Night Security Alert

Description

This Night Security Alert Circuit explains the principle of operation of LDR (light dependence resistor). LDR is a device whose sensitivity depends upon the intensity of light falling on it. The Night Security Alert is a resistance of LDR decreases when the intensity of light falling on it increases and vice versa (resistance increases when the intensity of light falling on it is decreases). In the dark or absence of light, LDR exhibits a resistance in the range of megaohms, which decreases to a few hundred ohms in the presence of bright light.

The Night Security Alert Circuit is a popular 555 timer IC is used. The 555 IC operates as a comparator with pin 1. If pin-1 is connected, the output will go high. So small change in voltage of pin 2 is enough to change the output state of pin-3 from 1 to 0 and 0 to 1. The output has only two states high and low and cannot remain in any intermediate stage. In the event of a thief trying to open the door at night, the LDR will create a sound through a buzzer when their light falls on it.