This circuit was suggested by General Electric in a 1965 documentation. The circuit can be implemented with equivalent SCR.
PIC18F “K40” Features Intelligent ADC with Filtering and Signal Analysis Capabilities Ideal for...
This circuit was found in a Radio Electronics from 1970. The coupler with LDR is from that time,...
This circuit is from an 80's documentation. The transistor can be any general purpose PNP and the...