Infrared Alarm Barrier Circuit

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.


Join the conversation!

Error! Please fill all fields.
  • Pistike

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

  • tan

    what is the alternative for BAT85?

  • rick

    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.

    • kyaw

      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

  • akhila

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

  • Diogene

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

  • Faraz

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

  • aaron

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

  • tope

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

  • T.K.Hareendran

    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!

  • vipin tyagi

    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

Looking for the latest from TI?