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wow that's neat! sampling between PWM cycles is a cool idea.

I'd guess the issue is that the required parameters are not well controlled in the fabrication of most LEDs. Possibly LEDs not used as indicators, with a tighter wavelength output... most likely this would remove any cost advantage however.

Fascinating stuff!

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Ya, they're not designed as detectors so there's no control over the parameters that determine how good they are as detectors. Interestingly, one of the reasons I was looking at light sensors was because our pyroelectric sensors were erratically sensitive to incandescent light. We wanted a reliable way to detect bright light and mitigate the effects in software and were hoping to use an existing component on the board as a sensor (our products were extremely cost sensitive due to the volume, so adding a $0.12 sensor was actually a huge deal).

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