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Car Alarm and Immobilizer

2017-01-18 03:54  
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Car Alarm and Immobilizer
The alarm is set by opening Sw1. It can be any small 1-amp single-pole change-over switch - but for added security you could use a key-switch. Once Sw1 is opened you have about 10 to 15 seconds to get out of the vehicle and close the door behind you. When you return and open the door the buzzer will sound. You have 10 to 15 seconds to move Sw1 to the off position. If you fail to do so, the siren will sound. The output to the siren is intermittent - it switches on and off. The speed at which it switches on and off is set by C6 and R10. While any trigger-switch remains closed, the siren will continue to sound. About 2 to 3 minutes after all of the switches have been opened, the circuit will reset. One of the inputs is connected to the vehicle's existing door-switches. This provides the necessary exit and entry delays. It's usually sufficient to connect a SINGLE wire to just ONE of the door switches - they're generally all connected in parallel with the return through the chassis. You can add extra normally-open switches to the door-circuit if you wish; but note that any additional switches will have to be able to carry the current required by your vehicle's interior light. Any number of normally-open switches may be connected - in parallel - to the Instant input. Since they don't have to carry the current for the interior light, you can use any type of switch you like. You may want an instant alarm on the bonnet, the boot, the rear-hatch, the rear-doors etc. It doesn't matter if these already have switches connected to the door-circuit. Simply fit a second switch and connect it to the instant input. It will override the delay circuit. You can use the chassis for the return. However, a ground terminal is provided if - for any reason - you need to run a separate return wire for either zone. If you're not using the instant zone then leave out Q2, R3, R4, R5 & D3. The exit delay is set by R1 & C1, the entry delay by R9 & C4, and the reset time by R7 & C3. The precise length of any time period depends on the characteristics of the actual components used - especially the tolerance of the capacitors and the exact switching points of the Cmos Gates. However, for this type of application really accurate time periods are unnecessary. The circuit board and switches must be protected from the elements. Dampness or condensation will cause malfunction. Fit a 1-amp in-line fuse AS CLOSE AS POSSIBLE to your power source. This is VERY IMPORTANT. The fuse is there to protect the wiring - not the alarm. Exactly how the system is fitted will depend on the make of your particular vehicle. Consequently, I CANNOT give any further advice on installation.