Found in a documentation from the 70s, this circuit can be implemented today with ease. The relay is of the alternating current type.
November 2016 - Maxim's MAX30003, an Analog Front End (AFE) for biopotentials with clinical grade...
This receiver was found in the Radio Electronics magazine of March 1953. It tunes to the medium wave...
Audio signals can be produced by this circuit. Frequency range is determined by C1 and adjusted by...