Umm, Chuck, to quote an unnamed person " I don't think you read my link. It
discusses .. " well, not only discusses, but dissects and dismantles (with
copious illustration via oscilloscope displays!) Apple chargers to
demonstrate that they use specific resistances across the two USB data lines
to signal the availability of currents in excess of the 0.5Amp 'standard'.
As I understand it, it's just passive resistors that do the job, there is no
voltage coming out of the charger on the data lines.
It's in the Vimeo clip, direct URL for which is http://vimeo.com/13835359
But thanks to all for the impetus to find out about this.
Piers
-----Original Message-----
From: Chuck Norcutt [mailto:chucknorcutt@xxxxxxxxxxxxxxxx]
Sent: 06 January 2013 01:36
To: Olympus Camera Discussion
Subject: Re: [OM] Another gadget obsoleted.
From what I read this morning Apple has been placing various voltages on
the two data lines for a USB charger with more than a computer behind it.
There have apparently been about 3 different incarnations of this scheme
with each one represented by a different voltage.
Chuck Norcutt
On 1/5/2013 1:57 AM, Chris Barker wrote:
> Chuck
>
> No, sorry, I didn't, only the first few lines in which the author
describes the bridging of the 2 ports. Thanks (and to Piers) for
enlightening me on the existence of such protocols.
>
> They sound like sensible restrictions, rather than sinister. And I
> now remember that I had USB output to use in the car which did not
> charge a previous iPhone: I was thoroughly confused by that, but no
> longer :-)
>
> Chris
>
> On 4 Jan 2013, at 23:10, Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
wrote:
>
>> I don't think you read my link. It discusses an *apparent*
>> proprietary signaling system in 12V/USB chargers that iPads recognize
>> and Androids do not. A high current charging device such as an iPad
>> or Android tablet needs to be aware of the USB connection and, if
>> it's attached to a computer, throttle itself back to the maximum
>> current draw specified for a USB port on a computer (0.5 amp IIRC).
>> However, if the charger is simply a USB connector connected to a 12V
>> outlet in a car then the device can safely draw 2 amps or more.
>> Certain of these 12V chargers will rapidly charge an iPad since the
>> iPad somehow knows there's a high current capacity automobile on the
>> other side of the USB connector. The Androids typically do not since
>> they don't understand whatever the iPad is doing to realize it's charging
from a car rather than your laptop.
>> The recommended charger in the link is one that does allow an Android
>> to draw 2 amps for charging... depending on which of the 2 USB
>> sockets it's connected to.
>>
>> There's a lot of detailed engineering study in that link.
>
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