This circuit was found in a Popular Electronics from the 90s. The counter circuit is not common today. The circuit can be programmed for hourly intervals, according to the values of R4 and C2.
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....