Turning LED's into photodiodes?

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Discussion Overview

The discussion revolves around the feasibility and methods of using LEDs as photodiodes, including their potential applications in tracking systems with lasers and photodiodes. Participants explore theoretical aspects, practical implementations, and challenges related to this concept.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • Some participants suggest that connecting an LED in reverse could allow it to function as a photodiode, although they acknowledge that this might be more complex than it seems.
  • Others argue that using actual photodiodes would be more effective than repurposing LEDs for this application.
  • One participant mentions that using a current-to-voltage converter circuit is necessary to convert the photocurrent from the LED or photodiode into an output voltage, referencing a specific op-amp circuit as an example.
  • There is a discussion about the use of high reverse voltage to enhance the performance of the photodiode or LED, particularly for detecting higher frequency signals.
  • A participant inquires about how to send signals from photodiodes to a computer, expressing a desire to create a targeting system with lasers and photodiodes to track movement.
  • Another participant provides information on traditional methods for connecting data acquisition and motion control modules to a computer, suggesting specific companies that manufacture such modules.
  • There is a request for clarification regarding what is meant by "impulse" type signals, indicating some confusion in the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of using LEDs as photodiodes versus using dedicated photodiodes. The discussion includes both theoretical considerations and practical applications, and it remains unresolved whether LEDs can adequately replace photodiodes in this context.

Contextual Notes

Participants have not fully clarified the assumptions behind their claims, particularly regarding the specific configurations and limitations of using LEDs as photodiodes. There are also unresolved questions about the technical details of interfacing photodiodes with computers.

Who May Find This Useful

Individuals interested in electronics, optical systems, and data acquisition methods may find this discussion relevant, particularly those exploring innovative uses of LEDs and photodiodes in tracking and sensing applications.

petitericeball
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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?
 
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In theory, although you would be better off with real photodiodes.
 
mgb_phys said:
In theory, although you would be better off with real photodiodes.

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.
 
how would i go about sending these "impulse" type things into a computer?
 
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.
 
petitericeball said:
how would i go about sending these "impulse" type things into a computer?

What impulse type things?
 
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..
 
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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