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?

Comments

links

[bellings]

http://www.google.com/search?q=usb+maximum+cable+l ength+specification

http://www.google.com/search?q=usb+extension+cable

Long cables

[orangesquid]

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).

Larry Flynt, hero of the people

[orthogonal]

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?

"For a low speed device the limit is 3 meters."

[Futurepower(R)]

"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.

Re:"For a low speed device the limit is 3 meters."

[evilviper]

Ethernet and FireWire are examples of properly designed computer communication interfaces. They are trouble free.

Quite right... What people don't usually realize is that FireWire is just a form of serial SCSI, meaning you should probably be saying 'Ethernet and SCSI'. The same is true of FiberChannel, Serial SCSI, and perhaps even standard parallel SCSI.

<rant>
If you think about it, manufactures NOT putting Firewire in their systems makes a good deal of sense. IDE is used rather than SCSI, so USB would be used rather than Firewire. It just makes sense.
</rant>

I have two complaints.
1. SCSI standards are too divergent. If they could just come together and make one controller that does Serial SCSI, Fiber Channel, and Firewire, all three would get quite a boost from the others.
2. Not enough devices support Firewire and Ethernet. I was looking at laser printers recently, and only the extremely hi-priced ones have NICs. (A 100Mbps Linksys NIC can be had for $5, so I don't see the problem) Perhaps more manufacturers should make their devices (printer, scanner, camera, et al) modular. That would be the best way to encourage easy interface upgrades (buy a new module, not a whole new device)

Profit!

[Karma Farmer]

Here's a plan!

1. Cut ends off existing USB cable, and solder to longer cable.
2. ...
3. 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?

Probably isn't going to work.

[CMiYC]

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.

Re:Probably isn't going to work.

[rcw-home]

Ethernet is also a differential signal - signal skew is simply not that big of a deal, especially at USB speeds. Light travels a long ways in one clock cycle.

Impedance also isn't a big deal. According to this, it's supposed to be 90 ohms, and the spec allows for 15% variation. Cat5 is about 100 ohms.

What is important is timing. According to this, the low-speed timing limitation is 18ns, or 300000000*.000000018 = 5.4 meters. Significantly under 30 feet.

Size of solder joints... sheesh.

You'd be surprisedwhat you can do

[brink]

Stranger things have been done. Once my brother-in-law and I were SOL on finding a serial-to-rj45 cable for the management port of a router. All we could find was a cd audio cable and a cat 5 patch cable, so we stripped one end of the cat 5 and plugged it into the pinholes of the audio cable, then pulled the wires out of the plastic on the other end of the audio cable and just shoved them onto the serial port pins. Worked like a charm!

'Course, it probably helped that the total length was only like 2 feet, but still.

Electrical Limitations

[SagSaw]

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.

Use an active USB extension

[no_such_user]

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!

Re:Is 80 feet enough?

[geoswan]

As an anonymous coward has pointed out this is a mis-reading of the KDS page. To get the 80 foot extension you have to connect 5 x 16 foot extension cables. I am repeating the anonymous coward's observation as I have a higher karma rating.