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An easy-to-build car burglar alarm Don’t fork out big dollars for a car burglar alarm. This unit can be built for far less than the cost of a commercial alarm & can be mated to an optional remote control unit. Design by BERNIE GILCHRIST Most car alarms are complicated to build or only offer a limited range of features but not this unit. It’s based on the Philips OM1681C car alarm IC and has a range of features that rival many commercial units. Those features are all listed in the accompanying panel and include presettable entry and exit delay periods, delayed and immediate trigger inputs, voltage drop sensing, a flashing status LED, automatic resetting after 60 seconds, battery backup and the ability to 32  Silicon Chip automatically operate a central door locking system. The alarm itself consists of two main parts: (1) a control unit that mounts somewhere out of sight (normally under the dashboard); and (2) a horn siren module with internal (nicad) battery backup that mounts under the bonnet. These two items are connected together via a 3-pin plug and socket, while the control unit is connected to the battery, the various sensors, the status LED and to other items (eg, the central locking circuitry) via an additional 12-pin plug and socket assembly. In operation, the alarm can be armed/disarmed either manu­ally via a hidden toggle switch and/or via an optional UHF remote control unit (to be described in a forthcoming issue). If the remote control unit is used, then the toggle switch can be delet­ed and the exit and entry delay periods set to zero. Alternatively, you can retain the toggle switch as a backup to disarm the unit if the remote control fails. Note, however, that this toggle switch will normally need to be kept in the ARM position. The UHF remote control will be unable to arm the alarm if the toggle switch is in the DISARM position. The alarm is armed by either setting the toggle switch to ARM or by pressing the button on the optional remote control transmitter until a “chirp” is heard from the horn siren. When this occurs, the status LED lights and remains on continuously for the period of the exit delay, after which it flashes on and off once every second to indicate that the alarm is armed. During the exit delay period (ie, while the LED is continu­ously lit), the alarm cannot be triggered. This gives you time to manually arm the system and leave the car without setting off the alarm. Alternatively, if the exit delay set to zero (ie, the optional UHF remote control is being used), then the status LED will begin flashing immediately. The unit is disabled by either setting the toggle switch to DISARM or by pressing the button on the UHF remote control trans­mitter until the status LED switches off. Note that the siren does not “chirp” when the alarm is disarmed, the status LED being the only indicator in this case. Once it has been disarmed, the alarm sounds only if the battery leads are cut or the leads to the siren module are cut (provided the backup battery is switched on). Triggering After it has been armed, the alarm can be triggered in three different ways: • First, it can be triggered if the battery voltage drops suddenly; eg, if the brake lights are activated or a dome light comes on (when a door is opened). When this happens, the status LED switches off for a period equal to the entry delay and then the alarm sounds. The purpose of the entry delay is to allow you time to gain access to the hidden toggle switch to disable the alarm before the siren goes off. Of course, if the UHF remote control is used instead, the entry delay can be set to zero. If the siren does go off, the alarm will automatically reset after 60 seconds, after which it is ready to be triggered again. The status LED will now flash at a rate of four flashes per second to indicate that an alarm has occurred; • Secondly, the alarm will trigger if a sensor connected to the immediate (or instant) sense input causes that input to change state (ie, switch from high to low or low to high). For example, if a • • • • • • • • • • • • Main Features Uses Philips new OM1681C car alarm processor IC Supplied with pre-built horn siren containing backup battery Flashing deterrent LED which indicates armed, disarmed and memory states Compatible with an optional UHF dual channel remote control kit (DSE Cat. K-3260) Siren is triggered if car battery or horn siren wires are cut Alarm automatically resets to armed state after 60 