Fullscreen HTML5Med Res (??MB)HTML4

The Digital Voice Board can store four separate voice messages, each up to 30 seconds long. The message played back depends on which of four on-board comparators has been tripped. A Digital Voice Recorder Board Here is a complete digital voice recorder board. It can be connected to a computer, used in a security system, or used to monitor various functions in your car. When triggered, it can deliver up to four separate • voice messages. By JOHN CLARKE This project is not a voice synthesiser which puts out those cornysounding announcements from computers. No, this is a complete digital audio storage system based on a new chip from Texas Instruments. It can be used to record and play back any audio signal but it is mainly intended for voice messages. You can record messages using 24 SILICON CHIP your voice in exactly the same way as you would with a telephone answering machine. The resulting recording will not sound like a voice synthesiser; it will sound like you. While we have suggested that the Voice Board be used with cars, security systems or computers, we are sure that readers will use this project in a wide variety of applica- tions. For example, it could be very effective on a model railway layout whereby it could provide a variety of trackside sound effects, station voice announcements and so on. If used in a car, the Voice Board could warn about doors being ajar, high oil or water temperature and perhaps low fuel. In a security system, the Voice Board could point to sensors that have been breached, call for a periodic sensor check or ask for a response from a remote check point. The Voice Board could also be used to give specific instructions to operators of machinery in factories. You could also have a lot of fun with this device. You could connect it to the front and back doors of your home and have it announce or query visitors. Anyway, we are sure you will think up plenty of other applications. Technical features The Voice Board can record up to four messages and then play them back in response to signals from four on-board comparators. Any or all of the messages can be played back at any time, depending on the sequence of signals from the four comparators. Each voice message can be up to 30 seconds long. That's long enough for virtually any message you could want - you can almost tell your life story in 30 seconds. The key integrated circuit on the Voice Board is a new device from Texas Instruments, the TMS3477. Texas Instruments refer to it as a "single chip voice recording/ playback controller using Continuously Variable Slope Delta modulation" [CVSD). In simple terms, the TMS3477 converts an analog [audio) signal into 8-bit digital data which is stored in dynamic RAMs [random access memory). Then on command, it will convert the digital data back into audio signals for playback via an amplifier and loudspeaker. So the TMS3477 provides both analog to digital (A-to-D) conversion for the recording process and digital to analog conversion [D-to-A) for playback. Inside the TMS3477 is an oscillator to control the sampling process, the A-D and D-A converters, and a number of enabling pins to initiate the various func-tions. Like a lot of these special chips, the TMS3477 requires a few support chips to make it do its job. As well as a number of dynamic RAMs, it needs an op amp to amplify a signal from a microphone, an audio amplifier for the output signal, various comparators and gates to initiate playback, plus a number of transistors to tell the user what is happening. Sound quality vs. duration Essentially, there is a tradeoff between recording quality and recording length, just as there is in any other recording medium. If you PARTS LIST 1 PCB, code SC07111891, 220 x 138mm 1 PCB label 2 8-way PCB terminal blocks 6 PC-mounting click action switches 1 4-AA cell holder 1 battery snap to suit 1 8-way DIP switch 1 electret microphone 1 80 loudspeaker Semiconductors 1 TMS34 77NL voice recorder (IC?) 4 TMS4256-15NL 1 x 256K dynamic RAMs (IC1O-IC13) 1 LM339 quad comparator (IC1) 1 4030 quad XOR gate (IC2) 1 4011 quad NANO gate (IC3) 1 4017 decade counter (IC5) 1 40106, 7 4C14 hex Schmitt trigger (IC6) 1 7 4HC32 quad OR gate (IC4) 1 TL072 dual op amp (IC8) 1 LM386 audio amplifier (IC9) 2 7805 3-terminal 5V 1A regulators (REG1 ,2) 4 BC558 PNP transistors (Q1-Q4) 17 1N914, 1N4148 signal diodes (01-01 7) 3 1N4002 1A rectifier diodes (020,021 ,022) want long recording times, you have to sacrifice sound quality. If you want good sound quality, you get shorter recording times. In a digital recording system like the Voice Board presented here, the recording quality is set by the sampling rate. In the TMS3477, the sampling rate is set by the internal clock and by the programmable internal divider. The internal divider can be set for a nominal sampling rate [depending on the clock frequency) of 16kHz, 32kHz or 64kHz. Depending on how you select the clock frequency and the internal divider, the recording duration will be between 5 and 30 seconds. The Digital Voice Recorder Board measures 220 x 138mm and includes all the circuitry necessary to make it work apart from offboard components which are the DC power supply, an electret 2 1 6V 1W zener diodes (018,019) 5 5mm red LEDs (LED1-5) Capacitors 2 4 70µ,F 16VW PC electrolytic 2 100µ,F 16VW PC electrolytic 2 22µ,F 16VW PC electrolytic 4 1 Oµ,F 16VW PC electrolytic 3 1µF 16VW PC electrolytic 4 0.4 7 µ,F 16VW pigtail electrolytic 9 0.1 µ,F monolithic ceramic 1 .04 7 µ,F metallised polyester (greencap) 1 .004 7µF metallised polyester 1 .0022µ,F metallised polyester 1 1 OOpF ceramic 1 47pF ceramic Resistors (0.25W, 5%) 4 2 .2MO 1 39k0 1 1MO 1 27k0 1 680k0 1 22k0 1 270k0 7 1 OkO 9 220k0 5 4700 11 1 OOkO 1 1 000 2 47k0 3 100 5 200k0 miniature horizontal trimpots 2 1 OkO miniature horizontal trimpots Miscellaneous Tinned copper wire, solder, etc microphone and a small loudspeaker [OK, you can use a large loudspeaker if you like). The DC power supply can be between 9 and 12 volts and there are two separate power inputs on the board. One is for standby power to keep the recordings in memory and the second is the main input to fully power up the board. Standby current is 5mA and when fully powered up the circuit draws a minimum of 15mA and considerably more on playback and when the LEDs are lit. We have included an on-board battery for memory backup when external power is removed. Four sensor inputs There are four inputs which can be used to trigger the various voice messages. The four inputs are connected to four comparators and DECEMBER 1989 25 N -0 ::i:: - n ~ 0 n t: ~ Ol D101 ·' 1N414B S9 MEMORY CATCH ~ I +5V:.l STANDBY + .,. 22.I 220k ~ ,1 1N4148 D9 +5V_._....,___ __ POWER ~ IC6c ! TL072 I 47k 100P. 13G>o12 IC61 1M ~ -:- O.lI 141 CK 15jR . 13 J;_E IC5 4017 . 16 716 5.1 3'7 ,.z .,. J: ,RESET 012 1N4148 PLAY S12 •• .!!.!.. RECORD -i"i PAUSE S13 • STOP S14 47pFI 200k DSC IN .Ill . 14 .,. . 114 AP6 24 17 RAS AP8 26 AP7 25 AP 23 AP4 22 AP3 21 -:: T 3 .L o.1I ::;:: SPKR 1 VDD2 +5V POWER IC7 TMS3477 C/181 12 IC6d' S J!.ipa BIREC lOIPAUSE lllSTOP 6 h'P--4 rl I 5 28 VDOl ::DSCOUT lr 10k 017 1N4148 ! RESET,. SlO ICBb~I +5V POWER 680k 0.1t . - - - - - - - - - - - - - - - -STANDBY +5V I 5tSos 74C14, 40106 -:- T + +5V POWER lOOpF +5V STANDBY I .00471! 27k~ 270k .0022 +5V POWER .047:t 0.1'+ 51 AO ~ 16 IC10 4256 MEMORY 1 +5V STANDBY +5V STANDBY .,. o.1I MEMORY IC11 4256 2 MEMORY 3 IC12 4256 MEMORY 4 IC13 4256 +5V STANDBY 0.1! STANDBY -: .~)o_ .----4..______,___________________......,_+5V 0.1 I BP. ..;J ~ t:lj I ::~ I tl:l ~ t:lj (") t, t:lj t) I Wit 1 OUT I 1 OUT ~ + •t ♦• T 2.2M ? I T 100k ' T J:I 3 + 1 0 T INPUT 4 T I 100k -: 2.2M •o• T 0.47I: DB 1N4148 ':t" I (;I;) 100ki • _- 0.47I~ ~I THRESHOLD 4 VR4 200k +5V .. STANDBY INPUT + I "--.. 141 sv '♦♦• 2.ZM T 0.47I- 9 ~ 4 o 220k Wlf IN Os6. 'O➔---.---, THRESHOLD 3 VR3 200k ' i6 T 0.47 1 I r..,.----.1-I~- ' 100k -$ l 04 1N4148 ~\•No~ +5V r STANDBY T 1 INPUT 2 0 ,rn .,. t THRESHOLD 2 +5V STANDBY I ? 0-..---.....---, +.___,.__ _ _, T INPUT O OUT THRESHDI.D VR1 200k1 - - - - - - - - . . . . 1Nf1\a( 220ki 100k < T - LOW TO HHlH\ SS I a Ck '" ST~ANOBY -+sv 7 IC211 STANDBY -+sv -.. - f{AJ~BY .,. b _L 220 k HlbH IU LUW6 = lOOk T I 403 12 ~ 1 4 11 13 LOWTOHIGH~1 HHlH TO LOW 100kt sT1~~BY I I 11 ~ IN 00 OUT ~ = -:- = T D18~ 470 16V J 16VWI 1W 100 A· ~I< D13 - '"' - l 4x1N414ar r DIGITAL VOICE BOARD • _ GND1 BATTERY +12V .,. + l ZV POWER UP INPUT OR IGNITION GND1 BELOW ~- B • E 0C ~ 7 ?