Sound-Operated Switch

Posted on Dec 4, 2012

This sound-operated switch will sense the ring of the phone and translate this to a lamp that will go on and off. The

Sound-Operated Switch
Click here to download the full size of the above Circuit.

amplified signal across R2 reaches D1 through capacitor C2. The rectified audio signals provide a negative bias for Q2, a pnp transistor. This causes Q2 to conduct so the current that triggers SCR1 is provided at the gate. Potentiometer R4 sets the sensitivity. R3 and C3 delay the operating voltage for Ql so that the circuit will not be triggered on by the sound of the on/off switch, SI or by the current surge. Set the lamp atop a TV receiver, turn it on and set the potentiometer so that a finger snap at two feet will trigger the lamp on. Place the speaker close to the telephone and give it a try.

Leave Comment

characters left:

New Circuits



Popular Circuits

Analog to Digital Conversion
Metal Detector Circuit Schematic using Beat Frequency Oscillator (BFO)
circuit diagram of remote control tester
waterpump safety guard for fish
3v fm transmitter circuit
Preamp Protection
NAND gate S-R flip-flop
Allarm antifurto
Mini FM Transmitter
Optical Pulse Generator
NE555 triangular wave loading system, square wave generator circuit
Relative humidity digitizer circuit diagram