seconds Output available to operate central door locks or to flash the hazard lights to indicate arming & disarming (for use with UHF remote control option only) Adjustable entry and exit delays Reverse polarity protection Immediate and delayed sensor inputs (one each) for use with external switches (eg, door switches & auxiliary pin switches) Voltage drop sensing to detect unwanted operation of lights, etc. Relay output to beep horn or flash hazard lamps when alarm triggers (optional) sensor switch is open when the alarm is armed and then subsequently closes, the alarm will trigger. Conversely, the alarm will also trigger if the switch is closed when the alarm is armed and subsequently opens. The sensors connected to the immediate input can be either normally open (NO) or normally closed (NC) but they must all be of the one type. You cannot have a mixture of both. These sensors would normally be spring-loaded (pin) switches that are used to protect the bonnet and boot. Note that the entry and exit delays do not apply to any sensors connected to the immediate input. Instead, the siren sounds immediately when the alarm is triggered. As before, the alarm automatically resets after 60 seconds and the status LED flashes at four times per second to indicate that the alarm has been triggered; • Finally, the alarm will trigger if one of the sensors connected to the delayed sense input closes and pulls that input low. These sensors must all be normally open and must pull the input low to trigger it. Typically, the door switches would be used here, provided that they are in the earth circuit of the vehicle. The normal entry and exit delays apply to this input and again the circuit automatically resets after 60 seconds with the LED flashing at four times per second to indicate that the unit has triggered. Backup battery The horn siren module contains a rechargeable 7.2V nicad backup battery which ensures that the siren continues to sound even if the main battery leads or the leads to the siren are cut. In this situation, the siren will continue to sound until the backup battery goes flat, since it can no longer be reset by the control unit. Because power is applied to the siren circuit at all times, the backup battery is normally kept fully recharged via an inter­nal regulator circuit. It should provide about two hours of useful output if either the siren leads or the main battery leads are cut. The backup battery can be switched on or off during in­stallation by means of the keyswitch at the rear of the siren module. If the backup battery is switched off, the siren will still function normally if the alarm is triggered, provided that the car’s battery is not disconnected or the leads to the siren are not cut. Flashing lights/beeping horns By installing a single link on the PC board, the alarm can also be made to flash to the car’s headlights or beep the car’s horn when triggered – this in December 1994  33 34  Silicon Chip C10 0.1 D6 1N4148 R22 4.7M R21 1.5M R20 10k 100k C4 10 R5 33k C2 1 R9 R8 100k C1 1 C3 0.1 VR1 2k R4 33k D1 1N4148 R2 470k R3 1M IC1c +12V R24 4.7M R23 1M D7 1N4148 C11 0.47 2 1 R27 2.2k R26 680  ENTRY DELAY VR2 50k D8 1N4004 R10 10k R18 10k MIC IN 3 C6 0.1 1 2 E RL2 C Q4 BC328 E B D9 1N4148 C12 0.1 7 6 R31 D10 1M 1N4148 CAR BURGLAR ALARM R29 1.5M R28 4.7M R30 4.7M R32 100k D12 1N4004 1 B R15 2.2k R33 680  R34 2.2k E R14 10k C13 10 RL3 Q5 BC328 C E D11 RL1 R17 15  C7 10 1N4004 RL1 D5 1N4004 Q3 BC549 C B 12 C14 0.47 IC3b D2 1N4004 Q1 BC557 R16 470  C E Q2 BC549 C B  3 4 D3 1N4148 STEADY 18 GND R13 16 270k FLASH 1 IC2 OM1681C HAZARD LIGHTS ARE REQUIRED WHEN ALARM TRIGGERS C8 0.1 R19 10k EXIT 5 IMMED 6 DELAY 15 14 ENTRY R11 10k B 330  R12 ONLY INSERT LINK 3-4 IF A BEEPING CAR HORN OR FLASHING C9 0.1 EXIT DELAY VR3 50k 13 DISARM STATUS 17 9 ARM 7 DOOR LOCK/INTERFACE CIRCUIT R25 100k 14 12 IC1b ZD1 6.8V 1N4736 3 3 IC1a LM339 14 4 5 6 7 IC3a 9 LM339 8 VOLTAGE DROP SENSOR 8 9 R1 10k R7 1M R6 1M C5 10 +7.3V +12V RL3 RL2 1N4004 D4 0V RESET +12V 3 11 7 8 12 4 9 1 2 6 10 E C E C B A C B A B VIEWED FROM BELOW B DOORS UNLOCK DOORS COMM DOORS LOCK 0V IMMEDIATE DELAYED ARM/DISARM LED RELAY NC RELAY COMM RELAY NO 12-PIN NYLON PLUG 5 +12V TO SIREN MODULE 3-PIN NYLON PLUG 15 14 +12V 13 C addition to sounding the siren. This function is provided by a floating relay output; ie, the relay contacts are not connected to anything inside the alarm. When the alarm is triggered, the relay contacts open and close at a rate of about once every second. This internal relay is