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'[EE]: Ideas on a Wideish area Data network'
2000\10\20@220155 by Mark Willis

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In an industrial environment, and/or a home environment, has anyone had
a fair amount of experience with Dallas 1-wire and/or a similar setup,
over say 200 foot ranges using slow communications (1200 baud to 9600
baud)?

I'd like to use RG58 coax for power plus comms for one design, unsure if
it'll actually be practical for power plus data though;  Thinking 9 to
12V DC power for this one, just thought I'd throw the idea out and see
if anyone had used something like this.  Lots of "hash" near the
machinery, the cable can be in conduit for longer runs (not that THAT
will save you!), it would just be really really convenient to have one
cable (Ethernet-style) for data plus power - Alternately could use
(cheap!) RJ11/RJ12 style cables, though they have resistance and noise
problems, or RJ45 Cat 5 cables, a little costly but do-able and still
with the problem of a noiceable resistance at each connection.  (With
those, go for say 14VAC power and opto-isolated RS422;  proven, works,
pricey at the PC end.)  Just would like to go Coax if I can <G>

Absolute requirement to be able to unplug each node, so just hard-wiring
isn't an option;  Could use a molex style connector, trying to use
something quicker and easier to "plumb", if practical...

Thanks!

 Mark

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2000\10\21@052404 by Andy Howard

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----- Original Message -----
From: "Mark Willis" <spam_OUTmwillisTakeThisOuTspamFOXINTERNET.NET>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Saturday, October 21, 2000 3:01 AM
Subject: [EE]: Ideas on a Wideish area Data network


{Quote hidden}

I've found coax to be quite unhelpful in noisy environments. Being
unbalanced it just soaks up those lovely impulses over long runs unless you
ground it at frequent intervals. You should certainly consider balancing the
1-wire with RS485/422 drivers or similar. Unless it's balanced you'll  not
get any benefit from UTP.

One solution I have used with some success in the past is to use a Belden
foil-screened-twin audio cable (e.g. #8723) and studio type XLR connectors
(Useful tip, don't use the chassis connection on the plug, connect the
screen to one of the pins and apply equipment ground to mating pin on the
socket.) This is much cheaper than UTP and gives good results for moderate
speed data (I've used it up to 300k). It'd probably start to lose
effectiveness at higher rates though.


> Absolute requirement to be able to unplug each node, so just hard-wiring
> isn't an option;  Could use a molex style connector, trying to use
> something quicker and easier to "plumb", if practical...

The Belden cable is thin and easy to run in and it strips easily. If you
want *really* quick and easy to install then there are solid core versions
suitable for use with Neutrik IDC type XLR connectors.

How much power do you need? Dallas have a suggested circuit for deriving
parasitic power in their 1-wire data sheets - or you could use a phantom
power scheme using centre-tapped transformers at each end, feeding power
between centre-tap and screen.


Hope this helps.

Andy.













.

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2000\10\21@060254 by Andy Howard

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Another possibility is to use current-loop drivers.



----- Original Message -----
From: "Mark Willis" <mwillisspamKILLspamFOXINTERNET.NET>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Saturday, October 21, 2000 3:01 AM
Subject: [EE]: Ideas on a Wideish area Data network


{Quote hidden}

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2000\10\21@082229 by Peter L. Peres

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imho think POTS wiring and remote power. You can buy and deploy shielded
pair (usually 2 pairs minimum) POTS wire for industrial use. It will
likely outperform RG58 in all mechanical and chemical aspects. Besides,
with RG58 and long cable runs you will need to match the ends for higher
data speeds and that is hard (PIC can't drive 100 ohms properly without
help - but it can drive 600 ohms or 1200 ohms ;-).

Peter

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2000\10\24@183419 by Mark Willis

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Andy:  That's why I asked <G>  Know in Apartment cable TV setups that
even better-shielded coax seem quite good at picking up Cell Phone
transmissions, was wondering if there was a trick I didn't know of.
RG-58 Seems to work fine for Ethernet here, OTOH - Dontcha just hate it
when experiences are contradictory?!  I don't claim to be good in RF...

