Clap On Clap off switch works as an automated switch that makes devices On and Off by making merely a clap sound or other similar pitch sound. It is based on 555 timer IC and electric condenser Mic, which is working 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 works as a Clock pulse for D-type flip-flop and would turn ON the LED, which will remain ON until the next clock pulse means until the next Clap/sound. So this is the Clap Switch which will turn ON with first Clap and turn OFF with the second Clap. If we remove the D-type Flip flop from the circuit, the LED will be turned OFF automatically after some time and this time will be 1.1xR1xC1 seconds, which I have explained in my previous circuit of clap switch. You can see that circuit for detailed understanding of concepts.

Step 1: Required Components

· Condenser Mic

· 555 Timer IC

· Transistor BC547

· Resistors (220, 1k, 10k, 100k ohm)

· Capacitor (10uF)

· IC7474 more precisely DM74S74N (D-type flip flop)

· LED and Battery (5-9v)

You can see the circuits and connections. 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 no output at OUT PIN 3, means no clock pulse for D-type Flip-flop (IC7474), means no response from D-type Flip-flop, and LED is OFF.

Step 2: Circuit Diagram

The complete circuit diagram of clap on clap of switch is shown in the above figure. In this circuit, Electric Condenser Mic is used for sensing the sound while transistor is used to trigger the 555 timer IC. The 555 timer IC further SET & RESET the D-type flip flop and D-type flip flop to remember the logic level (LED ON or OFF) until next Clap/sound. I have wrote a tutorial with the detailed version of the explanation of clap on clap off circuit. You can read it to understand the detailed working of flip flops in this circuit. As we are using the IC 555 in Monostable Mode, whose output has been used as a clock pulse for D-type Flip-flop IC. So the clock pulse will be HIGH for 1.1xR1xC1 seconds and then it would become LOW.

Step 3: IC 7474

We have used IC DM74S74N of 7474 series. IC DM74S74N is the Dual D-type Flip-flop IC, in which there are two D-type Flip-flops, which can be either used individually or as a master-slave toggle combination. We are using one D-type Flip-flop in our circuit. Pins for first D flip-flop are the left side and for second flip flop are at right side. Also there are PRE and CLR pins for both the D-type Flip-flops which are active-low pins. These pin used to SET or RESET the D-type Flip-flop respectively, regardless of INPUT D and Clock. We have connected both to Vcc to make them inactive.

After understanding the D-type Flip-flop and IC DM74S74N, we can easily understand the use of D-type Flip-flop in our circuit. When we first triggered the 555 IC by first Clap, the LED glows as we get Q=1 and Q’=0. And it will remain ON until the next trigger or next positive clock pulse (LOW to HIGH). We have connected Q’ to to INPUT D, so when LED is glowing, Q’=0 is waiting for Second Clockpulse, so that it can be applied to the INPUT D and makes Q=0 and Q’=1, which in turns TURN OFF the LED. Now Q’=1 is waiting for next clockpulse to make the LED turn ON by applying Q’=1 to INPUT D, and so on this process will continue.

Step 4: Working Explanation

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. So the output PIN3 will be high and a positive clock pulse will be applied to D-type Flip-flop, which makes Flip-flop to respond and LED will turn ON. This SET state of flip flop will remain as it is until the next clock pulse (next Clap). Detailed working of D-type Flip-flop has been given below.

Here we are using 555 timer IC in Monostable Mode, whose output (PIN 3 of 555 IC) has been used as a clock pulse for D-type Flip-flop. So the clock pulse will be HIGH for 1.1*R1*C1 seconds and then it would become LOW.

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. Also we should use a 220 ohm resistor to connect LED.

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).