Post by thread:[OT] 20 meter USB cable?

I believe for something that long you'd need an "active" cable, one that amplifies the signal (for lack of a better explanation). You can buy long ones, but I don't know how long they get, and I don't know anything about building one yourself. Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams Marcelo Puhl wrote: > Is it possible to make a 20 meter long USB cable? Will it work? -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

The USB spec limits you to 5 meters. To create a longer cable you have to place a hub every five meters. So, to go 20 meters you'd need three intermediate hubs. It is possible that cables longer than 5 meters would work, but they would be out of spec. There is a limit (5?) on the number of hubs between the computer and the peripheral. Bob Ammerman RAm Systems -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Thanks for the info. Is there a way to DIY such a cable? Mark On 2 Feb 2003 at 19:35, rad0 wrote: {Quote hidden}> I have used a 25 foot usb cable with no problems, that's foot. > > But over this, the computer coughs when you plug in the cable. > > UNLESS, you use an Active Extension Cable, which > lets you daisy-chain your USB devices up to 80 feet in most applications. > > I have used these things and they worked for me. I only went to 32 feet > though. > > FWIW > > > > {Original Message removed}

How did you make up the out of spec cable? Is it as simple as cutting a shorter cable & splicing? It would be very handy to extend the distance on an inexpensive usb video camera in a motor home to cover side & rear blind spots. The computer is already in place for navigation. John Ferrell 6241 Phillippi Rd Julian NC 27283 Phone: (336)685-9606 Dixie Competition Products NSRCA 479 AMA 4190 W8CCW "My Competition is Not My Enemy" {Original Message removed}

Marcelo Puhl <spam_OUTPICLISTTakeThisOuTmitvma.mit.edu> wrote: > Is there a way to DIY [an active USB extension] cable? Not easily, no. The active extension cables actually incorporate single-port USB hub chips; they're not just electrical amplifiers. This means, by the way, that active cables with full-speed-only (12 Mbps) hub chips will limit the communication between a high-speed (480 Mbps) host and a high-speed (480 Mbps) device to only 12 Mbps... So if you buy one of those active cables, make sure it's fast enough for your needs. The 5-meter maximum USB cable length was chosen to allow reflections from the far end of the cable to settle between bits; if a longer cable is used, reflections won't be damped as well, and the line voltage could rise high enough to cause physical damage to the drivers. The 5-hub limit on serially-connected hubs is a consequence of the USB spec for maximum turnaround delay between an outgoing packet and the incoming response. That spec allows for 70 ns of propagation delay through each cable/hub combination, and 30 ns through each cable alone; the sum of the propagation delays through 5 hubs and 6 cables (and back), plus the delay allowed in the device itself, beats the full-speed timeout spec by less than half a nanosecond. Adding even a few inches of cable to a full-length serial string of USB cables and hubs would violate that spec. There ARE very long-range USB links available, but they're more complicated than what we're discussing here; they consist of two USB chips -- one that looks like a device (peripheral) and one that looks like a host -- connected by ethernet or whatever. -Andy === Andrew Warren -- .....aiwKILLspam@spam@cypress.com === Principal Design Engineer === Cypress Semiconductor Corporation === === Opinions expressed above do not === necessarily represent those of === Cypress Semiconductor Corporation -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On 3 Feb 2003 at 15:34, Andrew Warren wrote: > There ARE very long-range USB links available, but they're more > complicated than what we're discussing here; they consist of two > USB chips -- one that looks like a device (peripheral) and one > that looks like a host -- connected by ethernet or whatever. > > -Andy > Thanks for your very enlightening reply! Are these USB-Ethernet links available? Mark -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Marcelo Puhl <PICLISTKILLspammitvma.mit.edu> wrote: > > There ARE very long-range USB links available, but they're more > > complicated than what we're discussing here; they consist of two > > USB chips -- one that looks like a device (peripheral) and one > > that looks like a host -- connected by ethernet or whatever. > > Are these USB-Ethernet links available? Yes; for an example (no endorsement implied) see Icron's "Ranger" series of USB extenders at: http://www.icron.com -Andy === Andrew Warren -- .....aiwKILLspam.....cypress.com === Principal Design Engineer === Cypress Semiconductor Corporation === === Opinions expressed above do not === necessarily represent those of === Cypress Semiconductor Corporation -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> Is there a way to DIY [an active USB extension] cable? Not easily, no. The active extension cables actually incorporate single-port USB hub chips; they're not just electrical amplifiers. Well, that implies to me that a DIY active extension cable can be made using several regular USB cables and cheap USB hubs... Given that a cheap cable is about $3, and a cheap hub is about $10, and both are commodity items, this kludge might be both cheaper and less expensive than a "rare specialty item" like an active USB extension cable :-) BillW -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.