Thread: (Nokia 770) + (USB host power hack) + (USB keyboard) != working
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mwiktowy is offline mwiktowy
2006-04-06 , 20:35
Posts: 373 | Thanked: 56 times | Joined on Dec 2005 @ Ottawa, ON
#14
Originally Posted by bhima
Did you do anything to feed power into the 770?

The USB host port on a powered hub is not supposed to actually provide power to the computer that you're plugging it into - it's supposed to _get_ power from that port. Normally, the power that goes into the hub is only used to power the gadgets you plug into the hub, not the hub itself.

If your hub provides power upstream to the 770 without something like a three headed cable - that is, if just a gender changer works - then your USB hub is totally violating the USB spec. It's convenient when they do that, since it makes it easier to use them on the 770. However, don't be surprised if most of the hubs _don't_ work.
My USB hub does this too and discovered this power back-feed by noticing that the fan on my video card would keep spinning even when my computer was turned off ... and unplugged!
I bought a USB gender changer to check if I could use this "feature" to my advantage. I haven't tried it yet but I did confirm that the voltage lines on the connector pinout are the same as when the cable is connected to the computer when you are operating the 770 in the normal slave mode. Not sure about the data lines ...

Update: I tried it out tonight and mounting a USB dongle works like a charm! :]
The exact model of USB hub that I have comes from the APC USB 2.0 Starter Kit (UPC 731304238706) that I bought at CostCo. Plug in the cable where the host computer normally goes. Plug in a USB gender changer into that. Plug in the cable that come with your 770 into that and you are all set. No soldering/cutting/splicing needed. Just a $20 hub and a $5 gender changer.
Last edited by mwiktowy; 2006-04-07 at 04:40.