On Fri, 13 Jun 2008 13:30:29 -0600, you wrote:

>Good day to all.
>
>I understand that Dell has some form of communications with their 
>laptop AC adapters so that the laptop knows what it is dealing 
>with.  Does anyone have any idea of how that is done?
>
>The reason I ask is that I want to steal some power from the same AC 
>adapter that runs my laptop.  That is a Dell XPS M170 laptop using a 
>PA-13 adapter.
>
>I want to grab whatever voltage is coming out of that adapter and 
>feed it to a pair of little DC-DC buck convertors to get the supplies 
>I need for another project.  In the old days, I'd simply grab that DC 
>and feed it into my cards.  These will be used at the same time as 
>the laptop (that is: while the laptop is on and running from the AC adapter).
>
>However, if Dell is modulating that DC line with signalling, I 
>suspect that input filter caps on my DC-DC boards might mess that 
>up.  I could just hack up that cable and put a scope on it, but I'd 
>wait 'til I know that its not a problem before I hack up that cable 
>for no good reason.
>
>Anyone have any knowledge of the signalling - or can point me to a 
>website that has that info.  Google has not been helpful - pretty 
>much all I see is places who want to sell me a new adapter and such.
>

It's a Dallas 1-wire chip. 
The power connector has 3 poles - there is an inner sleeve as well as the outer one and the centre
pin.



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