not capable of switching more than 2A and so should be used to switch external heavy duty relays if currents higher than this are involved; eg, it could be used to switch the hazard lights relay to flash the hazard lights or the horn relay to “beep” the horn. If this feature is not re­quired, then the internal relay can be disabled by leaving out the link between pads 3 and 4 on the main alarm PC board. Note that there is no backup battery for this feature. If the supply leads to the alarm are cut (or the battery is discon­nected), then the hazard lights (or the horn) will cease operat­ ing. Only the siren module will continue operating, as this is the only item that does have battery backup. operating central door locking systems can vary from car to car. Some have solenoid-operated locks which only require a short pulse to operate them (as described above), while some have motor-operated locks which may require a much longer pulse (eg, up to 10 seconds) to fully operate. It’s quite easy to increase the output pulse period if required, simply by changing a few component values (see in­stallation procedure). In addition, some door locking systems must be connected to a +12V control signal to operate them, while others must be con­nected to ground (0V). It’s simply a matter of connecting the common output from the locking circuit to +12V or to ground, as required. The door locking circuitry is all contained on a separate (optional) interface PC board that sits inside the same case as the main alarm board. If you don’t want (or need) the central door locking option, just leave the interface board out. Central locking How it works In addition to its alarm functions, the control unit also provides a 3-wire output for automatically operating central door locking systems. These three connections are designated common, lock and unlock. The central locking facility is intended for use only if you have central locking on your car and only if you also use the optional UHF remote control. It works as follows: When the alarm is armed, a relay in the control unit con­nects the lock output to common for about two seconds to operate the door locking solenoids. Similarly, when the alarm is dis­armed, a second relay connects the unlock output to common for about two seconds to operate the unlocking solenoids. Note, however, that the method of Refer now to Fig.1 – this shows the full circuit details of the alarm control unit, including the optional door locking interface circuitry. As already indicated, the circuit is designed around the versatile Philips OM1681C alarm control and timing circuit (IC2). The power supply for this IC and for most of the rest of the circuit on the main board is derived from the car’s battery via reverse polarity protection diode D4. In addition, IC2 has an internal shunt regulator which, in conjunction with current limiting resistor R12, sets the supply voltage to this IC and to IC1 to 7.3V. Capacitor C7 provides filtering for the +12V rail from D4, while C5 provides filtering for the +7.3V rail. IC2 (OM1681C) can be armed/disarmed using one of two meth­ods. The one which is not used here is to apply a short pulse to the TOGGLE input (pin 8). This input responds to the falling edge of the applied pulse, each pulse causing the chip to alternately arm and disarm. The second method is to control the chip via its separate ARM (pin 9) and DISARM (pin 7) inputs. Unlike the TOGGLE input, these inputs are level triggered, with ARM responding to a low level and DISARM to high level. Because they respond to Fig.1 (left): the circuit is based on the Philips OM1681C alarm control IC. It is armed when pin 9 is pulled low via IC1a, while VR2 & VR3 set the entry & exit delays. Comparator stage IC1c & its associated parts form the voltage drop sensor, while IC3a, IC3b, Q4 & Q5 & their associated relays make up the door lock interface circuit. PARTS LIST Main alarm 1 horn siren module with backup battery 1 PC board, code DSE ZA-1286 1 miniature 12V DPDT relay (RLY1) 1 12-pin nylon plug & socket 1 3-pin nylon plug & socket 5 3-metre lengths of mediumduty hookup wire (red, white, black, blue & yellow) 1 2kΩ trimpot (VR1) 2 50kΩ trimpots (VR2,VR3) 1 plastic zippy case, 41 x 68 x 130mm 1 plastic cable tie 2 car alarm stickers 2 bonnet/boot switches Semiconductors 1 LM339 quad comparator (IC1) 1 OM1681C alarm control & timing IC (IC2) 1 BC557 PNP transistor (Q1) 2 BC549 NPN transistors (Q2,Q3) 2 1N4148 signal diodes (D1,D3) 3 1N4004 silicon diodes (D2,D4,D5) 1 