Infrared Alarm Barrier Circuit


Posted on Feb 5, 2014

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. The transmitter and receiver circ


Infrared Alarm Barrier Circuit
Click here to download the full size of the above Circuit.

uits 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...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Xenon Strobe Light
    Buffered breakout box
    Tone-actuated relay
    Voltage Multiplier
    Transistor Checker Circuit
    Infrared (IR) Proximity Detector
    TDA7000 FM Radio IC Test Circuit and Datasheet
    Video/Audio Wireless Transmitter
    slow down a fuel pump
    Magneto Remote control switch circuit diagram
    Simply by remote control law circuit diagram
    555 lights remind



    Top