This alarm circuit was found in the July 1992 Radio Electronics magazine. The circuit uses a small power stage for the speaker and has the sensitivity adjustment at R5.
This circuit was obtained from a Popular Electronics of the 80's. It is set to a certain pulse...
Found in an Electronic Design from the 80s, this circuit generates a 500 Hz signal and can be used...
August 2016 - It can be purchased from Mouser Electronics the new digital isolators ADuM120N and...