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Can you n1ake the big escape? You've been incarcerated for six months in a remote prison camp and the escape tunnel has just been completed. Try to make it through the tunnel without being caught by the guards. By DARREN YATES "It is the sworn duty of every officer to try and escape. If he cannot, it is his sworn duty to make the enemy use an inordinant number of troops to guard him." These are the words that continually flow through your mind as you stare at what was once the shower block drainage outlet. Now, it's just a big hole in the ground that you hope will take you to freedom. "The Tunnel King" sits at the other end of the tunnel, just below the surface with only the top soil above him. The fat candles that line the tunnel are blown out as he starts to gently break through the loose ground. Expecting to be on the edge of the tree line east of the prison camp, he quietly pulls himself up through the hole. Behind him, is the prison camp and more importantly, the 5-metre barbed wire fence and the guards. He turns around and sees the trees nearly 10 metres away from him! "Big X", head of the Escape Committee and still in the tunnel, tries to figure out a way around the problem. An order comes back to you through the tunnel. "Send down 20 metres of rope". You're the next to go down the tunnel mouth. You hope that some- Block diagram 2-PHASE i - - - - - - t COMPARATOR 1 - - - - - - 1 COMPARATOR OSCIL!.ATOR CHAIN c~i1~gl LEDS D3 LOW FREQUENCY OSCIL!.ATOR IC3 R 270k Fig.1: block diagram of the Big Escape. If the switch is pressed while the output of the low frequency oscillator is high, capacitor C will charge via the 270kQ resistor. The voltage on the capacitor is then fed to a chain of 10 comparators inside IC3 and this in turn drives the LEDs. The 2-phase oscillator & the comparator control logic doubles the range ofIC3, so that it can drive 19 LEDs. 38 SILICON CHIP thing hasn't gone wrong and then word comes back that the tunnel is 10 metres short! You're told that there has been a change of plans. The electric lights through the tunnel have been linked to a common switch in "Hut 5". When the Senior Officer flicks the switch, you can move through the tunnel and follow the rope out of the tunnel to the trees - but only when the light is on. If you keep moving when the light is out, you push the men further up the tunnel to be discovered by the guards patrolling the perimeter fence and the escape bid is blown. Good luck. As "Big X" said, this is a situation where you need skill and patience, and a touch of luck! To play the game, when the green GO LED is on, you press the MOVE button to make your way through the tunnel. If you hold on for too long, you blow the escape for everyone and the guards round you up at the tunnel mouth. You can also change the difficulty level to make the game as easy or as hard as you like. All the circuitry, including the LEDs, is built on a single PC board, so there's no matrix wiring to be done. All you have to do is wire in the power switch, hook up four 1.5V cells and you're away. While the idea of this circuit is not new, what is new is the way it's been designed. If you look at the block diagram in Fig.1, what we have is a lowfrequency oscillator, with a switch in series between it and a storage capacitor. This is the pushbutton switch on the lid of the zippy box. When the output of the low frequency oscillator is high and the switch is pressed, the capacitor is charged up via the 270kQ resistor. If the switch is still down when the output goes low, the capacitor dis- range; ie, from Oto 0.625V in 62.5mV steps. If we now move the 10kQ resistor from pin 6 to between pin 4 and ground and tie pin 6 to the voltage reference, the comparators now respond to the upper half of the range; ie, from 0.625V to 1.25V in 62.5mV steps. So, in total, we now get 20 steps. Display multiplexing To make this work in the circuit, PARTS LIST The Big Escape is built into a plastic zippy case. Whenever a LED flashes on, you can press the switch & move along the escape tunnel. But press the switch while the LED is out and