QUASAR KIT No. 1019
CAR ALARM SYSTEM
General Description
This is a complete car alarm system that can be triggered by the vibrations caused by anyone
trying to break into a car, or alter natively by the small voltage drop that will be caused by any
courtesy light turning on when a door or the car's boot is opened, and also in direct mode that
the alarm is triggered when a certain point of its circuit is grounded. There is an entry time of
8", an exit time of 20" and the duration of the alarm (if it is not turned manually off by the user)
is 50". The alarm can control external devices (sirens, flashes, etc.) drawing a maxi mum
current of 3 A. If you wish to control heavier loads then you should use a relay as the output
device and control the loads through the relay.
Technical Specifications - Characteristics
Working voltage: 6-12V DC
Entry time: 8 sec
Exit time: 10 sec
Alarm time: 50 sec
How it Works
As it has already been mentioned the circuit provides the user with three time functions,
namely entry, exit and alarm time and also direct and pulse triggered alarm. The entry time is
controlled by the integrated circuit IC1 and the RC network R1-C2.
The transistor TR2 and its circuit which consists of C15, R16, R14, D2 & D5 is used as a
pulse detector which triggers the alarm if there is a sudden fluctuation of the supply voltage
which is an indication that the courtesy light - or some other light or apparatus - has been
turned on. The exit time is controlled by TR4 and the associated components D6, R8, R9, C4,
C6 & C7 and is 20 - 30 seconds. The alarm duration is again controlled by an IC, the second
555 timer of the circuit and it depends upon the values of R5 and C8. The output from IC2 is
used to drive the output transistors TR1 and TR2 so that the circuit is capable to switch
heavier loads. The pin number 5 on the p.c. board can be used as a direct trigger for the
alarm as it will trigger the circuit immediately if it is connected to ground. Across point 5 and
the negative supply rail is where you can connect a vibration sensitive switch that closes
when it is moved, or push to brake switches that make contact when a door or the car's boot
are opened. Please keep in mind that the maximum permissible current
through the output of the circuit is 3 A. If the devices that you want to control are likely to draw
currents heavier than this, you should use the output from the alarm to control a relay and
then switch the various loads by means of the relay contacts.
