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'[EE]: LED as a photodiode- theory'
2001\06\06@073817 by Saurabh Sinha

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Hi,

Here's a theory question:

Can a LED be used as a photodiode?

Thanks>!

Regards,

S. Sinha (Saurabh)
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2001\06\06@080706 by Spehro Pefhany

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At 11:57 AM 6/6/01 +0200, you wrote:
>Hi,
>
>Here's a theory question:
>
>Can a LED be used as a photodiode?

Sure. Here's a quick test. 7.25mA through a 3mm super-bright
LED nose-to-nose with a second similar LED with a 1M resistor
across it gives a photovoltaic voltage of 0.53VDC.

Reverse biased, same setup as above 0.714V (on) into a 1M load
with 21.7V reverse bias (way over the 5V rated), 0.000V with
source LED off.

As always, in production situations you may be better off using
a characterized part.. blah blah.

Best regards,
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2001\06\06@090414 by Matt Mosley

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Yes,

I grad school in chemistry a another member of our group used LED's as
bandpass filtered photodiodes. Worked fairly well and was very simple to
implement. This was a front end for some sort of basic colorimeter he was
building that used neural networks for interpeting the data. I beleive they
published an article on it in Applied Spectroscopy or some such (It is in
his master thesis Clemson University about 1996-1997, Chemistry). I'll look
through some old notes and see if I can find a reference.

Matt

{Original Message removed}

2001\06\06@092713 by James Paul

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Yes.  Although it is not optomized for this use, it will work
rather well.  I have used LED's in this way several times.

                                             Regards,

                                               Jim



On Wed, 06 June 2001, Saurabh Sinha wrote:

{Quote hidden}

.....jimKILLspamspam.....jpes.com

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2001\06\06@121211 by Robert A. LaBudde

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At 11:57 AM 6/6/01 +0200, you wrote:
>Hi,
>
>Here's a theory question:
>
>Can a LED be used as a photodiode?
>
>Thanks>!
>
>Regards,

Yes. Removing the lens helps a lot.


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2001\06\06@165132 by Alice Campbell

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By the way, remove the lens by sanding with fine sandpaper.
They burn up pretty nice if you sand them down too far.

alice

{Quote hidden}

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2001\06\07@021347 by Chris Carr

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> >
> >Here's a theory question:
? A practical Question Surely
> >
> >Can a LED be used as a photodiode?
> >
Yes no problem. It is a standard practice on cheap single fiber
bi-directional links. (Hint: Look for Ping-Pong Protocals)

> >
>
> Yes. Removing the lens helps a lot.
>

Huh, Please elucidate. Why does removing the lens help a lot ?

I see no reason for removing the lens. I could equally say Drilling a hole
in the lens helps a lot, nay, it is essential. It all depends upon your
application.

Regards

Chris Carr

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2001\06\08@120644 by Olin Lathrop

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> Yes.  Although it is not optomized for this use, it will work
> ather well.  I have used LED's in this way several times.

Physics is definitely on your side.  Reverse biased semiconductor junctions
will definitely "leak" more (sometimes a lot more) when you shine light of
the right wavelength on them.  While this pretty much guarantees that LEDs
will exhibit photodiode effects to some extent, this it neither a specified
nor tested parameter.  There could be large variations from batch to batch
or between "replacement" parts.  I would be nervous about putting this into
production, but go ahead if this is a one off or hobby project.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, @spam@olinKILLspamspamembedinc.com, http://www.embedinc.com

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