This circuit for very long-time intervals was found in the March 1993 Radio Electronics magazine. Times of several days or even weeks can be achieved depending on the value of C1.
This circuit is from a documentation from the 60s. The circuit can be built with transistors like...
Found in a 1966 General Electric documentation, this dimmer should only be used with incandescent...
To control relays safely with double insulation, we suggest the circuit in the figure. The optical...