Found in a 1966 documentation, this “coin finder” uses components from the era operating at 2.1 MHz. The circuit uses an audio amplifier for detection.
This circuit was found in a 1992 documentation consisting of a two-channel active filter for audio...
This is a simple solution for old vehicles that do not have this feature, having been found in a...
We found this circuit in the March 1999 issue of Electronics Now magazine. The indicator used is...