The clap switch circuit is
build around two IC's -
2. 7490 IC which is a decade and binary counter.
It contains four master slave flop and also contain divide by two and divide by
five counter. It can be used as divide by 9 counter by connecting Q0 with clock
input pin1 (CP1) and providing clock pulse to CP0 that is on pin14. It can also
be used as divide by 6 counter by connecting Q0 with CP0 and giving input pulse
at CP1.
7490 IC
will provide you the 9 different combination to "on" and
"off" the four different application in 9 claps. Similarly 7492 IC is
also available which will provide you 11 different combination of output
for controlling the four appliances. And another is 7493 which provide 15
different ways to control the four appliances.
When you clap
in front of the Mic, clapping sound is converted into electrical energy by the
microphone. These weak signals are then amplified by the transistor which acts
as preamplifier. Sensitivity of the signals can be improved with the help of
VR1. Now the transistor T1’s output is feed to monostable circuit which is
wired NE555 . Whenever you clap in front of microphone, output pin 3 of IC1
goes high and this is fed to clock input of IC2 pin 14. The output of IC2 is
now provided to transistor T2-T4 through 100 ohm resistor to derive the
corresponding relay connected to it. We have also connected different colour to indicate the state of the different appliances. If
LED glows means that device is "on". If LED does not glows means
device is "off". 
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