This circuit was found in Ferranti's 1967 documentation. The circuit drives a 40 V relay, but it can be adapted to operate with sensitive lower voltage relays.
Carbon microphones are no longer used in most projects. However, finding one in the scrap metal, it...
This circuit produces a strong tone of audio or ultrasound, depending on the values of components C1 and...
This alarm from an old 1978 publication uses PNP transistors and driver and output transformers that are...