1N4736 6.8V 1W zener diode (ZD1) Capacitors 2 1µF 50VW electrolytic (C1,C2) 4 0.1µF (100nF) MKT polyester (C3,C6,C8,C9) 3 10µF 16VW electrolytic (C4,C5,C7) Resistors (0.25W, 1%) 6 10kΩ – R1,R10,R11,R14, R18,R19 1 470kΩ – R2 3 1MΩ – R3,R6,R7 2 33kΩ – R4,R5 2 100kΩ – R8,R9 1 330Ω – R12 1 270kΩ – R13 1 2.2kΩ – R15 1 470Ω – R16 1 15Ω – R17 comple­mentary levels, they can be tied together, as in this circuit, to provide a single arm/disarm input. To arm the circuit, the ARM/DISARM input (pin 9 of the 12-pin plug) must be pulled low, either via a toggle switch or the optional remote control. December 1994  35 D12 LOCK 7 RL2 D8 R8 R9 R5 C2 C5 C1 R23 D6 R21 R22 R24 D7 IC3 LM339 10 NO 2 NC 14 DC OUTPUT 12 IMMEDIATE 4 DELAYED 9 ARMDISARM 8 0V IN C8 3 1 Q3 Q2 1 C6 R14 R17 D4 C9 ZD1 RELAY OUT D2 Q1 D3 R13 R15 VR2 VR3 R11 D5 R16 R4 4 2 R12 VR1 C10 RL1 C7 IC2 OM1681C IC1 LM339 C12 R19 1 R1 R2 R10 R18 C4 +12V IN 13 +12V OUT A  +12V OU T B  DOORS DOORS B R3 R6 C11 6 COMM Q5 RL3 C3 D1 R7 R25 1 1 STATUS LED (a) D11 +12V A 15 0V 0UT C 0V OUT C13 Q4 UNLOCK 3 0V C R34 R33 R26 R27 R20 R32 C14 R30 D10 R31 D9 R29 R28 COMM 11  PLACE A 10k RESISTOR BETWEEN "A" AND "B" IF THE DOOR L OCK I NTERF ACE I S NOT USED Fig.2: install the parts on the two PC boards exactly as shown here & don’t forget to bridge pads 3 & 4 (immediately above IC2) if you want to use RLY1 to flash the hazard lights or beep the horn when the alarm triggers. When this happens, the resulting 0V signal is fed via filter components R2 & C3 to pin 7 of compara­tor IC1a and to pin 4 of comparator IC1b. Diode D1 provides transient and reverse voltage protection for these two comparator inputs. As a result, pin 1 of IC1a goes low and pulls the ARM input (pin 9) of IC2 low, thereby forcing IC2 into its armed state. At the same time, the output of IC1b goes high and this does two things. First, it briefly pulls pin 8 of IC3a in the door locking interface circuit high via C10 to generate the door locking pulse (more on this later). Second, it briefly turns transistor Q2 on via C6 & R13. This, in turn, briefly turns Q3 off which releases the RESET line to the siren module. The siren now briefly “chirps” to indicate that the circuit is armed. Note that Q3 is normally biased on and clamps the RESET line low to keep the siren off. The status LED is driven by transistor Q1 via R16 and diode D5. Q1 and the LED are turned on when the STATUS output (pin 17) of IC2 goes low when the circuit is armed. Initially, the STATUS output remains low until the end of the exit delay 36  Silicon Chip period. It then briefly switches low once every second to flash the status LED on and off. Note that the STATUS output of IC2 is capable of sinking up to 100mA but Q1 was used so that the return path for the LED could be 0V rather than +12V. Trimpots VR1 and VR2 set the entry and exit delays for the delayed sense input by applying preset voltages to pins 14 & 15 of IC2 respectively. These inputs, in turn, feed internal analog-to-digital converters which process the input voltage level to give one of eight delay values ranging from 0 to 28 seconds. The delay and immediate sensors connect to pins 4 & 12 respectively of the 12-pin plug. These sensors trigger the DELAY & IMMED inputs (pins 5 & 6) of IC2 via transient filter networks R18 & C8 and R19 & C9. The state of each of these inputs is stored by IC2 at the moment of arming, so that the alarm can be triggered by either a low to high or high to low transition. Comparator stage IC1c and its associated parts form the voltage drop detector. Its function is to detect the small nega­tive-going transitions that occur on the +12V supply when any lamps (eg, interior or brake lamps) switch on. Let’s take a closer look at how this works. As shown on Fig.1, both inputs of IC1c are biased from the +7.3V regulated supply rail and VR1 is adjusted so that the vol­tage on pin 9 is normally 100mV higher than the voltage on pin 8. As a result, pin 14 of IC1c will be high and this high is fed to pin 6 (the DELAY input) of IC2. When a negative-going transient occurs on the +12V supply (eg, if a lamp turns on), it is filtered by R1, C1 and C2, to remove very slow transients, and coupled to pin 9 of IC1c (via C2). As a result, any transient that is greater than 100mV causes pin 9 to go more negative than pin 8 and so pin 14 of IC1c brief­ly switches low and triggers the delayed sense input (pin 6) of IC2. Note that because the output from the voltage drop sensor (IC1c) is normally high, the other sensors used on