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Re: unable to enumerate USB device

Mikkel L. Ellertson wrote:
Jim wrote:
To get a hub to work with all devices, hubs must have their own power
source externally.
Hubs that get there power source from the computer are the ones that
give you problems, because of voltage drop across the cable to computer.

Considering the amount of current we are talking about, I do not
think voltage drop is a problem. On the other hand, with a bus
powered hub, all the devices, plus the hub itself, are limited to
the max current of the port you are plugged into. A limit of
500ma/port is common, but it could be less.

Voltage drop = current x resistance
.5v = 500ma x 1 ohms.

I have had a number of bad experiences with bus powered hub, devices that would not work in hub I plugged directly to computer and they work fine, so i purchased external powered hubs and have had no more problems As far as the voltage drop goes it depends a lot on how the USB device was designed as to how much current it's going to draw. I'm quite familiar with OHMS Law.


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