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Infrared transmitter

Discussion in 'Electronic Design' started by Paul Horwood, Apr 26, 2005.

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  1. Paul Horwood

    Paul Horwood Guest

    I wonder if anyone can help me?

    I am looking at building a 6 band infrared transmitter.
    Now it seems that most infrared beams are modulated via a high signal like
    37Khz.

    What I want to do is to transmit all the 6 bands at once but on different
    infrared frequencies.
    The frequencies would be for example:- 935,5 - 937,8 - 927,2 - 948,1 -
    934,2 - 928,3 nm (nanometer) .

    How can this be done?

    Is there a meter that can be used to determin the frequency of infrared
    light?

    Or is there a calculation that can be done to determin which components I
    would need?

    Will the standard infrared emitters be capable of narrowed bandwidth like
    this?

    Paul...
     
  2. OBones

    OBones Guest

    This is not frequency, this is wavelength.

    Well, I guess any oscillating system could do. The problem might be with
    the emitter and receiver that might not be able to switch at the desired
    speed. Find the frequency and check the datasheets.

    The frequency of the light itself is a parameter of the emitter,
    indicated in the datasheet. The frequency of "on-off" switching depends
    on your oscillating circuit. An infrared receiver will convert the light
    signal into electricity, then use an oscilloscope to "see" that on-off
    switching.

    Decide which oscillating circuit to use first

    Bandwitdh is not directly impacted here, it also depends on the coding
    you use on top of your frequency. Which one(s) do you plan to use?
    Frequency modulation, amplitude modulation, phase modulation?

    Cheers
     
  3. Paul Horwood

    Paul Horwood Guest

    Whoops.. so it is.... :eek:)

    ok, looking at amplitude modulation for 29Khz,32Khz,29Khz etc..

    I am not sure though if I need the infrared Wavelength varied.. On the
    details for this transmitter it states:-
    " infrared sender radiating six different frequencies in the infrared range
    "

    This is why I asked the above questions...

    Paul...
     
  4. OBones

    OBones Guest

    No, you don't need the infrared wavelength to vary that's way too
    complicated. What you do is vary the frequency at which you turn on,
    turn off the light. The color of the light doesn't matter (well, not for
    this parameter), it's the frequency at which it goes on and off.
    Infrared is just "better" because it travels well in broad day light
    (well, not too broad).
    So what you will do is this:

    On-Off-On-On-Off-Off-Off-On

    and so on. Or if you do amplitude modulation, it could be:

    Full-Half-None-None-Half-Half-Full

    The frequency at which you send the states is the frequency that you
    have to look at. If the emitter is blue, red, green, infrared,
    ultraviolet, it does not matter, it does not impact on your driving circuit.

    What you need to look at in the datasheet is how fast the emitter and
    receiver can change their state and how sensitive they are. If for
    instance it takes 1ms for the receiver to go from fully off to fully on,
    then you can't send anything more frequently than every 1.1ms (security
    margin of .1) and that's a 1/1.1e-3 = 900 Hz
    That value here is just an example, I would hope the receiver is much
    better than this.
     
  5. Guest

    You *can* do this, but the cost would be quite high. Most
    semiconductor emitters are not single frequency, but put out a gaussian
    distribution over a hundred or so nm. You could use a monochromater to
    get to a very narrow band or single frequency. You would use an
    emitter/monochromater for each channel on the transmitter and a
    monochromater/detecter for each channel on the receiver.
    You say you want to do 6 channels "at once". Do you really need to do
    this, or is there a modulation scheme you can use (like time-domain
    modulation)? What is the data rate you need to transmit?
     
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