USB and ethernet cabling in the obs

pmrid (Peter) · #1 06-03-2011, 03:38 PM

I'm having a serious Spring-Clean (yes, I know it's autumn) in my obs in conjunction with a re-engineering of the way the roof rolls on and off.

Since all the furniture and non-fixed items have now been removed for that exercise, the opportunity is there for me to look at re-routing scope power and data cables as well. The obs has a raised wooden floor (only 250mm raised though, so sub-floor access is limited).

I'd like to look at making my data cabling a little less chaotic and am therefore wondering what others think about routing data (USB) with power in the same conduit. Bad news? What about ethernet cables and power or USB. Another no-no?

I have a couple of those Gigabit enthernet USB hubs I'm thinking of using in conjunction with the scopes/guidecams and imaging cams - hence the interest in ethernet cabling.

Peter

Tandum (Robin) · #2 06-03-2011, 04:03 PM

Peter, There shouldn't be a problem running DC with the USB cables. That said, if the DC is ripply, ie: not flat like a battery output, it may induce small signals into the cables around it. I'd err on the side of caution and run it seperately. Or you could run the volts in a shielded and earthed cable which would suck up any crap.

mithrandir (Andrew) · #3 07-03-2011, 10:52 AM

I presume any mains power is already running through separate conduit.

How long is the cable run? USB has much shorter limits than GigE.

If you are running solid core Cat6 for your GigE, have you considered running your USB over that too? The USB to Gig converters aren't cheap but you would eliminate crosstalk and power drop in the USB.

Also pulling one cable through a duct is easier than two, especially if you have to replace one at some stage.

If you were worried about lightning, you could use fibre between the switches.

Andrew

pmrid (Peter) · #4 07-03-2011, 12:59 PM

Quote:

Originally Posted by mithrandir

I presume any mains power is already running through separate conduit.

How long is the cable run? USB has much shorter limits than GigE.

If you are running solid core Cat6 for your GigE, have you considered running your USB over that too? The USB to Gig converters aren't cheap but you would eliminate crosstalk and power drop in the USB.

Also pulling one cable through a duct is easier than two, especially if you have to replace one at some stage.

If you were worried about lightning, you could use fibre between the switches.

Andrew

Thanks Andrew.
I haven't had much success so far with USB-GigE converters. I've tried 2 brands and each seems to be unable to deal with anything more complex than an external HD or a thumb-drive device. Might run a web-cam but try to get it to talk to a CCD camarea - like a QHY5 guide cam or a QHY8 imaging cam and it bottoms out.
Because this is not my area of expertise at all, I am fumbling in the dark a bit more than usual and - as usual - it costs 3 times what its worth before you stumble over the right combination. So any suggestions as to devices that would work would be gratefully received.
I have a broadband signal beamed to the observatory where it is is picked up by a dish and then into an access point and then into a wired 4-port switch. The individual computers in the obs are connected via Cat5 cable at the moment but maybe now is the time to go up a level there as well.

Peter

steve000 (Steve) · #5 07-03-2011, 04:19 PM

These will fix any USB distance issues.. basically they convert USB to ethernet cable then back to USB again.. ive ran a USB webcam about 30m away using one of these http://cgi.ebay.com.au/USB-2-0-RJ45-...item35b03fbbfd

Ethernet with power is not a good idea. id recommend 2 conduits, one for data and one for power.

pmrid (Peter) · #6 07-03-2011, 07:45 PM

Quote:

Originally Posted by steve000

These will fix any USB distance issues.. basically they convert USB to ethernet cable then back to USB again.. ive ran a USB webcam about 30m away using one of these http://cgi.ebay.com.au/USB-2-0-RJ45-...item35b03fbbfd

Ethernet with power is not a good idea. id recommend 2 conduits, one for data and one for power.

