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Turning LED's into photodiodes?

  1. Sep 23, 2007 #1
    I think that's what they're called. I was guessing that you just put them in backwards, but I'm betting its more complicated than that?
     
  2. jcsd
  3. Sep 23, 2007 #2

    mgb_phys

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    In theory, although you would be better off with real photodiodes.
     
  4. Sep 24, 2007 #3

    berkeman

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    You will connect the LED or photodiode up to a current-to-voltage converter circuit, in order to convert the photocurrent to an output voltage. See the example opamp circuit on this page, for example:

    http://sales.hamamatsu.com/assets/html/ssd/si-photodiode/index.htm

    Using a high reverse voltage across the photodiode or LED will help it to operate faster (detect higher frequency signals), because the high reverse bias decreases the capacitance across the depletion region.
     
  5. Sep 27, 2007 #4
    how would i go about sending these "impulse" type things into a computer?
     
  6. Sep 27, 2007 #5
    People who have green 532nm lasers have been known to try to test the output power by using green LED's. It works but it is not a very accurate way of approaching this problem.
     
  7. Sep 28, 2007 #6

    berkeman

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    What impulse type things?
     
  8. Sep 28, 2007 #7
    Sorry that was very vague.. bad day.. Okay, so how would i hook up the photodiodes up to a computer so that the computer can understand the signals that the photodiodes are sending out?

    Okay, so I'm trying to create some sort of a computer targeting system (nothing fancy) with lasers and photodiodes. I want to be able to be able to "track" the movement of the laser using the photodiodes. Later on I hope to somehow make the laser track movement.

    I know this is a terrible explanation, but I don't totally understand how I am suppose to do this..
     
  9. Sep 28, 2007 #8

    berkeman

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    The traditional way would be with some data acquisition and motion control modules, connected via RS-232 or USB to your PC. Here are three companies that make such modules:

    B&B Electronics http://bb-elec.com/

    Omega http://www.omega.com/das/index.html

    National Instruments http://www.ni.com/

    You can also "roll your own" modules, but you need to be fluent in RS-232 or USB interface hardware, and comfortable programming your own uC and data acq and motion control hardware.
     
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