the delay input at pin 4 of the plug must not normally pull this input low. If they do, the voltage drop sensor will be disabled. Alarm outputs The two outputs from the OM1681C that are used here are FLASH (pin 1) and STEADY (pin 18). These are both open collector outputs (active low) As an alternative to operating the central locking circuit, the optional door lock interface board could be used to briefly flash the hazard lights each time the alarm is armed or disarmed. If you elect to use the latter option, reduce C11 to 0.22µF so that the arming flash is shorter than the disarming flash. The main alarm board can be used on its own with the siren module to form a complete working alarm with battery backup. The two trimpots at bottom right set the entry & exit delay periods. capable of sinking 100mA. The FLASH output causes relay RLY1 to switch on and off at a 1-second rate when the alarm is triggered and this can then be used to trigger other relays to beep the car’s horn or to flash the hazard lights. The STEADY output, on the other hand, provides a constant low signal when the alarm is triggered. This low turns off tran­sistor Q3 which thus releases the RESET line and so the siren sounds. An internal timing circuit inside IC2 now takes over and, after 60 seconds, IC2 resets and its FLASH & STEADY outputs effectively go open circuit. RLY1 thus remains off, while Q3 turns on again and resets the siren module. IC2 is now ready for the next trigger input. Note that both outputs from IC2 are connected via links to allow them to be disconnected or rearranged if required. The normal configuration is to have pads 1 & 2 connected to use the external siren module. Pads 3 & 4 are only connected if other external devices are to be pulse driven (eg, the hazard lights or the horn). The alarm circuit is disarmed by opening the switch (or relay contacts if the remote control is used) on pin 9 of the plug. When this happens, pin 7 of IC1a is pulled high by R3 and so pin 1 switches high and IC2 switches to the disarmed state. At the same time, pin 2 of IC1b switches low and applies a brief low-going signal to pin 7 of IC3b via C12 to generate the door unlocking pulse. Door lock interface circuit The central door locking interface circuit consists of two monostables, one positive edge triggered and the other negative edge triggered. The positive edge triggered section is based Twist all related leads together in groups of three to keep them tidy before making the final connections to the boards & to the plug. A piece of cardboard is used to separate the two boards inside the case. December 1994  37 MAIN ALARM PCB 1 14 12 4 9 8 5 TO 12-PIN PLUG RED RED RED BLA WHI BLU YEL BLU WHI 10 2 6 1 12 4 9 8 WHI BLU WIRES 30cm LONG YEL 13 A B C 15 BLA 6 YEL 2 BLA 10 WIRES 10cm LONG 5 7 11 3 WIRES 34cm LONG TO 3-PIN PLUG 14 13 15 WIRES 2m LONG DOOR LOCK INTERFACE PCB B C A 3 11 7 Fig.3: run the wiring to the PC boards & to the two plugs as shown on this diagram. If you don’t need the optional door lock interface PC board, just leave it out & connect a 10kΩ resistor between A & B on the main alarm board. on comparator IC3a and provides the locking pulse, while the nega­tive edge triggered section uses IC3b to provide the unlocking pulse. The way in which these two circuit sections work is quite straightforward. Let’s look at the locking circuit first. Normally, the voltage on pin 9 of IC3a is greater than the voltage on pin 8 and so the output at pin 14 is high. This means that transistor Q4 and RLY2 will be off. However, when the cir­cuit is armed, a brief positive-going pulse is applied to pin 8 of comparator IC3a via C10 as described previously. This momen­tarily pulls pin 8 above pin 9 and so pin 14 switches low and Q4 turns on. This in turn drives RLY2 which closes to generate the locking signal. At the same time, pin 9 of IC3a is 38  Silicon Chip also pulled low via feedback timing components R25 & C11. C11 now charges via R23 until the voltage on pin 9 exceeds the voltage on pin 8. When this happens, pin 14 switches high again and Q4 and RLY2 turn off to end the lock signal. D7 is included to ensure that pin 9 can not be pulled below -0.6V when pin 14 of IC3a goes low. Comparator stage IC3b, on the other hand, ignores the high-going signal from IC1b when the circuit is armed. That’s because a brief positive-going pulse is coupled to its pin 7 input via C12 and this input is already higher than pin 6. However, when the circuit is disarmed, the low-going pulse applied to pin 