you quickly move back to your starting point. charges much faster though the diode (D3). The capacitor is also linked to a series of 10 comparators, in IC3. As the capacitor voltage rises above the preset reference voltage for each comparator, that particular comparator's output goes low, lighting the corresponding LED. However, we have 19 LEDs in our "tunnel" and only 10 comparators! That problem is easily solved. By using some switching logic, we can make those 10 comparators do double the work and cover double the range. The LM3914 Refer now to Fig.2 which shows the internal block diagram of the LM3914 (IC3). This IC contains a string of 10 comparators which respond to a voltage on the input at pin 5. Each of the non-inverting pins is connected to a point in a lkQ resistor string, which divides the reference voltage at pin 7 into tenths. So with a 1.25V reference, the lowest comparator responds to a voltage above 125mV, the next comparator to a voltage above 250mV and so on. The ends of the resistor string are brought out to pin 6 (RHI) and pin 4 (RLO). Looking now at Fig.3 which is a simplified version of the internal diagram of Fig.2, if we put in a 10kn resistor between pin 6 and the voltage reference (VREF), and tie pin 4 to ground, the string of comparators will now respond to the lower half of the Features Of The Game * Press the Go button only when the green light is on; otherwise you will slip back and possibly be recaptured. * The variable knob sets the degree of difficulty. Set it fully anticlockwise for kiddies and Kingswood drivers; fully clockwise for BMW drivers and video games fanatics. * There are 19 LEDs denoting 19 steps to freedom; escape while you can. * If you escape, an alarm will sound, so hightail it out of there. * Turn the unit off to reset the game. After all, why should the next player have an easy run? * Battery operation, with low current drain. Use alkaline cells for long life. 1 plastic case, 158 x 95 x 50mm 1 PC board, code SC08112901, 81 x 132mm 1 front panel label, 152 x 91 mm 1 100kQ linear potentiometer 1 knob to suit 1 flat 4 x AA battery holder 3 PC pins 1 DPDT toggle switch 1 momentary pushbutton switch 1 transducer (Jaycar Cat. AB3440 or equivalent) 6 25mm x 3mm machine screws 6 3mm nuts 6 3mm washers 4 10 x 3mm tapped spacers 1 9-volt battery snap connector Semiconductors 2 4093 Schmitt NANO gates (IC1 ,IC4) 1 4066 quad CMOS analog switch (IC2) 1 LM3914 LED driver (IC3) 2 BC558 PNP transistors (01 ,2) 1 3mm green LED (LED 1) 18 3mm red LEDs (LEDs 2-19) 1 3mm yellow LED (LED 20) 4 1N914 signal diodes (D1-D4) Capacitors 1 33µF 10VW PC electrolytic 1 22µF 25VW tantalum 3 0.1 µF metallised polyester 2 .018µF metallised polyester Resistors (0.25W, 5%) 1 4.7MQ 1 100kQ 1 1.2MQ 3 10kQ 1 1MQ 1 9.1kQ 1% 1 270kQ 2 4. 7kQ 1 220kQ 2 2.2kQ 1 150kQ 1 1.8kQ 1 120kQ 1 820Q Miscellaneous Hookup wire, solder, etc DECEMBER 1990 39 VREF V EF r-- - - - - LMJsa- - - - - , I _ COMPARATOR 1 OF 10 I IC3 ;1./ 10 ;1./ lk 11 I I 10x1k I 10x1k I I I I ;1./ lk 12 lk 13 ;1./ I (a) ;1./ 1k ml OUT 14 ;1./ lk 7 + THIS LOAD DETERMINES LEO BRIGHTNESS 15 REFERENCE VOLTAGE SOURCE 1.25V lk 16 ':' REF I ADJ ;1./ I ;1./ 8 1k ;1./ 11 ;1./ lk 1k y• FROM PIN 11 MOOE SELECT AWLIFIER 9 I TYPE CONTROLS OF DISPLAY, BAR OR SINGLE I LEO I y-~ IN I I -=- 5 I L- I I _-=-_ _ - - - - - ___ ..J Fig.2: the LM3914 contains a string of 10 comparators. These compare the voltage at the pin 5 input with a voltage derived from a 1.25V reference and a string of tlcQ divider resistors. we only need to use the old "handfaster-than-eye" trick; ie, we rapidly switch the lOkO resistor between the two pins. Because our eyes cannot react to high-frequency switching, the LEDs will appear to be on at a constant brightness. What we end up with is a string of comparators that for half the time test 40 SILICON CHIP .• . (b) Fig.3: this diagram shows how the LM3914 can be made to work over two ranges. If a 10kn resistor is connected between pin 6 and VREF, the comparators will respond to the lower half of the voltage range. Similarly, if the resistor is connected between pin 4 & ground, the comparators respond to the upper half of the range. 