this should be not higher than 36 V ifa 741C is used, or 44 V for other types(741A, 741E, and 741). If the voltage is toohigh, a transformer with a lower ratedsecondary (2 x15 V or 30 V) should beused. If, however, the voltage at pins 4and 7 becomes lower than 27 V, it maybe impossible to obtain an outputvoltage of 50 V.
POWER SWITCH FOR CARS
Motorist are generally well aware thatcar fuses do not blow just like that. Nonethe less, when something appears to beamiss in the electrical circuit, a newfuse is nearly always fitted prior to in-vestigating the possible cause for themalfunction, which then, of course,costs two fuses. The circuits shown hereare short circuit proof power switches,or electronic fuses with switch controldimensioned for relatively heavy (lamp)loads in a car. Both circuits are com-posed of a power switch, Ti, and a cur-rent limiter, T2. The circuit is fully short-circuit and overload resistant, providedT1 is adequately cooled, and the wholeunit is constructed in a sturdy enclos-ure. The circuit in Fig. la has the lowervoltage drop of the two, while that inFig. lb is used when a TO -218 style TypeMJE2955T or TIP2955 is not obtainable.It is interesting to note that the plasticTO -218 package is mechanically inter-changeable with the wellknown TO -3outline, and enables ready mounting of
1a
SI
T2
BD136BD140 t
R2
* see text (table)
12V
Ti
MJE 2955 TTIP 2955
RL
87457 - la
b
Si
12V 12V
R2
T2
BD135BD139
* see text (table)
MJE 3055 TTIP 3055
L
87467 - lb
SUPPLEMENT 47
EE JULY/AUGUST 1988
Table 1
Application RL (WI I (Al 111 (Q) Rz IQ) Cooling TI -T2
Dashboardlighting 1 0.08 5.6 3300 not required
Courtesy light 2 0.17 2.7 1500 not required
Rear light orparking light 5 0.42 1.2 680 25 cm'
Brake light 18 1.5 0.33 (5 W) 180 (1 W) 225 cm'
Fog light ortrafficator 21 1.75 0.27 (5 W) 150 (1 W) 225 cm'
the transistor onto a flat surface using aninsulating washer-see Fig. 2. The useof a die-cast enclosure and TO -3 styletransistors is illustrated in Fig. 3. Thisunit houses two power switches, one ofwhich has its contacts at the rear side.Pay great attention to the correct elec-trical insulation between the transistors
0 5
and the enclosure, and, if required, thatbetween the enclosure and the carbody. Switch S1 is the existing controlfor the relevant lamp in or on the ve-hicle. Note the difference in respect ofthe connection of Si in Fig. la and lb.Table 1 shows how Ri and R2 are dimen-sioned in accordance with the current
4
Wb-
0RL
01 R2
P1
0001-1
000T2
Part list
Resistors (±5%):131;R2= see text
Semiconductors:TI=MJE2955T or TIP2955 (Fig. la)T1= MJE3055T or TIP3055 (Fig. lb)T2 = BD136 or 80140 tFig. la).T2 = BD135 or BD139 (Fig. lb).
Miscellaneous:SI= see textPCB Type 87467 (not available through theReaders Services).
requirement of the load, and also givesa suggested area of the cooling surface.Finally, when the printed circuit boardis used, T1 should be a TIP2955 or aMJE2955T, not a MJE2955, since this hasits outer terminals (B -E) reversed.
48 MHz CLOCK GENERATOR
Currently, 48 MHz quartz crystals arewidely available at relatively low costthanks to their use in computer systems.In these, there is often a need for severalclock frequencies that can be derivedfrom a central oscillator. When this sup-plies a buffered 48 MHz signal, it is rela-tively simple to add a divider circuit thatprovides lower, phase -synchronous,clock signals of, say, 6, 8, 12, 16 or24 MHz. Obviously, this obviates theneed for separate quartz crystals and as-sociated oscillators, and so economizeson hardware expenses.A reliable 48 MHz oscillator is fairly dif-ficult to make with HC or HCT gates.The oscillator shown here is, therefore,built around discrete RF transistors. Itoperates with inexpensive, third over-tone series resonance quartz crystals inthe range between 44 MHz and about52 MHz. A parallel L -C network may be
BF240
5V<30mA
884078-112
48 SUPPLEMENT
EE JULY/AUGUST 1988connected in series with the crystal as quency to 48.000 MHz, but also for 'pull- frequency multiplier (local oscillatorshown in the circuit diagram for ac- ing' the oscillator a few kilohertz around chains in 2 in, 70 cm, or 23 cm amateurcurate setting of the oscillation fre- this frequency if it is used for driving a radio equipment).
