how can i increase the range of ir photodiode??

Discussion in 'The Projects Forum' started by ksar, Dec 19, 2009.

  1. ksar

    Thread Starter New Member

    Dec 19, 2009
    1
    0
    hi..i'm building a robot in this i need to use a ir (tx and rx) pair together ..
    so that when ir gets reflected from white surface it is to be sensed by ir rx
    but currently available diode works upto 5cm ..i need to increase the range to 40 cm
     
  2. Robin Mitchell

    Well-Known Member

    Oct 25, 2009
    732
    200
    Ok, im not the best at electornics but as far as i know, the signal weakens with distance and the electromagnetic wave spreads out. Now, my advice is to try using a samll but powerful lens. If you can try, you might be able to get the waves to focus 40cm away and see if it recives it. If not, try adding a lens on the reciver.

    Hope this helps, might be wrong. If it is, delete this :)
     
  3. marshsmello

    New Member

    Jun 8, 2009
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    If you don't have stronger diodes then put 2 or 3 in parallel and a stronger driver transistor if needed. I assume the voltage is low. If it is 10V or more they can be put in series.
     
  4. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    It would help if you can provide more details about the transmitter and receiver. Things like: power, wavelength, focusing lenses, optical filtering etc. all affect the performance. There are also electrical tricks, such a modulation, that can be used. It seems that 5 cm is much too short, but it's hard to know what is missing from your approach without details.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    At the expense of added cost, you can double up on the transmitters.

    hgmjr
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,144
    1,790
    The light output of most diodes a function of forward current. Once a slug of current has been forced through the diode there is some persistance of the light. Read the datasheet carefully to understand the typical forward voltage, the maximum continuous forward voltage, AND (this is the important one), the maximum pulsed forrward current.

    A typical diode may indicate 20 mA typical, 60 mA max continuous, and 300 mA max pulsed. So the idea would be to hit the diode with a 300 mA pulse with a 10% duty cycle. On the Rx side you can look for pulses at a specific frequency to eliminate extraneous sources.
     
  7. Forrest M. Mims III

    New Member

    Aug 31, 2007
    4
    1
    There are various ways to improve the range of your system:

    1. Drive the LED with high-current pulses. This will greatly increase the optical power.

    2. Use an external convex lens or reflector to tighten the beam of the LED so that more of it is concentrated on the target. Specs depend on the LED configuration. The wrong lens placement will expand the beam.

    3. Use a convex lens at the receiver (photodiode?) to concentrate more of the backscattered light onto its active surface.

    4. Shield the receiver optics from ambient light. (A phototransistor can actually become more sensitive when prebiased with some ambient light, but that's another story.)

    5. If ambient light is swamping the receiver, try using an optical filter that transmits the wavelength being used.

    I've used all the above to build very sensitive travel aids for the blind that could detect objects out to 3-4 meters.

    A very advanced version of what you want to do can be implemented with a low-cost video camera module and software that detects whatever you tell it to detect. This is not simple to implement, but it is very powerful.

    Forrest M. Mims III
    www.forrestmims.org
     
  8. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    How about posting up your schematic so that all of us can see what your current design looks like.

    hgmjr
     
  9. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Modulating the outgoing light will let you use a resonate reciever. This should let you use higher gain and ignore ambient light. An IR remote works for many meters. Sometimes even reflected off of walls.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I don't know how you got lucky enough to get advice from Forrest Mims III himself, but you most certainly did get lucky.

    Just a qualification: You will need to consult the datasheet for your particular LED(s) to determine their maximum drive current vs duty cycle. If you don't know how to do this, please supply us with the part number and we can help figure this out for you.

    You can fashion a very inexpensive concave reflector using aluminum foil (shiny side in) by forming it around a convenient spherical or semi-spherical object; even a common table spoon might be a good candidate.

    Similarly, a concave reflector as mentioned above can be used if the receiver is placed at the focal point of the reflector.

    A piece of black heat shrink tubing, carefully applied, would probably work quite well. (If you didn't know already, I got this from one of Forrest M. Mims III's books.)

    It would be very much appreciated if you could please explain what types of suitable optical filtering material(s) might be available to a hobbyist.

    I am grateful that you are using your talents to assist those who need them the most.

    Very true. If you have a cell phone with a camera on it, you can see the IR emitter of a TV remote flashing in it - or just about any other electronic video camera. To actually implement such technology would require a rather fast processor, and a good deal of programming expertise.

    Completely off-topic, but I wish you and your Family a very happy and healthy Holiday season - and a very sincere thanks in re-kindling my interest in electronics.
     
  11. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    "Holiday season"?
    Aren't we allowed to wish a Merry * (the celebration that happens with most English-speaking people of the world in 8 days)? Usually it goes with "and a Happy New Year".
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I was reserving the "Happy New Year" part for next year. ;)

    As for the 1st part, I'm attempting to be as non-religious and apolitical as possible, in the best interests of the Forums.
     
  13. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    My city hall has a * tree every year. A few "other" minority religions have people furious that the city hall doesn't use their religious articles.

    It is sad that schools do not say The Lord's Prayer anymore.
     
  14. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56

    VERY WELL SAID....

    Merry CHRISTmas..to all...
     
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