Thanks Steve. I'll order a couple and see how they go.
Peter

IanL · #7 07-03-2011, 10:52 PM

Hi Peter, Have a look at power over ethernet. I used to work in the mines doing IT and this was the way we used to run web cams in domes that took snap shots and sent them back to Southbank HQ via Next G via mobile.

http://www.dlink.com/products/?pid=368
Or google power over ethernet

Might not be the way you want to go but gives you options.

cheers

Ian

gregbradley · #8 08-03-2011, 08:09 AM

You also may want to consider a powered USB hub if you have more than one USB cable. That way you only have one USB cable to go from the hub to your computer. They are cheap too.

Greg.

pmrid (Peter) · #9 08-03-2011, 11:01 AM

Quote:

Originally Posted by gregbradley

You also may want to consider a powered USB hub if you have more than one USB cable. That way you only have one USB cable to go from the hub to your computer. They are cheap too.

Greg.

Yes. Thanks Greg. Had a look at that but I want to escape the limitations of USB cable lengths if I can. I am aware of powered USB cables that will extend that distance somewhat. But my obs is quite large, has 2 active piers working in it and I need to impose a bit more discipline on myself in terms of how I run power and data. And Gigabit Ethernet seems to me to be the way to go in order to have the bandwidth I expect to need in a few years time when we go through yet another technology evolution.
Peter

icytailmark (Mark) · #10 08-03-2011, 04:32 PM

you could just use a usb hub and a gigabit ethernet switch. USB hubs are dirt cheap and you dont even need to get a powered usb hub. Buy a usb hub that connects into your laptop/pc then run cameras etc off it. If you cant have a laptop next to your camera etc then just buy this.
http://dicksmith.com.au/product/XH68...etwork-adaptor

pmrid (Peter) · #11 08-03-2011, 05:24 PM

Quote:

Originally Posted by IanL

Hi Peter, Have a look at power over ethernet. I used to work in the mines doing IT and this was the way we used to run web cams in domes that took snap shots and sent them back to Southbank HQ via Next G via mobile.

http://www.dlink.com/products/?pid=368
Or google power over ethernet

Might not be the way you want to go but gives you options.

cheers

Ian

Thanks Ian.
I managed to track down an Australian distributor selling these at almost exactly double the US price. D-Link won't sell direct outside the CONUS but that's not a problem to get around so I've put a couple on order to give them a whirl.

Peter

alistairsam · #12 09-03-2011, 04:33 PM

Hi,

Power over ethernet or PoE (IEEE 802.3af) is meant for PoE certified devices. Commonly, VoIP phones and access points are run from PoE capable switches. I use them at work extensively.
if you don't have poe switches, you can also use power injectors between a normal switch and cable.

The switch checks the end device before granting power using a multistage handshake.
what exactly are you running at the ends of the ethernet cables?

you'd just need to make sure that devices are PoE certified before expecting them to work with a PoE switch.

in theory, if you had all usb converted to ethernet, you could have an 8 port gigabit switch at the scope end, one cat 6 cable and a gig switch or your laptop at the other end.
so there would be one power lead and one network lead. so you'd end up with only two cables in all.

have you considered USB over WiFi? its a pretty popular solution and would save a lot of wires.

crosstalk margins on cat6 cables are sufficient to tolerate single 230v single phase power leads running close. although not recommended, if they are kept a few inches apart they will work.

those USB to ethernet devices are interesting, but doesnt detail whether it converts usb signals to ethernet frames with proper mac addresses to use them on an ethernet switch. if it does, then thats very good as each usb device would have a unique mac address.

GrampianStars (Rob) · #13 09-03-2011, 05:47 PM

Quote:

Originally Posted by pmrid

........
I'd like to look at making my data cabling a little less chaotic and am therefore wondering what others think about routing data (USB) with power in the same conduit. Bad news? What about ethernet cables and power or USB. Another no-no?

I have a couple of those Gigabit enthernet USB hubs I'm thinking of using in conjunction with the scopes/guidecams and imaging cams - hence the interest in ethernet cabling.

Peter

I run 40Amps 240v ac power in a separate conduit covered with 6" blue metal gravel then another conduit with 2runs cat 5E on top both in the same trench. Run is 50mt from obs (8 port powered switch) to garage,(4 port powered hub) then another 20mt back to the house (wireless router /sat connection). There is NO cross talk what so ever.

Nice to have Internet in the Rural Obs