0
DO0
DI
0
D2
0
D30
D40
135
0
D60
D7
0
5DIGITAL ATTENUATOR
13
®8V
IH100n
7
IC4
C2 IH108Vicicin
RIB
(i)
1C3...C5100n
TOOn
.Cr
8V
(DI
8V
Digitally controlled attenuators almostinvariably use some kind of tapped re-sistor network to simulate a poten-tiometer. This solution is fine as long asthe number of steps required is small.When finer control is required, how-ever, the normal tapped resistor net-work is hardly ever used because of thelarge number of components that wouldbe required. The circuit shown here of-fers relatively high resolution (attenu-ation range: 48 dB) whilst requiring fewcomponents only.The technique used is similar to that ofmultiplying DACs (digital -to -analogueconverters). In a conventional R -2R lad-der DAC, the output voltage is given by(Ure/384)N where N is the binarynumber applied to the inputs. Thedirect dependance of the output volt-age on Use makes it easy to obtain avariable attenuator by substituting theinput for Uref. The output will then be(Um/384)N.The R -2R ladder network used here iscomposed of resistors RI to R17 incl.,while electronic switches ES! to ES:oincl. form the switching elements.These are of the two-way type (SPDT),connecting either the input voltage orground to the inputs of the ladder net-work. Buffer ICi presents a constant im-pedance to the source. Pin 7 of ICI, IC2and IC2 should be grounded unless thecircuit is operated with bipolar signals.In that case, pin 7 of all three ICs is con-nected to -8 V.The circuit can handle signals of up to400 kHz with a maximum amplitude ofabout 4 Vpp. With signals of lower level,higher frequency response should beobtainable. The high frequency limit isdue to the buffer at the input-the elec-tronic switches by themselves canhandle signals up to 10 MHz.The fixed attenuation of the circuit isabout -3.5 dB. Signal-to-noise ratio ismore than 100 dB at an input signal of
1 Vrrns. The output offset voltage is com-pensated by adjusting PL Current con-sumption of the circuit is about 6 mA atUb= ±8 V. Finally, it should be notedthat TTL circuits can not drive the circuitdirect, unless 47 kQ pull-up resistors arefitted at control inputs DO to D7 incl.
1C4= LF 356ES1...ES3 =1C1ES4...ES6 =1C2 4053ES7, ES8 =1C3R1...R10 = 22 k,1%R11...817=11k,1%
884083-10
SUPPLEMENT 49
EE JULY/AUGUST 1988
ELECTRONIC SAND -GLASS
This electronic version of the reversiblesand -glass uses a set of LEDs to simulatethe passing of sand grains from the up-per to the lower bulb. The simple tobuild circuit is accurate enough formost domestic timing applications.The circuit diagram appears in Fig. 1.On power -up, shift registers IC3 and IC4are reset by the low pulse from networkR35 -C7. A few seconds later, the sand -glass is started. The oscillator in IC2generates a clock signal for the shiftregisters. The clock frequency is adjust-able with PI. Switch S2 enables selectingone of the three timing periods stated inthe circuit diagram. Si is a small mer-cury or ball changeover switchmounted inside the sand -glass. Whenthis is reversed, the switch toggles andso selects the odd or even numberedLEDs. Assuming that Si is set as shown inthe circuit diagram, every clock pulsecauses a logic high level to be shiftedinto IC3, for as long as pin 13 of IC4 re-mains logic low. The MS bit of IC3 (out-put Q7) is shifted into the second shiftregister. IC4. Controlled by the shiftregister outputs, transistors T1 to T16incl. switch off the odd numbered LEDs,and light the even numbered ones
Parts list
Resistors (= 5%):Rt...Rts incl.;1140= 330RRo... R32 incl.;1317;Fi39= 10KR31= 100K1314:1335;R3s; art = 1 MORas =1K0132=100K presetP2 =2K5 or 2K2 preset
Capacitors:CI =100p; 16 V: axialC2;C3;Cs;Cs=1000C4 = 2ii2; 16 V; radialC7;Cs=1/1Cs=220n
Semiconductors:Di...033 incl.= red LEDD34...D49 incl.= 1N4148
incl.=BC547ICI =4093IC2=4060IC3;1C2=74HCT164IC:=7805
Miscellaneous:Bz, = PB2720 (Toko; Cirkit stock no.43-27201).
St = SPOT mercury. ball or tilt switch, e.g.Maplin order no. FE 11M, or ElectroValueno. 339-881.
Sz= single -pole, 3 -position rotary switchplus knob.
PCB Type 87406 (available through theReaders Services).
Suitable ABS enclosure.DC power socket.
1
2
05V
ft0310ic"
T,
035
R3
D2
03
516
ftD36 D5
73
ti " 51.ftDy141_,
4 TA
CT8-1gy520
56
57
ft,1F10.
15
itft039_0144011_.
T6
042
SV
0
it 012
ft013
014
5-
T7
" D15
075
Ta
1E1 11171D
Imm051 AI Simi oltsl
050
52
52
524
3
4
5
11
12
5V
V
535os
IC3 11 1C4 G,
02 A 0 b 0274 74
03 HCT Calm HCT 03164 164
04 Z--.7::.... 04g,
05
.1107 6.rCLK
05
A CS
L 8 07
A=20 I48=10min0= 5min
0 0 0 0 0 0077_,..1_0011 .
IC2 012 ,0111
4060 013 3 AA Dr"52
12
101
Bz 1
TOKOP52720
R37
CLK
Bi
525
L4
6
11
12
13
626
510
D17
19
It
DIGif
042
R9
ft.._121114145.10710 RID
020
D21 "
111
ors itff
D29 DAB
041
115
D30ei
ff031
115
032536 44
DA9
A11
Rt5
515
5?
