Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.electronics.design > #453909

Re: Output boards, SPI vs I2C

Show all headers | View raw

On 2017-03-27, rickman <gnuarm@gmail.com> wrote:
> On 3/26/2017 3:49 PM, David Lesher wrote:
>> 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.
>
> Yes, I saw that.  I don't have the various web pages open at the moment, 
> but you may have trouble using the built in SPI port because each port 
> will need an enable.  If you go this route you will need to use I2C.

save some pins: use a 4017 for the enable.

>>> 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.
>
> I'm no expert on PLC, but if you aren't using any of the hardware I 
> would suggest you get a microcontroller board instead.  There are TONs 
> of good products that are smaller and more cost effective.  But I 
> believe PLCs often have a special language for programming, ladder 
> logic.  I didn't think it was used much even for PLCs though.
>
> Arduinos mostly are programmed in Python.  Everything can be programmed 
> in Forth.  I'm working with Mecrisp these days.  Commercial versions of 
> Forth are SwiftForth from Forth, Inc https://www.forth.com/ and VFX from 
> MPE (Microprocessor Engineering) http://www.mpeforth.com/.
>
> Not likely you can change the programmer's point of view, but if they 
> are suggesting using a PLC just to get a CPU they aren't very informed 
> in my opinion.
>
>
>>>> 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.
>
> Make sure your power connections are solid and direct.  A few inches 
> won't hurt.  I2C isn't magic.  It uses a pullup resistor, about 4.7 
> kohms sticks in my mind.  All devices on the bus are open collector.  It 
> should be pretty robust.  You can use a smaller value pull up resistor 
> to get a bit more noise robustness.  Just check all the data sheets to 
> make sure they can pull the lower value resistor to ground.
>


-- 
This email has not been checked by half-arsed antivirus software 

Back to sci.electronics.design | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web