amplifier timer

Posted on Feb 7, 2014

This circuit turns-off an amplifier or any other device when a low level audio signal fed to its input is absent for 15 minutes at least. Pushing P1 the device is switched-on feeding any appliance connected to SK1. Input audio signal is boosted and squared by IC2 A & B and monitored by LED D4. When D4 illuminates, albeit for a very short peak, IC3

amplifier timer
Click here to download the full size of the above Circuit.

is reset and restarts its counting. Pin 2 of IC3 remains at the low state, the two transistors are on and the relay operates. When, after a 15 minutes delay, no signal appeared at the input, IC3 ends its counting and pin 2 goes high. Q1 & Q2 stop conducting and the relay switches-off. The device is thus completely off as also are the appliances connected to SK1. C5 & R9 reset IC3 at power-on. P2 allows switch-off at any moment. Needing to operate a device not supplied by power mains, use a double pole relay switch, connecting the second pole switch in series with the device`s supply.

Leave Comment

characters left:

New Circuits



Popular Circuits

Simple Microphone Mixer
Proximity Mask Head (A2045) Manual
Understanding FM transmitter circuit
Schematics Digital Blood Pressure Meter
TDA Amplifier Circuits
DAC with WM8740
Simple Robot That Drives Forward and Back
Radio receiver GEOLOG circuit diagram
STK4040x1 made HI-FI amplifier circuit