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motion detector alarm circuit

Motion Detector Alarm Circuit

This motion detector alarm can detect a moving person from a distance of 1 meter. It uses a dual IR Transmitter-Receiver module HOA1405. When the sensor detects the reflected IR rays, alarm will sound for 2 minutes. The circuit can be modified for various applications including AC operated alarm systems.

Schematic of the Motion Detector Circuit

motion detector alarm circuit

IR Dual Reflective Sensors

The main element in the movement detector circuit is the dual IR reflective sensor HOA1405. It has a built in IR diode and an NPN Photo transistor. The black covering of the module filters visible light rays and allow IR rays to fall on the Photo transistor.

When the Photo transistor receives IR rays, it conducts. The collector of the Photo transistor is connected to the trigger pin2 of a short duration Monostable timer built around IC NE 555.

With the given values of R4 and C2, output of IC1 remains high for two minutes to light LED and to activate the buzzer. In the standby state, the photo transistor inside the Dual Reflector module remains non conducting since its base is not getting IR rays.

When a person comes in front of the module, the reflected IR rays will trigger the Photo transistor and its Collector goes to ground potential.
This triggers the Monostable and Alarm sounds.

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