Clap On/Clap Off Circuit - Augie

This circuit uses a 555 timer and Flip Flop to toggle a LED when a microphone detects a major noise. Each "clap" or noise will cycle the LED, with little time between the inputs. The necessary materials are as follows.

- 1x 555 timer

- 1x 74HC74N

- 1x LED

- 2x Transistor

- Resistors (100k, 47k, 1k, 10k, 10k)

- 10uF capacitor

- 1x Condenser Mic

- Wires as needed

The actual theory behind this circuit relies on the pulses coming from the 555 timer, and the flip flop being able to regulate its power output. When the microphone picks up a loud sound it sends a signal into the trigger pin of the 555 timer. In turn the 555 timer sends a pulse into the flip flop. When the flip flop receives this pulse into the clock pin, it changes the output of the flip flop. So if the output is set to off when the clock is pulsed, the flip flop will change its output to on. This is how the LED is toggled between on and off. It is worth noting that there is a transistor between the 555 timer and the flip flop. This is because the 555 timer signal was not strong enough to make the rising edge that the flip flop uses to change its output. By adding in the transistor that is connected directly to power, the input becomes a 9v signal, instead of the weaker signal that came from the 555 timer. The resistor that is connected to this transistor provides a low input until the 555 timer is tripped. This change in input voltage creates the rising edge that the flip flop uses.

For all of my projects I prefer to work left to right. In this case that means starting with the condenser microphone. To start, connect the 47k resistor to your power source. Then connect the resistor to the base of the capacitor and the positive end of the microphone. To finish off this section connect the negative end of the microphone to ground.

This part of the schematic creates the part of the circuit that triggers the 555 timer. To begin connect the 1k resistor to power. Then connect the resistor to Pin 2 and the collector leg of the transistor. Finally connect the emitter leg to ground.

When connecting ICs I usually go in numerical order around the chip. In this case, pin 1 connects to ground, pin 2 should already be connected to the capacitor, pin 3 will be used later to connect to the Flip Flop. Pins 4, 5, and 8 both connect to power. Pins 6 and 7 will both connect to the capacitor, but more on that in the next step.

For this step we are going to connect the capacitor. Start with the 100k resistor, and connect it to pins 6 and 7. Then connect both of them to the collector end of the 10uF capacitor. Finish by connecting the emitter leg of the capacitor to ground.

For this step the only components that you will need are the transistor and a 10k resistor. Connect the collector leg to the power source, and connect the base to pin 3 of the 555 timer. Connect the 10k resistor to ground. Then connect the emitter leg of the capacitor to the resistor and pin 3 of the flip flop (more on that next step).

This is the most intensive component to connect in this circuit. For this step you will need the LED, the 10k resistor, and the Flip Flop. Again I recommend that you connect each pin in order starting from pin 1. To begin connect pin 1 to pin 14, and to power. Then connect pin 2 to pin 6. Pin 3 should connect to the resistor that is connected to the 10k resistor, as mentioned in the last step. Pin 4 should also connect to pin 14 and power, just like pin 1. Pin 5 is the one that you finally connect to the LED, then connect this LED to a 10k resistor, and finally to ground.

With the completion of the last step, your circuit should be finished. TO test it just make a loud noise near the microphone. Depending on the make and model of your microphone, the sensitivity could be different. Once the microphone detects noise, the LED should switch to on, and another noise will make it turn off.