>I have done several long-running arrays (casinos).
>
>The easiest way to do this is to use RS422 drops at all
>the sensors and at the PC, and run the whole thing at 4800baud.

I didn't think 422/485 would handle the long runs. That sure would
make life easy if it could work with it.

>Your 12C509's will work fine, but you'll need an RS422 transceiver chip
>on each sensor. With that much cable, you should use bidirectional MOVs
>on every PCB to protect from lightning and ESD.

The actual data I'm dealing with is very limited. For the most part it consists
of exchanging a few bytes of data every few minutes. My concern was that
the overhead from using ethernet would choke the pic.

Part of the reason for considering tcp-ip/ethernet was the number of required
sensors  On this demo sized field I'd guess I need to talk to around 250 nodes.
On a large field they would deploy anywhere from 3,000 to over 10,000 nodes.

>PS Its easier to bury stuff underground that you realise. You can rent a
>vehicle with a funny-looking tail that can dig a 3'deep hole 2" wide,
>and you can walk behind and drop the cable it in as you go along.
>Probably get it done for $100 USD or less.

This is all underground wiring. Even on the small sensor matrix I think I
figured on
about 2.5 miles of trenching for the basic wires.

I had considered RF but they do not want any emissions on any frequency. The
demo is planned to be setup near a radio telescope so I guess they want to
be good
neighbors.

>Sounds like fun!
Actually the more I look into this I think a nice paper route is the way to
go....be my own
boss, flexible hours...;-]

Now I'm sitting around here trying to think what kind of sensor you use for
dinosaurs or bigfoot...
That and if Russel or Jinx ever stop posting I'd actually get some work
done ;-]

Cheers

Dave

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