Stampers in NJ? and quick follow-up

Archiver

Quick follow-ups:

1) Does anyone have any thoughts on whether using 4-wire, twisted pair phone
cords is a sufficient way to do all of my rs-485 wiring? I'm thinking of
just using standard 5:1 phone connectors to create a "hub" to bring all of
the 485 signals together, to then send them to the main server (PC).

2) Is there anyone within driving distance of Princeton that may be
interested in doing some stamp development work on the side (preferably, but
not definitely not necessarily, an EE)? There is also a chance that this
could turn into a full-time opportunity on some exciting projects with a
talented group of individuals when we get follow-on funding for this project
(see www.proximities.com).

Thanks and have a great day!

John in NJ

---

John W. Lerch
Proximities, LLC
501 Forrestal Rd., Suite 202
Princeton, NJ 08540

p: (609) 951-9595
c: (609) 468-4959
f: (646) 514-5877
e: jlerch@p...
www.proximities.com

Archiver

At 10:55 AM 1/13/03 -0500, John W. Lerch wrote:
>Quick follow-ups:
>
>1) Does anyone have any thoughts on whether using 4-wire, twisted pair phone
>cords is a sufficient way to do all of my rs-485 wiring? I'm thinking of
>just using standard 5:1 phone connectors to create a "hub" to bring all of
>the 485 signals together, to then send them to the main server (PC).

Couple of things to think about:

1) Use 2 twisted pair cable, not Z wire or station cable. The stuff you
DON'T want to use is the flat phone wire or the round cable with
red/green/black/yellow wires in it. There is just too much crosstalk at
high data rates. The stuff you want has a blue/white and orange/white pair
in it.

2) make sure that all your rs-422 devices are referenced to a common
ground. The maximum common-mode voltage is generally about +- 7V. You may
need to use a 3 pair cable, with 1 pair being used for the common ground
reference.

3) a star topology does not work well at high data rates because of
reflections. The problem is that you can't put terminations at ends of
each of the star-fed run because the drivers can't supply enough
current. At slow data rates, you can get by without terminating resistors
and the star topology is fine.

dwayne

--
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax

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Archiver

you said does anyone have thoughts....so technically I qualify. Why not
go ahead and use CAT-5 or 6 network cable, and the corresponding ends and
crimp tool to make these cables.......preferably even the new punch down
style connectors..they are even better.

Those phone cables are such a pain to work with........ the thought of
troubleshooting a bad cable connector in a big star topology network makes
me ill. And you can get a great big roll of CAT 5 at frys and a bag of
connectors fairly cheap........as well as, it comes in different colors....
and you can buy those colored boots to ID each cable at both ends.

but I admit I know nothing about 485, but I do know about bad phone
connectors............and I know that it takes me an average of three
tries to get a good one............... ( can you hear me now? )

And in the event of a problem, you could use a regular RJ-45 cable
tester................I'd let you use mine, but its about a 35 hour drive
from here [noparse]:)[/noparse]


Dave