This alarm circuit with NC sensors in series was taken from an article in Radio Electronics magazine from May 1971. The SCR can be any of the 106 series.
We present a circuit formed by six voltage comparators. Each comparator will analyze the voltage...
This circuit can generate time base signals from 5 to 1500 Hz. We find it in a documentation about old neon...
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...