~ ~10 r ~ ll III~ 111 I II STANDBY +5V T 01 r·· iw• t D14 ~ D16 Rl -I. .,. ...L.. 4.5V: + -T I SEE TEXT ' ' sTAJ~ev .,. +5V STANDBY Fig.1: the circuit is based on the TMS3477 voice recorder chip from Texas Instruments. •·l~ I • 021 Pri~~R 03 4xBC558 10k Changing sense STOP PAUSE 1 3 4 PLAY RECORD i ~t. The four 256K RAMs store the digital data generated by the TMS3477 voice recorder chip during recording. If you don't need four channels, you can save money by leaving out the memory ICs for those channels you don't want. We used sockets for the memory chips but these are optional. each of these has a trimpot to set the voltage threshold at which it is triggered. There is also an 8-way DIP switch to set the polarity for the signal being sensed. This facility allows the comparator inputs to operate with signals which are either normally on or normally off or alternatively, normally high or normally low. There are six pushbutton switches on the board and these are used for control of the recording and playback functions, as follows: Reset which clears the memory of a recording, Record, Play, Pause, Stop and Memory Select. The Memory Select switch is only used when recording. It selects the memory into which each voice message is stored. Five LEDs are used to indicate the particular memory being accessed and whether record or playback is taking place. The board also includes several trimpots. These are used for adjusting the internal oscillator (to change the sampling rate), and for setting the microphone level and the playback volume. Circuit details Now let's have a look at the com28 SILICON CHIP plete circuit for the voice board (Fig.1). This may appear complicated at first but most of it is repetitive to provide for the four separate voice messages. Hence, there are four comparators, four memory select gates and four separate memories. First, let's have a look at the four sensor input stages, each of which is identical so we only have to discuss one stage. ICla is part of an LM339 quad comparator. VRl, a 200k0 trimpot, is connected to the non-inverting input of IC la to provide an adjustable threshold. A 2.2MO resistor between pins 1 and 7 provides a degree of hysteresis and the lOOkO resistor at the output (pin 1) provides an external load which is necessary since the LM339 is an "open collector" device. The sensor signal is fed to the inverting input of ICla via a voltage divider consisting of a 220k0 and a 100k0 resistor, with overload protection provided by diodes Dl and D2. The divider allows the circuit to function with logic signals of + 12V or more, even though the board logic runs from a + 5V supply. The 0.47µF capacitor removes any glitches which may be present due to switch contact bounce. Switch S1, together with exclusive OR (XOR) gate IC2d, is used to change the sense of the comparator output. For example, if S1 is open, IC2d's output will change from low to high when the sensor input to ICla goes high. If S1 is closed, IC2d's output will change from low to high when the sensor input to ICla goes low. Thus when Sl is closed, IC2d inverts the output of ICla. IC2d's output must change from low to high for the voice message to be played back. ICla and IC2d can be disabled by DIP switch S2 which simply removes the sensor input. Comparators IClb, IClc and ICld, and XOR gates IC2c, IC2a and IC2b, function in the same way as ICla and IC2d. They also have DIP switches to disable them: S4, S6 and SB. The outputs from the four XOR gates are connected to separate inputs of each of the gates in IC3, a 4011 quad 2-input NAND gate package. The second input of each NAND gate is connected to the '1 ', '3', '5' and '7' outputs ofIC5, a 4017 decade counter (pins 2, 7, 1 and 6, respectively). As IC5 counts, the four NAND gates are sequentially enabled so that they can pass signals through from the XOR gates. Only the odd outputs from IC5 are used so that there is a time gap between each of the NAND gates. As each output of IC5 goes high in sequence, the NAND gates will deliver a low output signal only if the respective XOR gate output is high. Diode OR gate The four NAND gate outputs are connected to an OR gate consisting of diodes D13 to D16, together with a 100k0 pullup resistor. If one of the NAND gate outputs goes low, the OR gate and its associated lµF capacitor delivers a momentary low signal to Schmitt inverters IC6a and IC6b which then pull pin 7 of IC7 low, via diode D12 . IC7 is the TMS3477 voice chip and when its pin 7 is pulled momentarily low, it goes into playback mode. The NAND gate outputs perform CERAMIC & POLYESTER CAPACITORS No. D 9 D 1 D 1 D 1 D 1 D 1 Value 0.1µF .047µF .0047µF .0022µF 100pF 47pF IEC 100n 47n 4n7 2n2 100p 47p EIA 104K 473K 472K 222K 10 1K 47K two other functions. Each output drives an associated transistor (Ql, Q2, Q3 or Q4) via