Found in Electronics now from the 90s, this circuit uses a sensor from the time, which is difficult to find today. The circuit activates a sonalert-type buzzer.
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...