This alarm circuit triggers when S1 opens. The circuit from a January 1975 Radio Electronics magazine can be used with interrupt sensors connected in series.
This circuit appeared in a noverber 1962s Practical Electronics. The magazine is no more, but the...
This circuit is from an American 80's documentation. The integrated circuit is from the time and...
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We...