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 2002 circuit uses many more electrical components than electronics. The keys are common, and...
This circuit provides an output voltage approximately 2 times that of the input voltage. The...
This circuit was suggested by National Semiconductor in its 1994 Linear Applications Handbook. The...