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why infrared??

Discussion in 'Electronic Basics' started by Ahmed Samir, Nov 6, 2003.

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  1. Ahmed Samir

    Ahmed Samir Guest

    Hi there
    Sorry if this question seems repeated or something but i have dont a quick
    web search and couldnt come up with a good answer.

    the question is : why for remote controls the infrared band of light
    frequencies is used and not visible light for example?

    shouldnt the infrared band be very noise since all hot objects emit infrared

    Best regards
    ahmed samir
  2. It's a matter of wavelength. Hot objects emit IR at much, much longer
    wavelengths than the shorter IR wavelengths - 880 nm - from the IR

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  3. Wade Hassler

    Wade Hassler Guest

    Remote controls use _very_bright_ IR light, cutting through the noise.
    (one I looked at pulsed the transmit LED at .4 amps.) In addition, the
    signals are encoded, using a precise carrier frequency.
    As for why visible light isn't used: dunno.
    Wade Hassler
  4. Bob Myers

    Bob Myers Guest

    Maybe because a visible light beam at comparable brightness (i.e.,
    enough to provide sufficient range w/o interference from other
    visible-light sources) would be REALLY annoying? Who would
    want to illuminate their TV screen with visible light every time they
    used the remote?

    Bob M.
  5. JeffM

    JeffM Guest

    why is infrared used and not visible light for remote controls?
    Think about all the hokey TV shows where the guy shines a flashlight
    into the photoelectric beam of the burglar alarm.

    The answer is false triggering by ambient light.
  6. John Larkin

    John Larkin Guest

    But there's plenty of ambient infrared... incandescents and sunlight,
    to name a couple of sources. Remotes use optical bandpass filters,
    coding, modulation, and tuned receivers to supress ambient light
    response. Those tricks would work just as well in the visible.

  7. Lord Garth

    Lord Garth Guest

    Ir LEDs are more efficient emitters than visible light emitters. They
    consume less battery for a given output intensity and nobody would
    use it as a flashlight. :)
  8. John Larkin

    John Larkin Guest

    Not unless they customarily wear night-vision goggles around the
    house. Kinda kinky.

  9. Lord Garth

    Lord Garth Guest

    Ala 'Silence of the Lambs' ...
  10. Luhan Monat

    Luhan Monat Guest

    Visible light is often modulated - especially from the TV screen, or
    florescent lights. I think this gives an edge to infared.
  11. norm d.

    norm d. Guest

    Visible light would radomly trigger the remote receiver every time you turn
    on the room lights, or walk past the receiver. IR receivers of the type you
    are asking about are not sensitive enough to trigger on body heat, but work
    well with IR light sources.
  12. John Larkin

    John Larkin Guest

    Would not. The IR signals are coded and modulated, generally about 40
    KHz. A *huge* amount of ambient light could block the receiver, but it
    wouldn't "randomly trigger the remote".

    Note that you can use multiple IR remotes, for different devices, in a
    room; the coding keeps them from interfering.
    because the wavelength is off a couple orders of magnitude.

    I don't buy that argument. There is *lotsa* IR in incandescent
    lighting. Rejecting false triggers is simply a matter of coding
    and filtering.
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