Found in a 1992 book, this circuit is intended for operation with audio signals. Equivalent operational amplifiers can be used. The optical coupler is an unusual type today.
This simple metronome, from 1985 documentation uses only transistors and has two settings. For...
This circuit is suitable for modulating AM transmitters. The circuit is from a 1977 radio amateur...
This flasher was found in an old Hands On, but uses common components. The optocoupler can be...