a silly question...but...

Discussion in 'General Hardware' started by gballard, Apr 29, 2004.

  1. gballard

    gballard Moderator

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    Is there a limit to the length that a USB cable can be? The reason I ask is that I wouldn't mind being able to keep check on the new kittens via my webcam. I just don't know if there is a theoretical limit for the length of a USB cable that I would need to be able to do this with. Anyone know?
     
  2. fantasi

    fantasi My Yngy is My HoneY! Folding Team

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    forgive me if im wrong but i think you need a repeater...the signal would actually be lost after a long line. how long is the cable u getting?
     
  3. fitz

    fitz Just Floating Along Staff Member Political User Folding Team

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    Proper credit goes to: http://www.usb.org/faq/ans5

    Q1: How long of a cable can I use to connect my device?
    A1: In practice, the USB specification limits the length of a cable between full speed devices to 5 meters (a little under 16 feet 5 inches). For a low speed device the limit is 3 meters (9 feet 10 inches).

    Q2: Why can't I use a cable longer than 3 or 5m?
    A2: USB's electrical design doesn't allow it. When USB was designed, a decision was made to handle the propagation of electromagnetic fields on USB data lines in a way that limited the maximum length of a USB cable to something in the range of 4m. This method has a number of advantages and, since USB is intended for a desktop environment, the range limitations were deemed acceptable. If you're familiar with transmission line theory and want more detail on this topic, take a look at the USB signals section of the developers FAQ.

    Q3: How far away from a PC can I put a USB device?
    A3: With the maximum of 5 hubs connected with 5m cables and a 5m cable going to your full speed device, this will give you 30m of cable (see section 7.1.19 for details). With a low speed device, you will be able to get a range up to 27m, depending on how long the device's cable is. With a straightforward cable route, you will probably be able to reach out 25m or so from the PC.

    Q4: I need to put a USB device X distance from my PC. What do I do?
    A4: If X is less than 25m or so (see previous question), buy a bunch of hubs and connect them serially with 5m cables. If you need to go farther than that, put another PC, or maybe a laptop, out where you need the device to be and network it with the first PC using something that's intended to be a long-range connection, such as Ethernet or RS-485. If you need to use nothing but USB, consider using USB based Ethernet adapters to hook the PCs together.
     
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  4. gballard

    gballard Moderator

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    well I am not buying any cable yet...just wanted to know if anyone knew..thanks for the info
     
  5. dreamliner77

    dreamliner77 The Analog Kid

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    What about wireless usb?