0
111._144 = IC1= 409371...T17.13C54713
5VD1....D33= LED red
* see teel
IVD1 033
034 - 049105 T114 14 P4 14 14 14 14 14 t4 14 14 14 P4 1.4
:14
#########bOR1
0 00 0Q Q 1111(11NACIft NO 30 ortesanrin"I PI iC3lT 104
t)aa T 4;n19VGIOC) U4Cbb* R3
UV cococtS
o --o 00 mi 03 01tlilrfeiritlACS Cbesn rs nap COO UB102 It10115-
OUUCP clr2 01) 120 0012 7171 000 10 0 132
1-1K G L-0 --e OR 37 i0 1c3)
0 0 0 0 0 00,m CsjSI IBZ1V 4219
5V
50 SUPPLEMENT
EE JULY/AUGUST 1988sequentially. When pin 13 of IC4 goeshigh, counter IC2 is reset via N1 -N2,while oscillator N4 is started. Buzzer Bziis actuated and sounds for about 2
co seconds (C4 -R41). The pitch of the tonecan be set with P2.When the sand -glass is reversed, SItoggles, ending the reset state of IC2.Logic low levels are shifted into IC3because pin 13 of IC4 is logic high. Theeven numbered LEDs go out one byone, and the odd numbered ones light,until pin 13 of IC4 goes low again. IC2 isreset, Bzi produces a short beep, andthe sand -glass can be reversed for anew timing period. LED D33 indicatesthat the sand -glass is operative. The cir-cuit is fed from a small mains adaptorcapable of supplying about 200 mA atan output voltage between 7.5 and12 VDC.Construction of the sand -glass isstraight -forward using PCB Type87406-see Fig. 2. The position of theLEDs on the front panel of the enclosureis shown in Fig. 3. Make sure that eachLED is connected to the correspondingsoldering island on the PCB. SPDTSwitch Si is made from two SPST mer-cury or ball switches, fitted together butmutually reversed at a suitable positionin the enclosure. The action of theswitches is tested by reversing the sand -glass and measuring the switch con-figuration with the aid of a continuitytester or an ohm meter. All parts in thesand -glass enclosure should be fittedsecurely in view of the reversibility ofthe enclosure. The socket for connect-ing the adaptor, and rotary switch S2, arefitted in one of ,the side panels. A proto-type of the electronic sand -glass isshown in Fig. 4. The detachable frontpanel that holds the LEDs was cut fromperspex sheet.
STEPPER MOTOR DRIVER
This stepper motor driver is simplewithout compromising versatility. It hasa conventional computer interface, anoptional on -board clock generator, andintegrated motor control and driverstages. The board can drive dual -statormotors, i.e., motors with two bipolar, orfour unipolar, phases. Maximum currentper phase is 2A.The circuit diagram of Fig. 2 shows thatthe circuit is designed around chip setL297 -L298 from SGS.The block diagram of the L297 is givenin Fig. 1. This IC generates controlsignals for a dual -stator motor, andenables selecting direction of travel andfull or half-step operation by appro-priate programming of its TLL-compatible inputs. One full or half stepis performed on the trailing edge of thesignal applied to the clock input (CLK).When the enable input, E, is held logiclow, the motor is not energized, so thatthe spindle can be rotated freely. Driv-
1
NKLY,FULLSTEP
RESET
DRECTICIS(CWICCY.)
CLOCK
NONE
884076 -11
ENKSLE
SYNC
SUPPLEMENT 51
EE JULY/AUGUST 1988
2 5_40V
(2)5V
5%.1
cwiccw 0C120H.,f 0
RESEr0ENAKE0
LATE
sroc0
OO
3
JP1
25k
SYNC
VpSA
SEI
909 12@74
8 11ENS C4.174
SA .i. S8
14
01 02 03 04
STr-FERMOTOR
AIL
3
El0
JYYL
15
151 2
3n3
C41 -9
0
C21=2 05 DIS 07 08XXXI
220p40V
inhibit chopping, pin 11 = to; 'st
DRIVE CURRENT---.-RECIRCULATION
C
:rill
SENSERESISTCCURRE N
LCL7- 4-
FLIPFLOP FLOP5E7 J RESET
CLK
1C3
4024
1, g 3 'a 3 Zi
KI
FAST DEEM
s tsat
'1'111'116
MINT
- OB
MIN
5V
01...08. BYV27
1C3
0
phase chopping, pin 11 = high
INHI
SENSI
SENSERESISTORCUSSENT
LOADCURRENT
E14076 -10
01 03
S-5141
_ICHOPPOIOSC PERICC
017 001
jinit
FUR FLOP [File FLOP RESET SLOWISH DECAYSE: BE OSC By CCHIFARATOR !THROUGH 314H003
NOTE THAT CI- RENT IkSENSE RESISTOR ISNTERIAITTENT
884076-12
52 SUPPLEMENT
EE JULY/AUGUST 1988
Parts list
Resistors (-±5%):Ri;R2=1R0; 4 WR3. . . R9 incl. = 22KR to= 330Rfill=15KPI =25K or 22K preset HP2=250K or 220K preset H
Capacitors:CI =3n3C2= 220y; 40 VC3:Cd;Cs= 10bn
Semiconductors:Di ...Ds incl.=BYV27 (Philips Components)Ds= LEDIC1=L297 (SGS)IC2=L298 (SGS)IC3= 4024
Miscellaneous:JPi = 3 -way terminal strip (pitch: 0.1 in.); 1
jumper.Kt = 2 off 7 -pin terminal strips (pitch: 0.1
in.); 1 jumper.14 off solder pins dia. 1.3 mm.PCB Type 884076 (see Readers Services
page).
