Clap Switch

This clap switch can turn on and off a light,fan,music system,alarm.....virtually any gadget,at the sound of a clap.The most amazing part of the design is that it gives an a efficient two state control without employing any op amp,any counters,timers or flip-flops but just four transistor.The design shows how basic circuits can do complex jobs.

The sound is sensed by a small button microphone(condenser microphone)whose internal FET is biased by R1.The signal is amplified by T1,T2,T3,andT4 provides the remaining control functions.There isn't much to explain but much can be understood by carefully observing the design.T4 drivers a  relay.The relay is further used to control the load as shown in schematic b.It is the contacts of the relay that determine the loads that it can handle.

Schematic a

Schematic b