Design and Construction of Security Dark Activated Switch

Abstract

The burglar alarm system is  based on the principles of the photo resistive detector (LDR) whose electrical resistance is usually very high up to 1mΩ or more when  dark and falls below to as little as a few hundred ohms when the detector is illuminated. When there is an intruder, due to his/ her shadow, the detector’s surface is dark or not illuminated causing the electrical resistance of the detector to become very high making the voltage of the voltage comparator (IC) to be higher than the reference voltage terminal causing its output to be high this then causes the alarm actuate/activate the alarm which then sounds to alert the household of an intruder.  The whole process continues as long as there is constant power supply.