How to carry out USB 2.0 extension over long (> 5m) distances?

[choochoo_baloo]

I have been reading a couple of webpages which give the impression that USB (2.0 devices in my case) cabling is only 'well behaved' at up to 5m in length. I understand that at greater cable lengths the increasing signal lag times lead to erratic behaviour of the connection.

I now need to lay the data cables from my pier to the house, a distance of 17m. I have fitted a quality serial to USB adapter to the mount's serial connection. This means that I need to cable 4 USB channels (imaging camera, guide camera, mount & focuser) through the 17m.

Am I correct in saying that the best way to carry these 4 data channels would be using a USB 2.0 extender that uses an ethernet cable ie 2 USB female blocks at each end of the run, with a male-male ethernet in-between? Here's the first link I came across of this sort of thing: http://www.cclonline.com/product/147761/USB2-BOOST/USB-Cables/USB-2-0-Extender-Supports-up-to-50m-requires-ethernet-cable-/CAB3333/

Could a single Cat6 ethernet cable be used to carry all 4 data channels, obviously it would be preferable to have 1 Ethernet cable + pair of USB-Ethernet extenders than 4! If so could I use a normal USB hub at either end of the run?

Thanks in advance for any information.

[kalasinman]

Although I have run a large network at a school, we never used these  http://www.pcmag.com/article2/0,2817,2415501,00.asp

To me, especially if you have USB3 (see review) running cat5 or 6 as a LAN makes perfect sense. CAT 5 is easily good for 100'

Any bottleneck would be the USB which would only be a few inches long and be near maximum.

I assume the USB will be from a device in the obsy, so why not use one of these and have a wireless router to the house?

[Macavity]

I control my telescope mount / focusser over a 30m run of Cat5. When

it became clear that *neither* of two £50-60 "USB extenders", I bought,

worked, I tried an Icon "Rover". I only need USB 1.0 (1.1) but... it works!

http://www.icron.com/products/icron-brand/usb-extenders/

They also make devices for USB 2.0 and 3.0 - All, "at a price"! Unlike

the cheaper ones, they do acknowledge the "5m problem" and attempt

to *correct* for it? I sense budget devices merely boost signal level?

[choochoo_baloo]

Thanks both, helpful info. once again. Admittedly I naively bought lengths of budget 20m USB extenders off of eBay a while ago and have since realised 'what the heck am I doing' - I'm not normally a bodger honest!!

[kalasinman]

Wouldn't a wireless router be elegant?

[choochoo_baloo]

Wouldn't a wireless router be elegant?

Yeah that does sound a good idea. I may well use the wireless route. Please excuse my ignorance, but how would I set it all up? Can wireless cope with these 4 X USB channels' bandwidth?

[jnb]

USB can not be extended very far because it is inherent to the design that there is no correction for timing issues. With the high speed of some USB that means that only short cable runs can be used. Ethernet of some form is a good solution because it's ubiquitous, cheap, versatile and resilient. It can mean that it's easier to put a second computer next to the scope and control that remotely but I'd regard that as a benefit.

[JamesF]

I think there are a couple of issues you may need to think about here.

One is that USB systems need each end of the connection to be able to communicate within a given timeframe.  That sets a limit on the distance between them.  The only way around that if you want to connect devices over a greater distance is to use active repeaters that accept the data sent, then store and resend it as it it were a new USB connection.  Typically active repeaters draw their power from the USB port, which does place a limit on how many you can daisy-chain.

Another is that some USB device drivers expect the device they control to respond within a given timeframe, or make assumptions about the actual total travel time for the signals between the PC and the device.  That can mean that the device driver will fail to work correctly even if you have active repeaters extending your connection.

Related to the second point is the issue that USB is not full duplex.  That is, both ends cannot send data at the same time (I think this changes in USB3 or USB3.1).  So, if you have a system at the far end generating data very quickly, you may get problems where it can't buffer enough whilst it waits for confirmation from the local end that the data was received correctly and lose data as a result.

None of this means that it won't work, nor even necessarily that it is unlikely to work.  Perhaps more that if it doesn't work you shouldn't particularly be surprised.

