You might consider using a wireless approach.  Cheap transmitters or
transceivers can be had in small quantities.  Using transceivers you
could make the sensers themselves act as repeaters (forming a wireless
network with automatic repeating) so you could use low power radios
running off solar if your sensors are not too power hungry.  No cables,
easy setup and replacement.  If you need to rearrange the sensing grid
it's easily accomplished.  Self healing (ie, node goes down or stops
repeating, others around can pick up the slack), no need to have several
hubs (=points of failure).

Plus it's a fun technical problem to solve...  Keep the ibuprofen handy.

-Adam

Dave King wrote:

> I wasn't quite sure this was the correct topic tag.
>
> 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
> are monitored by a master PC.  So the cables have to
> be waterproof etc and neither cause or be affected by
> RF.  Right now the big problem seems to be the layout
> without resorting to Cat-F.  Probably need a few hubs
> buried out there to make it work. Any good reference
> stuff to look at this type of extended net setup?
>
> I've been looking at building the interface using
> either a RTL8019AS or CS8900-IQ. Are there any others
> I should look at?
>
> The actual sensors are pretty simple and a 12C509A
> was selected and easily more than handles (on the bench)
> what it has to do.  I think the 509's will have to be replaced with
> something with a bit more power and pins such as a 870/877
> before it would handle both its sensors and the ethernet overhead.
> Are there any better suited pics?
>
> Dave
>
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