This sensitive circuit for triggering relays was found in an old English publication. It works with alternating signals applied to its input. Transistors are general purpose types.
This circuit uses a TL071 to differential amplify the signals from a microphone and thus reduce...
We found this circuit in a 1995 publication. It makes use of infrared LEDs of the type existing at...
This circuit is from September 1984 Radio Electronics. The frequency can be changed by changing C1 and...