On Sep 15, 1:00*am, Mike Bamberg wrote:
On Sep 14, 5:06*pm, Martin Gregorie
wrote:



On Mon, 14 Sep 2009 13:21:59 -0700, Darryl Ramm wrote:
That is *not* the only problem. This is a case where the devil is in the
details. Various (usually pull-up resistors) signaling schemes or funky
wiring are used by different manufactures to indicate charger
functionality or request higher current etc. As has been discussed here
the iPAQ 310 has some compatibility issues, there can be similar issues
with the iPhone, and so on.

I understand what you're getting at, but there's about zero chance that a
cigar lighter adapter would take any notice of pull-ups etc. - what would
you expect from a $US 5.00 charger? Or the USB socket on a cheap computer
for that matter.

I had a quick scout for specifications: the only ratings I could see were
one at 5v/700mA for one unit and 5v/1000mA for a second, so I guess they
nominally conform to the USB 2.0 current rating. *I'd suggest that a
device manufacturer who demanded more was being arrogant. Oh, wait, you
did say HP and Apple...

Martin

--
martin@ * | Martin Gregorie
gregorie. | Essex, UK
org * * * |

Martin,

There have been several individuals that have taken apart the HP-
supplied car charger and there ARE non-standard (as defined by the USB
spec) voltage divider resistors in the circuit on the charger side.
This provides a signal set to the device (throught the cable) to
trigger it to use the high current mode on the device. *If you plug
the device into a standard USB port on the computer it will not charge
at the same rate as with the HP charger. If you plug it into another
vendor's car charger there is no guarentee the device will operate in
high current mode.

In addition, the HP-supplied USB connector A-to-Mini cable has the
mini connector pins 4 & 5 shorted together. *This is also a signal to
the device that high current mode can be used. Using a "standard" USB
a-to-mini cable will not allow high current mode.

In short (pun intended) the HP design has many "safe guards" to insure
that the device does not use high current mode on a device or port
that cannot supply the needed current. *Or with a cable that may not
be designed for the higher current.

All of this because the HP IPAQ 310 series devices have a high current
drain if the backlight is in the brightess mode, which is desireable
for use in the cockpit and automobile.

I have tried several different USB port car chargers with the HP-
supplied cable and have not been able to get the high curent mode, I
have tried the HP car charger with a standard A-to_mini cable and also
failed to get the required current.

I *have been able to modify another charger by adding the resistor
divider circuit and using the HP-supplied USB cable to get the high
current mode to work.

So yes you're probably right there are "arrogant" manufacturers but
the power to "light-up" the unit has to be supplied some way and the
HP design team used the described method, with protection to assure
the device didn't cause damage with a non-HP setup.

Mike "in no way associated with HP" Bamberg

The setup HP (and others) is using is part of the USB 2.0 spec