Ultra-Sensitive Solid State Clap Switch

Here is the circuit of a highly sensitive clap switch that can be operated from a distance of up to 10 metres from the microphone. Signals picked up by the microphone are amplified by transistors T1, T2, and T3. Diode D1 detects clap signals and the resulting positive voltage is applied to the base of transistor T4. The output from transistor T4 is further amplified by transistor T5, whose output is used to trigger a monostable multivibrator wired around the 555 timer (IC1). The output of IC1 is used as a clock for decade counter 4017 (IC2) that is wired as a divide-by-two counter.

For each successive clap, transistor T6 conducts and cuts off alternately. As a result, for each clap signal, the lamp is either switched ‘on’ or ‘off’. Triac 8T44A (or ST044) can drive load of up to 4-amp rating. The 12V DC for operation of the circuit is directly derived from the mains using rectifier diode D2, current-limiting resistor R16, and 12V zener ZD1 shunted by filter capacitor C7.