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Help required for surface reflection circuit (IR-LED/ PHOTODIODE)

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Jun14-10, 02:20 PM
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I am new to this forum but have been interested in reading many threads and would like to know if any of the experts could help.

I am looking to make a circuit that I can measure different output levels of a photodiode from the ammount of "signal" reflected onto it from a particular glass surface

My idea is to set the angle of the transmitter / receiver to get the optimum reading on a known surface coating on the glass, I would then like to measure a range of coatings and see if I can establish a significant measurable difference between them.

Ideally the transmitter and receiver would be about 5cm apart and I coulkd make some sort of light tube to optimize the reflected signal if possible.

I am looking for advice on a circuit so that I can measure the output of the photodiode as I do not want to use it as a switch like high or low , I want to be able to measure the output in mV so that I can then process the different levels into some meaningful data. I would also like advice if it would be better to use a very bright LED to reflect off the glass or an infrared LED?

Sorry if I have not explained myself very well but I hope someone can understand what I want to do.

Thanks in advance
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