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From: Brian_Sullivan@Carleton.CA (Brian Sullivan)
Subject: Re: Long Serial I/O Lines
Message-ID: <Brian_Sullivan.44.2E1028C5@Carleton.CA>
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References:  <Donald.Heller.134.0010A506@jpl.nasa.gov>
Date: Tue, 28 Jun 1994 13:42:29 GMT
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In article <Donald.Heller.134.0010A506@jpl.nasa.gov> Donald.Heller@jpl.nasa.gov (Don Heller) writes:
>From: Donald.Heller@jpl.nasa.gov (Don Heller)
>Subject: Long Serial I/O Lines
>Date: Mon, 27 Jun 1994 16:38:33

>I would like to establish one-way serial communication between two
>microcontroller-based unit which will be 500 to 1000 feet apart.
>This is for a scoreboard for my local Little League.  The local unit
>will have a keypad (for bumping scores, strikes, etc.) and the remote
>unit will have drivers for (huge) 7-segment displays and lights.  I
>hope I can use cheap phone wire, using 3-wire RS232.  I assume I'll
>need some kind of driver to go the distance, though.  I've heard of
>something called I2C, a two-wire improvement, with available drivers.
>My plan is to use PICs for the brains.  This is my first project; I
>have the PICStart kit from a Microchip seminar.

You can, and we have run rs232c over a mile. The problem is that the longer
the wire the higher the natural capacitence (sp?).  It take a while for the 
bit's to go the length of the wire. At 1/2 mile don't try more than 1200, and 
at 1 mile 300 baud should work. This may seem slow to people who are
use to 56KB, but 300 cps should be enough to update the score board in
1/2 second. Even if you want to do graphics it might take a few seconds 
longer.

As for 2 wire, make sure it's twisted pair. In the early eighties I saw an 
article in BYTE which showed using two wire rs232. One for ground/signal ground
and one for TX/RX. They put two diodes on RX/TX . The diodes were reversed so 
that you could see your own transmission. Some thing like.

1,7 -----------------------------------------1,7

2 >|---+                      +---|<2         
          |-----------------------|
3 |<----+                      +--->|3

Don't know about the PIC in general, but the Stamps Serial I?O should be able 
to handle it.

>Any help or info will be very much appreciated.  When (if) I complete
>the project, I will post my results, chips, circuits, etc.

>Thanks
>Don Heller
>Donald.Heller@jpl.nasa.gov


