This is another circuit of IC 555 infrared burglar alarm project. It is very simple to construct and submit it as a mini project for your school and college level project submission.
The basic idea of the circuit is almost same used in the previous circuit of IC 555 simple burglar alarm, only the wire loop is replaced with LDR. You can also use infrared sensor in this circuit instead of LDR.
Working of the circuit
As shown in the above circuit, the IC 555 is used as simple astable multivibrator circuit, but its RESET pin-4 is grounded through the LDR.
When power supply is connected to the circuit keeping the LDR fully lighted, pin-4 remains grounded through the LDR. So the IC gets disabled and its output pin-3 remains LOW.
But when the light on the LDR drops or the LDR becomes dark completely, pin-4 can no longer be held to ground level and it is now returned to +ve supply of the battery.
So the AMV starts oscillating at a rate decided by the combination of R1, R2 and timing capacitor C1. You can check the actual working of the circuit is following video.
The practically tested PCB layout of the above circuit is given below. The following image is actual size PCB layout. If you want to get the hardcopy of PCB layout of this circuit for actual construction, then contact us. We shall send you the actual size PCB layout for free.