Infrared intrusion barrier

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).




  • 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.