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 of approximately 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 LED, which will be automatically turned OFF after some time. 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.
Here we are using Electric Condenser Mic for sensing the sound, transistor to trigger the 555 timer IC and 555 IC to turn ON the LED through a low voltage trigger.
555 Timer IC
Resistors (220, 1k, 47k, 100k ohm)
LED and Battery (5-9v)
Circuit Diagram and Explanation
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 (0.7v) base-emitter voltage to turn it ON. And the point A is at high potential, and point A 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 LED is OFF.
Now when we produce some sound near 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 Point A would become low and it will trigger the 555 IC because of the low voltage (below Vcc/3) at Trigger Pin 2 and LED will turn ON. We have connected the LED to Output PIN 3 of 555 IC through a 220ohm resistor.
After some time LED will be turned OFF automatically because we are using 555 timer IC in Monostable Mode. LED will remain turned ON for 1.1*R1*C1 seconds. So we can see, with this formulae, that we can change this duration, by changing the value of Resistor R1 or/and Capacitor C1. We can modify this circuit using Relay to control the Electronic devices (120/220V AC). Control PIN 5 of 555 Timer IC should be connected to Ground through a 0.01uF capacitor.
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 (like I have done in the video).
In this circuit LED will be turned OFF automatically after some time, but what if we also want to control the switching OFF of the LED? Means if we want to turn ON the LED 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.