[support-gang] XO brightness key operation
hmurray at megapathdsl.net
Tue Apr 10 02:26:06 EDT 2012
> As I have a tiny understanding of LEDs, I recall something about being able
> to detect light with them.
If you shine light on a reverse biased diode, it will leak in proportion to
the intensity of the light. The mechanism is a photon occasionally kicks
loose an electron and the reverse-bias field pushes the electron toward the
positive terminal. Enough electrons like that and you have a small current
Normally, that's not a problem since diodes and transistors are packaged in
opaque plastic. LEDs are packaged in clear plastic to let the light out.
But that means you can also also get light in.
There is an old story about one of the early SUN boxes. It had just booted
the OS (or something great like that) when somebody took a picture of it. It
crashed. The camera used a flash. The UV ROMs with the software didn't have
any stickers over the transparent lids, or maybe there was no lid over the
CPU chip. The light from the flash was enough to screw things up.
(If anybody has a good URL for that story, please let me know. I didn't find
it with a bit of searching.)
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