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 configuration from the 1970s can be applied to modern equivalent operational amplifiers. The...
This simple alarm using only transistors was found in a 1990 publication. It can be powered by D...
The circuit presented was found in the 1994 National Instruments Linear Applications Handbook and...