ing the reset input logic low causes themotor to remain halted in the home pos-ition (LED Di is quenched).Power driver Type L298 supports con-stant current drive of the stator win-dings. Current drive gives good resultsbecause it allows stepper motors to beconnected to a voltage that is higherthan specified for voltage drive. Currentdrive considerably improves themotor's dynamic characteristics (startfrequency and maximum step -rate). Aninternal oscillator sets a bistable at thestart of each period, when the statorwindings are connected to the supplyvoltage. Due to the stator inductance,output current will initially rise linearly,resulting in a linear voltage on currentsensing resistors RI and R2. When themeasured voltage reaches a certainuser -defined peak value, Vrei, two inter-nal comparators reset the bistables, andthe stator current is interrupted. Free-wheeling diodes then reduce the induc-ed stator field. From the above it is clearthat current drive works by peak detec-tion. The resultant avarage currentdepends on Vref (adjustable with Pi), theoscillator frequency (adjustable with P2)and the values of the sensing resistors.Ripple amplitude on the stator currentdepends on stator self-inductance andthe logic level at the MODE input. Whenthis is high, the outputs of 1C2 areswitched to high impedance during thefree -wheeling period. The stator field isreduced fairly rapidly via the free-wheeling diodes which conductbecause the instantaneous voltage on
5
K1O P2
SYNC H/P0 0 9 0GATE RESET0 0?K° ? 0
84076.13
the stator winding is slightly higher thanthe supply voltage. When MODE is heldlogic low, one transistor in the bridgecircuit internal to the L298 remains onduring the free -wheeling period. Thiscauses the free -wheeling voltage on thestator winding to remain relatively low,resulting in slower reduction of thestator field strength and, therefore, re-duced ripple (phase chopping, see Fig.3). This option is offered to enable ef-ficient current control of motors with arelatively low stator self-inductance.Synchronization of the oscillators in theL297s is required when multiple driversand motors are used in a single system.This is simple to accomplish by fittingparts P2, RI! and CI on one driver boardonly, and feeding the signal available atthe SYNC output to the SYNC terminalon the other boards.An on -board divider, ICE, is provided tosupply the clock signal when the rel-evant computer output line cannot beprogrammed to toggle at the requiredstep -rate. The divider is clocked withthe SYNC signal of the L297, and jumperblock Kt allows selecting 1 of 7available clock frequencies (step -rates).On -board clocking via 1C3 can bedisabled by driving input GATE logiclow. The CLOCK input then functions asan output, enabling the computer tokeep track of the number of steps per-formed. When external clock pulses areapplied to the board, IC3 is simply omit-ted.The 5-40 V supply rail need not beregulated - smoothing is adequate
6Al
U.4776 14
here. The maximum attainable step -rateincrease with supply voltage, but 40 Vshould not be exceeded.The chopper frequency (refer to Fig. 3),and hence the step -rate in stand-aloneapplications, is set with P2. Stator cur-rent is set with Pi. Lisping sounds pro-duced by the motor point to instability ofthe current drive. This effect can beremedied by either re -adjusting thechopper frequency, or by selecting theother logic level at the MODE input ofICi. When this still fails to stabilize thecurrent drive, the supply voltage mustbe reduced until the motor operateswith voltage instead of current drive.Stand-alone use of the driver is simple toaccomplish by connnecting three exter-nal switches as shown in Fig. 5. Figure 6shows how to connect the driver boardto a unipolar motor. The oscillator insideICI is used only for generating theclock signal required in stand-alone ap-plications of the driver. When it is used,the step -rate can be set by fitting ajumper in the appropriate position onKi, and adjusting P2.Finally, 1C2 is purposely located at theedge of the printed circuit board to en-able it to be bolted on a metal surfacefor cooling.
SUPPLEMENT 53
EE JULY/AUGUST 1988
0 5VIDEO DISTRIBUTION AMPLIFIER
The Type TEA5114 from Thomson-CSFcomprises three electronic switches fol-lowed by a buffer/amplifier. Normallythe voltage amplification is 2 (6 dB).When the input voltage exceeds1.2 Vpp, or when the output voltage ex-ceeds 1.5 Vpp, an internal selectorreduces the amplification to unity (0 dB).The threshold of 1.2 Vpp is created withthe aid of voltage divider Its -R5, whichalso forms the input termination of 75 Q.Series resistors RI -R3 ensure 75 Q outputimpedance for driving video equip-ment via standard coax cable. TheTEA5114 can be used as a video sourceselector also, provided each input hasits own 75 Q termination network. Thenon -connected inputs should then befitted with a coupling capacitor. Chan-nel selection is effected by controllingthe logic level at pins 10. 12 and 15. Notethat the logic 1 (high) level correspondsto +2.5 V here.
Parts list
Resistors ( -±5%):.. .R3 incl. =15R
R4 = 47RRs = 27R
Capacitors:CI incl.= 100n
Semiconductor:=TEA5114'
Miscellaneous:PCB Type 87466 (not available through the
Readers Services).
