This sensitive three-transistor circuit was found in Electronics Now magazine and is earphone-readable. The tuned range depends on the coil.
This circuit was found in a 1977s English magazine. The transformer is 15 V x 500 mA but...
This circuit is from a 1997 publication. In it, the circuit uses a light emitter that points to a...
This circuit, from the 1990 Motorola Dataar Databook, can use any LM139 series comparator. The circuit...