This approach alarm circuit was found in the September 1970 Radio Electronics issue. The 1 mH coil is wound on a ferrite rod. The relay is 12 V sensitive.
This circuit is from a documentation from the 70s. The circuit uses logic gates of the time, which...
Found in the July 1968 Supertena Bulletin of a Popular Electronics, this receiver makes use of the...
The circuit shown was found in the February 1994 issue of Electronics Now magazine. The circuit...