This circuit was found in a Radio Electronics from 1970. The coupler with LDR is from that time, but the circuit can be adapted to use modern components and act as a shield.
It can be obtained from Mouser Electronics, sensors (receivers) transmitters and benders for...
Suggested by General Electric in a 1965 documentation, this circuit can use the TIC106 as an SCR....
The circuit shown is from the 1994 Linear Applications Handbook from National Semiconductor. The...