This is the circuit of a very sensitive clap switch. It switches ON/OFF a White LED or electrical appliances through claps. The circuit can sense the sound of claps from a distance of 1-2 meters. Condenser Mic picks up sound vibrations caused by the clap.
These sound vibrations are given to the inverting input (pin2) of IC1. It amplifies the sound collected by the Mic.
Resistor R2, R3 and variable resistor VR1 adjust the sensitivity of the amplifier. Resistor R1 set the sensitivity of Mic. The amplified output pulses from IC1 passes to the input of IC2 (CD 4017). Resistor R4 keeps the input (pin14) of IC2 low so as to prevent false triggering.
IC2 is a decade counter IC which is wired as a toggle switch. That its outputs 1 and 2 (pins 2 and 3) becomes high and low when the input pin14 receives pulses. Pin4 (output4) is connected to the reset pin15 so that further counting will be inhibited. The high output from IC2 passes through the current limiter R6 to the base of switching transistor T1. When T1 conducts, White LED (D2) turns on. If a 6V 100 ohms relay is connected to the points marked (A and B), the relay will also energize and the load (bulb or electrical equipments) will be switched on. In the next clap, output pin 2 becomes low and relay and White LED will be switched off. LED D1 (Red LED) indicates the OFF position.
PCB Relay Pins
2 + 5 – Relay coil
1 – Common- Here connect the phase line
3 – NO ( Normally Open) – Here connect the load phase in series to switch ON the load when relay turns on
4 – NC ( Normally Connected) – Here connect the load phase in series to switch OFF the load when relay turns on
In the PCB layout, points A and B are used to connect relay coil pins 2 and 5