low cost networking suggestions needed

We're putting together a network of 10 environmental sensor stations that
connect to a central terminal (ie. a PC).  Each sensor generates about 500
bytes/sec.  Unfortunately RF is not an option, so we have to use a wired
network.  The maximum distance between sensors is 1 mile.  We'd like to be
able to run an IP network if possible.  Fibre-optic cable is the first
option that comes to mind but is fairly costly.  Does anyone here have any
suggestions for some other options that would be worth looking into?

Thanks very much,
Mark

How about telephone cable? Your serial protocol must be prepared for
lots of data errors at this distance in addition to potentially large
DC currents induced in your cable every 11 years due to sun spots.

Preventing nearby lightning strikes from blowing up your equipment may
be your greatest challenge.

-howy


Mark wrote:
> We're putting together a network of 10 environmental sensor stations that
> connect to a central terminal (ie. a PC).  Each sensor generates about 500
> bytes/sec.  Unfortunately RF is not an option, so we have to use a wired

howy wrote:
> How about telephone cable? Your serial protocol must be prepared for
> lots of data errors at this distance in addition to potentially large
> DC currents induced in your cable every 11 years due to sun spots.

I would go for optically isolated rs422 repeaters.

>
> Preventing nearby lightning strikes from blowing up your equipment may
> be your greatest challenge.

Important consideration for any outdoor equipments/connections.

>
> -howy
>
>
> Mark wrote:
> > We're putting together a network of 10 environmental sensor stations that
> > connect to a central terminal (ie. a PC).  Each sensor generates about 500
> > bytes/sec.  Unfortunately RF is not an option, so we have to use a wired

Mark wrote:
> We're putting together a network of 10 environmental sensor stations
> that connect to a central terminal (ie. a PC).  Each sensor generates
> about 500 bytes/sec.  Unfortunately RF is not an option, so we have
> to use a wired network.  The maximum distance between sensors is 1
> mile.  We'd like to be able to run an IP network if possible.
> Fibre-optic cable is the first option that comes to mind but is
> fairly costly.  Does anyone here have any suggestions for some other
> options that would be worth looking into?
>
> Thanks very much,
> Mark

google: short range modem outdoor -wireless
results in
http://www.bestdatasource.com/RAD/RAD_BMLMA.htm

-- 
Best Regards,
Ulf Samuelsson
ulf@a-t-m-e-l.com
This message is intended to be my own personal view and it
may or may not be shared by my employer Atmel Nordic AB

"Mark" <mark_2811nospam@excite.com> wrote in message
news:J586g.5076$Fg4.4786@clgrps12...
> We're putting together a network of 10 environmental sensor stations that
> connect to a central terminal (ie. a PC).  Each sensor generates about 500
> bytes/sec.  Unfortunately RF is not an option, so we have to use a wired
> network.  The maximum distance between sensors is 1 mile.  We'd like to be
> able to run an IP network if possible.  Fibre-optic cable is the first
> option that comes to mind but is fairly costly.  Does anyone here have any
> suggestions for some other options that would be worth looking into?
>
> Thanks very much,
> Mark
>
>

Thanks for the suggestions so far.  I'll look into RS-422 and optical
isolation.  For telephone cable we would need to run modems on either end
(Sixnet?)

Running outdoors over the long distances we require is not that simple.

Mark

Mark wrote:
> 
> We're putting together a network of 10 environmental sensor
> stations that connect to a central terminal (ie. a PC).  Each
> sensor generates about 500 bytes/sec.  Unfortunately RF is not an
> option, so we have to use a wired network.  The maximum distance
> between sensors is 1 mile.  We'd like to be able to run an IP
> network if possible.  Fibre-optic cable is the first option that
> comes to mind but is fairly costly.  Does anyone here have any
> suggestions for some other options that would be worth looking
> into?

That's about 5000 baud.  Duck soup for a 20 mA current loop, which
can be totally opto-isolated, and highly noise resistant.  The
medium will be ordinary POTS twisted pairs.  This even gives you
the option of renting pairs from the TelCo.

-- 
"If you want to post a followup via groups.google.com, don't use
 the broken "Reply" link at the bottom of the article.  Click on 
 "show options" at the top of the article, then click on the 
 "Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>
Also see <http://www.safalra.com/special/googlegroupsreply/>

"Mark" <mark_2811nospam@excite.com> wrote in message 
news:J586g.5076$Fg4.4786@clgrps12...
> We're putting together a network of 10 environmental sensor stations that
> connect to a central terminal (ie. a PC).  Each sensor generates about 500
> bytes/sec.  Unfortunately RF is not an option, so we have to use a wired
> network.  The maximum distance between sensors is 1 mile.  We'd like to be
> able to run an IP network if possible.  Fibre-optic cable is the first
> option that comes to mind but is fairly costly.  Does anyone here have any
> suggestions for some other options that would be worth looking into?
>
> Thanks very much,
> Mark
>
>
RS485/422 will work at that distance, environmental effects ( lightning 
etc.. ) will
be your main problem.. wireless may be a better solution..
why do you say it is *NOT* an option ?
Presumably you will implement a data compression alogorithm to reduce
your bandwidth requirements ?? 

