USB Cable Length

[phil.b]

I want to connect up a webcam for surveillance after hours at work. If I get a webcam & use a power supply for it so it doesn't draw from the computer, then use alarm PIR sensor wiring to make a USB cable. Do you think I can connect the camera about 30 metres away from the PC without bothering with hubs?

Phil

[andrew93]

this webpage might help

[Graham L]

If you use alarm wire to make a USB cable, you won't have a USB cable: you'll have 30 m of alarm wire with USB connectors.

A USB cable is made to a standard,and won't work if it's not standard. The data lines are a twisted pair, with a shield. The impedance is critical. The power wires carry only DC, but their resistance matters (for voltage drop).

Most critical is the time it takes for a transition to go the length of the cable. If it's too many nanoseconds, the protocol will cough. And it won't work.

USB2.0 is more fussy than 1.1 about its cables. 1.1 will work with 2.0 cables. The other way won't.

The standard max length (per cable) is 5 m. You can get extenders (which are effectively "one port hubs" -- a repeater). You might be able to chain them.

I have seen reference to adapters which take USB in and then use Cat5 cable (for, I think, up to 50m). They will certainly use non-USB signalling in the cable.

If you've got lots of money, Axis make web-cams which have a RJ45 connector. There's a webserver in the case. Give it an IP and plug it into your network.

[phil.b]

I've more or less given up with that one. I'm now playing with an old video camera. I'm hoping that'll be more forgiving. By trying that I found that my vfwwdm32.dll file was corrupt. I replaced it & now things are working properly again.

Phil

[Graham L]

So the burglars can steal a camera too.

In case anyone's interested in a USB extender which gives 50m through Cat5 cable, it's advertised for $AUS105 by http://www.mgram.com.au . Their catalogue number is 11666-1. That's all I know about it ;-)

[phil.b]

The reason I'm doing this is some kind person broke into a customers car that was parked outside my work premises. I want to use sensor lights & a motion sensitive program to use on the existing work computer. The camera will be mounted inside. There is a fair distance between camera & pc, & I don't particularly want to spend an arm & a leg. The video camera gives a much better picture quality when compared to a webcam & it's a lot cheaper than coughing up for a specialist camera that does the business. I'll look into that 50m usb though. Maybe svhs cable doesn't like 30m either.