CL1B power distribution

david at lang.hm david at lang.hm
Tue Apr 28 20:42:53 EDT 2009


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



More information about the Devel mailing list