Slashdot Mirror
DIY USB Extension Cables Using Cat5/6?
TheDarkRogue asks: "Ok, I have a small USB device that I need to position a distance from my computer, more then the cable, at least 30 feet. The thing is that I don't think it can go that far very well. I looked around for a solution and found a few products I could get for a price way out of my price range, so now I'm looking at this as a doit-myselfer. How can I extend the distance using Cat5/6? Does anyone know of any schematics for something or is that in its self more then is needed?" Extending a USB cable to this length (or more) can't be this easy, can it? What's the maximum length of USB cabling one can get in a single stretch?
http://www.google.com/search?q=usb+maximum+cable+l ength+specification
e
http://www.google.com/search?q=usb+extension+cabl
Slashdot is jumping the shark. I'm just driving the boat.
Can long cables really be this easy? Maybe...
I dunno, I needed to network two machines QUITE a distance apart, so I made a crossover UTP network cable out of an existing UTP patch cord and several hundred feet of speaker wire, as two pairs (send pair and receive pair).
Works perfectly. Blazing fast, too. I would say that I just got lucky but I do these sorts of things all the time....
You may very well be successful with the Cat5/6 option. My excessively-long ethernet cable made out of speaker wire has been functioning flawlessly for months (in fact, I built another to network hubs at vertically and horizontally opposite corners of my household, and it has also worked like a charm).
--TheOrangeSquid Is it any wonder things seem so awry? We swim in a sea of confusion and don't have to think to survive
Ok, I have a small USB device that I need to position a distance from my computer, more then the cable, at least 30 feet.
Hot chick moved in next door, huh?
And you've found the perfect perch for your webcam, right outside her bathroom window?
And you don't want to get a wireless X-10 camera, for fear of being spammed and popped-under every day for the rest of your life?
Opinions on the Twiddler2 hand-held keyboard?
"For a low speed device the limit is 3 meters (9 feet 10 inches)."
From USB.ORG's USB Info: Frequently Asked Questions
In practice, manufacturer's technical support representatives often say that their devices will not work with a cable longer than 2 meters (6 feet), and they supply a cable of that length. In many office situations, a cable that short is useless. But they are right, a longer cable doesn't work, and a hub doesn't work.
Ethernet and FireWire are examples of properly designed computer communication interfaces. They are trouble free.
USB 1.0 is an example of a poorly designed and poorly implemented interface. USB often interferes with computer hibernation, to give another example.
Here's a plan!
- Cut ends off existing USB cable, and solder to longer cable.
- ...
- Profit!
But seriously -- what exactly are you asking? If want to know if a longer cable will work, then just solder up a longer cable and test it. If you want to know if twisted pair will help with electrical interference, or what wires to choose to run to which pins to give the greatest benefit from the twisted pair, then ask that instead. If you're looking for inexpensive passive or active extensions, ask that. If you want to know where to find cheap cable ends from a reliable vendor, ask that. If you want to build your own USB repeater (or whatever they're called), ask that. But I can't figure out what your current question is. If your question is "How can I extend the cable length using a longer cable," then the answer might be, umm... maybe you could use a longer cable?Yes you could build some hardware that would convert between USB and ethernet. Would it be that difficult, not especially. If you could find a micro with a USB and ethernet controller you'd be mostly set. However, you could probably only find either a micro with USB or ethernet controler but not both. Then you need to add the other controller. Ethernet's protocol isn't very complex. Most of its complexity is in detecting and avoiding packet collisions. I imagine to just read USB packets and forward them on to the ethernet layer wouldn't be all that hard either.
You would just have to build two of them.
Now would you really want to do that? Not unless you thought it would be a fun project or you REALLY needed that USB device and had no choice in physical placement of that device. If you have no experience in electronics, then forget it. If you haven't tried google, someone else might have already created something like this. You might even find a USB repeater too, who knows.
"active USB extension"
16 foot for 30 bucks.
30 foot for 45 bucks.
60 foot for 60 bucks.
Relatively cheap, zero signal degradation.
Roll you own from CAT 5....
Expencive when you destroy your device and/or motherboard.
If voting were effective, it would be illegal by now.
if i am correct the longer "active" cables use in-line power to keep the signal alive
so you could just put a small amplifier on ?the far end? of the connection and viola!
cello!
