Imagine the Panic situation in the Midnight when an intruder tries to break into the house. This Alarm will help you with its loud Police siren to abort the attempt of intrusion. With a single clap, the circuit generates the alarm for three minutes and then goes off. This is sufficient to catch the attention of neighbours.
The circuit is a sensitive Clap switch with timer action. IC1 is designed as a sensitive inverting amplifier to amplify the sound signals from the condenser mic. Variable resistor VR1 set the sensitivity of mic and resistor R1 and VR2 set the gain of the amplifier. If the sensitivity of mic and amplifier is suitably adjusted, the circuit can detect the sound from a distance of 5meters or more.
When the mic detects clap sound, the ac signals pass through C1and IC1 amplifies the signal. This triggers T1 .When T1 conducts, the trigger pin of the Monostable Timer IC2 will be grounded and the timer triggers. With the given values of R5 and C2, output of IC2 remains high for three minutes. This high output provides power to the ROM IC UM3561. It generates the Police Siren since its pin6 remains unconnected. Resistor R8 determines the frequency of oscillation of IC3.The siren signals are amplified by T2 and the alarm tone can be heard through the speaker. Zener diode ZD gives 3.1 volt regulated supply to IC3.