This simple circuit was found in a Japanese magazine in 1967. The circuit is listening on a headset and the coil is 50 + 50 turns of wire 28 or thinner on a ferrite rod.
This complex circuit with many digital components measures inductances in 6 ranges ranging from 100...
This circuit triggers a photographic flash when the microphone picks up a sound. The SCR can be...
This simple MW radio circuit with two transistors was obtained in an Argentine publication from...