Bueno aqui coloco un circuito. Esta en ingles, particularmente no lo he probado, pero parece ser un buen circuito.
Hand Clap Electronic Control
Circuit operation is as follows. A single hand clap will be picked up by the electric mic which is coupled through C1 into the op amp IC1. The ouput of IC1 triggers the 555 IC timer IC2 which is configured as a monostable multivibrater. The trigger pulse is stretched by IC2 and outputs a pulse to IC3 a D type flip flop. Because of the three state counter arrangement of IC3, two sharp claps are required before IC3 will output a high to Q1 which will turn on K1 relay and any device connected to K1's switch contacts. Two more claps will clock IC3 again and will turn off Q1 and any device connected to the K1's contacts. I had my unit connected to my xmas tree lights so that I wouldn't have to crawl behid the tree to turn the lights on and off. Sensitivity for the circuit is R3 and should be adjusted so that the circuit ignores normal room noise