James

[peroni]

I've successfully used the 20m USB active repeater cables .

http://www.amazon.co.uk/dp/B005LMWD48/ref=pe_385721_37038051_pe_217191_31005151_3p_M3T1_dp_1

(Hopefully that edit worked

[JamesF]

I've successfully used the 20m USB active repeater cables .

http://www.amazon.co.uk/dp/B005LMWD48/ref=pe_385721_37038051_pe_217191_31005151_3p_M3T1_dp_1

Hmmm.  This is why I think there should be no surprise if it doesn't work...

The USB2 spec, for instance, demands that the cable delay be less than 26ns.  If you don't meet this requirement, the device isn't truly USB2 (as the above cable claims to be).  Using a signal speed of 2/3rds of the speed of light (which I think is about right for copper), 26ns allows the signal to travel 5.2m assuming I haven't misplaced any zeros.

Now it may be that the unit on the end of the above cable ignores that requirement and that whatever device you have plugged in lives with it; it may even be that quite a few devices do, but it is outside the spec and a device that strictly interprets the spec may not work at all or may work unreliably (which might be worse).

There are other requirements of the USB spec. (such as the times allowed for a signal to be acknowledged after which the sender will consider it "lost") that set limits on the cable lengths too.

You can get devices that take the USB datastream buffer it, retransmit it over, say, ethernet, and then unpick it all at the far end and convert it back to USB before transmitting it to the target device.  These can and do work even over great distances, but there are limitations particularly where large volumes of data are involved.

James

[peroni]

Another option to consider, if you have mains power to your pier is using a ethernet over power adapter. I have my laptop outside in obsy and remotely control that using Teamviewer. Shorter usb cables can then connect from mount etc to laptop.

[mhard26339]

My dome to study is approx 27M and I run mount, 2 cameras, full dome control, focuser, all sky camera, IP camera etc etc through a powered hub and USB cable (similar to that shown by Peroni) to my computer in the study and it all worked OK, no problems. However, I settled on a Cat6 Ethernet cable hard wired through my router to a computer in the dome. This is controlled via TeamViewer and works very well from anywhere in the world; however when laying cables I did lay the 30M USB down as well just in case I need it in the future.

If you do decide to go the USB route make sure that you get an industrial grade USB hub such as (My dome to study is approx 27M and I run mount, 2 cameras, full dome control, focuser, all sky camera, IP camera etc etc through a powered hub and USB cable (similar to that shown by Peroni) to my computer in the study and it all worked OK, no problems. However, I settled on a Cat6 Ethernet cable hard wired through my router to a computer in the dome. This is controlled via TeamViewer and works very well from anywhere in the world; however when laying cables I did lay the 30M USB down as well just in case I need it in the future.

If you do decide to go the USB route make sure that you get an industrial grade USB hub such as (http://www.amazon.co.uk/StarTech-com-Mountable-Rugged-Industrial-Port/dp/B003AVPUZG/ref=sr_1_2?ie=UTF8&qid=1435918386&sr=8-2&keywords=industrial+usb+hub). the cheap, even powered hubs, do not stand up to being left outside in sheds and domes and expected to work every time when required IMHE

My build can be viewed at New Observatory in Norfolk UK.

regards). The cheap, even powered hubs, do not stand up to being left outside in sheds and domes and expected to work every time when required IMHE

My build can be viewed at New Observatory in Norfolk UK.

regards

Mike

[Macavity]

Might be worthwhile having separate links. One, your "ultra-reliable" low speed connection for

mount control (maybe focusser too!) and a second faster link for data transfer, cameras etc.

I also envisage a "hardware" Emergency Stop cable, if I totally lose control of mount slewing!

Despite my claim of "perfection" re. the Icron USB units, there are still occasions when the whole

system stalls? Usually when the focuser is connected. In the past, people used to checkout IRQ

settings (sharing?), but admit I haven't yet made an effort. Scope Focus can be fairly stable!

Much of the general wisdom re. *quality* cables and hubs applies. "Every little helps"? Don't

give up! It's probably taken three years of hardware swapping and frustration to get this far.

[kirkster501]

How do you guys use the USB to Serial adapter to control the NEQ6 when plugged into a USB hub?  Will the PC still recognise the USB<>Serial adapter (assuming the driver is installed of course) when plugged into a USB hub? I don't have a USB hub on which to try it currently...

Perhaps this should be another thread....

[kalasinman]

I got the adapter that saves the com port selection. After the com port (usually COM1) is assigned ASCOM sees a serial connection and everything works flawlessly, at least for me.