Thread: powering a usb cable

you can do this no problem, just send power twards the front & not connected to the motheboard.... this may or may not be your issue... some devices just don't like long cable runs... there are usb extenders that can help if the power doesn't, worth a shot though..

Originally Posted by FC3S

if you splice into the hub like that, it'll put power back into the mobo, which is probably a bad thing

If he cuts the +5v wire in the extension cable and only applies +5v to the wire going to the device-side plug, and leaving the +5v wire coming from the computer disconnected, then it wouldn't harm anything.

The computer does have control of the +5v line on its USB ports, ie - it can shut off devices as it wishes... so there is a chance that the computer might be unhappy that you are powering the device all the time, taking control away from it... but during normal operation that probably wouldn't be an issue.

Though, that would only solve it if it is in fact a power issue; it's also quite likely that it is a signal issue, in which case you would need either a hub or an active USB repeater cable as others have suggested. The USB spec for maximum cable length is something like 5 meters, and I think that that is probably assuming the cable is used in a "normal" household environment, as opposed to a car where there is a lot more interference, etc, so if you are using a cable that is anywhere near to that long, signal problems might very well be your issue.

you can run a jumper wire from the ps to the hub because its all coming from the same power source.

i also heard that if you have a hub and are using usb 2.0 and 1.0 devices at the same time it goes to 1.0 disabling the 2.0 device. havent ever proved this theory though.

each motherboard header for usb can only provide about 500ma before it's overloaded, but then again, for a device to be usb compliant it should be able to be run on 500ma or less, unless they provide an external power source...

I'm guessing your issue isn't power related, but worth ruling out anyway by testing this...

Originally Posted by albysure

I also heard that if you have a hub and are using usb 2.0 and 1.0 devices at the same time it goes to 1.0 disabling the 2.0 device. havent ever proved this theory though.

no, that's not the case. in fact, in case you're interested, the system is pretty cool: all communication between the PC and the usb 2.0 hubs is done at usb 2.0 speeds; even if the PC is trying to communicate with a usb 1.x device on a hub. the hub gets data from the PC at high speed, "dumbs it down" to low speed to communicate with the device, and then gets the device's response and transmits it back to the PC at high speed. while the hub is communicating with the device at low speed, the rest of the hubs and devices on the bus can continue operating at high speed, even those on the same hub, so the low-speed transaction isn't wasting valuable bus time. consequently, all this extra conversion and control is why usb 2.0 hubs are usually a lot more expensive than 1.x hubs; they're not just faster, but also a lot 'smarter' and have to do a lot more than simply pass data straight through.

sorry for going off on a tangent, can you guess who's been spending too much time reading about USB?

see, now I thought the oposite was true, & that only special hubs can share both without reducing the 2.0 to 1.X.... I didn't think just any 2.0 hub can support both speeds simultaniously???