This circuit consists of a stereo audio compressor. We found it in Radio Electronics magazine from October 1968. The circuit uses an opto-coupler made with a neon lamp and LDR.
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...