The UK Home Automation Archive

Archive Home
Group Home
Search Archive


Advanced Search

The UKHA-ARCHIVE IS CEASING OPERATIONS 31 DEC 2024


[Message Prev][Message Next][Thread Prev][Thread Next][Message Index][Thread Index]

Re: One for the Apple-ites!


  • Subject: Re: One for the Apple-ites!
  • From: Ian Oliver <lists@xxxxxxxxxxxxx>
  • Date: Fri, 06 Nov 2009 13:04:16 GMT

In article
<f55662fc0911020103n77610019l5efc99ef10cec3ce@xxxxxxx>, Mark
McCall wrote:
> One of the problems with hubs and cheapo usb adapters is that they
> dont have the logic or the means to deliver 500mw. They're just dumb
> 100mw devices.

A few corrections.

USB initially provides a guaranteed 100mA and devices can then
negotiate additional helpings of 100mA up to a maximum of 500mA.

"Dumb" chargers do not do enumeration and negotiation, so the
base case
is that a device plugged into one of these will only take 100mA. Apple
devices, in their wisdom, often refuse to charge at all.

Obviously this is a serious limitation, and "something had to be
done".
What everyone has done is to define a new standard, and this specifies
that if a device detects that the USB D+ and D- lines are shorted
together and floating, they can take up to 1.3A from VBUS.

Of course, Apple have gone their own way. They need 2.5V on D+ and 2.0V
on D- before they will charge. I'm not sure what current they take if
they detect this.

The easiest way to provide this is -
5v---100k---(D+)----50k(2x100k in parallel?)----(D-)---100k-----0V

Any resistors will do, and some people supply 2.5V to both D+ and D-,
so experiment. A standard USB lead can be hacked to add the resistors
to make it into an Apple charger lead.

Ian Oliver
Sunny Leeds, UK
Using Java on Tini for control via Dallas 1-wire




------------------------------------


UKHA_D Main Index | UKHA_D Thread Index | UKHA_D Home | Archives Home

Comments to the Webmaster are always welcomed, please use this contact form . Note that as this site is a mailing list archive, the Webmaster has no control over the contents of the messages. Comments about message content should be directed to the relevant mailing list.