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Burglar Alarm is basically a security alarm, which detects thief when they enters our home. For detecting, we use IR transmitter and Receiver. IR Sensor continuously takes the value, when interrupt occurs it will shows the variation.
IR sensor is directly connected to LM311 IC. It is a voltage comparator IC, here it is we used for reference voltage.Whenever the IR signal is interrupted, its output in receiver feed to LM311. and IC2 is triggered at pin 2 through transistor LM311. IC2 NE555 work as in the monostable multivibrator mode. We can adjust the time period through R7 & C2. The output of monostable directly connected to clock of the D-flipflop. In D-flipflop when input data is high then output is also high. Here we input pin of the D-flip flop connected to +5v(Always high). As a result when clock signal appear, a high voltage(+5v) is feed to the base of the transistor BC547 & LED. Buzzer is connected to transistor collector and VCC. When Transistor ON Buzzer will produce sound. Finally a thief interrupt the IR signal simultaneously a buzzer sound will produce.
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