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.


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  2. Are you sure pin numbers in receiver TSOP 1836 are correct ? I recall pin 1 is for ground

  3. Sir.
    i really want to assemble this circuit and make it surround my yard, but i was thinking that, i may use mirrors to extend the transmission of the IR to the receiver, will it work this way??
    then how can i replace the Buzzer and use a relay that may switch on something different of my security choice, is it possible to finally adapt a relay instead of the buzzer??
    please sir i really need your help to complete my home project….my email is .
    I look forward to read from you.

  4. juma hassan

    hellow! iwant to try to build that infrared cct so i need more instructions.

  5. will this work on 4 or 4.5 v battery?,need quick replies please

    • Sherin Varghese

      A 555 timer IC will work for any voltage between 4.5V to 15V.. But it is advisable that u go for a 5V regulated supply…….

  6. i need pin diagram and abstract for infrared intrusion barrier

  7. i want a circuit which detects cell phones when it is switched off.

  8. seetharaman

    Hi Hasi the buzzer can work continuously till the power supply 5 volt is available, no need for any modification.

  9. did the buzzer give the sound for a long range of time?or for a short range of time? can we make it for a long range by using a cd4001 ic and switches

  10. ihsan khan

    respected Sir;
    i have assigned the project “PROCESS CONTROL MACHINE”,
    will u plz help me out in this case,
    my mail adress is
    wating fr your response

  11. seetharaman

    Hi TMR with the transmitter on, check whether receiver IC1 pin 1 is going low. Try by adjusting Pot R4 for minimum voltage at Pin1. Once this is achieved still if buzzer is not stopping add a diode(say 1N4001) in series with R2 and Pin no. 4 of IC2 in the receiver circuit. This should solve your problem.

  12. i tried that circuits, transmitter and receiver both of them working, but i cant tune R4. IR led is working i can see that with webcam, receiver creates sound bur i can’t tune R4 clearly. buzzers sound change but never stop. what can i do? i tried 25K, and 47K for R4 trimpot but nothing changed.

  13. seetharaman

    Hi transmitter and the receiver circuits are ok. by adjusting R4 the system can be tuned to correct required frequency practically.

  14. i have 2 questions;

    1. is that circuit working? anyone worked before?
    2. i couldn’t find tsop1836 instead of that if i use 1838a and change pot R4 levels, will it work on 38 khz?

    thanks alot for interesting.

  15. I revised my statement above when IR falling the output about 2-3 volt and when cut off the output 6 volt.

  16. I have build the circuit and i have some question ?
    1. The transmitter section already tested and the range output is more than 2 meters, its good news. But 1st part – ic1, when i measure the output pin 3 of ne555 the signal is 600Hz , why not 300Hz ? is it problem ?
    2. The receiver section not completely build because in my local market is difficult to find dioda bat85 so i just connect it with a wire, And i used buzzer 6-15volt unless piezo buzzer. The result is :
    when IR falling on the TSOP1738, the output pin 3 about 6 volt and when cut off the output is about 2-3 volt . and buzzer still make a noise not quite. Any suggestion ?

  17. i cant find TSOP 1836….can i use normal IR sensors in place of it??
    can u please suggest me other R4 values if i use other TSOP ICs……….
    witing for your reply…

    • TSOP 1736 is good. Pin numbers change in that for Vcc, Gnd and Out so connect accordingly.

  18. I can not find TSOP 1836 , can it be exchanged with tsop 1738 ?

    • Operating frequency of TSOP 1836 is 36 KHz and TSOP 1738 has an operating frequency of 38KHz. So they can’t be directly replaced.
      In order to use TSOP1738, the operating frequency of IC2 in the transmitter section has to be changed to 38KHz by adjusting the POT R4.