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Photodiode help? Answered

I bought a photodiode (not really knowing what it was) and I don't undersand how and where to use it. I tried it as a light switch but it seems to pass electricity through it in both in light and in dark 

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rickharris (author)2011-07-07

The photo diode will conduct electricity when light falls on the junction See here for details of how to pass audio over a light beam

http://en.wikipedia.org/wiki/Photodiode

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/photdet.html

Whereas a photo transistor can amplify the light signal the photo diode will not.

Actually any LED can act as a photo diode sensor.

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iceng (author)rickharris2011-07-08

It used to be any LED would respond best to a sister LED of the same color.
That does not exactly apply to today's LEDs of white or enhanced colors by use of phosphors transmuting base light to other frequencies.

A

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orksecurity (author)2011-07-07

A photodiode is essentially a light-controlled transistor -- it passes different amounts of current depending on how much light hits it. You will generally need some kind of amplifier or relay to take that response and use it to control other things.

Websearch "photodiode circuit" for some examples.

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or_ford98 (author)orksecurity2011-07-07

Will a computer detect the signal without any amplifier, ie with a mike jack?
I read that you can transmit audio with light this way.

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iceng (author)or_ford982011-07-07

Photo diodes can be used two ways.
Reverse biased or voltage generating and responds differently in both.
A small photo cell will work better as a light beam audio pick up.

Anyway, I do not believe a computer mic input will work but
I never tried it without a pre-amp.

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steveastrouk (author)iceng2011-07-08

He could bias the diode, and see what happens. It might work.

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steveastrouk (author)2011-07-07

Its like any diode - too much current and you'll kill it. Unless you limit the current, it will have burned out pretty well instantly.

Steve

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iceng (author)steveastrouk2011-07-08

OOnly.... way to really see what's what :-Þ     A

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steveastrouk (author)iceng2011-07-08

That's a curve tracer !I haven't seen or used one of them for 25 years !
He he

Steve

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Jack A Lopez (author)2011-07-07

A photodiode produces a small current in response to light. To measure this current, or rather to change it into a voltage, you need a photodiode amplifier, and this is the sort of circuit you can build with a single op-amp, and just a few passive components. 

Here:
http://www.google.com/search?tbm=isch&hl=en&q=photodiode+amplifier+circuit

Most of those circuits are based on the old op-amp current-to-voltage converter, here:
http://en.wikipedia.org/wiki/Current-to-voltage_converter#Op-amp_implementation

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