This 80's circuit uses a germanium transistor like the AC121. The circuit has an output transformer of the type found on many transistor radios of the time.
This 1995 circuit uses interruption sensors or NC connected in series in any quantity. With the...
This circuit, suggested by a 1975 documentation, detects an electrical discharge in a storm by...
Found in an old Electronic Design, this circuit provides an output voltage that is the absolute...