Thomson Components Limited RingwayHouse Bell Road Danneshill Basingstoke Hants RG24 OGG. Tele-phone: (0256) 29155. For distributors seeInfocard 502 (EE February 19871.
1
750video outputs
-0- 0-0 ® 000 0 0
R1E R211 R3E
100n
470...140mA
16 15 14 13 12H11 1-110
IC 1
TEA 5114
75 n 0,0 0videoinput
°-
0
VREF
H,
o-
fi t4I I
6-N-414-1
R5
EEO
4 5 6
C3 C4
R4
100n .1.1.00n
0
2 Vedrigl0-43Y f
To -0-1 t fro(1/
137466
Q a a
57-6-6-6-norteineninLy
IC1rfaVUCUOVULP
[40 1-4:1PI5
87466
0
12V0
I
54 SUPPLEMENT
EE JULY/AUGUST 1988
DISCRETE +5 to
This negative voltage converter differsfrom a host of other designs in not beingset up around the latest integrated cir-cuit. The circuit diagram shows that onlya handful of commonly available partsare required to build an efficient +5 to-15 V converter.ICI functions as a self -oscillating multi-vibrator that supplies an output signalwith a relatively high duty factor. TheLM311 is designed to operate from asingle 5 V supply, and has a high outputcurrent capability for driving switchingtransistor Ti. Duty factor of the outputsignal is determined mainly by voltagedivider Rz-R3, and frequency of oscil-lation by Cz-R4. Transistor T2 forms partof a regulation loop that modifies the os-cillator duty factor to maintain -15 V atthe output of the converter.The output voltage, Uo, is calculatedfrom
U0= -(UDI Us-E(TI))(R8/R9 +1)
The component values shown give thefollowing design data:
Efficiency (P0/R): max. 75%Oscillator frequency: 6 kHzDuty factor: approx. 0.8Output ripple voltage:
100 mV at IL=200 mA.Maximum load current: 200 mA
Ti should be fitted with a small heat-sink.
0 6
5V/1A
0
0
15 V CONVERTER
R10
R2 R4
C2 R3
a
IC1
R5
IC1 = LM311
R8
O
9
12
2N2727
01
6V8400mW
02 c3=1N5408 i°,234A'
15V/200mA
884.3- 10 0
Source: National Semiconductor LinearBrief 18.
OVER VOLTAGE PROTECTION
It happens from time to time that verylarge voltage spikes (lightning;switching of large loads) are superim-posed on the mains. Although thesespikes are of very short duration, theymay have disastrous consequences formains -operated equipment. A mainspower supply can be effectively pro-tected from such spikes with the aid ofvaristors. These components canhandle, but only for a few microsec-onds, currents of thousands of amperes.In the proposed protection circuit,three varistors are used: one betweenLive) and N(eutral); one between L enE(arth); and one between N and E. Thevaristors are preceded by fuses, so thatonly the equipment connected via thecircuit is protected. If these fuses wereomitted, the entire household supplywould be protected with the risk thatone of the main fuses blows during an
10A
10A 884089 -10
over -voltage.The circuit is best built into a small man-made -fibre enclosure with integral plugand socket. The mains -carrying barewires should be kept separated by atleast 3 mm.
SUPPLEMENT 55
EE JULY/AUGUST 1988
0FROM ALTIMETER TO VARIOMETER
The altimeter published some 18months ago (i) can be adapted to func-tion as a variometer by the following cir-cuit. The difficulty in the design of thecircuit is, of course, that it has to workwith very small input voltages. It isbased on the fact that differentiating theabsolute height gives as result the rateof change of altitude.In the diagram, ICI is the differentiatorthat operates with a time constant, RICI,of 1 s. Since this type of differentiator in-verts, it is followed by an inverter.If the amplification is arranged at 60 (PIset to 60 k), the eventual read-out showsthe rate of change of altitude in m/min,assuming, of course, that the altimeterhas been calibrated as prescribed inRef. 1.Because of the very low levels of signalinput, the choice of components iscritical. For instance, Ci must be anMKT, not an electrolytic, type. The dif-ferentiator is a CMOS opamp that notonly has a very high input impedance,but also extremely small drift of offsetvoltage with temperature. This drift is sosmall only if the opamp is used in thelow -bias mode (pin 8 connected to +).This has the additional benefit of verylow current (typically 10 uA). It also hasa disadvantage in that the slew rate isonly 0.04 V/ps, but that does not matterhere, since for all practical purposes thestage functions as a d.c. amplifier.Offset voltages are also undesirable inIC2, because they are added to those ofIC! and appear amplified at the output.Therefore, P2 has been incorporated tocompensate all offset voltages.Preferably, IC2 should also operate in
0 6
5V
RI
CI
(51A) $5-i-1 II 2
ty
MKTIC1
R2
3
C2
2
aim
the low -bias mode, but it may be foundnecessary to connect pin 8 to pin 3(medium bias) or even pin 4 (high bias)to obtain full offset compensation. Thishas to be tried out in each and every in-dividual unit. Simply adjust P2 for a dis-play reading of 000 when the unit is atrest.The terminals should be connected tothe corresponding ones in the altimeter.The switch at terminal F allows selectionbetween altimeter and variometer use.The add-on circuit may conveniently bemounted above or under the altimeter
3
470n
P1
100k
7
IC2+ 4
5
Pz
R3
C5
I100n
0(in 1o)
1C1 , IC2 = TLC271
*see text
134:144-10
PCB, and should be well screened.When the unit is used as variometer, themultiturn potentiometer (P7) in thealtimeter must:not be turned. If the unitis used as barometer, the switch shouldbe set to the altimeter position.Readers should note that the circuit hasbeen tested in laboratorium conditionsonly and NOT in practical use.
