CL1B power distribution

Bobby Powers bobbypowers at
Tue Apr 28 21:38:15 EDT 2009

On Tue, Apr 28, 2009 at 8:36 PM, John Watlington <wad at> wrote:
> On Apr 28, 2009, at 8:16 PM, david at wrote:
>> On Tue, 28 Apr 2009, John Watlington wrote:
>>> On Apr 28, 2009, at 7:31 PM, david at wrote:
>>>> On Wed, 29 Apr 2009, James Cameron wrote:
>>>>> On Tue, Apr 28, 2009 at 10:15:47AM -0400, C. Scott Ananian wrote:
>>>>>> I wonder if one could easily support running an LED backwards
>>>>>> as an
>>>>>> ambient light monitor in Gen 1.5 - it seems that automatically
>>>>>> powering off the backlight in bright sunlight would lead to a
>>>>>> lot of
>>>>>> power savings for most young users.
>>>>> I agree that an ambient light detector and automatic adjustment of
>>>>> backlight would save power.  It would happen transparently,
>>>>> magically.
>>>>> But I don't think the LEDs are often specified in terms of their
>>>>> ambient
>>>>> light detection properties.
>>>>> Perhaps it would be better to use a photodiode, or light dependent
>>>>> resistor.
>>>>> Then there's the spectrum of light being received.
>>>>> Then there's reflection from the laptop display itself to consider.
>>>>> I recall we also once had a discussion on whether the camera
>>>>> could be
>>>>> used as an ambient light detector.
>>>> you don't want to have to run the camera to detect the light
>>>> (this will
>>>> eat far more power than you would save)
>>>> the LED trick has the advantage of not requiring a change to the
>>>> case,
>>>> just a single additional drive pin to be able to run it as a
>>>> detector.
>>> And where would you place said detector LED, without modifying the
>>> case ?
>>> (I have the pin...)
>> use one of the existing LED's.
> I have no intention to use one of the existing LEDs.   They don't run
> off logic level
> voltages for power reasons, and adding switches would be more
> expensive than
> dedicating an LED.
> Hence my question...

could you squeeze another LED in right next to the Battery/Charge one?
 we would probably only be interested in checking the ambient light
when unplugged, so the the charge light would most likely be off
except for when the battery is low.


>> I would guess probably the power LED as it has the largest opening
>> (and so would probably be the best choice for detecting light)
>> David Lang
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