On 23/08/12 16:26, Tony Firshman wrote:
I find mine *does* need an external power supply when running some
keyboards.
Yes, the two USB ports are poly-fused to 100mA each. Some keyboards
and/or mice draw more so the fuses kick in and increase resistance (why
am I telling you this?) reducing current. This causes the keyboards to
act like a QL with a dicky membrane, and misses keys or start
auto-repeating at a huge rate.
I have a USB wireless keyboard and mouse for mine, a Perixx Periduo 707
Plus, and it too draws too much from the USB port.
Plugged into the Benq monitor's powered hub, though, it works as good as
it does on my work laptop - both show the same problems such as it hangs
unless I leave it connected after power up, for about 30 seconds - or I
can unplug and replug the wireless dongle to get it working fine again.
The Apple keyboard for instance wouldn't work at all when Pi
was run off my monitor usb. I know they say 700ma, but it can be a
*lot* less than that.
700 mA is the minimum required for the Pi, but the USBs are limited to
100 mA each.
I suspect a wireless keyboard (and mouse if really wanted) and the pi
would quite happily run off a TV usb output.
There's a web page at http://www.elinux.org/RPi_VerifiedPeripherals
which has a list of what works and what doesn't. Of course, I didn't
find it until after I'd bought by keyboard!
HTH
My USB powered hub, separate from the monitor, seems to feed power back
down the interconnect cable to the Pi. The Pi's power LED comes on when
the hub has power and the Pi doesn't. :-(
It also refuses to boot with the hub attached.
It also kills the network when I connect the hub after booting the Pi.
Guess what, I bought that before finding the above page as well!
Sigh!
Cheers,
Norm.
--
Norman Dunbar
Dunbar IT Consultants Ltd
Registered address:
Thorpe House
61 Richardshaw Lane
Pudsey
West Yorkshire
United Kingdom
LS28 7EL
Company Number: 05132767
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