Reference: Elektor Electronics,November 1986, pp. 20-26.
BACKGROUND -NOISE SUPPRESSOR
Hiss, crackling, and other discordantsounds are disconcerting and frequentsources of annoyance to most musiclovers. Unfortunately, the sources of thisbackground noise are not easy toeliminate, but the circuit proposed herewill be of help. It should be ap-preciated, however, that the suppres-sion of noise is always a last resort: thebest way of getting rid of it at source.The circuit is based on the fact thatbackground noise is always at its mostannoying during quiet music passages.It attenuates the output signal by some45 dB when there is no or very lowmusic signal input. When the inputrises, the attenuation decreases propor-tionally, becoming 0 dB with normal to
loud passages.The input signal is taken direct to theoutput terminals via Rli and R12 respect-ively. At the same time, they aresummed via RI and R2 and applied tonon -inverting amplifier ICI via poten-tiometer Pi. The cross -over point in thegain characteristic of ICI is determinedby Rs and CI. Frequencies above thecross -over point are not amplified, andso do not contribute to the suppression.The output of ICI is rectified by D:-D2and used to switch off Ti. This enablesT2 and Ts to short-circuit the output andthus suppress the noise signal.When Ti begins to conduct, the basevoltage of both T2 and T3 decreases andthe output attenuation is reduced: noise
signals are thus suppressed to a lesserdegree.The sensitivity of the circuit may bevaried by PE the higher the sensitivity,the sooner the suppression lessens.This allows the sensitivity to be matchedto different music sources.The peak sianal level the circuit canhandle is about 210 mV. Distortion at thatlevel is not greater than 0.01%.The delay before the circuit operates isdetermined by time constant R7C4. Withvalues as shown, it is about 1 s but can,of course, be altered to individual taste.The circuit operates from a 12-30 Vsupply and draws a current of 2 to3 mA. 14
56 SUPPLEMENT
EE JULY/AUGUST 1988
L
R
R1
R2
P1
R3
IC1 = pA741C2
1M
470n
R4 5
+. 7IC1
720n
411-C&220z40V
C3 131 R7
100n
D2
2x1N4148
C4
100n
R8
BC550C
T1
C5
10p40V
100k
R12
12-30V
0 0
T2
CBC550C
BC550C
D.C. DETECTOR
The d.c. component of a signal can onlybe detected by separating it from thea.c. component. This is most con-veniently done by filtering the a.c. com-ponent. In the proposed circuit this iseffected with the aid of the common -mode rejection ratio (CMRR) of anopamp. (The CMRR is a measure of theability of the opamp to produce a zerooutput for like inputs).The complete signal is applied to the in-verting input of opamp Al, and only thea.c. component, via Ci, to the non -inverting input. The lowest frequencythat can be detected is determined bytime constant (R3+R4)Ci. With values asshown, a.c. suppression amounts toabout 50 dB at 20 Hz.The output of Al is fed to a low-passfilter to further attenuate high fre-quencies. This is necessary because theCMRR of an opamp decreases at higherfrequencies. The difference signal isthen applied to comparator Az. DiodesDi and D2 ensure that Az reacts only tovoltages greater than +300 mV.A negative direct voltage at the input ofthe circuit results in a positive potentialat the inverting input of Az, whichcauses the relay to be deactuated (it isnormally energized as long as the 12 Vsupply is on). A positive direct voltageat the input results in a negative poten-tial at the non -inverting input of Az, sothat, again, the relay is deactuated.In normal operation, the voltage at thenon -inverting input of Az is arranged bypotential divider R7 -131 -Rs -R9, so that therelay is energized. Because of Ca, therelay is energized a few seconds afterthe supply has been switched on.
Capacitors Ca and C; serve to smoothlow -frequency signals so as to preventclattering of the relay.The relay is driven by a BC547B whichcan switch currents up to 100 mA. Thesupply to the relay should be not higherthan 18 V.If the circuit is powered by a not entirelysymmetrical supply, it may happen thatthe travel of P: is insufficient: the valueof R7 should then be altered as re-quired.When the circuit is used in an active
R2 I
RI rs
10p40V
0
R3 IY
R4
AlR5
Ik
884075
loudspeaker system, each output stageshould have its own detector, consistingof A: and associated components up topoints A and B in the diagram. The out-puts of these detectors are then connec-ted in parallel to A and B.For mid- and high -frequency sections ofthe loudspeaker system the time con-stant of the input to Al may be madesmaller to obtain a faster reaction to d.c.components.Finally, the current drawn by the circuitis determined primarily by the relay.
