Outdoor Light Sensor

James Cameron quozl at laptop.org
Thu Jun 14 00:43:42 EDT 2012

On Thu, Jun 14, 2012 at 12:07:36AM -0400, Chris Leonard wrote:
> Entirely impractical, but one must wonder about turning the wiggling
> ears into eye stalks :-)

I did.  Too many parts to change.  Besides, the ears can be in any

I also wondered about using the backlight as a sensor.  This would
require the backlight to be turned off for the sample time, so it
would need a much reduced sample time, to avoid perception of flicker,
which suggests circuit design with:

- gating to turn off the drive current fully,

- gating for a faster charge path, rather than rely on a
  microcontroller pin configured for output,

- gating for a faster discharge path with a series resistance, rather
  than relying on microcontroller input pin current,

- merging into the existing drive circuit.

But there's one irritating thing about white LEDs used in the
backlight, and that is that they are really blue LEDs with a YAG
phosphor, and the phosphor glows for enough time to destroy the idea.

> On a more serious note, other than the OLPC folks, the people who
> run repair centers have probably had more facetime with the guts of
> the XO than most and seen the worst that kids can do to them.  It
> would be nice to hear from them.

Yes, their involvement on this mailing list would be valuable, so
you'll have to let some through without grabbing them for translation
duties.  ;-}

James Cameron

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