I'll look at that Audio cable, 300k's more than enough for these jobs.
Those XLR connectors aren't "free" though so POTS wire may be it due to
cost for at least the home setup.

Power:  About 12-15 nodes in the home system, I'm guessing 40+ for the
industrial setup and may be low (Could be 100?);  Probably 'F84's at
4MHz on Resonators at a guess, guessing between 5 and 20mA (@5V) per
node average power, sensors may "feature bloom" and drive that up - Some
home nodes will be higher power use with the LCD display and all.  (All
guesswork so far, who KNOWS what customers'll end up demanding?!
<SadG>)

Current Loop, A good thought;  Not enough power probably, though <G>

Peter:  Thanks, more I think of it more I think I'll do that, RS422,
POTS unshielded is a good start and easy to convert to STP if needed.

 Mark

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2000\10\25@045328 by Alan B. Pearce

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>guessing between 5 and 20mA (@5V) per
>node average power, sensors may "feature bloom"
>and drive that up
Surely the way to deal with this is to insist that the "new features" go into an additional sensor on the network? That way they become another (chargeable?) additional item on the network which you can develop later, and get the original spec ones done "on time". You did design the network interface to be feature expandable?

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2000\10\25@051851 by Mark Willis

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Alan B. Pearce wrote:
> >guessing between 5 and 20mA (@5V) per
> >node average power, sensors may "feature bloom"
> >and drive that up
>
> Surely the way to deal with this is to insist that the "new features" go into an additional sensor on the network? That way they become another (chargeable?) additional item on the network which you can develop later, and get the original spec ones done "on time". You did design the network interface to be feature expandable?

If they ask for TOO much at any given node, it'll require AC power to
that node, is the plan <G>  Better proper function and a PO'ed
electrician than network failure from their not thinking.

Design on this monster's starting from the electrical wiring, actually -
Until they start payin' I'm doing it mostly in my head, minimal costs
etc.  It'll help once they present an NDA and I sign it, then I'll have
lots more facts to work from...  The home project is going to be a
practice run for the other, network interface debugged and tested on
that.  THAT one is all really low current except for a few stations with
LCD displays - those will have AC power probably <G>  Did re-plan it all
somewhat recently, got a neat gizmo at a local store and had a couple
better ideas.

I usually use ASCII based protocols (easier to read / debug, log to a
file, etc.), have a lot of it pretty clear really from the last such one
I did <G>  RS-422 is NICE for Polling, probably will use that at 9600 or
14.4k baud I think, plenty of speed for their needs.  All features will
be "local per-node" - when I poll Node 123 for "ID yourself" it'll
respond that it's type J, I can then ask it what packets it has and
it'll supply a Type J version 0 packet initially {with version spec and
checksum!} - Always Always Always leave expansion room as otherwise the
client will break your poor brain!  <G>

 Mark

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2000\10\25@114716 by Bill Westfield

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I was thinking along somewhat similar lines - formalizing an rs232-based
ring network so that you can put in a good number of nodes (including things
like PCs.)  OTOH, I'm wondering if it's worth it, what with people here
having done equally complex (?) things using I^2C, which is more
"microperipheral friendly" but less "largish computer friendly" (which is
easilly fixed via an rs232/I2C "gateway")  Using I2C would get rid of a
good bit of "protocol development effort", I think.

Thoughts?

BillW

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2000\10\25@155341 by Mark Willis

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If we go for 3-wire I2C, how to power the PIC nodes though?  Could use
6-conductor POTS wiring, use 3 wires for ground and 1 for Vin then the
last 2 wires for SCL and SDA, might do nicely.  Don't know if I'd want
to try I2C as a Ring though?  (I'd think it'd ring really really well
without termination?)

