Description.
Here is the circuit diagram of an infrared motion
detector that can be used to sense intrusions. Infra red rays reflected
from a static object will be in one phase, and the rays reflected from a
moving object will be in another phase. The circuit uses this
principle to sense the motion.
The IC1 (NE 555) is wired as an astable multivibrator. The IR diode
connected at the output of this IC produces infrared beams of frequency
5Khz. These beams are picked by the infrared sensor, photo transistor
Q1. At normal condition, that is, when there is no intrusion the output
pin (7) of IC2 will be low. When there is an intrusion the phase of the
reflected waveforms has a difference in phase and this phase difference
will be picked by the IC2. Now the pin 7 of the IC 2 goes high to
indicate the intrusion. An LED or a buzzer can be connected at the
output of the IC to indicate the intrusion.
Circuit diagram with Parts list.
Notes.
- Comparators IC2a and IC2b are belonging to the same IC2 (LM1458). So the power supply is shown connected only once. No problem.
- When there is disturbance in the air or vehicles passing nearby, the IR motion sensor circuit may get false triggered.
- POT R5 can be used for sensitivity adjustment.
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