14)
'8
C2MIMIMEM
Mtn
D2
110'
C1R
221]25V
01.-04= 1N4148Al ,A2.= IC1 = TL072
R7
P1
250(1
5
C4
2p25V
C911
722P5V
e
012V
12V
Rio 11
mi.BC5478
o ®
12V
88.1050 - 10
SUPPLEMENT 57
EE JULY/AUGUST 1988
STEPPED VOLUME CONTROL
The circuit consists of three distinct sec-tions. The first consists of a straightfor-ward amplifier, ICIa and IC1b. The sec-ond is a digital counter, IC3, which con-verts a binary code into a resistancevalue via IC2. That value is used to con-trol the degree of amplification. Finally,there is a pulse shaper, IC4, whichenables IC3 to count up or down.Amplifier ICib has a switch -controlledgain of 0 dB or 24 dB. The controlswitch, S3, is an electronic type drivenfrom output Qa of IC3.The gain of ICI. can be set between0 dB and 21 dB in steps of 3 dB. The totalgain of the two amplifiers can thus beset between 0 dB and 45 dB.The bandwidth of the amplifier extendsfrom 10 Hz to 40 kHz. The peak value ofthe amplified signal should not riseabove 8 Vpp with a supply voltage of5V.The pulse shaper, formed by bistableNI -Ma and network Cs -R:6, indicates toICs whether it should count up ordown. The RC networks suppressspurious pulses.The delay introduced by the RC net-works before N3 ensures that the clockpulse can not appear at the clock inputof IC3 before the direction of countinghas been set. The count position can,therefore, be increased or reduced byswitches Si or S2 respectively.Inputs Ck and D/U of IC3 may be usedto connect a software potentiometer: atwo -wire connection per control is suf-ficient. An 8 -bit user port can thus ac-commodate four of such digital poten-tiometers.A standard CD4051 must be used forIC2, because HC or HCT types do notallow the use of a negative supplyvoltage on pin 7. The other ICs may beHC or HCT types. If an LS type is usedfor IC3, 4k7 pull-up resistors arenecessary at the outputs of this circuit tomatch the voltage levels of the two logicfamilies.Note that C2, C6, and C7 are bipolarelectrolytic types.The total current drawn by the circuit isabout 10 mA.
0
CI .° it100n w R13
3
IC1a
R12
R11 RIO R9 R8 R7
J
0 0
0
04 2 5
0
0
0
R6 R5
0
TL082
2 15 14 113
7 6 5 4 3 2 1 0
IC24051
COM C
8 3 C610V16V
9
6
10
2
11
3
*see text
ES1
3
6
V
®5v
IC1b
11010y16V
11110016V
R14
R15
7
°c Is Oa Od
IC3 ck74HC(T)191 Du
CTEN
C710p16V
14
C2
IF10y16V
4 8 11 16
®5V
RI
ECM
F12
ES1 = 1/4105 = 4066N1...N4 = IC4 = 74HC132
® SV
R3
U
R4
C3 C4t. mlm
¶OOn TOOn
108
11
C5
100n
12
U
13
R16
884065
5V
5V
NOSTALGIC SINE WAVE GENERATOR
As far as young engineers and techni-cians are concerned, a sine wave gener-ator is something you make from anXR2206. In the pre -IC era, sine wavegenerators were designed arounddiscrete components. The generator
described here has, however, more thanjust nostalgic value: it is also educational(and perhaps suitable for writers of thehistory of electronics).The (fixed) output frequency is fairlystable at 1 kHz, and the distortion, after
proper adjustment, below 1%. The gen-erator is suitable for use as an audio testgenerator or as a morse code trainerand costs only a couple of pounds tomake.The generator is of the so-called
58 SUPPLEMENT
double -T type, which has the advantageof not needing any inductors. The oscil-lator proper, Ti, is followed by an emit-terfollower, T2, which ensures a suffi-ciently low output impedance.The frequency is set to 1 kHz by P:, andP2 minimizes the distortion of the wave-form. With P2 set for minimum resist-ance, the amplitude of the output signalwill be maximum, but the distortion willbe quite appreciable. Increasing the re-sistance will reduce the distortion, but itmay happen that when P2 is nearing itsmaximum value oscillations stop. SettingP2 is thus finding a compromise be-tween acceptable distortion and re-liable oscillations. The output level alsodepends on the setting of P2: it lies be-tween 1.5 Vpp and 3 VFF.The circuit may be powered by a 6 to12 V supply: a PP3 battery (9 V) isperfect. Power consumption is about48 mW.
0
PI
R2
R4
CI C2 C4
113n3 3n3 10n
RI100k
R3
R5
BC547C
EE JULY/AUGUST 19884...8mA
17-0CI 6...12V
16V
BC5478
C6 1kHz
101,16V
0 0
6641C4 10
I
FOUR -CHANNEL STEREO SWITCH
The circuit described here enables achoice to be made from four differentstereo channels with only one switch.Internal switching is effected by CMOSdevices to obviate crackling, bounce,and other annoyances associated withmechanical switches.The two D -type bistables in IC2 are con-nected as binary dividers by linkingtheir Q output to the D input. The Q out-put of FF: is also linked to the clock in-put of FF2, which results in a kind offour -bit counter.The push-button is connected to theclock input of FFi. The four OR gates,N: to N4, decode the output states of thebistables, so that at all times only onegate has a high output.The outputs of the gates drive theCMOS switches in IC3 and IC4. The out-puts of the four electronic switches inthese ICs are strapped together.The input of each switch incorporates apotential divider, ensuring that theswitches operate in their linear regions.This arrangement ensures minimum dis-tortion of the audio signals: the negativeparts of these signals would otherwisebe distorted, since the switches workfrom an asymmetrical supply.The circuit draws a current of onlyabout 1 mA at a supply voltage of 5 V.The supply voltage may be increased toabout 15 V.
sv
3 B 10
g-1"1-1--1
clo
41°-11
0
5v® . T T
1C3
4066
13
5
IC4
4066
12
6
3 a /0
sv
0 CL
5V
C15
917
2
12
13
FF1
D
0 CL
FF2
-6
N1. -N4 = ICt .4001FF1,FF2 = IC2 = 4013
LiL1LciLc,, CILic, .., IC2 IC3 IC4
I 11-T T -T T -T
264342
SUPPLEMENT 59
EE JULY AUGUST 1988
"It's a pretty small battery -powered PROM -programmerso what?"
