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Clap
Switch
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Several
circuits for sound operated switches have been published
earlier. The circuit shown here for clap operated switch
is inexpensive and easy to assemble by hobbyists of any
level. Clap sound signals picked up by condenser microphone
are first amplified by transistor T1, which is a simple
common-emitter amplifier. Amplified signals are rectified
by diode D1. Positive half cycle of clap signal is applied
to a 3-stage DC amplifier formed by transistors T2, T3
and T4. Output from transistor T4 is used as a clock for
flip-flop IC1 (7472). For each clap, the output of IC
7472 toggles alternately to on/off state.
Transistor T5 functions as relay driver since output level
of IC1 is insufficient to drive a relay directly. The
entire circuit, except the relay driver, operates at 5
volts regulated. The 5-volt supply is derived from 12V
supply (used for relay driver transistor T5) using a zener
diode with series resistor R11 (150-ohm, 1-watt). Using
this circuit any electrical or electronic load can be
controlled by just clapping in front of the microphone.
The microphone should be housed inside a suitable funnel
shaped enclosure to improve sensitivity. Potmeter VR1
is used as sensitivity control.
The entire circuit can be powered from simple 12-volt
unregulated supply using 12-volt step-down transformer,
followed by full-wave rectifier and a filter capacitor
of about 1000µF, 25V. |
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