This circuit is from a 1977 Radio Shack manual. The photocell is an LDR and the operational one is a 741. Components with non-standard values can be approximated.
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....