7 causes pin 1 to switch low and this turns on Q5 and RLY3 to generate the unlocking pulse. YEL BLA RED BLU WHI YEL Note that in this case, the RC timing network (R32 & C14) is connected to the collector of Q5 instead of to the output of the op amp. This is done to ensure that pin 6 is initially pulled high when pin 1 of IC3b switches low. The duration of the lock pulse is thus determined by R25 & C11, while R32 & C14 set the duration of the unlock pulse. These pulse widths can be altered if required (eg, for motor operated locking mechanisms) by increasing the capacitor values. Construction The assembly is straightforward since all the parts mount on two small PC boards. Fig.2 shows the parts layout on the two PC boards (main board at bottom, optional door lock interface board at top). Begin the assembly by installing all the wire links on the alarm PC board (code ZA-1286), then install Arming/Disarming Options As it stands, the circuit is designed to briefly “chirp” the siren when it is armed and this is particularly handy if you are using a remote control. There is no “chirp” from the siren when the circuit is disarmed, however. Instead, you have to confirm that the status LED has stopped flashing and this can only be done by inspection. A better way to confirm arming or disarming is to briefly flash the hazard lamps, as is done by many commercial circuits. This can easily be done by using the relays on the door lock interface PC board. As it stands, this circuit activates RLY2 for two seconds when it is armed and RLY3 for two seconds when it is disarmed. Thus, by connecting the NO contacts of these two relays in parallel across the hazard lights switch, the hazard lamps will briefly flash whenever the circuit is armed or disarmed. Note, however, that the relay contacts can no longer be connected to operate the door locking solenoids if you do this (otherwise the door locking solenoids will operate repeatedly if you have occasion to activate the hazard lights). If you do intend using the board to flash the hazard lights, reduce C11 from 0.47µF to 0.22µF. The circuit will now flash the hazard lights for one second when it is armed and flash them for two seconds when it is disarmed, thus making it easier to differen­tiate between the two states. 13 14 15 3-PIN PLUG ALLOCATIONS 3-PIN NYLON PLUG VIEWED FROM BACK 13 +12V TO SIREN MODULE 14 SIREN TRIGGER (0V = OFF) 15 0V TO SIREN MODULE PARTS LIST Door Lock Interface 1 PC board, code DSE ZA-1287 2 miniature 12V DPDT relays (RLY2,RLY3) Semiconductors 1 LM339 quad comparator (IC3) 2 BC328 PNP transistors (Q4,Q5) 4 1N4148 signal diodes (D6,D7,D9,D10) 3 1N4004 silicon diodes (D8,D11,D12) Capacitors 1 10µF 16VW electrolytic (C13) 2 .01µF (10nF) MKT polyester (C10,C12) 2 0.47µF (470nF) monolithic (C11,C14) Resistors (0.25W, 1%) 1 10kΩ - R20 2 1MΩ - R23,R31 2 100kΩ - R25,R32 2 2.2kΩ - R27,R34 2 1.5MΩ (5%) - R21,R29 4 4.7MΩ (5%) - R22,R24,R28, R30 2 680Ω - R26,R33 12-PIN PLUG ALLOCATIONS 1 2 3 4 5 6 7 8 9 10 11 12 12-PIN NYLON PLUG VIEWED FROM BACK 1 TO ANODE OF STATUS LED 2 ALARM RELAY OUTPUT (NC) 3 CENTRAL DOOR LOCK (UNLOCK) 4 DELAYED ALARM SENSING (0V SENSING) 5 +12V INPUT 6 ALARM RELAY OUTPUT (COMMON) 7 CENTRAL DOOR LOCK (LOCK) 8 0V INPUT 9 ARM (0V)/DISARM (OPEN) 10 ALARM RELAY OUTPUT (NO) 11 CENTRAL DOOR LOCK (COMMON) 12 IMMEDIATE ALARM SENSING (0V OR 12V SENSING) Fig.4: this diagram shows the pin allocations for the 3-pin & 12 pin plugs (as viewed from the back, or wiring side, of each plug). the resistors and capacitors. It’s a good idea to check each resistor value on your multimeter before installing it on the board, as some of the colours can be difficult to decipher. Take care to ensure that the electrolytic capacitors are correctly oriented. Normally, pads 1 & 2 on the PC board should be linked to­gether so that the external siren can be used. Pads 3 & 4 should only be linked if you wish to use RLY1 to drive other external devices (eg, the horn or hazard light relays) when the alarm triggers. The transistors, diodes and IC can be mounted next, again taking care to ensure that these parts are correctly oriented. In particular, take care with the ICs; they must be oriented so that their notched ends exactly match the wiring diagram (the label on each IC does not indicate orientation). Be careful when pushing the transistors into the board as the hole spacing is greater than the lead spacing and the tran­sistors may be damaged if pushed down too far – just push them down onto the board as far as they