This shield circuit, from a documentation from the 70s, employs an optocoupler with two SCRs to control a small load of 1.5 W.
This circuit provides both frequency and voltage division. The circuit was found in a 1966...
This circuit visually indicates that a high voltage is present in an outlet or other point. The...
Used with infrared remotes at the time, this circuit was found in a 1991 RE Experimenter Handbook....