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Webcams from 40' away

By MAS4261
May 3, 2014
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  1. I am trying to stream video from 3 cams in my billiards room.

    Equipment to date:
    3-Genius F100 webcams
    3-3 Cat5e patch cables 15', 20', and 40'
    3- RJ45 to USB adapter sets
    1- 8 port powered hub at the laptop

    Windows 7
    Many Cam 4.0

    Testing done so far:
    Ran Many Cam it detected cam 1 (15') , cam 2(20') nothing from cam 3(40') However did not pick up a video signal it ran a continuous search for 30 minutes.
    Plugged all the cams into laptop ran Many Cam with success.
    Plugged flash drive into each run and could read the files on runs 1 and 2. Run 3 has a power light on flash drive but laptop doesn't detect the drive. Tried a 4 port powered hub at the adapter at the far end of the run still negative results.

    Any and all critiques and suggestions would be appreciated I am a very newb please use basic terms and be as detailed as possible.

    Thanks, Mark
  2. nismo91

    nismo91 TS Evangelist Posts: 926   +31

    Hey Mark,

    I've been in a pretty much similar situation before. I got a couple of IP cameras but since they're expensive, I'd also like to recycle my older USB webcams, so I've made some customized long USB cables but those never worked. It's not the matter of the 5V power at the end of the cable, but the data delay is too much when your cable exceeds 5m. Here are the quotes from the usb.org website:

    1. Why are there cable length limits, and what are they?
    A: The 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.

    2. I want to build a cable longer than 5 meters, why won't this work?
    A: Even if you violated the spec, it literally wouldn't get you very far. Assuming worst-case delay times, a full speed device at the bottom of 5 hubs and cables has a timeout margin of 280ps. Reducing this margin to 0ps would only give you an extra 5cm, which is hardly worth the trouble.

    3. What about using USB signal repeaters to make a cable longer than 5 meters?
    A: Don't bother. The best solution is self-powered hub with a fixed 10m cable that had a one-port bus powered hub in the middle. The maximum range will still have to deal with the timeout, so any out of spec tweaking of the terminations between the two hubs and the timing budget still won't yield more than 5cm of extra distance. A better solution is described in the following question.

    4. I really need to put a USB device more than 30 meters away from my PC. What should I do?
    A: Build a USB bridge that acts as a USB device on one side and has a USB host controller at the other end. Use a long-haul signaling protocol like Ethernet or RS-485 in the middle. Using cables or short-haul fiber, you can get ranges upwards of a kilometer, though there's no reason why the long-haul link in the middle of the bridge couldn't be a pair of radio transceivers or satellite modems.
    Embedded host solutions capable of doing this already exist. Also, two PCs connected via USB Ethernet adapters are essentially a slave/slave version of this master/slave bridge.

    For a 40" application, I think a wireless IP Cam would be a better choice. You can always tone down the video quality once the framerate drops.

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