a 10k0 resistor. These transistors drive the memory LEDs. Thus, the LEDs indicate which comparator is tripped to play its respective voice message. Finally, the NAND outputs select the requisite memory via the four OR gates of IC4, a 74HC32. The chip select output of IC7 (pin 12, CAS1) connects to one input of each of the IC4 OR gates. Each OR gate will pass this chip select signal when it is enabled via its r espective NAND gate output. Note that we have specified a high speed CMOS OR gate for IC4 because it has to pass through the fast rise times of the memory refresh signals without degradation. Memory select At this point we should explain some of the labelling on the dynamic memory chips, which otherwise will seem very obscure. The la belling on the pins is as follows: address inputs AO-A8 column address strobe CAS data in DI data out DO row address strobe RAS write enable WE You will see that there are corresponding pins on the TMS3477 chip (IC7) for the connecting lines to the memory chips. The CAS and RAS lines are used for refreshing the data in the memories but as far as we are concerned, the CAS input on each memory can be regarded as the chip select line. When IC7 is in the record or playback mode, its CAS line is ac- Fig.2: here's how to install the parts on the PCB. Be sure to install switches S11-S14 with their flat sides as shown. The DIP switch (S1-S8) is installed with the open side nearest the edge of the PCB. tive (ie, strobing at the nominal sampling rate of 32kHz or 64kHz). The CAS line from IC7 is fed via four OR gates (IC4) to the CAS inputs of the four memories. The CAS line also goes to Schmitt trigger IC6d. When the chip select output from IC7 is active, Schmitt trigger IC6d performs two functions. First, it lets us know that record or playback is in progress by lighting up LED 5. This is done by charging up the 0.1µ.F capacitor at the pin 9 input of IC6e via diode Dl 1. The resulting low output of IC6e drives LED 5. The output of IC6d also stops the clock of IC6f via diode DlO. This holds the lµF capacitor at pin 13 of IC6f high, which disables IC6f and IC5 for the duration of the record or playback period. The Memory Catch switch (S9) stops the clock in a similar manner by pulling the input (pin 13) of IC6f high. S9 is used to select the reDECEMBER 1989 29 Switches 2, 4, 6 & 8 of the DIP switch select the inputs to be used for triggering while switches 1, 3, 5 & 7 select the polarity of the input. For low to high triggering, these odd numbered switches should be off (open). For high to low triggering, the switches should be on. quired memory for recording. The final control over IC5 is the reset at pin 15. Both IC5 and IC6 run from the + 5V standby supply which is derived from either a car battery or on-board battery. When the circuit is operating only from the standby supply, diode D9 pulls the input of IC6c low. This causes IC6c's output to go high and reset IC5. The 22µF capacitor and 220k0 resistor at the input to IC6c provide a turn-on delay when the main supply is applied. Memory The memory chips from IC10 to IC13 are wired in parallel and connect to the voice annunciator chip IC7. Note that the AO-A8 address lines of IC7 do not connect to the corresponding address lines for the memory ICs. This does not matter and is done so that the printed circuit board layout is more convenient. The 10k0 resistor connected to the AP6 address line selects the 64kHz data sampling rate. If this resistor is removed, the rate drops to 32kHz, with a corresponding drop in the sound quality. The external oscillator components for IC7 are the 47pF capacitor, the 10k0 resistor and the 200k0 trimpot. These are at pins 6 and 7 of IC7. The power up reset is at pin 5 and uses a 47k0 30 SILICON CHIP resistor and lµF capacitor. Reset switch S10 provides manual resetting. The Play, Record, Pause and Stop switches connect directly to the respective inputs at pins 8 to 11. When a switch is pressed, it pulls its corresponding pin to ground via a 1000 resistor. The microphone input to IC7 (pin 2) is driven by op amp ICBb which is fed by an off-board electret microphone. The gain of IC8b is adjustable over a modest range by VR5, a 10k0 trimpot. IC8b has a high frequency cutoff of 2.6kHz due to the 100pF capacitor across the 680k0 feedback resistor. The reconstituted audio signal from IC7 (ie, playback) is fed to IC8a, a low pass filter with a high frequency rolloff above 2kHz. This