17 lk SIG I the lower half of the voltage range, and for the other half, test the upper half of the range. If you go back to the block diagram in Fig.1, you can see we also have a 2phase clock, which produces two "out-of-phase" waveforms; ie, when one output is high, the other is low and vice versa These signals are fed into our control logic which consists of a 4066 quad analog switch and a couple of transistors. The 4066 switches the inputs to the comparators while the transistors switch two rows of LEDs to the outputs of the comparators. The idea of the control logic is to make sure the correct LEDs turn on in the right sequence. In effect, the 10 comparators are multiplexed to two sets of LEDs. The circuit Now let's take a look at the circuit diagram of Fig.4. The circuit uses two 4093 quad Schmitt trigger NAND gates (ICl and IC4), one 4066 quad analog switch (ICZ) and the LM3914 LED driver (IC3). NAND gates ICla and IClb form the 2-phase clock oscillator which has a frequency of about 90Hz. ICla is connected as a standard Schmitt RC oscillator while IClb simply inverts the Fig.4: the final circuit contains all the • elements shown in Fig.4. IC1a,1b form the 2-phase oscillator, ICtc is the low frequency oscillator, & IC2a,2b form the comparator control logic which switches IC3 between the upper & lower ranges. Also included on the circuit is a 2-tone chime circuit made up ofIC4a-d & a piezo buzzer. ~ .... 0 cc cc ..... t?J :t:I ~ to t?J (") t?J t:l I G\ 01 1N914 25VWr TANT° GREEN 2.2k K ,. "'F~r 01! 0 4.7M .,. :, IC2b 12 • 101Mr 33 82001 1 I I 'K"YI LE03 ~ I LED12~ I LED4~LED~ ,CYI LED~ISiKI L E D ~ THE BIG ESCAPE I 1 IC3 LM3914 L. I I J ~1 I 9.1 1'/o 1 4 .,. +6V 0.1+ ,. 220kS ~- .,. o.1I .l I I .... l!! .l V B 4 .018 I .011! I VIEWED FROM BELOW eOc ~ _J WINNER~ LED19 1-. YELLOW K 150k 120k 1 ...I- &V 'I T + VPIEZO BUUER S2a -~f When installing the capacitors, bend their leads so that they lie parallel to the PC board to provide sufficient clearance for the lid. The LEDs should all be installed so that there is 20mm between the board & the bottom of each LED body. Take care with component orientation. output to give the second of the 2phase signals. These two signals are fed to the control inputs of two analog switches, ICZa and ICZb, as well as to transistors Ql and QZ. •The analog switches are used to short out the lOkQ and 9. lkn resistors from pins 4 and 6 of the LM3914. For their part, transistors Ql and QZ switch the two strings of LEDs. The reason for the 9. lkQ resistor is that to make the circuit work prop- erly, we can't use comparator 10 in the usual way. This is due to the fact that when the input voltage is higher than the voltage at the non-inverting input of comparator 10, its output goes low and the LED naturally turns on. Because this is the last comparator, the LED would then remain on as the input voltage increased for the top half of the range. The 9. lkQ resistor overcomes that problem by allowing the first LED of the upper range to The potentiometer is installed with its back cover resting on the PC board & its terminals soldered to three PC stakes. Trim the pot shaft to suit the control knob before installing it on the PC board. 42 SILICON CHIP turn on just as the ninth LED of the lower range is going out. Basically, we need to allow lkQ for each comparator. Since we only need the first nine comparators in the lower range, we only need 9kQ (9. lkQ is the closest value). We can still use comparator 10 on the upper voltage range but this requires some extra circuitry, which we will come to shortly. The input voltage comes from the 33µF storage capacitor connected to pin 5 of the LM3914. This capacitor is also connected via a momentary contact pushbutton switch to an RC oscillator built around IClc. The frequency of IClc is about 1Hz. (This is the low frequency oscillator shown in Fig.1). When the output of IClc is high and the switch is depressed, the 33µF capacitor charges up via the 270kQ resistor. If the button is depressed when the output is low, the capacitor will rapidly discharge through diode D3. The green LED at the output of IClc turns on when it goes high, indicating that it is alright to move. The 4. 