Description This circuit was intended to activate a relay by means of a hand clap. Further claps will turn-off the relay. An interesting and unusual feature of this project is the 3V battery operation. The circuit's sensitivity was deliberately reduced, in order to avoid unpredictable operation. Therefore, a loud hand clap will be required to allow unfailing on-off switching. Q1 acts as an audio amplifier. IC1 timer, wired as a monostable, provides a clean output signal and a reasonable time delay in order to allow proper switching of the following bistable circuit. A discrete-components circuit formed by Q2, Q3 and related parts was used for this purpose, in order to drive the Relay directly and to allow 3V supply operation. Circuit Diagram: Parts: R1 = 12K R2 = 1M R3 = 6.8K R4 = 220K R5 = 2.2M R7 = 100K R8 = 22K R9 = 6.8K R10 = 100K Q1 = BC550C Q2 = BC328 Q3 = BC328 C1 = 220nF-63V C2 = 22nF-63V C3 = 220nF-63V C4 = 22nF-63V C5 = 22nF-63V C6 = 47uF-25V D1 = 1N414...