will comfortably go before soldering their leads. Finally, the board can be completed by installing the three trimpots (VR1, VR2 & VR3) and the relay. Note that VR1 is a 2kΩ vertical mounting pot while VR2 & VR3 are 50kΩ horizontal types, so there should be no confusion here. If exit and entry delays are not required (ie, if the optional UHF remote control is used), VR2 and VR3 should be set fully clockwise (0V) to get no delay. VR1 is used to set the sensitivity of the voltage drop sensor and can be set to its mid-point for the time being. The door lock interface PC board can now be assembled in similar fashion. As before, make sure that all polarised parts are correctly oriented and note that Q4 and Q5 face in opposite directions. Important: if this board is not being used, a 10kΩ pullup resistor must be connected between external wiring points A and B on the main board. Wiring Fig.3 shows how the two boards are wired together, while Fig.4 shows the connections to the 12-pin and 3-pin plugs. Cut the various coloured leads to the lengths indicated and twist them December 1994  39 SIREN MODULE FUSE BLOCK KEY 12V BATTERY DOME LIGHT DOME LIGHT FUSE TRIGGER 14 13 15 +12V 5 0V 8 STATUS LED 1 ARMDISARM 9 DELAY SENSE ALARM CONTROL UNIT ANODE STATUS LED 4 IMMEDIATE SENSE 12 RELAY NO 10 RELAY NC 2 RELAY COMM. 6 DOORS LOCK 7 DOORS UNLOCK DOORS COMM. DOOR PIN SWITCHES 3 13 12-PIN NYLON PLUG AND SOCKET DUAL CHANNEL UHF REMOTE CONTROL K-3260 ARMDISARM SWITCH AUX PIN SWITCHES ARM DISARM 9-PIN NYLON PLUG AND SOCKET SHORT WIRE ANTENNA +12V 4 0V 6 CH1 RELAY NO 2 CH1 RELAY NC 1 CH1 RELAY COMM. 3 CH2 RELAY NO 8 CH2 RELAY NC 7 CH2 RELAY COMM. 9 UHF REMOTE ARMDISARM OPTION COMMON TO HORN OR HAZARD LIGHTS SWITCH 40  Silicon Chip TO CENTRAL DOOR LOCK IF THE CAR HORN OR HAZARD LIGHTS OPTION IS USED THEN LINK PADS 3 AND 4 ON THE MAIN ALARM PCB 5 Fig.5: use this wiring diagram as a general guide when installing the alarm but note that the details may have to be varied to suit your particular car (see text). The ARM/DISARM switch can be deleted if the UHF remote control is used. together in groups of three, keep­ing related leads together, before making the final connections to the boards and the plugs. Note that Fig.4 shows the two plugs as viewed from the back. Each lead is terminated by first soldering it to a special pin which is then pushed into its appropriate location from the back. Each pin is spring-loaded and snaps into position when pushed home inside the plug body. Make sure that you install each pin in its correct location, as they are impossible to get out again if you make a mistake. The two PC boards are designed to fit into a small plastic zippy case and are separated by a 125 x 33mm piece of stiff card­board which slides LOCK UNLOCK between the middle end slots – see photo. A notch will have to be filed in one end of the case to provide an exit point for the wiring loom, while a plastic cable tie can be used as a restraining clamp. Installation Building the alarm is the easy part; by far the most time-consuming part of the job will be installing it (neatly) in a car. Fig.5 shows the recommended wiring details, including the wiring to the optional UHF remote control & the beeping horn (or hazard flasher) option. Note, however, that this diagram is a guide only and some of the details may have to be varied to suit your car’s wiring. For example, in most cars the door switches connect to earth but a few have their switches in the positive supply line. Unfor­tunately, the latter cannot be used on the DELAY input so check carefully first and be prepared to install additional door switches if necessary. A wiring diagram of your car’s electrical system will be an absolute must when it comes to installing this alarm. This will be necessary for tracking down the wiring to the horn and hazard light switches, checking whether the door switches go to the +12V supply or to earth, and locating the control wiring for the central locking. Make sure that you install the alarm in a professional manner so that it doesn’t interfere with any of the car’s existing functions. The general procedure is as follows: (1). Choose a secure location under the bonnet for the siren module where it is not likely to get damaged by flying stones or covered in mud. The keyswitch on the back of the unit should be accessible so that the unit can be disabled if the battery needs to be removed for servicing. (2). Mount the control unit in a secure location (eg, under the dashboard) and mount the status