Based on Radio Shack 276-137, this circuit was found in the December 1995 issue of Electronics Now magazine. The circuit drives an LED but could use a relay instead.
This bargraph circuit is from an ancient American documentation. It indicates the charge state of...
This circuit monitors the current of a series of 40 V lithium battery packs connected in series....
Of course, the range of this transmitter found in a 1992 documentation is not exactly 4 km, as it...