This 1967 Raytheon circuit uses a Raystor, an optical coupler with a lamp and an LDR. The circuit can be adapted to use another type of coupler.
This original 70s RCA circuit appears elsewhere on this site, including original RCA...
This circuit was found in a British documentation from 1969. It can be implemented with modern...
In the figure we show an application in which the 4093 excites a stage with 4 transistors in the...