LED on the dashboard so that it can be readily seen from outside the car. The ARM/ DISARM switch (if used) should be mounted in a suitable hidden location (no; not inside the glovebox) but should still be readily accessible. (3). Connect suitable lengths of medium-duty hookup wire to the 12pin female socket, then run each lead to its correct destina­tion. The 0V (ie, the negative supply) lead should be connected as close as possible to the negative terminal of the battery, while the +12V lead should be connected to either the fuse block, the dome light +12V lead, or to some other point that is fed from the fuse block and still has +12V on it when the ignition is switched off. If you elect to use the beeping horn option, it should be simply a matter of connecting the NO relay contacts (pins 10 & 6) across the horn switch. Alternatively, connect these contacts across the hazard light switch if you want the hazard lights to flash when the alarm triggers. Note that you can either have the beeping horn or flashing hazard light but not both. Do not connect these switches in parallel, otherwise the hazard lights will flash each time you blow the horn in normal use and vice versa. Note that the status LED must be connected with the correct polarity for it to work. Its cathode can be connected via a short lead to some convenient earth point. (4). Connect the leads from the DELAY (pin 4) and IMMEDIATE (pin 12) inputs to the various sensors. Remember that the sensors connected to the DELAY input must all be normally open and must pull the input low to trigger it. Either normally open (NO) or normally closed (NC) switches can be connected to the IMMEDIATE input but, as previously men­ tioned, you can only use one type; ie, they must either be all NO or all NC. If normally closed switches are used, they must The horn siren module comes with an internal nicad backup battery & this may be turned on or off using a key-operated switch. In normal use, the backup battery is kept fully charged by the car battery via an internal regular circuit. be wired in series (NO switches are wired in parallel). (5). Connect the siren module (via the 3-pin plug) & connect the lock, unlock and common outputs (pins 7, 3 & 11) to the central locking system. As described, the circuit should be suitable for solenoid-operated systems (2-second pulse width). If the pulse width needs to be increased, for example, to 10 seconds for motor driven door locks, replace C11 and C14 (0.47µF) with 2.2µF bipolar capacitors. If you want a shorter pulse, use values that are less than 0.47µF. Test & adjustment Once the installation is complete, the unit can be tested for correct operation and the entry and exit delays set. VR2 sets the entry delay, while VR3 sets the exit delay. For both trim­ pots, the fully clockwise position is zero delay and fully anti­clockwise is a 28-second delay. Only the following delay periods can be obtained: 0, 4, 8, 12, 16, 20, 24 & 28 seconds. Finally, VR1 can be adjusted to set the sensitivity of the voltage drop sensor. The best way to do this is to initially set the trimpot fully anticlockwise (least sensitive), arm the alarm, and then try to trigger it by switching on the dome light or brake lights. Note that this sensor connects to the DELAY input of IC2, so the alarm will not sound until the end of the delay period. Note also that all other sensors connected to the DELAY input must be opened for the voltage drop sensor to work, so do not open a car door during this procedure. If the alarm fails to trigger, rotate VR1 slightly clock­wise and try again. Repeat this procedure until the alarm trig­gers reliably but don’t make the setting too sensitive otherwise you SC may get false triggering. Where to buy a kit of parts This alarm circuit was designed by Dick Smith Electronics and kits are available from all DSE stores or by mail order from PO Box 321, North Ryde, NSW 2113. Phone (02) 888 2105. Prices are as follows: Main Alarm Circuit (complete kit with case, PC board, siren module with backup battery, two boot/bonnet switches and alarm stickers, but not including door lock inter­face components); Cat. K4312 .................................. $89.95 Door Lock Interface Circuit (optional), Cat. K4314 .......................... $16.95 Please add $7.00 for packaging & postage if kit K4312 ordered, or $8.00 if both K4312 and K4314 are ordered. Note: copyright of the two PC board artworks associated with this project is retained by Dick Smith Electronics. December 1994  41