[olpc-help] External DC Power Jack Specs

[Sameer Verma]

Steve Holton wrote:
> Jim-
>
> The XO power jack defines an interface. There are physical
> characteristics and electrical characteristics.
> The Physical Characteristics are as Richard stated before:
>
>  1.67mm Center pin     (or 1.65 on the Wiki)
>  5.5mm Outer barrel    (or 6mm on the Wiki, 4.75 or so from Richard)
>  11mm contact length  (or 9.5 as Richard states above)
>
> A full technical description with tolerances in not available. The
> best I can do is reference the de-facto standard Richard gave us:
> Digikey part # CP-2195-ND
>
> When I get hardware in hand, I'll seek out the original manufacturer
> of the part. I'm sure they have a story to tell.
>
> We should probably include in here something about the coaxial cable
> they're using for power, if that was selected for physical
> characteristics. Many questions here. Again, I'll know more when I see
> one for myself.
>
> The Electrical Characteristics
> From the Wiki pages (me hopes they are correct and up to date) you'll
> need a source which is/can:
>
> - Maintain supply voltage somewhere between 5V and 25V.  DC
> - Be able to supply upwards of 15 Watts of power.
> - Not melt down under current loads up to 3 amps.
> - The positive polarity goes to the center pin.  Presumably also the
> coaxial core. "Shield Ground" in audio/telco language.
>
> Architecturally, the AC adapter (or the hand crank, Yoyo, solar panel,
> bovine generator, etc) is a  seperate subsystems from the XO. You have
> to get the public interfaces correct, but the private implementation
> details need only be effective.
>
> Trying to build one from DigiKey parts is a good learning exercise,
> but probably not the best way to approach this. If I were doing this,
> here's how I'd go about it:
>
> - Find a suitable, readily available mated connector set which can
> handle 30 volts, and 3 amps.  Get several sets.
> - Cut your XO AC adapter power cort and put a mated pair of connectors inline.
>   

After you cut the cord, you can attach a male/female pair of some easily
available connector so that your power end can be switched easily from
wall wart to 12V cigarette lighter. I did something like this when I
re-did the power supply for my Cobalt Qube2. I used a co-axial M plug
like this one. http://www.zooomr.com/photos/sameerverma/282145/

Sameer

-- 
Dr. Sameer Verma, Ph.D.
Associate Professor of Information Systems
San Francisco State University
San Francisco CA 94132 USA
http://verma.sfsu.edu/
http://opensource.sfsu.edu/


> - find another similar DC adapter, snip the core, and add on one of
> your connector mates.
>
> Now you have two AC adapters you can use, in case one breaks.
>
> - Add a connector to a 12V cigarrette  lighter car adapter, observing
> polarity, and now you have a car adapter, too.
> - Use the same technique for a hand crank (if you can find one) solar
> panel (or gang of solar panels, if you need more power capacity.
>
> - DO NOT run AC power mains (120V) directly into your XO. This will
> destroy the XO.
>
> - Once you have that working, you can focus on building a more generic
> power supply with all the bells and whistles (like a replacable fuse,
> etc.)
>
> Once I get XO hardware and can spend some times understanding and
> testing solutions, I'll write-up a page for the wiki discussing other
> similar ideas.
>
>