[kwlug-disc] USB Webcam curious behaviour

Chris Irwin chris at chrisirwin.ca
Sun Aug 15 14:14:26 EDT 2010


On Sat, 2010-08-14 at 09:20 -0700, Raul Suarez wrote:
> When I plug just the usb webcam it works, when I have the wireless mouse plugged it stops working.

It could also be a power issue. From my limited understanding of USB
(and a quick check of wikipedia appears to confirm this), devices can
accept power in 1 to 5 units of 100mA, where 500mA is the maximum the
bus supports. So if your camera required higher power (say 4 or 5
units), and your wireless mouse dongle required enough power to push
them over the limit (say 2 units), there would be insufficient power to
run both.

http://en.wikipedia.org/wiki/Universal_Serial_Bus#Power

Usually USB ports are in pairs on the same bus. If you had four ports,
two would probably be on a separate bus, which should allow you to run
the devices together. Assuming it is a power issue.

-- 
Chris Irwin <chris at chrisirwin.ca>
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