Clap Based Relay Control

Components

Electric Condenser Mic

555 Timer IC

Transistor BC547

Resistors (220, 1k, 47k, 100k ohm)

Relay and Battery (9v)

Clap switch is an interesting hobby circuit which turns on the lights with a clap sound. Although its name is “Clap switch”, but it can be turned ON by any sound that is approximately the same pitch of Clap sound.

The main component of this clap switch circuit is the Electric Condenser Mic, which has been used as a sound sensor. Condenser Mic basically converts sound energy into electrical energy, that in turns used to trigger 555 timer IC, through a Transistor and triggering of 555 IC would turn ON the Relay. I have made this circuit as simple as possible. you can find many complex Clap switches (using 555 IC) with some more components in it, and merely doing the same thing. Even make things simpler require more effort than making it complex.

Clap Based Relay

You can see the circuits and connections in the above schematic diagram of clap switch. Initially, the transistor is in OFF state because there is not enough base-emitter voltage to turn it ON and the point near the collector is at a high potential, and the point is connected to Trigger pin 2 of 555 IC, as a result, Trigger pin 2 is also at high potential. As we know that, to trigger the 555 IC through Trigger PIN 2, the voltage of the PIN 2 must be below Vcc/3. So at this stage Relay is not excited.

Now when we produce some sound near the condenser mic, this sound will be converted into electrical energy and it will raise the potential at the Base, which will turn the Transistor ON. As soon as the transistor becomes ON, the potential at the Point would become low and it will trigger the 555 IC because of the low voltage (below Vcc/3) at Trigger Pin 2 and Relay will get excited. We have connected the Relay to Output PIN 3 of 555 IC.

TEST:-

To test this circuit you need to clap loudly as this small condenser mic don’t have long range. Or you can directly hit at the mic lightly.

In this circuit the relay is always in ON State, but what if we also want to control the switching OFF of the Relay? Means if we want to turn ON the Relay with a clap/sound and turn OFF it with second sound/clap? We can do this by using D-flipflop/IC 7474, I will show you this in my next circuit.