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    This infrared alarm barrier can be used to detect persons passing through doorways, corridors and small gates. The transmitter emits a beam of infrared light which is invisible to the human eye. The buzzer at the output of the receiver is activated when the light beam is interrupted by a person passing through it.

    Infrared Light Alarm Transmitter Circuit Schematic

    Infrared Alarm Barrier Receiver Circuit Schematic

    How to make an infrared barrier alarm

    The transmitter and receiver circuits of the infrared alarm system shown here have been designed for a range of several meters, almost independent of ambient light conditions. Only in the rare case of the receiver sensor being exposed to bright, direct sunlight, some screening measures have to be added.

    The transmitter does not emit a continuous infrared signal, Rather, it is modulated, that is, the 36-kHz carrier used to pulse the IRED (infrared emitting diode) on and off is itself switched on an off at a rate of about 300 Hz. The reason for doing so is that most infrared sensors, including the ones suggested in the diagram do not respond very well to continuous incidence of infrared light. Switching the IR source off, even for a small period, allows IR detectors to ‘recuperate’, and so optimise their ability to minimize the response to ambient light.

    The transmitter consists of two oscillators built around the ubiquitous 555 IC. Here, the current-saving CMOS version TLC555 (or 7555) is used. Alternatively, the two 555’s may be replaced by a single TLC556 (or 7556). IC1 is the 300-Hz generator, IC2, the 36-kHz source. The IRED type LD274 is pulsed at a relatively high peak current via driver transistor T1. If in your application the distance covered by the IR beam is relatively short, the value of resistor R5 may be increased to save on current consumption. Preset P1 is adjusted for a carrier frequency of 36 kHz exactly (failing test equipment, adjust it for optimum range).

    The receiver is equally simple and also based on a CMOS 555. As long as the sensor picks up infrared light from the transmitter, the reset input of the 555 IC is held low and the buzzer is silent. Components D1 and C2 act as a low-frequency rectifier to cancel the effect of the 300-Hz modulation on the transmitter signal. When the infrared light beam is interrupted, the oscillator built around the 555 is enabled and starts to produce a warning tone.

    Finally, the test values indicated in the infrared barrier alarm circuit diagram are average dc levels measured with a DVM, under light/no light conditions. In fact, most test points carry rectangular or sawtooth waveforms.

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    47 Responses to "Infrared Alarm Barrier Circuit"

    1. Hi, can i know why the IC1 is produce 300hz?
      f =1.4/[(R1 + 2R2) × C1]
      from the formula
      substitude the value
      R1= 4.7k
      Frequency should be 683.92hz

    2. Hi,

      Do you know what is the maximun distance between the transmitter and the receiver?

      Thank you

    3. I am building these circuits but the Infrared Light Barrier Receiver isn’t working as is shoudt be.Can i have a reponse if anyone now wy it doesn’t work.
      Or has anyone a reponse wat to do.

      Thank you

      • Important checkpoint:
        You should not use just LM555 series. It does not work under 4.5 volt.
        So, you can use TLC555(2-15volt) or TS555(2-16volt) series only.

    4. Hi,
      The theoretical frequency will differ from actual. because you have to consider the tolerence of capacitor and resistsnce used.
      If the circuit is not working, most probably one would have connected the BD140 transistor or the IR sensor pins in wrong way.

    5. can anyone tell me what is this preset p1 in this ckt and what is its function

      • D.Mohankumar says: on November 4, 2010 at 3:48 am

        Preset P1 is the small variable resistor. Its value shown is 25K.It adjusts the frequency of the Astable 555 to give desired output frequency to drive the LED.By changing the wiper of preset, it is easy to set the correct frequency of IR beam

    6. i want to build this circuit, can we use NE 555 instead of TLc 555 ? how can we adjust the friquency without CRO. tell me this plz

    7. TLC 555 is a CMOS version of 555 timer & use of NE555 as an alternative is not recommended.Adjusting frequency without a CRO/Frequency counter is not possible.Anyway,you can adjust it using trial&error method ie switch on receiver and then tune transmitter so that they are perfectlylocked!

    8. I want to know more about how to build a security alarm

    9. i like to build this circuit…’got to gather all the components…

    10. what do the vaules like 2V5, 2V6 (transmitor circuit) means??
      and same is the quiry for receiver circuit i.e values stating 4V92…

    11. Can anyone tell me the equivalent of the LD274 and the transistor BD 140?

    12. what is need of bd140. what is the maximum distance between transmitter and receiver

    13. Please contact us for more detail ,also we have different types of passive infrared radiation detector like active beam infrared detector/passive motion detector/combustible gas detector/smoke detector/Glass break detector/heat detector.
      And wireless home alarm system with their accessories.
      CCTV camera including waterproof camera and high speed dome camera.
      We can also Supply spare parts and accessoires for alarm system like alarm siren,door magnetic contact,sound&flash light ,emergency button and their bracket.

