Intruder alarm is very common project for diploma or basic level. Here, by dreamlover technology a verified project on intruder is published, used in door of your house for sound an alarm when anyone open or pushed the door. The circuit of intruder alarm can be used against thieves or intruders.
Circuit description of intruder alarm
The project intruder alarm consist two circuits each of transmitter and receiver separately. Transmitter section comprising a laser diode and power is given from a 9V power supply. Here the receiving section consists of LDR for sensor and work on principle of LDR. When light falling to LDR from laser diode provides base current to transistor T1 which start conducting (but not T2) and the alarm remains off.
When door is pushed, light incident on the LDR is interrupted and it offer high resistance which stop conducting transistor T1 but transistor T2 receive base current and start conducting. The input is given to AND gate N1 from the emitter of transistor T2. Here IC2 work as latch when high output from AND gate N1 is connected to pin 1 and 14 respectively. High output form output pin 12 of IC2 is given to base of transistor T3 through R7 and it cause transistor conduction and consequent sounding of the alarm.
Dreamlover Technology Note: While testing at dreamlover technology Lab, a laser torch in place of the transmitter was used.
Resistors (all ¼-watt, ~+mn~ 5% Carbon)
R1, R2, R6, R8 = 1 KΩ
R3 = 2.2 KΩ
R4 = 10 KΩ
R5 = 100 Ω
R7 = 2.2 KΩ
IC1 (N1) = 7408
IC2 = 7473 JK flip-flop
T1 = BEL187
T2, T3 = SL100
LED1, LED2 = RED
LD1 = Laser diode
SW1, SW2 = On/off switch
SW3 = push-to-on switch
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