7MQ resistor in parallel with the 33µF capacitor slowly bleeds off the voltage. This is to stop people from sitting at one level for hours on end; the longer you wait to make your next move, the further back you slip! Each 30 seconds or so, you slip back one position. Reset to start The second pole of the on/off switch (SZb) is used to reset the game, when a player has either just won or wants to start again. Diode D3 can only allow the 33µF capacitor to discharge down to +0.6V (ie, the voltage drop of a diode), so when the power is turned off, S2b shorts out the capacitor. This way, when the game is switched back on again, the capacitor has no voltage across it and the game is ready to go. Potentiometer VRl changes the rate at which the ZZµF timing capacitor on the inputs of IClc is charged and discharged. This sets the time for which the output is high and low, and so becomes our DIFFICULTLY control. With the pot rotated fully anticlockwise, the game is set at its most difficult level. Note that this control only changes the mark/space ratio, not the frequency. To give the storage capacitor a wider Fig.5: you can install the parts on the PC board in any order although it's best to start with the wire links & PC stakes (for mounting VRl). Note particularly that the LEDs don't all face in the same direction so watch your step here. Check Fig.4 for the pinout details of the LEDs & transistors when mounting these components. voltage range to work with, we have increased the reference voltage of the LM3914 from 1.25V to 2 volts. This is done by adding the 1.8kQ and 8200 resistors to pins 7 and 8 of IC3. As mentioned earlier, the 2-phase clock also controls PNP transistors Ql and Q2. These are switched on and off at a rate of 90Hz and they give the LEDs the appearance of being on continuously. The transistors are wired so that when IC2a switches on due to a high voltage to pin 5 from ICla, transistor Q2 remains off and Ql is turned on via the out-of-phase signal coming from IClb. Thus Ql controls the lower nine LEDs and Q2 controls the upper nine, but what about the 19th LED? As we mentioned earlier, the last LED requires some extra circuitry because of the problem we face with comparator 10. Normally, the voltage at pin 10 is switching from the positive rail to ground at 90Hz. However, once the input voltage at pin 5 of IC3 rises above the threshold level of comparator 10, the output at piri 10 goes low. Double inversion Diode D4 half-wave rectifies the switching waveform and dumps the resulting charge into a 0.lµF capacitor. The voltage across the capacitor is also fed to the control input (pin 12) of IC2c, which is connected to function as an inverter. When pin 12 of IC2c is high, the analog switch turns on and pulls the output at pin 11 low. Pin 11 is connected to the input of ICld, which is also connected as an inverter to drive the 19th LED. Some of you may be wondering why bother with a double inversion and why not just wire the LED in series with IC2c? The problem here is that CMOS analog switches don't like high currents, whereas the NANO gate can easily handle the current demand of the LED. The output of IC2c drives a 2-tone alarm to indicate that an escape has been made. The alarm comprises all four gates in IC4, which is a quad 2input Schmitt trigger IC. Three of these gates are wired as oscillators while the fourth, IC4c, functions as an inverter. Sounding the alarm IC4a is· connected as an RC oscillator, operating at about 10Hz. When its pin 1 is high, it oscillates and when pin 1 is low, the output at pin 3 is kept high. Pin 3 is connected to pins 8 and 9 of IC4c which functions as an inverter to enable oscillator IC4d. IC4d therefore oscillates when IC4a's output is high, and it stops oscillating when IC4a's output is low. The third oscillator in the trio, IC4b, TABLE 1: RESISTOR COLOUR CODES 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D No Value 4-Band Code (5%) 5-Band Code (1%) 1 4.7MQ 1.2MQ 1MQ 270kQ 220kQ 150kQ 120kQ 100kQ 10kQ 9.1kQ 4.7kQ 2.2kQ 1.8kQ 820Q yellow violet green gold