      • Can anyone suggest me what IC i should use to design 10 emitting diode instead of one? if i use same circuit design for 10 leds, it could be complicated and not able to produce require output.

        Many Thanks

    14. what is the alternative for BAT85?

    15. vysakh,still need the pcb drawing? home made ​​but it works,if you need …

    16. any one have this circuit by proteus program

    17. for tan :1N5819

    18. how long does the alarm sounds when i just interrupted the signal for 1 sec?\
      pls repz ASAp

      • Out of the box, these worked percfetly in our Nissan Pathfinder. I was so pleased & relieved I would not have to hassle with returning them through the mail. The only (minor) thing I don’t like about them is that they don’t adjust small enough for very little heads. They should be fine for my 7 year old, though. MUCH better than wasting time trying to search for the same kind that came with our vehicle no need!!

    19. hi,do you know the distance between the receiver and the transmitter cant operated normally.thanks

    20. Looks Great do you have pcb design or veroboard design you could send to me.
      Many Thanks

    21. Hi still wainting on reply

    22. Thanks for posting the article “Infrared alarm barrier circuit”, (using 555 Ic’s) Works great. I see u also posted a ” IR High Power Transmitter ” version using a 4047 IC. Would this work with the other Receiver circuit?

      • Jim Keith says: on July 28, 2012 at 2:16 pm

        This should also work with the receiver on this project, but the range will probably be less–while it perhaps offer more average power, the peak power is lower than the transmitter indicated in this project. The peak power of the short pulses is what gives it good range. The object is to set the transmitter for sufficient power, but not excessive power as any additional power serves only to increase the LED temperature rise–the LED may already be operating close to its maximum temperature rating.

    23. Hi all, Can anyone please help me tune circuit regards component P1. I do have an oscilloscope but don’t know which pin to connect it to.

    24. Reduce the resistance of P1 until the receiver fails to respond–this provides minimum output pulse width and minimum LED power dissipation–observe short voltage pulses at collector of T1.

      The oscilloscope can be used to focus the beam accurately by observing the voltage across C2 while rotating the the transmitter in either axis–tune for minimum voltage of the sawtooth waveform–if it hits zero V, further reduce the value of P1. Then rotate receiver while observing the same point to get minimum voltage again–then fix orientations of both transmitter and receiver.

      • Thanks Keith for your comments, I best I could manage was to do a bit of both of your suggestions, adjust P1 to zero ohm, & while RX is buzzing, start adjusting P1up. I did this outside (but with RX not in direct sunlight) & progressively adjusted P1 & separated units farther apart until I got a good 3/4m apart & RX stopped buzzing. I did try the CRO on T1 assumed the oscillating signal would vary in amplified from 1-5V but it didn’t. I’m out of my depth with that I think. The unit works well now so I’m happy with it. Thanks again.

    25. The receiver circuit is not working with NE555.Can it be solved by using TLC555.Plz reply and I will be obliged if u give any other solution.

      • In the Jaycar Catalogue page 56 under linear ICs, is an IC , called an LM7555. It works. There catalogue part number is ZL-3455

    26. I used an LM7555 from Jaycar Electronics, cat. ZL-3455

    27. Hello all tronics Gods, I’d like to make a vertical array of this circuit using about there or more pairs, mounted on ducting or the like. Only if all units are passed by should the buzzer be sounded. I’ve been into PIC’s before but have packed it all away for a while so hoping to do it with Gate Chips. Any heads up on how to would be appreciated.
      Thank you, bye 4 now.

    28. Regards my previous comments above, I meant to say an array of ” THREE ” units. Sorry about that.

    29. I built and works fine, I got a little more than 8 meters and got 12 meters with lens (can´t test longer due to phisical space limitiations), I will make a double barrier clonning r5 and d1 in the transmitter and r1, ic1, c1 and d1 in the reciver, connecting all d1 anodes together like an OR logic.

    30. I want a simple ir buglar alarm circut.. Please help..

    31. Will it work if water breaks the circuit??????

    32. it’s been a great learning journey via your correspondences! Congratulations to you all.

    33. I need to switch ON the LED(or buzzer) when IR beam is not interrupted by any object. Plz help me.
      Thank you

    34. s balasubramanian says: on December 5, 2014 at 7:45 am

      Sir , can you inform me this circuit will as ir proximity sensor or arrange me circuit for ir proximity sensor for sensing distance around 50cm

    35. According to Mouser, the IR emitter LD274 is obsolete. Osram recommends the SFH4544 as a replacement but haven’t tested yet.

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