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.