Subject:
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Re: Vision Command [cables]
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 11 Sep 2000 19:36:37 GMT
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Original-From:
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Tilman Sporkert <TILMAN@WEBMETHODS.COMantispam>
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Viewed:
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1167 times
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USB cables aren't like the old serial or parallel port cables, where not all
cables had all the "optional" pins connected. USB has only 4 wires, and
that's it. So a missing wire won't be your problem. USB however is picky
abou t cable length, and that might be your problem. For the FAQ at
http://www.usg.org:
---
Q2: How long of a cable can I use to connect my device?
A2: 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).
Q3: Why can't I use a cable longer than 3 or 5m?
A3: 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.
Q5: I need to put a USB device X distance from my PC. What do I do?
A5: 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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The interesting part is that a high speed device allows for a longer cable!
Tilman
> For some time I have used a Logitec Quick Cam Pro with the Mars set and
> other applications for a Lego camera, Pre-Vision Command. It has about
> a five foot cable. I got a 10 foot extension. It was balky about • installing
> but did eventually install and work fine with the extension. I tried
> the extension on the Lego Vision Command camera and it would not install.
> The extension is more flexible and smaller diameter than the Lego semi-
> flexible metal rod cable. It may be missing a wire. I am going to try
> the two cameras at once now that I have replaced all the Quick Cam • software
> that Vision Quest announced it was erasing, 14 megs of it, because it was
> allegedly obsolete. I have a powered hub with about a five foot cable.
> It is possible that using a powered USB hub as a "repeater" might allow a
> bit longer cable, I will see. The cameras are power hogs and really • strain
> a USB port, sucking up most of the 500 ma such a port is rated to provide.
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Message is in Reply To:
 | | Re: Vision Command [cables]
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| For some time I have used a Logitec Quick Cam Pro with the Mars set and other applications for a Lego camera, Pre-Vision Command. It has about a five foot cable. I got a 10 foot extension. It was balky about installing but did eventually install and (...) (24 years ago, 11-Sep-00, to lugnet.robotics)
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