Ir led modulation

Discussion in 'The Projects Forum' started by KOOPI, May 11, 2014.

  1. KOOPI

    Thread Starter New Member

    May 11, 2014
    3
    0
    Hi guys,

    Is there any communication protocol for 1Mhz or greater (IR LED) ?

    Does the frequency effect the range of communication ? (i.e the greater the freqcuency the less range or the opposite)


    tnx very much!
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,148
    1,791
    A typical IR modulation scheme (NEC) uses a 38 kHz carrier and is described here:

    http://techdocs.altium.com/display/ADRR/NEC+Infrared+Transmission+Protocol

    As you can imagine the data throughput is very much less than the 38 kHz carrier frequency. I doubt that the IR LED could go light and and then dark fast enough at 1 MHz. due to the persistence of the light emitting material.

    Drive current is the prime determinant of LED brightness, not frequency.

    But knock yourself out looking for one.
     
  3. DickCappels

    Moderator

    Aug 21, 2008
    2,658
    632
    There popular standard in the 1990's that ran at about 250 kb/s (from memory) is a site, http://irdajp.info/ that might have some helpful information. Don't know of anything using LEDs that ran over 1 MHz, but you might find something on the referenced web site.

    Yes, as you in crease the bit rate, the receiver's bandwidth must increase, and along with the increased bandwidth come increased noise, so an increased implies shorter range if everything else is held constant.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    The webpage implies greater speed than the original which was not very popular if I recall correctly. High speed IR communication is not exactly compatible with low power handheld devices which limits the potential for many popular devices. The range of 3 meters seems quite limited to me; maybe suitable for a mouse with no cable but little more. That application has been mostly replaced with a wireless USB dongle.
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    In the Ronja project they are using optical devices for communication at 10 Mbps full duplex:
    http://ronja.twibright.com/
    They have reached a distance of 1.4 km with the setup.

    Bertus
     
  6. Little Ghostman

    Member

    Jan 1, 2014
    294
    97
    That would imply that 1Mb is well withing reach, alot I guess relies on using a good receiver. What range are you after?
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Fibre optic TX LEDs are good for MHz. Likewise their receivers.

    You may be able to adapt those to your free air comms (instead of an optic cable).
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    Optical fiber is a much different transmission medium than air. In particular signal degradation is avoided by constructing fiber that maximizes the internal reflections.

    IR in air is just not the same problem
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
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    To maximize distance, use an IR LED with a narrow angle of transmission (10 degrees or less). It makes a huge difference in energy transmitted (power/mm2) vs a 25 or 50 degree LED.

    Also, a photo-transistor has a fairly slow rise and fall time so they are limited to some 10s of kHz to 100 kHz. Better and faster is a photodiode (or another ir LEd in reverse bias). The diode will give nice, fast response.
     
    Papabravo likes this.
  10. Papabravo

    Expert

    Feb 24, 2006
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    Excellent point. Fiber optic transmitters have a very narrow angle of transmission.
     
  11. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    In the Ronja project they are using focused beams.
    The lenses used are 90 or 130 mm.
    Here is a drawing of the setup on one side:

    [​IMG]

    and a picture

    [​IMG]

    Bertus
     
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