This circuit uses a resonant reed relay to recognize the frequency of an input signal. Adaptations can be made to obtain functioning as a shield. The circuit is from 1965 documentation.
This circuit, which can be used safely, has been obtained in a 1987 documentation. It consists of a...
Suggested by Fairchild in a 1980s publication, this multiplier uses operational amplifiers from that...
We found this circuit in an old 1980s documentation. The circuit can be implemented with modern...