CL1B power distribution

John Watlington wad at
Tue Apr 28 20:51:32 EDT 2009

All of our LEDs are dual (one on the inside and one on the outside).
Instead of running these in parallel, and throwing away the extra
voltage, I run them in series directly from the battery voltage
(ever notice that their brightness changes when you plug in
the charger ?)


On Apr 28, 2009, at 8:42 PM, david at wrote:

> On Tue, 28 Apr 2009, John Watlington 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...
> 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

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