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| Tahnok:
I read somewhere that USB cable has a 6' maximum before it becomes unreliable. But I just realized that my web cam has a 12' USB cable! I was wondering if it would be possible to extend a gamepad hack to 12'. My cab is across the room from my computer, right now I send a 15' length of wire from the PS/2 port without any problems. 12' would be enough, though it would be nice to have it a bit longer. I was also wondering if USB cables must be manufactured in a certain way. I know certain network cables can not be spliced without messing them up, is USB similar? If so, does anybody know where to get the cabling and a good guide to working with it? Thanks, Tahnok100 |
| SideShow Rob:
From the USB.org FAQ: " 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. " Hope this helps.. |
| daywane:
I watched Patrick and Leo on screen saver extend over 100feet. I wish i could remember how they did it but they had web cams running on both ends of the building try |
| IntruderAlert:
I saw that too. They just kept hooking USB extension cables together and it still worked fine. |
| IntruderAlert:
--- Quote ---USB extension limits Tom in Arlington, Virginia, took time out from his duties as a TechTV Chat moderator to give us a call. All hell broke loose in the chat room, but Tom really wanted to ask about the cable limits of USB. He wants to put a netcam in his backyard, which means he needs a connection that's about 100 feet long. Can he do this? USB has a specified cable length limitation of 5 meters (16.4 feet). This doesn't mean that USB won't work on longer cables. It just means that 5 meters is the "guaranteed" length that USB will work. Go longer than 5 meters and you might encounter problems. Back in January, we did an experiment on the show to see how long we can go with our USB cables. We used all of our USB cable extenders and got to a length of over 17 meters, and our USB connection was still working. Leo recommends using passive USB extension cables until you get to your desired length. It may still work. You can also try using optical USB extension cables, but they're pricey ($165 to $245). You can also try using a USB extender, but they cost $299 to $369. Thanks for calling, Tom, and thanks for helping out in the chat room. Now get back in there before we lose complete control of chat! --- End quote --- http://64.233.187.104/search?q=cache:AZfp-F97dG4J:cache.techtv.com/screensavers/shownotes/story/0,24330,3419744,00.html+&hl=en&client=firefox-a --- Quote ---USB Limits How far can you go with USB? By David Prager Print Printer-friendly format Email Email this story Video Highlight The Limits of USB USBQ: Do you know if there is a USB cable length limit if you only hook one device to it, such as a netcam? -- Richard, via email A: According to the USB Implementers Forum (the designers of the USB spec), USB cables have a range of optimal operation no longer than 5 meters. In fact, they go out of their way to avoid approbation of using any kind of signal repeater to create a longer cable. Of course, we decided to give it a shot anyway. We've overclocked far too many processors here on "The Screen Savers" to not test out USB's limitations. First, we connected a generic USB netcam with the 10-foot cable it came with, and turned on the video so that we could see it on the monitor. The video looked great. In order to create a longer cable, we used Belkin's 6-foot Pro Series USB extension cable (sells for under $20). This made our camera 16 feet long (equivalent to the 5-meter limitation), with the video still looking great. Luckily, we still had several more of these extension cables at our disposal. After systematically hooking each cable up, we finally exhausted our supply, yielding a USB cable 56 feet long (17.07 meters). The picture still looked great, although the video's appearance on our monitor exhibited more latency than our original connection. A low powered, low bandwidth single USB device such as a netcam can function at significantly longer distances than the spec designates, although no company would assume the liability of recommending it because of the potential problems you can encounter (much the same way no company recommends trying overclocking). For more taxing USB devices, more expensive products exist that can extend the range of USB. One example is QVS's Active Repeater extension cable. Unlike the passive Belkin cables that we used, an active extension will actively regenerate signals to prevent data errors. These cables boast effective operation at up to 80 feet. The best and most expensive option is using a product such as Icron's $270 USB Ranger that uses Ethernet to increase USB's range to 100 meters (328 feet). Here is the USB Implementers Forum explanation to USB cable limits: The [USB] cable length was limited by a cable delay spec of 26ns to allow for reflections to settle at the transmitter before the next bit was sent. Since USB uses source termination and voltage-mode drivers, this has to be the case, otherwise reflections can pile up and blow the driver. This does not mean the line voltage has fully settled by the end of the bit; with worst-case undertermination. However, there's been enough damping by the end of the bit that the reflection amplitude has been reduced to manageable levels. The low speed cable length was limited to 18ns to keep transmission line effects from impacting low speed signals. More questions about the USB spec can likely be answered in this FAQ. Posted January 29, 2002 --- End quote --- http://64.233.187.104/search?q=cache:LH-YNaTVFSMJ:cache.techtv.com/screensavers/answerstips/story/0,24330,3370002,00.html+&hl=en&client=firefox-a |
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