brown red green gold brown black green gold red violet yellow gold red red yellow gold brown green yellow gold brown red yellow gold brown black yellow gold brown black orange gold not applicable yellow violet red gold red red red gold brown grey red gold grey brown brown gold yellow violet black yellow brown brown red black yellow brown brown black black yellow brown red violet black orange brown red red black orange brown brown green black orange brown brown red black orange brown brown black black orange brown brown black black red brown white brown black brown brown yellow violet black brown brown red red black brown brown· brown grey black brown brown grey brown black black brown 1 1 3 1 2 2 DECEMBER 1990 43 ~tlt)t° + 0 0 ~~ii,, -~ ~o • 0 I ~---1-0 . . . . . ... .. . . . ..' . ...... .. .. . . .. . .. . ...... . ...' ......... .. .. .. .. ...... . . . .. :::::::::::::::::+::::::::: ........... ... . .... . .. . . . ' . ' ' .. . .' ... . . ............ ......... .. . ' . .. 0 ' ' •••I • I • o • o • ' . oscillates at roughly the same frequency as IC4d but since IC4b's pin 5 is also connected to pin 11 of IC,Zc, it oscillates whenever IC4d is muted. Just · to make it interesting, the piezo buzzer is connected between the outputs of oscillators IC4b and IC4d. That way, both oscillators contribute to give the 2-tone sound. The current drain of the circuit is about 13mA, so the four "AA" cells should last quite a long time. Construction Most of the components fit on a single PC board. This carries the code number SC08112901 and measures 81 x 132mm. Before you begin soldering in anything, check the board carefully for breaks or shorts in the tracks. These should be touched up now. 44 SILICON CHIP . . .:.·.:: . .. .. .......... . .. . -:.:..: . .- 0 ' .' 0 SC08112901 0 Fig.6: here are full size artworks for the front panel & the PC hoard. Compare your PC hoard to the artwork shown above & repair any damaged tracks before installing any of the parts. Fig.5 shows how all the parts are mounted on the board. Begin the assembly by installing three PC pins for the potentiometer, then install the wire links and resistors. The 5% resistor values should be easy to distinguish (see Table 1) but if you're not sure, use your multimeter to double check, especially the 9. lkQ 1 % resistor. Now insert the capacitors. Because there is little clearance between the zippy box lid and the PC board, you'll need to lay the capacitors over on their sides. This includes the electrolytics as well. Make sure that all polarised capacitors are correctly oriented. Once you've completed this, solder in the diodes and transistors. Again, make sure they are correctly oriented on the board. Now you're ready to solder in the 20 LEDs. When you do this , make sure that you leave a lead length of 10mm from the base of the LED to the PC board. Since they have to poke through the front panel, you need to keep them as straight as possible. Again, use the overlay diagram to make sure they are each installed correctly. Ne~t. solder in the four ICs. Again, check that they are the right way around. Finally, the pushbutton switch and the potentiometer can be soldered into place. The switch should sit flush on the board, while the tabs of the potentiometer are soldered to the three PC pins (see photo). Now for the front panel artwork. If 111• comp,,t.,- •nd .i.ctronlc ,,.,,,. joyatlclt ,. c/a119t1y dnlgMd for two handH ,,,_,.lion. Tiu not only he/,,. :o Iner.- control and accuracy but •l• o prolong. pl•ylng tlma by rwluclng hand fatl(lw th•t can be ...ocl•lad with nonnlll a/ngle hand o,,.r• IIBd unll& JSC-$ fa a/ff de•lgnad iMJ Iha hmd(lrl,- can eully be on• tabla or oth.,- /fat ~~>==;;;:-- • urf•ce for .i.b/1/zlng Iha 111lt during ,-, It la compatlb# lli#th moat computets lncludng ~.