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10th May 2007, 02:56 AM
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What exactly is a photodiode?
I am looking for a in depth answer to what a photodiode is and where can I get them.
Remember, photoDIODE, not Photoresistor |
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10th May 2007, 03:05 AM
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It's a diode... like any other diode, although with a transparent package. Sometimes the external package material is tuned for a specific spectrum, but EVERY PN junction exhibits a photo electric effect. Light applied to the junction will produce current through it. The photons knock around the free electrons. Any LED will exhibit a photo diode effect. (Just put one on a scope and shine a light at it) Basic semi conductor physics. Also little known, is all semi conductor junction emit some form of light =) One of the reasons why they come in opaque packages.
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"Because I be what I be. I would tell you what you want to know if I
could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har." Last edited by Sceadwian; 10th May 2007 at 03:11 AM. |
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10th May 2007, 07:50 AM
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.... so if you connect a photodiode in series with a resistor and connect the whole lot accross a dc supply, the current through the resistor (and therefore the voltage accross it) will vary with the light intensity.
With specially made diodes light variations in the MHz region can be monitored. I have used PIN photodiodes to detect laser pulses only about 10ns duration. |
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10th May 2007, 07:51 PM
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still, where can i get them?
Also, by hooking them up to the base of a NPN transistor, could I use them for a light following robot? |
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11th May 2007, 05:07 AM
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A Photo-diode can be used in one of two ways:
1) If it is reverse-biased then it leaks a small current when it is exposed to light or IR. The reverse-bias voltage reduces its capacitance so it is fast. 2) If it has no bias voltage then it generates a small forward voltage when it is exposed to light or IR. It is very sensitive.
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Uncle $crooge |
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12th May 2007, 01:09 AM
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Any generic LED can be used as a photo diode. But you need relativly sensative circuits to really use them.
__________________
"Because I be what I be. I would tell you what you want to know if I
could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har." |
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12th May 2007, 02:37 PM
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Well I've managed to use a 400nm violet diode to detect 407nm light from a black light using a multimeter so I wouldn't agree, you just need a simply high impedance amplifier.
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I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez |
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12th May 2007, 09:16 PM
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still i dont get how to use them and where to get them!!!
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