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Topic: Multiplexing Photodiodes (Read 2 times) previous topic - next topic


I'm not entirely sure as of yet, it depends on how fast the board can read of the data, I have access to a lot of lighting, doing a photographic science degree you see.

Flash duration syncs at 1/60th of a second, I can however use a continues light source, such as tungsten or even LED.

If you were talking about regard to the spectral power distribution of the light source, i plan to filter UV and IR so I am only dealing with the visible light spectrum.


Not exactly concurrently but practically concurrently.

Led's leakage current varies with light shining on it. So you can read back the leakage to detect light sensitivity (or to use led as a switch to detect fingers).

Google a paper by folks from Mitsubishi.

You can light up an led, and then turn it off by applying a reverse voltage on it while measuring its leakage (usually via adc or timer). If the measurement phase is very short, you can have an led that can self-adjust its brightness based on ambient lighting.


Check the photodiode specs, see if they're responsive to the light frequency you're after.
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When I went to tech school years ago to learn electronics, one of sections of our course was to build a device to "read" stencils in the shape of letters, and have the computer (an Amiga 1000) interpret the shape. Basically a primitive form of OCR and/or computer vision. Our array was an 8 x 8 phototransistor array (64 elements); the input to the Amiga was via the 8 bit parallel port. We basically had a multiplexing scheme where we used an 8 bit shift register, setting the parallel port to output to select which "row" we wanted; once that was latched in, we switched over to "read" mode and read the outputs of the row. There was also some buffers and such built in (so we didn't blow anything by attempting to write when in read mode, etc). As I remember, it wasn't a terribly complex circuit, but still interesting nonetheless. I keep meaning to dig it up, scan it in, and post it on my website (you could make a nice low-vision "eye" using such an array made from SMT photo transistors, and a simple convex lens, all mounted in a box - would be pretty neat for a small robot).
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Cheers dhenry, I'll have a read.

CR: they're sensitive up to 820nm, from around 300, so more than enough.

Thanks for the input cr0sh, I'd need a hell of a lot more than that though I think, I suppose the other alternative is to use multiple arduino boards, each diode, or whatever I decide to end up using will act as a pixel to create a image/video - depending on which route I go down, hence why more is better.

I found out there is an electronics department which is combined with the computer science department at a different campus as part of my uni so going to try and have a meeting with them see if they can help me with the project, but cheers for all the input - it gives me an excellent start!

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