17-10-2017, 03:16 PM
This circuit is designed to alert the user when an intruder enters the house. If there is an obstacle in front of the IR sensor, it generates an interrupt signal. This interrupt signal is given to the speaker to alert the user.
Principle of Super Sensitive Intrusion Alarm Circuit:
The IR transmitter always emits the IR (Infrared) rays that must be received by the IR receiver. When there is an obstacle in front of the IR sensor, the transmitted infrared rays are reflected back into the infrared receiver. The Op-Amp output is high when the IR receiver receives the reflected IR rays. This output of the operational amplifier is connected to the RESET pin of timer 555.
The output of the timer 555 is low when the input voltage applied at the pin 4 of the timer 555 is low.
When the input voltage at the pin 4 is high, then the timer 555 produces the frequency that can be adjusted by the different combinations of values of the resistors R1, R2 and the capacitor C3.
• Obstacle Present → IR receiver receives IR rays → Optical amplifier output → 555 RST High Pin → Speaker produces sound.
• No obstacles → IR receiver does not receive lightning → Optical amplifier output is low → RST button is low → No sound
The NE555 output is filtered through the 1uF capacitor and fed to the speaker.
Many IR sensors are organized at home in different places. The outputs of all these sensors are given to the RESET pin of common timer 555. When any sensor detects the intruder, the reset pin of timer 555 becomes high and the speaker will produce the sound.
Super-sensitive intruder alarm circuit diagram:
![[Image: Super-Sensitive-Intruder-Alarm-Circuit-Diagram.jpg]](http://www.electronicshub.org/wp-content/uploads/2014/06/Super-Sensitive-Intruder-Alarm-Circuit-Diagram.jpg)
It can be understood in the following video: