Here is
a Hobby Circuit for electronics hobbyists that can switch on & off a
light, Fan, Radio etc. by the sound of clap. The sound of clap is
received by a small microphone that is shown biased by resistor R1 in
the circuit. The microphone changes sound wave in to electrical wave
which is further amplified by Q1. Transistor Q1 is used as common
emitter circuit to amplify weak signals received by the microphone.
Amplified output from the collector of transistor Q1 is then feed to the
Bistable Multivibrator circuit also known as flip-flop circuit.
Flip flop circuit is made by using
2 Transistor, in our circuit Q2&Q3. In a flip-flop circuit, at a
time only one transistor conduct and other cut off and when it gets a
trigger pulse from outside source then first transistor is cutoff and
2nd transistor conducts. Thus output of transistor is either logic-0 or
logic-1 and it remains in one state 0 or 1 until it gets trigger pulse
from outer source.
The pulse of clap which is a
trigger for flip-flop which makes changes to the output which is
complementary (reverse). Output of flip-flop which is in the low current
form is unable to drive relay directly so we have used a current
amplifier circuit by using Q4 which is a common emitter circuit. Output
of Q4 is connected to a Relay (Electromagnetic switch) which works like a
mechanical switch and it becomes easy for connecting other electrical
appliance.
The relay contact is connected to
the power line and hence turns on/off any electrical appliance connected
all the way through relay.
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