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An alarm-triggered security c3lllera Have you been through the trauma of having your house burgled? This device will capture the thief's action on film using a low-cost motor-drive camera. By TONY NIXON There have been numerous designs for burglar alarms presented over the years but never one to record a thief in action. It's a simple security camera system that's designed to photograph a thief in action. It's similar in concept to the security cameras used in many banks and building societies, 32 SILICON CHIP except that this unit takes photographic stills. Imagine a family that has just returned home from an outing only to find that someone had robbed them of their valuables. After the initial shock they check the alarm and, yes, it had gone off only to be ignored by neigh- hours as a false alarm. Obviously, the burglar had quickly taken all he could and fled the scene with no-one the wiser. A subsequent call to the local police station reveals that they know of a burglar operating in the vicinity but they don't know who the person is. "We'll get the offender sooner or later but we don't have any clues at the moment", is the reply. So the family sits down, feeling somewhat helpless by it all. Hang on a minute - the camera! A quick scurry to its hiding place reveals that , yes, it has taken a few shots . Within a few hours, the film has been processed and there 's the ◄ Left: the author, caught in the act of "nicking" his own VCR. Provided it's properly set up, the hidden security camera should be able to provide positive identification of a thief should the need ever arise. burglar in all his glory, lifting up the video player. From that point on, it should be relatively easy for the police to identify the burglar and put an end to his activities. The point is that if it can work for the banks, it can also work at home. The project described here can accomplish this at a fraction of the cost of commercial units. It uses a passive infrared (PIR) sensor, a low-cost motor-drive camera, and a small electric motor and gearbox. It's easy to build ·using "off-the-shelf" components and the mechanical work is quite straightforward. The installation is also straightforward and the unit can be used on its own or integrated with an existing burglar alarm system. In the latter case, the unit is armed only when the main burglar alarm has been triggered and ceases to- operate when the alarm has timed out. In addition, you can either switch the unit to take a single photograph each time it senses movement or to take a complete sequence of photographs at preset intervals (AUTO mode). How it works The circuit may appear complicated at first glance but can be broken down into .sections. Fig.1 shows the circuit details. When power is first applied to the circuit, presettable up/down counter ICl (4029) is reset by a high pulse from Cl. This high is inverted by IC3f, the output of which then resets the latch formed by IC2a & IC2b. It also resets 556 timer circuits IC4a & IC4b. At the same time, pin 13 of IC2d is pulled low via D11, which means that pin 11 of IC2d is high. When ICl resets, its internal counter is preloaded with a value that corresponds to the logic states on its J1-J4 JAM inputs, as set by switches SW1-SW4. This sets the number of "shots" that can be taken by the cir- The Alarm Security Camera is connected to the main alarm system & is armed only when the alarm is triggered. The camera is then activated when a passive infrared sensor detects movement. Alternatively, the unit can be used by itself & armed using a hidden switch near the front door. cuit. Since the maximum possible · count is 15, a 12-shot film should be used and the film counter set to 12. This film count can be changed at any time by altering the switches and then momentarily operating reset switch SW5. If switches SW1-SW4 are all left open, then the maximum film count will be set. SWl sets the most significant bit (MSB). As long as this count is not zero, the circuit is enabled. Arming options The circuit is armed when pin 9 of IC3d is pulled low via optocoupler IC5. This optocoupler is in turn controlled by a relay in the central alarm system. Normally, the "Y" terminal is connected to ground in the central alarm system and the "X" terminal switched to +12V by the external relay when the alarm triggers. This then turns on the transistor inside the optocoupler to arm the camera circuit. In this way, no photos can be taken during exit and or entry