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Thread: Connecting devices via a USB hub

  1. #1
    Registered User Clive Long's Avatar
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    Connecting devices via a USB hub

    I have a problem connecting a scanner to Windows XP through a USB hub.

    If the device is cabled directly to the laptop, the scanner software detects the scanner. If I connect all USB devices via a hub, the scanner software cannot "see" the scanner. The attached Western Digital Hard Drive and mp3 player can be "seen" when attached via the USB hub.

    The same behaviour occurs when I connect to the laptop running Linux.

    Any idea why this may be?

    Thanks

    Clive

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    Re: Connecting devices via a USB hub

    Hi Clive

    I can only hazzard guesses.

    - Is your scanner switched on BEFORE you start your computer?

    -> should be because the module may not be loaded on the fly. Did you try a modprobe?


    - Could be that the hub does not provide enough power for the scanner

    -> kinda unlikely, though because the scanner is powered but perhaps this influences the signal strenght. As I said, unlikely


    - hub prioritisation

    -> Have you tried disconnecting the other devices from the hub to see if the scanner works then? I mean a hub doesn't deal with multiple requests at a time (-> not a switch), so perhaps your external hard disk causes it never to get any sufficient transfer time? I am not sure how much this can be an issue, though it is worth trying.

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    Re: Connecting devices via a USB hub

    Is it an active or passive hub?

    A active hub has its own power supply. As Andreas said, you prob don't have enough power going through a passive hub to be running all the devices at the same time.

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    Registered User Clive Long's Avatar
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    Re: Connecting devices via a USB hub

    Quote Originally Posted by woodface View Post
    Is it an active or passive hub?

    A active hub has its own power supply. As Andreas said, you prob don't have enough power going through a passive hub to be running all the devices at the same time.
    Hi

    It is an active hub with an external power supply.


    Clive

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    Registered User frodo's Avatar
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    Re: Connecting devices via a USB hub

    Quote Originally Posted by Clive Long View Post
    Hi

    It is an active hub with an external power supply.

    Clive
    If you haven't yet tried swapping ports I've found sometimes some ports on a USB hub work OK and others don't.

    Even with an external power supply I've found some hubs have power difficulties - some can be very low quality.

    Have you checked device manager (rather than the scanner software) in Windows to see if it detects any problems.

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    Re: Connecting devices via a USB hub

    Also might be worth checking that you are not connection a usb 1.0 device to a USB 2. 0 or vice versa. Although they should be backwards compatible, it's not always the case.

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    Registered User Clive Long's Avatar
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    Re: Connecting devices via a USB hub

    Quote Originally Posted by woodface View Post
    Also might be worth checking that you are not connection a usb 1.0 device to a USB 2. 0 or vice versa. Although they should be backwards compatible, it's not always the case.
    Good point.

    I did have an unpowered USB 1.0 hub. I replaced it with a powered USB 2.0 but this didn't improve the problem.


    Clive

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    Papa Smurf
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    Re: Connecting devices via a USB hub

    I think Frodo has it right - certainly sounds like power to me. I would try a different powered hub to test this. Do you have any friends with a powered hub ?

  9. #9
    Registered User Clive Long's Avatar
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    Re: Connecting devices via a USB hub

    Quote Originally Posted by Dreadful Scathe View Post
    I think Frodo has it right - certainly sounds like power to me. I would try a different powered hub to test this. Do you have any friends with a powered hub ?
    I have a powered USB1.1 hub somewhere in a box in North London. I'll ty that. If the device is seen, then are there any quality / reliable makes for USB 2 hubs?

    On a different tack, I vaguely remember seeing some devices that have a setting for when the device is either connected directly over USB to the host or connected via a USB hub? Is that relevant? Why should it matter?

    Clive
    Last edited by Clive Long; 6th-February-2007 at 10:00 AM. Reason: Added connection scenario

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