[support-gang] XO brightness key operation

[John Watlington]

On Apr 9, 2012, at 11:02 PM, Kevin Mark wrote:

> On Tue, Apr 10, 2012 at 11:33:01AM +1000, James Cameron wrote:
>> G'day Kevin
> 
> thanks for the intro to LEDs and answering my question.
> oh, well, so its only on the 1.75.

Yes.  It's a bummer that it took us this long to get it into the laptop.

It is a perfect example of adding $0.004 to the BOM cost and
saving 1W every time an XO laptop wanders outdoors.  Once you
are outdoors, you can't even tell if the backlight is on!

Our manufacturer kept wanting us to use a $0.50 part (which does work very well).
But the biggest problem turned out to be placing a sensor LED without altering
the existing ID (plastic parts).  We ended up using a dual LED package
shared with the storage LED (third from the right), to minimize damage
due to PCB handling prior to laptop assembly.  The storage LED can
be forced off by the EC to allow a light reading to complete undisturbed.
Many of you might remember the flashing WiFi LED in B1 prototypes due
to poor consideration of this mechanism on a constantly-on LED...

It turns out that the effect of the backlight on the outdoor light sensor is
not negligible either.   These things are very hard to retrofit!

Cheers,
wad