Infrared intrusion barrier

Description.

Here is the circuit diagram of an infrared intrusion detector. Whenever a trespasser cuts the invisible infrared beam an alarm sound will be raised. The arrangement consists of a receiver circuit and a transmitter circuit.

The transmitter circuit is based on two TLC555 ICs (IC1 and IC2). The first 555 (IC1) is wired as an astable multivibrator operating at 300Hz.The second 555(IC2) is also wired as an astable multivibrator operating at 36 KHz which can be adjusted by using POT R4.The output of IC1 is given to the reset pin of IC2. So the output of IC2 will be a burst of 36 KHz pulses modulated by a 300Hz signal. In simple words, the output will be a burst of 36KHz pulses with a spacing of 3mS in time. This signal is fed to the base of Q1 which drives the IR LED to transmit the waveform.

The receiver stage is based on a TSOP1836 (IC1) IR receiver and a TLC555C timer IC1. When the IR signal is falling on the TSOP1836, its output will be low and this prevents the TLC555C from oscillating. This is because the output of TSOP1836 is connected to the reset pin of TLC555C and this makes the reset pin low as long there is IR waveform falling on the receiver .When the IR waveform is cut by a passing intruder, output of IC1 goes high and makes the IC2 to start oscillation. The piezo buzzer connected at the output of IC2 sound to indicate the intrusion.

Circuit diagram (Transmitter and Receiver).

Notes.

• Transmitter and receiver can be powered from 5V DC.
• TLC555 ICs must be mounted on holders.
• Adjust POT R4 to get exactly 36KHz.The TSOP1836 responds only to 36KHz IR signals. So this part is very important.
• Transmitter and receiver must be assembled on two different PCBs.

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INFRARED MOTIN DETECTOR

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 photo transistor Q1 .At normal condition ie; 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 circuit may get false triggered.
• POT R5 can be used for sensitivity adjustment.

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