We found this circuit in a Popular Electronics from the 90s. Transistors can be modern equivalents. Observe the high supply voltage.
This configuration makes use of an integrated circuit of the time having been found in a 1976 NASA...
This circuit activates an old cassette recorder when the phone is being used, thus making it...
This circuit came out in a Frances Toute LÉlectronique magazine from July 1978, but can still be...