Powered hubs

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Powered hubs

Post by fulci » Tue Nov 10, 2009 2:07 am


I've got a lil project I'm working on where I need four webcams running. Each one needs to be located at least several metres from the source computer, so I bought some extension cables (non-active). I was only able to get one running decent and the other was pixelated.. so I'm guessing active was the way to go.. so I bought some active extenders, I was only able to get 2/4 running tho.. Apparently those active extenders gobble up lots of power, so I went out and bought a Powered USB HUB.

Anyway long story short..

ATM.. I have three of them running fine, like this:

CAM1 ---> NON-ACTIVE EXT (tried with ACTIVE EXT, no luck) ---> PC

CAM2 ---> ACTIVE EXT(a) ---> POWERED HUB(a) ---> ACTIVE EXT(b) ---> PC

CAM 3 ----> ACTIVE EXT(c) ----> POWERED HUB(a) (Same as above on 2nd port) ---> PC

I've tried mixing and matching, but no luck with the fourth.. So anyway I guess I need another powered hub for the fourth cam? They one I bought is pretty cheap mind you ($20) and has 7 ports with AC Adaptor.. Do they really differ in quality?


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Post by eit412 » Tue Nov 10, 2009 8:27 am

USB does not take extension well past a couple of meters especially with multiple devices. If you can find a firewire web cam like the unibrain fire-i, then you can use longer cords. the fire-i has an input and an output so multiple cameras can be linked together. Of course the down side is the fire-i is more expensive than standard web cams, but the picture quality should be much better. From what i hear it rivals camcorders.

Mr Evil
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Post by Mr Evil » Tue Nov 10, 2009 8:42 am

USB hubs do differ in quality - I've used some that were horrendously unreliable.

Some possible solutions that spring to mind:
  • Connect the cameras to different USB controllers on the PC (assuming your motherboard is one with multiple controllers). This should result in more available power (and bandwidth, in case that's the problem).
  • Wireless USB hub.
  • USB over Cat5 extender.
  • Buy new cameras (wireless or ethernet or whatever works over longer distances).

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Post by |Romeo| » Tue Nov 10, 2009 11:10 am

From my experience, USB hubs are often of questionable quality (particularly the AC adaptors shipped with them) but I know of no good way to evaluate without taking the adaptor apart. The worst I've seen to date was rather unsafe (false markings on the casing. The wall wart would not have passed a test for a CE mark and was not double isolated).

I think the first thing you need to do is check if you are trying to draw >500mA per port. If you are (and I doubt that you are) then you should put in additional powered hubs downstream. However I strongly suspect that your problem will turn out to be that the current you are trying to draw downstream of the hub is greater than the rated supply current of the power supply for the powered hub (but still <500mA on each port). The rating should be written on the power supply (my bet is 1A @ 5V and you are drawing 3-400mA per port). Assuming this is the problem, your solution is either to put in powered hubs downstream of the extension cables (the same as if you were trying to draw >500mA per port) or replace the power supply on the hub with one capable of supplying more current. Many (possibly most) USB hubs simply connect the +5v on their downstream ports to the input +5v. HOPEFULY with a switch so it is not connected directly to the +5v supply from the PC (Although I haven't ever seen a failure because of this -I suspect motherboard manufacturers have got wise to this).

Finally, if I was doing this I would ditch the USB cameras an go with wifi cameras. I don't know your application, but if you are needing to reposition the cameras, 6 ft cables are a bitch because they get tangled and people trip over them etc.

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