IR LED frequency (peak wavelength)

Discussion in 'The Projects Forum' started by gotumal, Feb 25, 2009.

  1. gotumal

    Thread Starter Active Member

    Mar 24, 2008
    99
    0
    Hi reader,

    In my project I am going to use an IR communication (analogue) with IR LED. I was wondering about the exact frequency to be used. What is the frequency which is least affected by solar (ambiant) radiation. I couldn't get the solar spectrum in NIR band on net. I also wish my system should not get affected by IRDA and IR remot controls around. What frequency at which common remote control and IRDA modules operates?

    P.S. :Since it is an analogue, I can not modulate it to have less interfernce.

    Thanks for your time.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You have only the choices dictated by the hardware as to frequencies. There is a narrow band of peak emission for IRLED's, so you have to work within it.

    One of the reasons that IR remote controls use a 38 KHz or higher carrier frequency is to allow the receiver to discriminate against other IR sources - lamps, the sun, and so on.

    It is possible to transmit "pure" analog data by IRLED, but some rules apply. The distance must be fixed or else there must be some means of calibrating the 0 and 100% levels for each session. The distance between emitter and receiver must remain fixed during each session to to the attenuation caused by distance between emitter and receiver.

    Because there is no way to discriminate between a significant change in emitter output and a change in the ambient IR illumination, the signal link will need to be confined to a shielded housing that excludes the interference.

    It's much easier to modulate the 38 KHz.
     
  3. gotumal

    Thread Starter Active Member

    Mar 24, 2008
    99
    0
    Thanks beenthere

    Code ( (Unknown Language)):
    1. You have only the choices dictated by the hardware as to frequencies. There is a narrow band of peak emission for IRLED's, so you have to work within it.
    2.  
    I have choices from 660 nm to 960 nm. I want to choose optimal wavelength least affected by surroundings.

    Code ( (Unknown Language)):
    1.  
    2. It is possible to transmit "pure" analog data by IRLED, but some rules apply. The distance must be fixed or else there must be some means of calibrating the 0 and 100% levels for each session. The distance between emitter and receiver must remain fixed during each session to to the attenuation caused by distance between emitter and receiver.
    3.  
    As of now the idea is to switch IR LED on and off for 0% and 100%. Intensity can be controlled proportionally once this calibration is done.

    Code ( (Unknown Language)):
    1.  
    2. Because there is no way to discriminate between a significant change in emitter output and a change in the ambient IR illumination, the signal link will need to be confined to a shielded housing that excludes the interference
    3.  
    I would think of having such shielded housing.

    Code ( (Unknown Language)):
    1.  
    2. It's much easier to modulate the 38 KHz.
    3.  
    I did not get this really. I was under the impression that it is modulated with some (harmonics) some common multiple of 50/60Hz to have same effect at each transmission. Is it so?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Under the conditions given, you can look for results. In the case of using a shielded path, just find an emitter you like. Wavelength probably will not matter as much as output intensity. The receive end could be fun - the device might not be totally linear in response. The light to voltage converters from these people - http://www.taosinc.com/productfamily.aspx?sel=ltv - are quite inexpensive and work into the IR.
     
Loading...