> I'm working on a project that involves a large sensor
> array spread over a couple acres. I think the longest
> run so far is about 2500 meters (~8000 feet) with a
> sensor every 75 meters (~200 foot).  All the sensors

As long as you have sensors every 75m, you should be able to
use an rs-485 network. You may have to put a few repeaters in
the line.

You can use a simple addressing scheme. You may even be able to
use the 9-bit protocol available on some PICs (where the PIC only
gets an interrupt if the 9th bit is set -- this is used for the
address byte).

You can use CAT-5 in some conduit if you need full duplex, or telephone
wiring. I like CAT-5 because it enables me to use one twisted pair for
power, one for ground, and the other two for signals.

I'm starting to move that way for my mid-sized robots because rs-485 is
more immune to electrical noise.
--
D. Jay Newman           !
jay@sprucegrove.com     ! Xander: Giles, don't make cave-slayer unhappy.
http://enerd.ws/robots/ !

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