Tools which are convenient get used a lot - that justifiestheir existence. There is no way we couldexplain all the usefulness of S3 here.Instead, if you're interested we'regoing to let you see it. use itand evaluate it in your ownworkshop. We went to a lotof trouble to design S3 justthe way it is - no otherPROMMER is all CMOS andall SMT. So we must be con-vinced that S3 would be a for-midable addition to yourarmoury. Now all we have to dois to convince you.
"Such a little thing can't bepowerful, like a big bench-programmer - er - can it?"Yes, it can. It is more powerful. S3 leavesother prommers streets behind. S3 hascontinuous memory, which means that youcan pick it up and carry -on where you left offlast week. S3 has a huge library EPRON1S andEEPROMS. S3 can blow a hundred or morePROMS without recharging. S3 also works re-motely, via RS232. There's a DB25 socket on theback. All commands are available from your computer(through a modem, even). Also S3 helps you developand debug microsystems by memory -emulation.
"What's this memory -emulation, then?"It's a technique for Microprocessor Prototype Develop-ment. more powerful than ROM emulation. especiallyuseful for single -chip "pig*back" micros. You plug thelead with the 24/28 pin headerin place of the ROM/RAM.You clip the Flying -Write -Lead to the microprocessorand you're in business. Thecode is entered using eitherthe keyboard or the serialinterface. Computer -assembledfiles are downloaded in standard format - ASCII, BINARY.INTELHEX, MOTOROLA. TEKHEX.Your microprocessor can WRITE to S3 as well as READ. Youcan edit your variables and stack as well as your program, ifyou keep them all in S3.S3 can look like any PROM up to 64K bytes, 25 or 27 series.Access is 100ns - that's really fast. Memory -emulation ischeap, it's universal and the prototype works like the realthing".
S3 loads its working programs out of aPROM in its socket, like a computer
loads from disk. Software expansion isunlimited. Upgrades will come in a
PROM. Programs can be exchangedbetween users. How's that for
upgradability?
"Can I change the way it works?"You surely can. We keep no secrets. System Variables can be"fiddled.- New programming algorithms can be written fromthe keyboard. Voltages are set in software by DACs. If youwant to get in deeper, a Developers' Manual is in preparationwhich will give source -code, BIOS calls, circuit -diagrams, etc.We expect a lively trade in third -party software e.g. dis-assemblers, break -point -setters and single -steppers for variousmicros. We will support a User Group.
"I'm bound to let the battery go flat."Quite so. But in practice it doesn't matter. S3 switches
to off after a half-hour of non-use anyway. or when the414- battery gets low. You don't lose your data. Then a
slow -charge overnight or boost -charge for threehours will restore rull capacity. You can keep using
it when charging. So there really is no problem.
- "I already have a programmer."Pity it doesn't have S3 features. eh? Buthere's a trick worth knowing. If you plug
S3's EMULead into the master socket of aganger then you get an S3 with gang
capacii) . Isn't production separatefrom development anyway?
"It looks nice. Will I bedisappointed?"Dataman tools are designed to
be used by Engineers. Notjust sold to Management.Have you ever been misledby some mouthwateringad for a new product.
Great artwork and ex-citing promises whichfeed your fancy? Onimpulse you buy and
when the thing arrivesyou feel let down. The pic-
ture looked better. The claimsare hardly justified; not exactly
misrepresentation, justpoor implementation.But you've bought it.And you're stuck with it.It stays in the cupboard,most of the time. So howabout this: buy S3 anduse it for up to a month.If you're not still thrilledthen you can have yourmoney back.
Soirty3 Fo:"Refund in the first month! How can you offerthat?"We trust S3 to fire your enthusiasm. We trust you not to use usas a free hire -service. We bet you won't send it back. Howwould you manage without it?
"These things cost a fortune and take months toarrive."We wouldn't get you all excited and then let you down. It Costs£495 plus VAT. That includes P & P. Charger, EMULead,Write Lead and a HELP program in ROM. S3 is in stock. Buyit today. Use it tomorrow. (That's a fair promise. But pleasereserve product by phone or telex to make it come true).
arra iamiLombard House.Cornwall Rd.DORCHESTERDorset DT1 1 RX.Phone 0305 68066 Telex 418442If you purchase while this ad is current. you have 28 days toexamine the goods and return them for refund. Carriage will becharged at cost The right to charge the cost of refurbishmentof damaged goods is reserved.
VISA
60 SUPPLEMENT Please mention ELEKTOR ELECTRONICS when contacting advertisers
