LEDS as Photodiodes

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A few weeks ago this subject was mentioned. Think some of you may find this interesting.

Scroll down to the image of the led matrix and download the video.
How is it done?http://mrl.nyu.edu/~jhan/

Yes I am getting grumpy!

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I also read that all diodes and transitors emit light but most are packaged in opaque plastic and it can''t been seen.

Too bad!

Would be a great diagnostic tool to be able to stare at a circuit board and be able to tell exactly what chips were working and/or not working juat by sight.

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That's a GREAT video!

I think the trick is that the array is muxed.

You light one row, and then measure the voltage generated by the off leds in the previous row.
Light is coupled from the 'on' row via fingers tips, to the 'off' row. Hmmm, maybe you have to do it with individual leds versus rows to isolate and access the 'sense' led, but that's just a detail. Also, calibration to eliminate background light.

If you can actually measure the voltage generated from the leds by avr pins directly, or if you need an external adc, is another pesky detail.

-carl

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retro
Many years ago I think OC71's you could scrape of the outer layer of paint and use the transistor as a photo diode.

Keep it simple it will not bite as hard

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The idea is to use some leds in the matrix as light sources and others, reverse biased, as receivers. In the video they all seem to be emitting light, but in reality they are scanned so it's not a problem. I haven't seen a published circuit of something like this (not with a full LED matrix anyway). Very cool stuff!

The Dark Boxes are coming.

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How this works: Click me :mrgreen: