Light sensor on XO-1.75

John Watlington wad at
Wed Aug 31 19:20:23 EDT 2011

On Aug 29, 2011, at 7:52 PM, James Cameron wrote:

> 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
> quickly.

I am moving the LED and blanking circuitry to the storage LED tonight for
the C-build and beyond.   I tried a yellow LED for sensing, and it was less
sensitive to interference from the WiFi LED than the green LED, but not
enough to matter.   The diffusing nature of the lightpipe ensures lots of
back reflection.


More information about the Devel mailing list