View Full Version : Maximum sensor cable length?

11-25-2007, 11:59 PM
I would like to place sensors within my house and connect them to my computer, but some of my target locations are pretty far, e.g. 40ft or so. Can I string a couple of the 12ft cables together or is it too far?

11-27-2007, 04:17 PM
It depends... are you talking about stringing the USB cables together or the analog cables? USB cables are limited to about 15ft. If you want to go beyond that, you'll need something like a USB to RJ45 Extender. (http://www.trossenrobotics.com/store/p/3462-USB-to-RJ45-Extender.aspx)

However, we've seen the analog cables up to 100ft in length. Keep in mind though that the longer the analog cable, the more degraded the signal becomes.

01-09-2009, 08:40 AM
Define inconsistent. Are they varying by orders of magnitude or are they +-1?

01-09-2009, 04:35 PM
Aren't I2C cables limited to a foot? That said I had a Devantech compass on a mast with over a foot and a half cable still working, but think that was pushing a bit.

01-09-2009, 05:17 PM
The max length and # of devices is regulated by the max bus capacitance (400pF as memory serves) - the more devices you add, the shorter the length. Ditto using different gauges, shielding, and routing of wire. Dropping the speed can improve that.

Ultimately, repeaters can be used to carry I2C for miles.