AVR-Chat

>> -----Original Message-----
>> From: Mike Payson
>>
>> Hmm... This sounds to me like a perfect application for a Zigbee
>> network. The modules are a bit more expensive, but since you wouldn't
>> have to run wires, the final cost should be roughly comparable if not
>> substantially less. ....
>
> As with many potential solutions it has pros & cons that I have looked at.
> You'd have to have more info on the project, install sites, etc.
>
> In a nutshell: One of my other hobbies is ride-on, live steam railroading
> (see: http://whitetrout.net/Chuck/844/photos and
> http://whitetrout.net/Chuck/844).  The tracks are 7.5" gauge using aluminum
> rails on treated wood ties.  The application I am working on is a robust,
> automatic signal system for tracks around the country.  One of the major
> things the system addresses is detecting a train shunting the rails.  This
> becomes challenging in very wet weather where a 900 foot long "block" can
> contain ~2,700 ties and they all conduct a bit, to make it worse, a block
> that long starts to take on the characteristics of a very lossy transmission
> line (w/distributed R & C) and it can get difficult to detect a "shunt" out
> of the noise.  Oh, yea, 1,000's of feet of aluminum rail and cable-carrying
> conduit makes a great antenna and lightning magnet and the system needs to
> survive a nearby lightning strike (disregard DIRECT lightning strike, these
> tracks don't have a NASA budget <g>).
>
> The "nodes" I keep referring to are located at switches (detect point
> position, control a point motor, etc.), connected to "blocks" of track (~10
> to maybe ~1,000 feet long) to detect trains, at signal heads to drive the
> signals, etc.
>
> I really need to get a web page up on this thing but that's yet another
> project - So many projects, so little time :-(  I think that the major
> factors effecting RF .vs. hardwire in my case are:
>
> 1) Power
> 2) Node density
>
> All the nodes need power and they are not near local power sources.  I could
> provide solar chargers but that would dramatically increase cost and many of
> the nodes are in areas with dense tree cover and batteries are not an option
> in most situations.  I am using a #16 pair for power distribution (48vdc) in
> a conduit along the track ROW with plenty of room for a CAT-5 cable.
>
> I am getting CAT-5 for ~$55/1000, so if, in a particular area, the
> inter-node distance is long enough or node density is low enough, Zigbee
> might be cost effective.  I was planning on having network segment bridges
> for various reasons and Zigbee might fit in there also.  But those issues
> are for large installations and are down the road (track? <vbg>) at the
> moment.
>
> There are also a couple of cases where someone using my system might only
> need a couple of nodes and might want to use RF w/batteries so they can take
> in the equipment when not in use (vandalism), don't have to trench, etc.  I
> see nothing in my design that would preclude this.
>
> I have checked out the links you provided, thank you.  It's always good to
> keep informed about potential solutions in case project factors change.
>
> Thanks to all for the info ...
>
> Cheers,
>
> Chuck Hackett
> "Good judgment comes from experience, experience comes from bad judgment"
> 7.5" gauge Union Pacific Northern (4-8-4) 844
> http://www.whitetrout.net/Chuck
>

I'm confused by the power issue... You say you are already providing
48vdc, so why not just step the power down for the Zigbee? Running
cable isn't quite as bad since you already have the conduit, but it
still seems that running cable would be a hassle, and the cost would
be almost identical or even cheaper.

As for the RF concerns, Zigbee is designed for use in noisy
environments, so it would likely be a good candidate. It actually
sounds like a good candidate for a white paper on Zibee technology.
:-) Might be worth contacting Digi and see if they'd help you in
exchange for writing up your experiences.