what is the max USB cable length?

[bob_s]

I have moved my PRS alpha to a new shop. In order to get the best set up I need to have the computer about 16or 17 feet from the control box. I was using a bus powered hub with a 5 foot USB cable in my old shop and had very few comm problems. Am I looking for trouble going to a 16 foot USB cable and the hub?
If I needed it can a longer (30 foot) cable be used if it's the repeater type?
thanks
Bob
I tried to search for this, but unfortunately USB is too short a word to search with.

[myxpykalix]

Bob,
The way mine is set up the control box is mounted to my table and then a usb which is about 10 ft long straight to the computer.

Why would you need/want to separate the control box from the table? The chances of comm errors i think would be greater doing that.
I would think by having to bundle the lines from the steppers with the electric lines for your router/spindle would cause problems also.

If anything I would keep the control box at the table, keep your computer close and if you had to, increase your electrical line length. But there are other far more knowlegable that might say its fine

"If it ain't broke. don't fix it":

[garyc]

Bob...
Here is a search that may get you some info: (USB Cable Length) http://www.talkshopbot.com/forum/sea...earchid=644206


To ensure a reliable comm rate ShopBot does not recommend a cable length over 10 ft. Some (maybe even many) have done this, but high speed communucation may suffer, especially on the newer tools with higher resolution.

[richards]

I found this on Wikipedia:

"The USB 1.1 Standard specifies that a standard cable can have a maximum length of 3 meters with devices operating at Low Speed (1.5 Mb/s), and a maximum length of 5 meters with devices operating at Full Speed (12 Mb/s).

USB 2.0 provides for a maximum cable length of 5 meters for devices running at Hi Speed (480 Mb/s). The primary reason for this limit is the maximum allowed round-trip delay of about 1.5 μs. If USB host commands are unanswered by the USB device within the allowed time, the host considers the command lost. When adding USB device response time, delays from the maximum number of hubs added to the delays from connecting cables, the maximum acceptable delay per cable amounts to 26 ns. The USB 2.0 specification requires cable delay to be less than 5.2 ns per meter (192,000 km/s, which is close to the maximum achievable transmission speed for standard copper wire).

The USB 3.0 standard does not directly specify a maximum cable length, requiring only that all cables meet an electrical specification: for copper cabling with AWG 26 wires the maximum practical length is 3 metres (9.8 ft)."

[ssflyer]

I think the main thing in Richard's excellent descriptions is this:
"the maximum acceptable delay per cable amounts to 26 ns."

The maximum USB cable length only applies to each cable segment in the system, not to the total cable length between your computer and the peripheral.

I use an active 16" cable from my computer to my control box. This is actually connected to a hub at the computer, so basically I'm going through 2 repeaters.

While I'd certainly recommend the shortest run possible, you can go farther. While maybe not the best, I get ~76-78% transmission rate in the diagnostic app, and do not have lost comm errors.

[bob_s]

Thanks to everyone
I think I will though in an active cable and run the tests before I decide for sure
Still have hours of table reassembly to go
Moving is such fun!

[beacon14]

My plan is to mount the CPU right next to the control box (on the wall next to the SB), then use keyboard and monitor extension cables to locate the keyboard, mouse, and monitor on my computer stand where I actually work. That would keep the USB between the computer and control box to a few feet, and hopefully allow me to use the spindle control card as well.

Hopefully I will have time to do this some time this month. I'll let you know how it works out. Anyone know why this would not work?

[garyc]

David...
This works well. I have tested a 25 or 30 foot KVM and sound extension. Its getting harder to find non USB mice and keyboards.