periods, or if the alarm times out. Alternatively, if the alarm relay switches to ground, the "X" terminal should be connected to the +12V supply rail in the alarm and the "Y" terminal connected to the relay contacts. When movement is detected, the PIR sensor's normally open (SNO) contacts close and IC3e's pin 10 output switches high. R14 and C4 prevent any glitches from false triggering the circuit. The resulting low from IC3a is then inverted by IC3b and turns on Ql and relay RL1 for the same duration as the relay in the PIR sensor. RLl thus operates as a slave relay for the sensor and its contacts can be used to trigger the main alarm panel. This means that the P IR sensor can function as an alarm sensor in addition to its role as a trigger for the security camera. When the alarm triggers, pin 9 of IC3d is pulled low and R7 pulls pin 13 of IC2d high. If SW7 is open, no further action takes place. If, on the other hand, SW7 (ACTIVATE) is closed, the high from IC3b pulls pin 12 of IC2d high via D3. IC2d's output thus switches low and the resulting MARCH 1993 33 ;:; ; ~ + ;; r ~.. "' I• ,. > !; ; . 1;-1•· + ~ . .,- <0- c~ c( a: w c~ ~; 0~ ... m a~~ ~g ~., WW ; w !!! > :E < (.) >r- cc ~ :::> (.) w w en < .... ==~ :E ... ,-.u, a: 0 < c( ...J c( I• I• ~ g;g a.; + I• :I 0 0 <O~ -o a::;! ... <O ~~ _o a::,! ... 0---,•· ::, 0 "'~ ~"' I· + ~ tjt,-1•· .,->., 0~ "'., a:..; I• >< ► ~ ~ ., !a? I• -"' o .,; <O~ cc:;! ...w"' "' "'~ a: Wu, ~ I&~ !! ., ., "' o"! ...... 0 ~ -·. t ~ ~-H•· I• .... !a? C .;i --~ I· ... ~ ~ :; + "'~ >:;! ...._o ~ ~ •- I-;--!•· I """ 0"' a:O \!! I-;--!•· I ::;- + a::;! ~ "' ~ •· ; ~ "' ~ "'o ~•- "':;! - o ~ "' ~•· "':;! ~ "' 34 SILICON CHIP ;!: H •· oo ......., I· !,?V> <O o- ii:,. >- I-;--!•· +..,,._ I 0 .. Fig.1 (left): the circuit is armed when pin 9 of IC3d is pulled low via optocoupler IC5. When the IR sensor detects movement, pin 11 of IC2d switches low & resets monostables IC4a & IC4b via C2 & D2. IC4a sets the delay between consecutive photos, while IC4b generates the starting pulse for the motor. negative-going pulse from C2 sets the latch formed by ICZa & ICZb. This switches pin 3 of IC2a high and lights LED 2 to indicate that the unit has triggered. In addition, the negative-going pulse from CZ triggers monostables IC4a & IC4b. These two monostables are part of a 556 dual timer IC and work in the same way as the morefamiliar 555 timer IC. When triggered, their outputs at pins 5 and 9 switch high. IC4a sets the delay between con secutive photographs. When its output switches high, C7 charges via Rl 7 and, after a short delay, pulls IC3c's input (pin 5) high also. The resulting low output from IC3c then pulls pin 13 ofIC2d low, thus forcing its output high for the duration of IC4a's delay. Any further sensor pulses are now ignored until this delay is over. The high from IC4a also clocks !Cl to reduce the film count by one. When this count reaches zero, pin 7 (carry out) of !Cl goes low and pulls pin 13 of IC2d low via Dl to disable the circuit. This also extinguishes LED 1 to indicate that the film has run out and to indicate that no further photos can be taken until the circuit is reset. IC4b is also wired as a monostable but has a much shorter delay than IC4a. Its function is to start the motor via D9, R18 and Q2 . Once the motor is running, it closes microswitch S9 via a motor-driven cam. This ensures that the motor completes one full revolution only, so that only one photograph is take!]. each time the system is triggered. When the motor has completed one revelution, the microswitch opens again and the motor stops. IC4a now times out and its output at pin 5 switches low again and reenables IC2d via IC3c and D7. Any further input pulses from the sensor will now retrigger the circuit, provided ICl 's counter is not at zero. Thus, each time the IR sensor detects +12V 0 - - - 1 - - . . - - - 1 + 01 ov~ · 100 + 25VW+ GND t------•8V 10 + .,. 