[Arm-netbook] Laptop Housing Questions

Luke Kenneth Casson Leighton lkcl at lkcl.net
Wed Dec 21 03:52:47 GMT 2016

crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68

On Tue, Dec 20, 2016 at 8:28 AM, mike.valk at gmail.com
<mike.valk at gmail.com> wrote:
> 2016-12-19 22:56 GMT+01:00 Luke Kenneth Casson Leighton <lkcl at lkcl.net>:
>> ---
>> crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
>> On Mon, Dec 19, 2016 at 9:45 PM, Jonathan Frederickson
>> <silverskullpsu at gmail.com> wrote:
>> > Hey, I have a few questions about the laptop housing.
>> >
>> > - How does one connect it to power?
>>  standard DC jack, anywhere between 7 and 19v.
> I've never found a standard DC jack ;-).

 can't remember the P/N, it's in the PDF,

> I presume a "dognut" type plug?

 it's not the 5.5mm one, it's too big.

> If
> so, of what dimensions and which polarity or does it have a polarity
> switcher or at least a polarity safety?

 pin positive.  don't know.

> I think the USB-C connector is going to be the first "standard" "universal"
> charging connector. Standard USB-C cable should be able to provide 60W
> (20V*3A) and power cables 100W (20V*5A). But not "ominous" enough yet.

 too much involved in the way of electronics.

>> > Can it be powered over USB
>>  powered no, charged, yes.  current limit on the OTG port.
> Well if the input minimum is 7V than neither.

 7-19V on DC jack.  standard voltage on OTG port (4.somethingsomething
to 5.somethingsomething)

> But if I understood correctly the EOMA-68 card accepts power over the OTG
> port and passes through, any surplus, to the housing.

 they're hard-wired on the EOMA68-A20.  it's not a matter of
"surplus", there's no way there's enough current to power the Card
*and* the laptop - the currently limit is something like 450mA for
standard OTG.

> Thus slowing down the
> battery drainage of the housing(laptop/tablet). And charging, although slow,
> when the housing is turned off. And a little faster when both, housing and
> card, are turned off.

 all correct.

> Standard USB only delivers 5V*500mA= 2.5W. But various options are allowed
> apparently. https://en.wikipedia.org/wiki/USB#Power

 not with the AXP209 (the PMIC on the EOMA68-A20) they're not.

>> >  or does
>> > it require a specific AC adapter?
>>  no.  min 4A is best, but if you're prepared to reprogram the
>> STM32F072 yourself you could get away with less
> 4A on the output side I presume so 19v*4A=76W, So a 95W power supply with
> 80% efficiency (90*80%=76). Or 85W at 90%.


 4A @ 5V, absolute max 20A.   look up the bq24193 datasheet.

>> > I have a portable solar array with a
>> > battery pack that can charge portable devices over USB, and I'm trying
>> > to work out whether or not I'll be able to power the laptop from it.
> If it has 12v out that would be your best bet I guess.

12v is within acceptable range of 7-19v, yes.


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