How far away max can you have two Basic Stamp apart using cat-5 cable

sam_sam_sam

Hi EveryOne

Can any one tell me how far away·I can have two Basic Stamps apart and
·have them talk to each other using cat-5 cable


I Would Like To Thank AnyOne That Can Help Me With This.................

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Sam

stamptrol

Sam,

At lower baud rates (2400 or 4800) I've done this to at least 100 feet.

For longer distances, I convert to RS-485 by using a 75176 chip on each end. This allows about 4000 feet between stations.

Cheers,

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Tom Sisk

http://www.siskconsult.com
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steve_b

I'm running 2400baud for nearly 200ft.
Now, I'm using a level converter so my actual rs232 signals are based on +/-10Volts. 5V levels would get too noisy for that distance.
Drop the baud rate and you can go a bit further....this is really a "test and see".

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Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Steel

just to add...what about ridiculously higher baudrates...say 1MBps?

Would a RS485 chip still work for that?

stamptrol

The rs-485 chip would work fine. The Stamp likely could neither effectively talk nor listen at those speeds.

Maybe, with an off-board serial buffer......

Cheers,

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Tom Sisk

http://www.siskconsult.com
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sam_sam_sam

·stamptrol

Thanks for your reply and i am going to order some SN·75176 Chips from Digikey and let you how it come along when·I get them




·steve b

Thanks for your reply

I will be using about 300 feet of cable when it all said and done with




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Sam

Beau Schwabe

sam_sam_sam,

300ft of cat-5 will give you about 200pF of capacitance.

24AWG wire is about 5.24 Ohms per 100ft, so 300ft of wire (round trip) would be about 31 Ohms

F = 1 / (2 * Pi * R * C)

This comes out to be about 25.67MHz for the the cut-off frequency·(-3dB)· using 200pF and 31 Ohms.

Reference:
http://www.epanorama.net/documents/wiring/wire_resistance.html
http://amasci.com/tesla/wire1.txt
http://www.consultrsr.com/resources/eis/induct5.htm
http://www.wireville.com/news/news11.html

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 5/8/2007 11:36:12 PM GMT

sam_sam_sam

Thank you for your replys


stamptrol


How do you set this up with the sn75176 and the Basic·Stamps

I know that you have to have a sn75176 on each Basic Stamp

I have not had time to read the data sheet for the sn75176
yet because the computer at work has trouble opening pdf files so
if i have time at home to night i will try to look at the data sheet



Beau Schwabe


Is to mean that if· would you use·a 2400 baudrate or less·that this would work for 300 feet or would you pick up to much noise or you still have use
the sn75176 to make this work


Steve_b

What type of chip did you use in your set up





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··Thanks for any··that you may have and all of your time finding them

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Sam

Beau Schwabe

sam_sam_sam,
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In an ideal circumstance without any interference, data compression, differential mode transmission, etc.·you could go up to about 12.5Megabit·(nyquist·... 1/2 of·25.67MHz calculated earlier).· 2400 baud is only·2.4Kbit ... you have a ways to go before you reach 12.5Megabit
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What happens though is that long wires tend to act like a broad band antenna and will pick up anything in it's path. You can greatly reduce this by using a differential transmission approach.· Instead of tying one line to ground, drive both lines phased 180 Deg apart.· I believe that the suggested IC in·this thread uses this method.· The idea here is that any interference picked up on one wire will also be picked up on the other·wire, but in opposite phase.· As a result when the data is reconstructed at the other end, the interference·ends up being canceled out leaving you with your original signal intact.
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In a Cat-5 cable there are 4 twisted pairs, each of which uses a differential transmission method.· Among differential transmission, there are other techniques to minimize and reduce reflections (another phenomena to deal with at high speeds).· After a few tricks are·applied, each twisted pair has the potential to transmit at about 25Megabit.· To achieve·100MegaBit·transmission speeds, the 4 twisted pairs are combined to provide an effective throughput of 100MegaBit baud rates.· Cat-5e can go 10 times faster than this for 1000MegaBit or 1GigaBit speeds.
·


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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 5/9/2007 9:08:55 PM GMT

sam_sam_sam

Beau

Thank for your reply that help me alot to understand what would happen
using that long of a run

How would i do this.....................
·Instead of tying one line to ground, drive both lines phased 180 Deg apart.·

Would you do this with the sn75167 chips and how

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··Thanks for any··that you may have and all of your time finding them

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Sam

Beau Schwabe

sam_sam_sam,

"Instead of tying one line to ground, drive both lines phased 180 Deg apart"
The chip does this for you.

"Would you do this with the sn75167 chips and how"
Yes, the datasheet is pretty straight forward, but you might want to swap the 6 and 7 before you use Google.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

sam_sam_sam

Beau


Thank you for all of your help in this matter

·I will try to read the data sheet for the sn75176

I made a typo mistake

Thanks for see that

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··Thanks for any··that you may have and all of your time finding them

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Sam

sam_sam_sam

Beau

I found this web page while Googling

http://www.parallax.com/dl/docs/prod/appkit/rs485Communication.pdf

This Appkit helps me alot and also· has a Demo so i can try it out

Thanks for all of your time and help in this matter..............................................

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··Thanks for any··that you may have and all of your time finding them

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Sam

Post Edited (sam_sam_sam) : 5/15/2007 12:39:09 AM GMT