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.
We found this circuit in an old publication from Argentina. The relay must be of the sensitive type,...
Found in a PE Hobbyst Handbook of 1991, this circuit was originally proposed to time photographic...
We found this circuit in a 2005 Linear Technology manual. Observe the component values and...