External wired small USB keyboard

Stefan Monnier monnier at iro.umontreal.ca
Sun Oct 26 03:53:12 CET 2008

> On power drawing from an USB hub in a keyboard, I have the following
> question. Is it possible to connect at the same time:
> - USB power charger or network over USB with your desktop/laptop (does
> this also charge a little bit the Neo?)
> - external USB keyboard
> - perhaps one other USB device (low power consumption, almost passive)

As explained it's possible.  Regarding your last point, since the USB
port can provide up to 500mA (as the USB standard stipulates), there's
a good deal of power left: My Thinkpad UltraNav travel keyboard
(i.e. a keyboard just like the one on a Thinkpad laptop, with
integrated trackpoint and touchpad, as well as a 2-port USB-1 hub) uses:

   % egrep 'MxPwr|Product' /proc/bus/usb/devices
   S:  Product=USB 1.1 2 port downstream low-power hub
   C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr= 40mA
   S:  Product=IBM USB Travel Keyboard with UltraNav
   C:* #Ifs= 2 Cfg#= 1 Atr=a0 MxPwr= 70mA
   S:  Product=Composite TouchPad / TrackPoint
   C:* #Ifs= 2 Cfg#= 1 Atr=a0 MxPwr=100mA

I.e. it uses 210mA, and would leave 290mA left (for reference my
Logitech mouse uses 100mA, and my USB wifi 11g dongle uses 300mA).


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