attenuates any high frequency hash which is a normal byproduct of any digital to analog converter. Following IC8a, the signal is fed to volume control VR6 and then to IC9, an LM386 power amplifier. DC bias for IC8a and ICBb is derived from a voltage divider consisting of 39k0 and 47k0 resistors and an associated 10µF bypass capacitor (shown near to the electret on the circuit). Power Power for the Voice Board is provided from two separate 5V supplies. All of the RAMs and IC1, IC2, IC3, IC4, IC5 and IC6 are powered from the standby + 5V supply while the analog circuitry, IC7, IC8 and IC9 are powered from the main + 5V supply. Both supplies are based on 7805 3-terminal regulators. The main + 5V supply is the simplest. Its 7805 regulator (REG1) is fed from an external + 12V supply via a 100 resistor and protected against reverse polarity and excessive input voltages by 16V zener diode D18. A 470µF capacitor filters any hash from the input line to the 7805. The standby supply is more complicated but uses the same components for input protection and filtering. However, the standby regulator (REG2) has diode D20 in series with the GND leg to jack up the output voltage by 0.6V which is then "dropped" by diode D21. This gives an output of + 5V which is bypassed with a 100µF capacitor. Diodes D21 and D22 are included so that a 4.5V backup battery can be included. The diodes provide isolation of the normal 5V regulator output from the 4.5V battery. If the standby regulator is powered down due to disconnection of the offboard supply, the onboard battery maintains the data stored in memory. It feeds the + 5V standby rail via D22 and provides about + 3.9V which is adequate to keep the memories powered up. Construction The voice board is coded SC07111891 and measµres 220 x 138mm. While we have not done so, it could be housed in a large standard plastic instrument case, as available from Dick Smith Electronics, Jaycar and Altronics. Construction of the board is quite straightforward. First, insert all the links and resistors as shown on the overlay diagram (Fig.2). Next, the ICs can be inserted and soldered into place. Be careful with their orientation and ensure that when soldering there are no shorted pins. The next step is to solder in all the diodes. Most of the diodes are 1N914 types except those in the power supply section which are zeners and 1N4002 types. The capacitors can also be installed at this stage but take care with the ror~====---rro:~~~ir=~, -~. 00 00 "'n ~ ~ • ~ \.....l::::::=!1111!50'45; l.!jiOOC>OOOOC~i»---11 ===-.1 ea.: ~ 0 r-0 Fig.3: here is a half-size reproduction of the PCB. The full-size board measures 220 x 138mm. T'" N M ~ ~ ~ ~ ~ ::) C ::) C ::) C ::) C c. z C, z c. z c. C, z zC, z C, ~ ~ MEMORY PB/ REC 4 3 1 2 c. C, osc RESET 4 PAUSE STOP 3 C z zC, C 2 > a: ~ := v, II + CL 12V MIC SPKR CATCH RECORD PLAY 1 1 2 MEMORY 3 4 ---.----L·H _ __.___.l_H-L THRESHOLD + + + + Fig.4: use this artwork to label the various switches and controls on the PCB. The labels can be attached using double-sided tape. polarity of the electrolytics. Now install the transistors and other semiconductors, taking care to ensure that each device is correctly oriented. Finally, complete construction by soldering in the pushbutton switches, DIP switch and other hardware. The flat side of each pushbutton switch must be oriented as shown in Fig.2. Install the DIP switch so that the open side is at the edge of the PCB. Powering up To test the circuit, a 12V supply capable of providing up to 500mA is required. Connect the power supply and check that + 5V is present at pin 3 of ICl; pin 14 of IC2, IC3, IC4 and IC6; pin 16 of IC5; pin 8 of ICB, IClO, ICll, IC12 and IC13; pins 1 and 28 of IC7; and pin 6 of IC9. If all are correct, the circuit can be tested for recording. Connect up an electret microphone and loudspeaker to the terminal strip. Now close Sl, S3, S5 and S7 of the DIP switch. All four memory LEDs should now slowly flash in sequence. To record, press the Memory Catch switch to stop the LED at the required memory. For example, to record in Memory 1, press the Memory Catch button when LED 1 flashes on. Hold the Memory Catch button down and press the Record button. This starts the recording process, as indicated by the playback/record LED. The Voice Board will then continue recording until either the stop or pause switches are pressed or the memory is filled, which takes 30 seconds or so, depending