1 Sound controlled circuit

The idea of this circuit is when there is sound the circuit will activate or trigger some other circuit. From the circuit below, the sound is picked up by the microphone. This sound is amplified and causes the transistor Q2 and Q3 to turn on and off. You can connect any load across point a and b in transistor Q3.
simple sound activated circuit
Part List:
R1 - 1.2 kilo ohms 1/4W
R2 - 1 Mega ohms 1/4W
R3 - 5.6 kilo ohms 1/4W
R4 - 1.2 kilo ohms 1/4W
C - 100nF capacitor
Q1, Q2 - 2N2222, 9013, or any similar NPN transistor
Q3 - 2N2907, 2N4403, 9012, or any similar PNP transistor
Mic - electret microphone
Bat - 4.5V to 6V battery
LOAD - LED, motor, bulb or any load (see possible loads below)

Part List jpg: Click to enlarge

electret microphone
2N2222 or 9013 pinouts
2N2907, 2N4403 or 9012 pinouts
Possible loads
You can replace the LOAD marked a and b in circuit above by the following circuits below.
Different loads
Part List:
1. bulb - any 2.5V to 4.5V bulb rated 50mA to 200mA
2. R - 220 ohms 1/4W
    LED - red, yellow, or orange LED (3mm or 5mm)
3. motor - 3V to 6V small DC motor


  1. Thanks for posting this design - I have couple of questions.

    Would this be sensitive enough to turn a load of 30 leds on and off as if it were responding to the music or is it more of it will turn on to noise, then turn off again until another noise?

    Also, if I wanted to insert a switch to bypass the microphone and send power straight to the load, where would it be best put?

    Thanks a lot.