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How do IR LED work?

Discussion in 'Electronic Basics' started by Ricky Spartacus, Oct 15, 2003.

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  1. I am trying to find out what`s behind an infrared LED output. When the
    IR LED`s terminals are hooked to an analog oscilloscope the waveforms
    are square. The waveforms does not change in appearance when other
    buttons on the remote are push. It seems any buttons produce the same
    patterns. Does this mean I need to use another kind of probe or just
    means I don`t know how remote control works?
  2. You may have the horiz.. sweep set too fast. This would show you the
    carrier (30-40khz) which would look like it didn't change. Set the
    horiz. sweep to about 1-2mS/div, this should let you see how the carrier
    is turned on and off to modulate the data onto it.

  3. Baphomet

    Baphomet Guest
  4. Jim Large

    Jim Large Guest

    It's been many years since I did the same experiment, but I
    seem to recall that the remote I was looking at way back when
    would send a very short code burst to identify the key,
    followed by a continuous waveform that seemed to say, "and
    he's still holding it down." The continuous waveform was the
    same for most keys, except one or two (like maybe the power
    key) that sent the code pattern over and over.

    -- Jim L.
  5. Could very well be, IIRC some do work that way. Most remotes fall into
    one of two categories: RC5 and RECS-80. One is kind of a PWM system
    where 0's are shorter than 1's. Others use a manchester scheme that's
    real easy to send, but a pain to decode in software. Sony uses a fairly
    simple PWM type protocol.

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