This circuit detects when an audio signal exceeds a certain level or even occurs due to an object falling, a door slamming or other. The circuit is from a Radio Electronics from January 1980.
Found in old English documentation this circuit can be made with a BF245 or equivalent. Coils are...
This circuit is indicated for the generation of signals in the 40 meters range. The circuit was...
Carbon microphones are no longer used in most projects. However, finding one in the scrap metal, it...