Found in a PE Hobbyst Handbook of 1991, this circuit was originally proposed to time photographic baths in developing rooms but can be used for other purposes. The circuit beeps at 30-second intervals.
This circuit was found in the March 1997 Electronics Now magazine. It uses a common analog...
This tunnel diode circuit was found in American documentation from 1966. The tunnel diode is the...
This circuit was found in the comparator's own documentation, serving others in the same series. The...