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 obtained in an 1975 English publication. It is a voltage regulator circuit for...
In the figure we have an infrared receiver circuit using an operational 741. The circuit is an...
This circuit is suggested by National Semiconductor and makes use of the negative regulator LM2990...