About: iam udayakumar,working as design engineer.

IR based security alarm circuit can detect any movement and trigger the alarm. This circuit is very useful in homes, banks, shops, restricted areas where an alert alarm is needed on any movement. This circuit is based on IR sensor where an IR beam is continuously falling on a photodiode, and whenever this Infrared beam breaks, by any kind of movement, alarm is triggered.

IR sensor consist an IR LED and photodiode, in which IR LED emits IR radiation and photodiode detects the radiation. Photodiode conducts current in reverse direction, whenever light falls on it, and voltage across it changes, this voltage change is sensed by voltage comparator and generates output accordingly.

In this IR based security alarm circuit, we have placed IR LED in front of photodiode, so that IR light can directly falls on photodiode. Whenever someone moves through this beam, IR rays stops falling on photodiode and Buzzer start beeping. Buzzer automatically stops after some time, as buzzer is connected to 555 timer in monostable mode.
This kind of Alarm can also be build Laser light, (like Laser Security Alarm Circuit) but the benefit of using IR sensor is that IR light in invisible while Laser is visible. Although both are useful and have different scope.

Step 1: Pcb

pcb for TX and RX

Step 2: Block Diagram

block diagram of tX and RX ckt,


IC1,IC2 AND IC3 are created the different frequency. Ic1 is created the low frequency 250hz for control IC2 and IC 2 will create the carrier frequency 37-kHz .in the section IC1/4 is created the low frequency of 10Hz .all frequency will mix by IC 1/3 and transferring to tr1 for amplifying anf presenting by led infrared .jumper j is used for display the operation of transmitter section

Step 4: Receiver and Control

the module receives the infrared light . ic in the module detects the low frequency through the out terminal and transmit to TR5 and TR4.this low frequency is amplified by TR4 and TR5 .the collector of TR4 is connected passed on the switch ,as the switch is turned to pos 1,when someone blocked the ckt IC1 function to delay input about 30 sec as well as LED3 light IC1 stop function and LED# is unlighted .THE IC2 works and LED4 is lighted within a minute If the sw is turned to pos 2,when the ckt is blocked,IC1 does not function and LED3 is unlighted so input time is noot delayed .The input of IC2 is transmitted to TR9 to drive the relay to function.Everytime that IC3 eorks ,the relay will also function .the out spot of the relay is connected to a warming alarm device .the ckt delays approximately a minute .after that LED2 lights resulting IC1 and IC2 to works whenever the ckt is blocked .juper Jis used for set LED5 to display the receiving of infrared module.



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