This shield circuit with an optical coupler was found in an 90s EDN. The circuit can be used with voltages from 0 to 600 V with the indicated component values.
Disabling this circuit from a 2002 documentation can only be done by pressing 4 keys in a correct...
This circuit was found in a 1979 magazine. We can use any JFET like MPF102 or BF245. The relay is 12 V...
This circuit was obtained in a 90’s documentation. The operational amplifiers are from that time....