16VW+ Fig.2(a}: this circuit can be used to generate an +8V supply rail for the camera circuit if this rail is not already present in your central alarm system. r----------------•12V t12V FROM PLUG-PACK ~ + BATTERY T BACK-UP I 12V 1.2AH .l_ l IGO Fig.2(b): use this circuit to generate the required +12V & +8V supply rails if the security camera is to be used independently of an alarm system. movement, the camera takes another photo. VRl sets the delay for IC4a and thus sets the delay between photographs. The maxi_m um setting is about 60 seconds. VRZ controls the length of the motor start pulse from IC4b. Auto function Switch SW8 controls the AUTO function. If SW8 is closed, a high logic level will remain on pin 12 of IC2d after the first photograph has been taken. Thus, as soon as IC4a times out, pin 13 of ICZd will go high again and retrigger IC4a & IC4b to take a second photograph. This sequence will continue until the counter reaches zero. As a result, the camera will take a complete sequence of photos, the interval between each photo depending on the setting of VRl. Cut wire sensor Pin 9 of IC2c is normally held low by a link which connects the CUT terminal to ground at the sensor. If the sensor wires are cut to try to defeat the system, pin 9 of IC2c is pulled high by R16 and its pin 10 output switches low. This in turn pulls pin 11 ofIC3e low via DlO and thus turns Ql on to trigger the alarm. The camera circuit now goes into AUTO mode and takes a sequence of photos until the film counter (ICl) reaches zero. SW6 functions as the TEST switch. When this switch is closed, it pulls pin 9 of IC3d low and this enables the camera circuit so that its various functions can be tested independently of the central alarm system. If, at any time, the photographic option is not required, it can be disabled by opening SW7. The alarm system will still trigger via the slave relay (RL1) however, either due to the sensor detecting movement or the wires being cut. Note that if the alarm times out, then the camera circuit will be disabled even if there is still film available. Power supply Power for the circuit is derived from +12V and +8V rails in the main alarm system. Fig.Z(a) shows how a suit.able +8V rail may be derived using a 3terminal regulator if this rail is not already present. Fig.Z(b) shows a suitable power supply for the circuit if it is to be used without an alarm system. The motor is operated by a separate 3V battery which connects via switching transistor QZ. This method was used because the start-up current of the motor is quite high and this may cause difficulties with some alarm PARTS LIST 1 PC board, code 03103931, 140 X 85 1 PC board, code 03103932, 105 X 57 1 motor drive camera (eg, Hanimex 35HL) 1 plastic jiffy box, 196 x 113 x 60mm 1 self-adhesive front-panel label, 186 X 100 1 motor-gearbox kit (Jaycar· Cat. YG-2712) 1 8-way SPST OIL switch (SW1SW8) 1 microswitch (S9) · 1 12V SPOT relay 8 2-way PC-mount screw terminal blocks 1 2 x AA square battery holder 1 1MQ trimpot (VR1) 1 100kQ trim pot (VR2) 1 75mm length of aluminium angle (25 x 25 x 3mm) 1 piece of aluminium sheet, 30 x 87 x 1mm 6 plastic cable ties 1 passive infrared sensor Semiconductors 1 4029 presettable up/down counter (IC1) 1 4011 quad NANO gate (IC2) 1 74C14 hex Schmitt trigger (IC3) 1 556 dual timer (IC4) 1 4N25 optocoupler (IC5) 1 BC548 NPN transistor (01) 1 BO649 Darlington transistor (02) 10 1N914 silicon diodes (01-03, 05-011) 1 1N4002 silicon diode (04) 2 5mm green LEDs (LED1, LED3) 1 5mm red LED (LED2) Capacitors 1 100µF 25VW PC electrolytic 1 47µF 25V PC electrolytic 1 22µF 25V PC electrolytic 2 2.2µF 16VW PC electrolytic 1 1µF 16V PC electrolytic 3 0. fµF metallised polyester 2 .01µF metallised polyester Resistors (0.25W, 5%) 14100kn· 210kQ 1 3.3kQ 31.5kQ MARCH 1993 35 Fig.3: here are the wiring details for the two PC boards & the passive infrared sensor (PIR). Take care with the orientation of the ICs when installing them on the main board & note that Q2 is installed with its metal face towards the relay (RL1). SWl-8 is the DIL switch & its settings are shown in the table below. PASSIVE INFRARED SENSOR - +12V NC COM NO 1 n1=1 GND +12V CUT SNO TO MAIN PCB DIL SWITCH SETTINGS Switch Function systems, particularly those with "power fail" detection. These batteries should last a couple of years and can also be used to power the camera. Finally, the circuit should not affect the operation of the back-up battery in the main alarm system since its standby current is only about 25mA. This rises to about 80mA when the relay and LEDs are on. Assembly Most of the parts are mounted on a main PC board coded 03103931. A second PC board (coded 03103932) provides interfacing for the motor and microswitch (S9). Fig.3 shows the wiring details. Comments SWl Film Set Open for logic 1 (MSB) SW2 Film Set Open for logic 1 SW3 Film Set Open for logic 1 SW4 Film set SW5 Reset Normally open. Resets film counter. SW6 Test Normally open. Close for testing. SW7 Activate Norma lly closed. Open to disable circuit. swa Auto Close for full sequence of shots at first triggering . Begin construction of the main board by