Clapper Light Control Circuit
 

This circuit acts as a relay switch which is triggered by clapping ones hands twice.   The noise generated by the claps is detected by the microphone, which produces a small electrical pulse.  This pulse is cleaned up a little bit then amplified and sent to the 555 timer.   If the sound is loud enough, the 555 timer will respond by lighting up an LED.   The D flip-flop in the circuit waits until two claps are detected before it allows anything further to happen.  The output of the flip-flop goes to a transistor to source enough power to control the relay.  Using a relay rather than a transistor allows for applications that involve wall power (such as creating a clapper circuit to turn on a desk lamp).   If two claps are heard by the microphone, then the relay changes positions, creating a clapper-controlled switch.

 

Activity (pdf )