Mea navis aericumbens anguillis abundat
KDS has active cables for 20 bucks that go 80 feet. 20 bucks (with a return policy) is worth skipping the hassle of soldering together a cat5 hack.
;)
On the subject, I've been looking for a source for cheap "APC Smart cables" for my UPS. I have pin-outs, so I know I could run down to Fry's and buy cable and ends. The cheapest I've found pre-built cables is 50 bucks, which seems extreme for a simple cross-wired DB9 cable. I need three of them, so I'm stuck between being too lazy to solder together three cables or paying $150. So far my solution is to skip the whole subject and wish really hard for one.
You can't just go hacking into a USB cable and make it longer. Probably the #1 reason is that USB uses a differential signal. That means that however you extend the cable you have to do it exactly the same on both D+ and D-. If you don't, part of your diff signal gets skewed and becomes corrupted at the receiver. Secondly you have to maintain an imepedance match. Anytime you introduce an impedance mismatch you generate reflections. The wire used in a USB cable has a certain about of reactiance (X). The X of a twisted wire pair is completely different.
In order to do what you want, you really need to build a fairly preceision amplifier/receiver setup. The difficulty is the fact that you are dealing with differential signals. Each "side" of the diff signal must be treated the same way. It is almost impossible for you to make the exact same size solder joints, exact same size wires, and have the exact same impedances throughout. Its especially important on long runs because of the highly immentant signal attenuation.
I'm just curious -- does the USB port put out a strong enough signal to go 20 or 30 feet or more without some kind of booster/amp? And how about the device? Especially if it does not have its own power source.
I remember trying to extend serial cables and keyboard cables on some computers in the past and it didn't work simply because there wasn't a strong enough signal.
'Course, it probably helped that the total length was only like 2 feet, but still.
- Jonathan
From The USB FAQ
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.
Essentially, the USB cable is a mismatched transmission line. As a result, the signal reflects off of the ends of the cable, resulting in a stair-step pattern whenever the voltage level on the line changes. As the cable gets longer, it takes more time for this stair-step pattern to settle to the final voltage.
Come test your mettle in the world of Alter Aeon!
The only way to properly do this is to find a USB extension cable. It's a device that has a small hub controller in one end. (looks like a regular cable with male& female A connectors on each end, but has a larger housing at one end and in that housing, there's a hub.)
You might find that you can extend it in other ways, but they will be very finicky.
The other option is to connect multiple cables together using regular hubs.
I read this story earlier and just happened across this device a minute ago:
16 ft. USB Active Extension Cable
I have ZERO relation to this company (though I have bought from them before) and have ZERO experience with the product. But it looks like what you're after. I'm sure there are other vendors who supply this device as well.
Good luck!
I have a 10 metre usb extention cable, it runs along side 2 cat5 cables, one for lan and the other carrying kvm data. I run it to my linux router which is up in the attic (to keep things quiet).
In order to get 10m out of usb I used 2 x 5 metre usb(A) to usb(B) cables and a 5 port minihub, the cables cost me 5(ukp) each from Tesco of all places, and the hub was 15(ukp) from maplin electronics. It all works like a dream and only set me back 25(ukp)
I think this must be working at both high and low speed as I'm running a speedtouch usb adsl modem on the end of the usb as well as my keyboard and mouse. I was even toying with the idea of usb speakers if I can find some that are supported by linux and are available in the UK.
Maybe someone could help me out with tails of usb audio experiances.
I admit I don't know a whole lot about USB, but have you looked into powered USB hubs? I don't think this would overcome the signal problem, but it would fix the power problem.
Work is punishment for failing to procrastinate effectively.
They did this on an episode of the ScreenSavers once. They started stringing USB extension cables together on a USB webcam to see how far they could get it to work. I don't remember what the distance was, but they made it quite the distance beyond the USB spec before it quit being properly detected by the computer and functioning.
Something to try if you can get some cables on the cheap.
I wanted to play about with an extended USB cable, so I could have a webcam at my door. Here's what I did:
Of course, I only wanted a cable for a cheap USB webcam, and it was the only thing on the bus. The specification calls for much shorter cables, and that's presumably for a reason. Your mileage may, or course, vary.
I've had success though. Good luck.
Michael
"Goodness me, how unlike the FBI to abuse the trust of the American public." -- The Onion