Light sensor on XO-1.75

James Cameron quozl at
Mon Aug 29 19:52:15 EDT 2011

On Mon, Aug 29, 2011 at 07:38:20PM -0400, Richard Smith wrote:
> On Mon, Aug 29, 2011 at 1:06 PM, Bert Freudenberg <bert at> wrote:
> > And it seems to sit "behind" the blinking left-most LED? And the
> > blink rate is proportional to the light sensed? Why?
> Its proportional because that's how  the sensor works.  The amount of
> light changes the time to bleed off the charge stored in the diode
> when you reverse bias it.

Hmm, we could schedule the samples to start at a constant time relative
to the previous start, and thereby only change the amount of off time of
the wireless LED, but this would suck because the sample rate would be
much slower in bright light.  We would not notice encroaching darkess as

Bert, the sensor was chosen for low cost, within the constraints of the
update rate we needed for potential automatic display backlight control.

James Cameron

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