(David Arnstein) wrote in news:hlaqaf$d3i$1
> I would prefer not to pack a dedicated phone charger when I travel. Is
> there a hack to allow me to charge my cell phone from my notebook? My
> current cell phone is a W755.
> Thanks for any suggestions.
Motorola goes to some trouble to protect your USB devices from the
overcurrent their cellphones would cause by charging off your USB ports.
USB ports are rated for only 500ma of current drain and may damage your
computer if you exceed that value. So, to prevent this possibility,
Motorola has encorporated protective circuitry to measure exactly which
power supply it has been plugged into as there are several types of USB
power cables available. The pinouts and special circuitry in the proper
power cables look like this:
Motorola RAZR V3 mini-USB Charger pinout http://pinouts.ru/connectors/mini-usb_male.gif
RAZR V3 will not charge by simply supplying 5V through USB (it's
possible to use common USB cable for charging if you are using Motorola
special PC driver software).
Motorola uses the pin between Pin #3 and #4 (Pin X) to sense what device
is attached to the mini-USB port. Shorting Pin #3 to #2 and #X causes
the phone to go into handsfree/carkit mode and the LCD backlight will
ignore timeout settings and stay on.
Shorting pin X to pin 2 and to pin 4 via R=200KOhm causes the phone to
go into charge mode.
Pin Name Direction Description
1 +5 VDC -?- PC USB Pin 1 (+5 VDC).
2 USB Data -?- shorted to pin x in charger cable.
3 USB Data -?- not connected
X -?- Shorted to pin 2 + shorted to pin 4 via R=200KOhm in charge cable.
4 GND -?- PC USB pin 4 (GND). Connected to pin X via R=200KOhm in charge
Comment by Darrin
A standard Motorola USB charger puts ~1.4vdc onto the x pin of the mini
USB plug. A 200k resistor between pin 2 and 4 produces ~1.9vdc on the x
pin. This works for Motorola Q (which works from ~1.2vdc to ~1.9vdc),
but not for Razr V3m. I had to lower the resistor to 165k. This produces
~1.5vdc and allows the charger to become authorized.
End of quoted text.....
By overriding this safety feature, you load the USB device the phone is
plugged into upwards of 2 amps of operating (transmitting) and very
quick charging current as consumers demand the battery recharge so
rapidly. To recharge quickly, requires lots of current your USB ports
are not designed to supply.
Obviously, the nice high current switching charger Motorola has provided
you that is SO TINY, not some heavy old 2A transformer, is the correct
device to charge and operate your phone.
"iPad is to computing what Etch-A-Sketch is to art!"