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TSOP1738 when used as a Beam Break Detector

    Blog entry posted in 'General Purpose Circuits.', November 30, 2011.

    When using the TSOP1738 IR Receiver Module in a Beam Break application it is necessary to interrupt the 38KHz signal being generated by the IR Emitter.
    An example is a 'People In/Out Counter', where the beam break is used to detect a person entering or leaving a room.

    If the TSOP detects a continuous 38KHz pulse if will consider it as a interference source and will not work as expected.

    The attached circuit transmits at 38KHz, with a break in the transmission at approx 650Hz.

    This gives a group of ~45 IR pulses, with a gap equal to ~ 20 pulses.

    The circuit shows two options for the LED IR driver.


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