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.
The integrated circuit used in this project is unusual. However, we can take advantage of the...
This alarm, found in a 2002 documentation, uses several sensors and has a 12 V supply, not...
This instrument was found in a publication for radio amateurs in 1973. The tuned circuit consists of...