CL1B power distribution

[david at lang.hm]

On Tue, 28 Apr 2009, John Watlington wrote:

> On Apr 28, 2009, at 8:16 PM, david at lang.hm wrote:
>
>> On Tue, 28 Apr 2009, John Watlington wrote:
>> 
>>> On Apr 28, 2009, at 7:31 PM, david at lang.hm 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...

if it's not reasonable to use an existing LED, then I guess this idea 
will need to be scrapped. I think the people proposing the idea were 
figuring that in the hardware update one of the LEDs could be re-wired so 
that it could be run directly (between two pins, the pin that currently 
controls it, and a new one)

I will admit to not understanding the power reasons comment. is it that 
the LEDs in use draw more power than you want to run through the control 
chips?

David Lang