On Wed, 03 May 2006 23:30:29 GMT, "TheDoc" <thedoc@ev1.net> wrote:

>
>"Mark" <mark_2811nospam@excite.com> wrote in message 
>news:J586g.5076$Fg4.4786@clgrps12...
>> We're putting together a network of 10 environmental sensor stations that
>> connect to a central terminal (ie. a PC).  Each sensor generates about 500
>> bytes/sec.  Unfortunately RF is not an option, so we have to use a wired
>> network.  The maximum distance between sensors is 1 mile.  

Is this central terminal in the middle of the area, i.e. the cables
would fan out to different directions from the central terminal or are
the sensors in a singe line with the maximum distance between the
central unit and the last sensor could be up to 15 km ?

If they are all on different directions, RS-422 or 20 mA point to
point connections would be simple alternatives and only about 5 kbit/s
would be needed. If there are several sensors along a single line, it
would make sense to use some RS-485 multidrop connections, but the
date rate would have to be much higher to transfer the same amount of
data from multiple sensors and the protocol overhead.

>>We'd like to be
>> able to run an IP network if possible.  Fibre-optic cable is the first
>> option that comes to mind but is fairly costly.  

Fiber optics would nicely solve any ground potential differences as
well as lightning problems.

>RS485/422 will work at that distance, environmental effects ( lightning 
>etc.. ) will
>be your main problem.. 

RS422/485 is specified for up to 1200 m with ordinary wires, however,
with thicker wires and possibly higher than normal termination
resistance (which is an option at least at 5 kbit/s, since the length
is still much less than the wavelength) might be used.

Galvanic isolation would be essential due to ground potential
differences and voltages induced by lightnings. If the sensors are
operating from floating power supplies, this might be enough and
proper optoisolation at the central unit. To protect the central unit,
it might even make sense to use an RS-4xx/fibre converter, use a few
meters of fibre before connecting to the PC with an other converter.
 
>wireless may be a better solution..
>why do you say it is *NOT* an option ?
>Presumably you will implement a data compression alogorithm to reduce
>your bandwidth requirements ?? 

Data compression over unreliable links is not a good idea, since you
will need an intermediate layer that will guarantee a 100 % transfer
(e.g. with repeats) in order to get _any_ data through.

In typical sensor applications some measurements are periodically
transmitted and if some measurement is corrupted, it is usually not a
big deal, since the next measurement will most likely get through and
the missing value can be interpolated. The important thing to know if
a measurement is valid or not, which can be done with CRC checks etc.
With a bad quality link, it makes sense to use short frames with CRC
checks or a long message (e.g. due to half duplex delays) and split it
into sections with independent CRC words within the message. This way
a single bit error does not corrupt all measurements for a sample
period.

Paul

"Mark" <mark_2811nospam@excite.com> wrote in message 
news:J586g.5076$Fg4.4786@clgrps12...
> We're putting together a network of 10 environmental sensor stations that
> connect to a central terminal (ie. a PC).  Each sensor generates about 500
> bytes/sec.  Unfortunately RF is not an option, so we have to use a wired
> network.  The maximum distance between sensors is 1 mile.  We'd like to be
> able to run an IP network if possible.  Fibre-optic cable is the first
> option that comes to mind but is fairly costly.  Does anyone here have any
> suggestions for some other options that would be worth looking into?

You can buy little RJ45 jacks with builtin microcontrollers and everything. 
I think they are called smart ports or something like that. Shouldn't be to 
hard to find. We have some that are no bigger than a typical normal plastic 
right angle RJ45 jack. 

"DAC" <Mister@Enigma.net> wrote in message
news:4459aa50$0$9697$afc38c87@news.optusnet.com.au...
>
> "Mark" <mark_2811nospam@excite.com> wrote in message
> news:J586g.5076$Fg4.4786@clgrps12...
> > We're putting together a network of 10 environmental sensor stations
that
> > connect to a central terminal (ie. a PC).  Each sensor generates about
500
> > bytes/sec.  Unfortunately RF is not an option, so we have to use a wired
> > network.  The maximum distance between sensors is 1 mile.  We'd like to
be
> > able to run an IP network if possible.  Fibre-optic cable is the first
> > option that comes to mind but is fairly costly.  Does anyone here have
any
> > suggestions for some other options that would be worth looking into?
>
> You can buy little RJ45 jacks with builtin microcontrollers and
everything.
> I think they are called smart ports or something like that. Shouldn't be
to
> hard to find. We have some that are no bigger than a typical normal
plastic
> right angle RJ45 jack.
>
>

Thanks everyone for the info.  I think the issue with any copper-based
solution is the difficulties associated with running it outdoors over long
distances.  Fibre gets around all these issues, but then we have to have
fibre-ethernet conversion in each weather station.  We don't have alot of
experience running these kinds of distances.  Has anyone here seen this work
with a copper-based solution?