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How do IR remote controls work so well?

Discussion in 'Electronic Basics' started by Kasterborus, Jan 21, 2008.

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  1. Kasterborus

    Kasterborus Guest

    I've been experimenting with detecting reflected laser pulses in the
    532nm (visible green) wavelength. By modulating the pulses and tuning
    a receiving circuit I've been able to get the detector to work over a
    distance of several feet in a darkened room.

    I'm thinking that mixing infrared laser light with the 532nm and using
    IR photodetectors. Would this allow for more ambient light in the
    room?

    My TV remote control seems to do very well in detecting pulses from an
    IR diode, even in bright sunlight - is there more to it than just the
    shift to the IR spectrum? Or is the modulation a key factor in the
    detector being able to "see" the remote?

    Dave
     
  2. Guest

    The modulation is a big part of it. The remotes I've worked with
    (Samsung and Sony) both send 32 bits total and the last 8 bits are
    sent twice, the second time inverted which helps data verification.
    Both remotes continously repeat the 32 bit sequence as long as a
    button is held so there's a good ghance some af the commands will get
    through.

    GG
     
  3. Bob Monsen

    Bob Monsen Guest

    I guess it depends on the detectors. Some may filter out other frequencies.

    For example, the TSOP11xx set of photo modules are very good at filtering
    out light at other wavelengths. That is how IR works so well for TV, for
    example; they filter everything except the 950nm IR between 900nm and 1um
    down to -6db, and then only respond to modulation frequencies between 0.95
    and 1.05 percent of the target modulation (ie, 40k).

    See the figures in this data sheet:

    http://www.tranzistoare.ro/datasheets/restul/305097_DS.pdf
    Again, the detector is tuned to both the frequency of light, and also to the
    modulation frequency of the signal.
     
  4. Jamie

    Jamie Guest

    They have a IR passive filter that helps reduce non IR light .
    also, the modulation scheme has a lot to do with it.

    Normally common mode input receivers are used with capacitor
    offsets on one input so that the DC component can be nulled out
    while the AC component will be visible with high gain..
    they may even have a band pass filter after that stage..

    This means, your modulation scheme must use a steady stream
    of pulses for 1's or 0's.




    http://webpages.charter.net/jamie_5"
     
  5. John Fields

    John Fields Guest

     
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