on the setting of VR7. When the first recording is complete, the record/playback LED will extinguish and the next memory will be accessed. It will begin playing back what is in its memory. Since this has yet to be recorded, you will just get a loud buzz. Now press the Stop switch. The next memory will now be accessed and this will also play back noise. Each time you press Stop again, the Voice Board will move on to the next memory. When the first memory is accessed again, it will play the message just recorded. You can re-record at a faster or slower clock speed by adjusting VR7. Recording at a faster clock speed will give better sound quality but will reduce the maximum possible length of the recorded message. Normally this will not be a problem because most recordings you are likely to make will usually be much less than the nominal 30 seconds. You should also adjust microphone level control VR5 for best results. The three remaining memories can be tested by recording as before. Note that while the Stop pushbutton can be used to cut short a recording, this will mean that the recorded messages for the remaining memories will all be cut to the same length. The Pause pushbutton operates in a similar manner to a tape recorder. It halts the recording process until pressed again. The 4.5V battery pack can now be connected to test that it maintains the memory when all other continued on page 109 DECEMBER 1989 31 3½-digit capacitance meter hazard to faxes , modems and computers from the double whammy of transients on phone lines and mains wiring. The price? Just $59.95 from all Arista stockists. For further information, contact Arista Electronics Pty Ltd, PO Box 191, Lidcombe, NSW 2141. Phone (02) 648 3488. If you have trouble reading the codes on capacitors or you have caps with the labels rubbed off, it is so convenient to be able to measure them on a capacitance meter. Many digital multimeters now feature capacitance measurement but they can rarely handle the full range of values in normal use. This new capacitance meter provides nine ranges between 200pF and 20,000µF and a zero adjus t ment for the l ow capacitance ranges (ie, 200pF, 2nF and 20nF). Accuracy is ± 0.5% of reading + 1 digit for the 7 ranges from 200pF to 200µF, ± 1 % + 1 digit for the 2000µF range and ± 2% + 1 digit for the 20,000µF range. Over-range and low-battery indicators are also given on the display, which updates itself at the rate of about twice a second. The new capacitance meter is priced at $109.95 complete with instruction manual and test leads and is available from all Jaycar stores. 12V/2A power supply for CBs and car radios Ceiling loudspeaker grill looks like a downlight This hew power supply is designed for use with CB's, car radios, alarm systems and DC power tools and provides a regulated 12 volts DC at up to 2 amps output. The unit is fitted with 4mm banana socket/ terminals and is double insulated. Price is $69.95 from Altronics Distributors Pty Ltd, 174 Roe Street, Perth WA. Phone (09) 328 2199. Digital voice board ctd from page 31 This loudspeaker grill is designed to look like a downlight and could find many uses in homes and office buildings, shopping centres and restaurants, or anywhere normal speaker grilles are not wanted. They are only $3.95 each and are available in white or black. They are supplied by Altronics Distributors Pty Ltd, 174 Roe Str eet, Perth WA. Phone (09) 328 2199. power is disconnected. The battery pack can be secured using cable ties around it and through the holes on the board. You can check the operation of the comparators by turning the VR1-VR4 trimpots two thirds anticlockwise (from their maximum clockwise setting). Now switch S1, S3, S5 and S7 off and S2, S4, S6 and S8 on. Connect a jumper wire from + 5V to input 1 and check that memory LED 1 lights up after a brief pause (IC5 needs time to cycle round). Simila rly, check that memory LEDs 2, 3 and 4 also light when input 2, input 3 and input 4 are connected to + 5V. Once all functions have been tested, the Voice Board can be installed in its final location. First select the options for switches 1 to 8. Switches 2, 4, 6 and 8 select the inputs while switches 1, 3, 5 and 7 select the polarity of the input. For "low to high" signal triggerings, these odd numbered switches should be off while for "high to low" signal triggering the switches should be on. Unused inputs can be left with the switches off. ~ DECEMBER1989 109