Voice-Activated LED
Électronique / Electronic
NE5532

You can use a microphone to detect sound. Here we make a circuit that lights the LED when the microphone detects sound, using the speaker as a microphone.

Slide the switch to position OFF and assemble the circuit.

When you finish the wiring, turn on the power by sliding the switch to position ON. Then speak into the microphone-the speaker-or give it a light tap.

The LED flashes in response. Look at the schematic. IC 1 acts as a microphone amplifier,a noninverting amplifier with a gain of about 100.

IC 2 works as a comparator. Its positive (+) input terminal receives a reference voltage from the battery. The output of the microphone amplifier goes to the comparator's negative (-) input terminal. When this input voltage is higher than the reference voltage, the comparator's output level becomes low and the LED lights.