We found this solid-state relay circuit that can function as a shield in a Radio Electronics magazine from December 1989. The optocoupler is a phototransistor type.
This circuit has its application suggested in an alarm system. The circuit is from an old RCA...
Found in a 1967 RCA manual, this circuit uses components from the era that can be replaced by modern...
This circuit for voltages up to about 20 V was found in a 90s Popular Electronics. The LED can be...