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.
Found in a Popular Electronics from the 90s, it applies to the old answering machines that used...
The operation of this circuit is not common today, but equivalents can be experienced. The circuit is...
This circuit was found in an English publication from 1989. The integrated circuits are of the...