installing the wire links, then install the resistors diodes, transistors, capacitors and ICs. IC sockets were used on the prototype but these can be considered optional. Be sure to install Q2 as shown, with its metal tab towards the centre of the board. Once these parts are in, the larger components can be installed on the board. These include the relay, the miniature DIL switch (SW1-SW8) and the two PC-mounting insulated screw terminal blocks. Fig.4 shows the dimensions of the mechanical parts. After the parts have been made, remove any burrs on them and make sure that the plunger fits Open for logic 1 (LSB) easily into its support bracket. The mechanism is designed around a motor-gearbox kit from Jaycar Electronics and a Hanimex 35HL motordrive camera. The motor sells for around $20.00 and the camera for about $50.00. All of the parts, apart from the main PC board, fit into a large plastic case as shown in the photos. The three aluminium brackets and the gearbox mounting holes can be used as templates for drilling mounting holes. You will also have to drill a large hole in the case directly in front of the camera lens. .The 0. lµF capacitor can now be soldered directly to the motor terminals, along with two flying leads which can later be connected to the interface board. This done, the brackets and motor-gearbox assembly can RESISTOR COLOUR CODES D D D D D 36 Value 4-Band Code (1%) 5-Band Code (1%) 2 100kQ 10kQ 1 3 3.3k0 1.5k0 brown black yellow brown brown black orange brown orange orange red brown brown green red brown brown black black orange brown brown black black red brown orange orange black brown brown brown green black brown brown No . 14 SILICON CHIP 14 I 12.5 ... "' ~ ~r'I. FRONT FRONT "' N '-IJ' -- I A PLAN PLAN A 15 PLUNGER MATERIAL: 25 x 25 x 3 ANGLE ALUMINIUM 25 PLUNGER SUPPORT BRACKET MATERIAL: 25 x 25 x 3 ANGLE ALUMINIUM SHAFT SUPPORT BRACKET MATERIAL: 25 x 25 x 3 ANGLE ALUMINIUM I I I I I I~ 10 zl ~I o, C> N HOLES: A • 3mm DIA B • 3mm DIA, CSK ... C> 1::: I I I I ~ z ffi• ml 20 - ~"' 50 I I I ~ I 20 f.-JL.-~ I 90 CAMERA HOLDING BRACKET MATERIAL: 1.6 ALUMINIUM ti: .. J-:=::::::::-:::::---i-•1--~ 1. . . . 1• • •1 .. 1. .. :I DIMENSIONS IN MILLIMETRES DRIVE SHAFT Fig.4: this diagram shows the dimensions of the three metal brackets, the plunger & the motor drive shaft. These parts may have to be varied to suit different cameras. be secured inside the case using machine screws and nuts. Note that the two mounting screws for the plunger bracket will have to be countersunk to clear the plunger. The dimensions shown for the motor drive shaft are for the Hanimex 35HL camera. If a different camera is used, then this distance may need to be altered. The microswitch is attached to the motor board using two screws and its normally closed contacts (ie, the two outer contacts) wired to the terminal block. If necessary, the microswitch can be adjusted by filing a slot in the PC board at the top mounting position. The motor board can now be slid partly into the case using the second set of guides and the leads from the motor connected. This done, the board can be pushed right down into the case so that the microswitch arm sits between the switch body and the motor shaft (see photo) . Don't install the wiring between the motor board and the main board at this stage - that step comes later. Testing To test the motor and plunger assembly, go to the interface board and MARCH 1993 37 The PC board was mounted on the back of the case but there's no reason why it cannot be housed in the case used for the alarm system if there's sufficient room. The IR sensor can also be mounted separately from the camera. temporarily connect the "+8V" terminal to the "M" terminal and connect the "H" terminal to the "GND" terminal. This done, connect the batteries. If the microswitch contacts are closed when the battery is connected, the motor will operate until the contacts open again (ie, when the motor shaft presses the actuating arm down). When the motor stops, momentarily short the "GND" terminal to the "M" terminal and check that the motor starts again and completes one revolution. If the motor continues to operate, adjust the position of the microswitch so that the motor stops when the actuating arm is pushed down by the motor shaft. At this point, the shutter plunger should be in its normally up position. When everything is working OK, remove the batteries °from their holder. The motor board can now be connected to the main board so that the entire assembly can be tested (do not connect the infrared sensor or install the camera at this stage). VR1 and VRZ should initially' be set to mid- The large cutout in the motor interface board is used to provide clearance for the motor. Don't forget to solder a 0.1µF capacitor directly across the motor terminals. 