-+-~Atn.trad,Awf, Commodore n. ,..,lid •nd ~ ELECTRONICS SOUND AUSTRALIA Your P.A. Accessory Specialist STEEL SPEAKER GRILLES CHROME CATCHES 5·. $ 8.95 6"- $ 9.95 Large Lockable $9.95 8"- $11.95 10"- $15.95 Small Lockable $4.95 12"- $19.95 15"- $23.95 STEEL SPEAKER 18"- $34:95 Clamps for GRILLES Grilles Pk4- $2.95 5" $8.95 STEEL DISHES The PC board is mounted on the lid of the case on 10mm spacers & secured using 25 x 3mm machine screws & nuts. Check that the tops of the LEDs sit flush with the surface of the lid & adjust the LED lead lengths if necessary. The 4 x AAA battery holder sits in the bottom of the case, beneath the PC board, and can be either glued in place or secured using foam rubber. you are making your own Scotchcal panel, we suggest you use an aluminium-backed panel as they are much easier to work with. Once it is ready, peel off the backing and carefully place it on the zippy box lid. Remember this is sticky stuff and once it's on, it stays on, so make sure you get it right first go. Once it's on, you can drill the holes for the pot, switch, mounting screws and the 20 LEDs. The crossmarks on the front panel artwork show where the holes are to be drilled. The holes for the LEDs and the screws should be 3mm in diameter, the switch hole 7mm and the hole for the potentiometer should be 8mm in diameter. Note that the two larger holes (for the switch and pot) are best made by drilling small pilot holes and then ehlarging them with a reamer. The next step now is to wire up the 2-pole power switch, the battery and the transducer. The transducer itself is secured to the right wall of the box with two 25 x 3mm machine screws. Don't forget to drill a 7mm diameter hole to allow the sound to escape. The last step is to mount the board on the lid using four 10mm spacers and another four 25 x 3mm machine screws and nuts. To do this, first slide the lid over the potentiometer shaft and the pushbutton switch, then carefully line up the LEDs with the holes. You may need to tilt the outer LEDs towards the middle of the board to get them to fit but this should not be by very much. Once everything is lined up, you can slide the spacers into position between the board and the lid and install the mounting screws. You should end_up with the pushbutton switch sitting flush with the lid and the 20 LEDs just poking through their holes. Adjust the LEDs if necessary. Suit 1 x Male XLR + Female XLR As above also 2 x 1/4' Sockets Suit 2 x 1/4" Sockets $4 .95 $5.95 $4.95 PLASTIC DISHES Suit 2 X 1/4" Sockets $3.95 PLASTIC CORNERS Large Corner/Foot$2.95 Large Stackable$2.95 Large lnterlocking$1.95 Medium lnterlocking$2.95 Extrusion for above $5.95/M HANDLES 6' Strap $ 1.95 8' Strap 10" Strap $ 4.95 8' Nylon Briefcase Style Chest Handle Metal Recessed Spring Handle $ 2.45 $ 2.95 $ 2. 95 $ 5.95 $12.95 HEAVY DUTY CARPETED ROAD CASES 4 Unit $100.00 8 Unit $135.P0 12' Unit 6 Unit $115.00 10 Unit $155.00 $175.00 Rack Cases can be made to order in any size and any colour carpet. MICROPHONE WINDSHIELDS BLACK, YELLOW, RED, BLUE, ORANGE ALL $5.50ea RACK HANDLES, GOOSE NECKS, CABLES, CONNECTORS and lots more available Please Call tor a Catalogue SOUND AUSTRALIA 28 Walker St. Dandenong, VIC, 3175 Telephone: (03) 791 1622 Testing Before you finally secure the lid to the box, switch the circuit on and make sure that it works. If it doesn't, first check that there are no solder splashes shorting out any of the tracks on the board. If that doesn't help, check that you have the power switch correctly wired up. Lastly, check again that all components are correctly installed, particularly the LEDs, by comparing your work with the parts layout diagram. Now you're ready to see if you have the patience and skill to escape the prison camp! At Last!!! Public Address & Hi Fi Combined Now you can Mlf9 Hi R qu•lty audio anywhe,.. n. ) SP352L T .,,.• •,. haw thalr Jown on board 100 wit IIM 'x'former• to o IIWV:Offlfl lofl(I, ·crowded cab/a tuM. 111- speakers t:1tn I» connected up to •ny 100 'IIO/t line output on mo• t mono public llddrfla ampllfiflta. If true ste,.o is required they can ew,n be hooktld up to • domastic Hi R •mpllfler with II• •Id of •NY to ins,.// •tep up tr• nsfonne,.. Ideal for office •nd warehoUN aetupa or nen If you almply want HI R • udio piped through to your •wlmmlng pool •nd beckyard. The SP352L T• ar• dealgntld •round• high Impact black cabinet with .n.&\,W ,I ,,,.,.I maah grille and conu, ELECTRONICS lli#thmountingb,.ck•I& ,an T ~ ft DECEMBER1990 45