Written in an article in Radio Electronics magazine in April 1987, this circuit triggers an alarm via a relay. Details of the sensor are given in the article.
Of course, with a change in the cable length, the frequency can be changed as long as it is within...
This circuit is basically the same configuration as the previous one with a power stage with...
Using the ZN1034E which reaches 19 days interval, this is a simpler circuit which can be...