The above circuit uses a 555 timer U1 in mono stable mode. If once push button is pressed, it drives pin2 of timer momentarily to ground that triggers the 555 to deliver a high output at pin 3 to ...

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 ...