This alarm with sensors in series and parallel was found in the 1995 Encyclopedia of Electronic Circuits. The number of sensors can be changed at will.
The Motorola MOC501O optocoupler has a complete amplifier inside the sensor, enabling the...
This circuit is suggested by the Texas Instruments manual of linear applications of the 90's. The...
This circuit was found in the Radio Electronics magazine of May 1990. The supply voltage depends on...