 Mark

William Chops Westfield wrote:
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2000\10\25@163258 by Shawn Yates

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I missed the beginning of this thread, so this may be way off, but why not
go with RS-485?  Isn't that pretty much a standard for
longer-that-rs232-distance?

Talking about number of wires, have you looked into any of the data over
power wire type technologies?  I am researching using that (over the 110
mains) for communications and hitting lots of dead ends.  A company called
Metricom has a good product, but only sells the right to make the chip, not
the chip itself.

Oh well.

Shawn

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2000\10\25@171028 by Mark Willis

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RS-422 is easier, I've found, to deal with than RS-485 (Basically the
same beast but no confusion on who's master thus talking) - Been a while
and perhaps I'm mis-remembering / whatever.  With a PC controlling a
bunch of PICs, I use Poll / reply not multi-master usually <G>

 Mark

Shawn Yates wrote:
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2000\10\25@181229 by Douglas Wood

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RS-232/422/485/??? are electrical specifications, not protocol
specifications. Any problems you've had with masters/slaves/multi-masters,
etc. were outside of the scope of the RS-###. RS-485 is good for noisey
environments and (if memory serves) has a distance of 4500 ft.

Douglas Wood
Software Engineer

{Original Message removed}

2000\10\26@053512 by Alan B. Pearce

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>I missed the beginning of this thread, so this may be way off, but why not
>go with RS-485?  Isn't that pretty much a standard for
>longer-that-rs232-distance?

Or Rs422 using 26C31 & 26C32 transmitters and receivers. These will also do multidrop as they have enable pins and are guaranteed hi-Z state with power off.

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2000\10\26@055602 by P.J. McCauley

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I've been down this road too. I first tried I2C. It worked better than
expected, but I found that unless I used slow data rates I had problems. The
system was being used in a noisy environment, and this caused me some
problems too. I eventually switched to RS485 and was able to work at 19200
over a couple of hundred meters no problem. I used the snap protocol which
is a free protocol available at http://www.hth.com/plm-24/

Joe

----- Original Message -----
From: Douglas Wood <EraseMEdouglas_woodspam_OUTspamTakeThisOuTARIUSA.COM>
To: <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Sent: Wednesday, October 25, 2000 3:08 PM
Subject: Re: [EE]: Ideas on a Wideish area Data network


> RS-232/422/485/??? are electrical specifications, not protocol
> specifications. Any problems you've had with masters/slaves/multi-masters,
> etc. were outside of the scope of the RS-###. RS-485 is good for noisey
> environments and (if memory serves) has a distance of 4500 ft.
>
> Douglas Wood
> Software Engineer
>
> {Original Message removed}

2000\10\26@112137 by Douglas Wood

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RS-232/422/485/??? are electrical specifications, not protocol
specifications. Any problems you've had with masters/slaves/multi-masters,
etc. were outside of the scope of the RS-###. RS-485 is good for noisey
environments and (if memory serves) has a distance of 4500 ft.

Douglas Wood
Software Engineer

{Original Message removed}

2000\10\26@144754 by Peter L. Peres

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>I2C

I2C sucks for anything larger than a box with a few boards and multi
mastering with collision detection is a medium large nigtmare unless you
use a token ring type of discipline. So you are limited to one master and
many slaves, or you will spend a lot of ROM on collision avoidance and
recovery. This will be OK until you run into glitches RFI or ground loop
problems. According to my experience this ONLY happens at far removed
installation sites and causes comments of the type 'Oh, we didn't think
about THAT. THAT cannot be. Their installation should prevent it. Noone
ever heard of such a thing. Oh sh..'.

There are other buses and protocols out there that were meant for use in
exactly your situation, like Profibus, Modbus, star-wired RS232C (optical
current loop). Search the net. All of these have in common the fact that
they outperform the electrical immunity (as in ground loop resistance)
specs of I2C by a few orders of magnitude and that data exists so you can
calculate what might work and what might not.

Peter

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