38 SILICON CHIP position and a jumper wire temporarily connected between the CUT terminal (middle of the board) and the GND terminal (top of the board). The "X" and "Y" terminals should be left disconnected and all of the switches should be left open except for SW6 (TEST) which should be closed. When the switches have been correctly set, reconnect the batteries and apply power to the main board. LED 1 and LED 2 should immediately light to indicate that the power is on and that film is available. Check that the slave relay operates if the SNO terminal is momentarily shorted to ground. The main board can now be tested for correct operation by closing SW7 (ACTIVATE) and momentarily shorting SNO to ground again. If all is correct, the slave relay will operate as before, LED 2 will light to indicate that the circuit has triggered, and the motor will start and complete one revolution. If the motor now keeps going or if it just starts and then quickly stops , adjust VRZ until it operates correctly. When the adjustments are correct and the motor stops turning, no further action should take place until IC4a times out, even if SNO is shorted to ground again. After IC4a times out, the sequence can be repeated. Now check that LED 2 goes out if the RESET switch (SW5) is closed. If it does, open SW5 again, close the AUTO switch (SW8) and momentarily short SNO to ground again. The motor should now start and stop as before and LED 2 should come on again. As soon as IC4a's delay ex- This close-up view of the motor-gearbox assembly shows how the motor shaft normally holds the microswitch arm depressed to keep its normally closed (NC) contacts open. OFFER- CRAZY BATTERY The first generation (XX 1080) passive IA night viewer lube features excellent gain. and when used with a ve ry low light objective lens, it can · produce useful images under almost as little as submoonlight illumination. Cal also be IR assisted. 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MOTORS · We have good stocks of 5 different high quality JAPAN ESE DC Motors. These should suit many industrial, hobby, robotics and other applications . Check out the SPECIAL prlces, and com pa re! M1 • 24V, I No load = 50mA · 22 ,000 RP M at 24V, main body 28mm Diam - 40mm long ... $5.50 M4 • 3-15V, I No load, 20 mA at 12V, main body 3 1mm Diam · 22mm long ... $ 3 M5-3-15V, I No load • 60mA · 5700 RPM at 12V, main body 28mm Diam • 40mm long ... $2.50 M9-12V, I No load= 0.52A · 15,800 RPM at 12V, ma in body 36mm Diam • 67mm long ... $8.50 M 14 • Made for slot cars. 48V, I No load = 0.84A at 6V, at max efficiency 1,,. 5.7A. 7500 RPM, main body 30mm Diam - 57mm long ... $9.50 Further to the above special prices, during Feb.-March we are offering an introductory package w hich includes O NE O F EACH O F TH E ABOV E MOTORS, and one of the STEPPER MOTORS advertised elsewhere in this ad . (Item No. 0 140) . PROJECTION LENS .a See S.C. May 88 for this high quality crystal locked ultraso nic design. Ca n be used as a detector or a self standing alarm , has provision for bonnet/boot protection and flashing light and back up battery . Easily combined with ou r U.H. F. Remote Control. CL EARANC E PRICED AT ONLY: $29.90 (Cat. No. GK125) For the P.C. B. and all parts, except the screw term in als. A pair of ultrasonic transducers is included!! DON'T MISS OUTI ELECTRONIC KEY KIT =·- ~ Main body has a diameter of 117mm and is 107mm long. The whole assembly can be easily unscrewed to obta in three very large lenses : two plastic and one glass. The basis of the cheapest large magnifier or projection sy$1em? Experimenters delight at ON LY$28 - "~'~.,.~.~~ strikers for entering buildings, car alarms , central locking , the most secure key ever (See E.A. July 92): ON $49.90 SPECIAL<at> For two keys, and one decoder kit. Cat. No. GK138 . !afl~f~!~!s~~~•cs I/ f:-Telephone : (02) 579 4985 Fax : (02) 570 791 0 1..i • MELBOURNE AGENT TRUSCOTT S (03 ) 723 3860 ..... MAJOR CARDS ACC EPT ED WITH PHONE ,. . FAX ORDERS . P+P . ~:~.''!'· . . • i,,.,,£,Q.R MOST MI XED ORDERS : AU STRALIA : $6. N .Z . !Air Mail) : $ 10 :-c. • ,-.