Groups > sci.electronics.design > #453794

Re: Output boards, SPI vs I2C

From	David Lesher <wb8foz@panix.com>
Newsgroups	sci.electronics.design
Subject	Re: Output boards, SPI vs I2C
Date	2017-03-26 19:49 +0000
Organization	NRK Clinic for habitual NetNews Abusers - Beltway Annex
Message-ID	<ob960e$p4u$1@reader1.panix.com> (permalink)
References	(1 earlier) <ob6b9p$9a2$1@dont-email.me> <ob7f1h$ktg$1@reader1.panix.com> <ob7nd0$nvi$1@dont-email.me> <ob8ju3$ap4$1@reader1.panix.com> <ob8r5i$ua3$1@dont-email.me>

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rickman <gnuarm@gmail.com> writes:

>> Not sure I follow; there is SPI on the board, but thinking out
>> loud, we would have to add selection to the existing SPI users,
>> the display, touch screen, and flash.....

>Flash???  The other stuff is up to you.   I"m just talking about the 24 
>relays.  You didn't mention the other items.  Is everything going to be 
>on the 8 digital outputs?

I was talking about using the existing I2C or SPI system to also
drive the outboard relay boards. It's mentioned only in passing in the
writeup.

>The display, touch screen and other things they talk about connecting 
>through SPI or I2C connect directly to the CPU.  This will not be the 
>same as using the digital outputs.  If you want to use the dedicated 
>I/Os on the CPU for the relay drivers you might as well not use the PLC 
>but get a CPU card instead and save some bucks.  What does the PLC unit 
>do for you exactly?  Does it provide a way of programming it that you 
>understand well that an Arduino won't?

No, because I'm not the programmer at all; (To paraphrase Bob
Pease) <https://tinyurl.com/kby566u> I just solder wires. 
Two people working with it suggested this platform for this project.

....

>> Do you echo krw's concerns on I2C cabling?

>It's not an absolute on leaving the CPU board.  But both SPI and I2C are 
>sensitive to noise and poor impedance matches.  If your wire runs are 
>short you should be ok.  Use ribbon cable with every other wire a ground 
>or twisted pairs with a signal wire mated with a ground.  How far apart 
>are the PLC and the relay boards?

A few inches; directly adjacent.

-- 
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Thread

Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-25 02:46 +0000
  Re: Output boards, SPI vs I2C krw@notreal.com - 2017-03-24 23:25 -0400
    Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-26 04:13 +0000
  Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-25 14:04 -0400
    Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-26 04:11 +0000
      Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-26 02:37 -0400
        Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-26 14:41 +0000
          Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-26 12:47 -0400
            Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-26 19:49 +0000
              Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-27 10:49 -0400
                Re: Output boards, SPI vs I2C Jasen Betts <jasen@xnet.co.nz> - 2017-03-27 18:41 +0000
                Re: Output boards, SPI vs I2C Martin Riddle <martin_ridd@verizon.net> - 2017-03-27 19:07 -0400
                Re: Output boards, SPI vs I2C Jasen Betts <jasen@xnet.co.nz> - 2017-03-28 08:03 +0000
                Re: Output boards, SPI vs I2C Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-28 10:44 -0400
                Re: Output boards, SPI vs I2C Jasen Betts <jasen@xnet.co.nz> - 2017-03-28 18:59 +0000
                Re: Output boards, SPI vs I2C Martin Riddle <martin_rid@verizon.net> - 2017-03-28 15:37 -0400
                Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-04-03 17:49 +0000
                Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-04-03 15:18 -0400
                Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-04-04 02:59 +0000
                Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-04-04 00:54 -0400
                Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-28 05:08 +0000
                Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-28 02:16 -0400
  Re: Output boards, SPI vs I2C Martin Riddle <martin_ridd@verizon.net> - 2017-03-27 19:03 -0400
    Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-28 03:28 +0000
      Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-28 00:38 -0400
        Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-28 14:47 +0000

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