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.
This simple PWM control was found in American documentation. We can use any power transistor...
Found in a 303 Circuits from the 90's this circuit can use the lowest current range of a common...
The figure shows how to implement a filter against interference caused by the switching of a...