·~ Each time the motor starts, the motor drive shaft operates the plunger, the camera shutter trips & the camera automatically "winds on" to the .next frame. The motor drive shaft also releases the microswitch arm to ensure that_the motor completes one full revolution. pires, this cycle should repeat automatically and continue to do so until the film counter reaches zero. At this point, LED 1 (FILM) should extinguish and the motor should stop permanently. If all is well so far, reset the system again (by closing and opening SW5), open SW8, and remove the link fitted between the CUT terminal and GND (this simulates the sensor wire being cut). The slave relay should now come on and stay on, while the motor should operate repeatedly until the film counter reaches zero. Finally, the camera can be installed in the case and tested for correct operation. There should be a small clearance between the bottom of the plunger and the camera button, otherwise the button may not fully release. If this happens, the film will not automatically wind on. Note that the base of the camera may need a bit of packing under it to wedge it into the correct position. 40 SILICON CHIP Don't forget to open SW6 (TEST) when the above test procedure has been completed. . ALARM REL~Y CONTACTS +t2V 1 IC5 4N25 ALARM SYSTEM Installation On the prototype, the main board was mounted on standoffs on the outside of the lid and secured using screws and nuts. Alterna-· tively, it could be mounted in a separate case or, if there is sufficient room, inside the case used for the central alarm system. Obviously, the camera must be installed in a location so that it doesn't stand out. Some houses are fitted with removable vents in the walls near the roof. This makes an ideal spot in which to hide the camera, although you will need to cut a neat hole in the vent X .....,_-------0-----, y DV R20 3.3k (a) X +t2V IC5 t 4N25 ALARM SYSTEM Y R20 3.3k ALARM RELAY CONTACTS DV (b) Fig.5: the alarm s_e curity camera is armed using a relay in the main alarm system. Connect the X & Y inputs as shown in (a) if this relay switches to +12V & connect them as shown in (b) ifit switches to OV. so that the camera lens can "see" the room. Another approach would be to fit the unit into a strong steel box and use "Bandit" glass over the lens opening. This could then be mounted up high in a garage or workshop. When the camera unit is in position, the various connections can be run to the central alarm system. These include the power supply connections, the "X" and "Y" terminal connections, and the (optional) slave relay contact connections. Fig.5(a) shows how to wire the "X" and "Y" terminals if the external alarm relay switches to +12V, while Fig.5(b) shows how to wire the terminals if the external relay switches to ground (GND). The infrared sensor can either be mounted on the camera box or installed separately. It should be wired to the main board as shown in Fig.3. Satellite siren Because the camera generates some noise while it is operating, a small piezo siren should be mounted inside the room. This siren should be wired to sound at the same time as the main alarm siren and will mask any sounds from the camera. As a bonus, it will also annoy the intruder with its piercing sound and hopefully encourage him to leave quickly. · The flash on the camera should be turned off to ensure good battery life. This means that the system as described will only work satisfactorily during daylight hours or if the lights are on. It cannot produce useful results if the room is in darkness. Note that, for normal operation, switch SW7 (ACTIVATE) -is closed while switch SW6 (TEST) is left open. SW8 should be closed for AUTO operation, while switches SW1-SW4 should initially be set to suit the number of shots on the film. For 12 shots, leave SW1 and SW2 open and close SW3 and SW4 (leave all switches open for a maximum count of 15). Switch SW5 (RESET) is normally left open. It should be closed and then opened again when· the camera is set up to reset the film counter. After that, it is only used to reset the film counter if it counts down to zero. If the unit is to be used on its own, . connect it to the power supply shown in Fig.Z(b). The unit can then be armed or disarmed by connecting the Y terminal to GND and using a hidden SC03103932 Fig.6: here are the full-size etching patterns for the two PC boards. switch to connect the X terminal to the +12V rail. This switch will have to be located somewhere near the front door, so that you don't trigger the unit while you are leaving the house. One last point: it's worth keeping any security system like this a secret. Word does get around. SC MARCH 1993 41