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Re: Output boards, SPI vs I2C

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rickman <gnuarm@gmail.com> writes:

>> This would be driven by a
>> <http://www.digital-loggers.com/plchw.html>
>> which claims to support both flavors.

>Oh, I see.  The page you link to is for the "hardware" and the other 
>pages are a general PLC page and a software PLC page, etc.  $89 sounds 
>like a bargain.


>> Data rate is virtally irrelevent here; I need a response time
>> far slower than the relays themselves are.....
>>
>> My hand may be forced by what boards are actually available. I
>> found <https://www.industrologic.com/r8spiprod.htm> and

>The manual for this one says it uses optoisolators on the inputs with a 
>1 kohm current limiting resistor.  They recommend a minimum of 0.5 mA 
>current, bit prefer 10 mA.  10 mA would require 12 volt drive.  The 
>digital outputs on the PLC are open collector relay drivers.  They will 
>be compatible and you can use the power supply to the PLC as the common 
>power to the + terminal on each of the three SPI signals.  Or I think I 
>see a direct input connector for the open collector outputs, J1.  They 
>don't mention using these inputs, but what's the diff?  The optos will 
>be less sensitive to noise I expect.  There is some irony in that they 
>are using the same relay drivers your PLC uses for the digital outputs.

Yes, I noticed that aspect.

>This unit has no serial output, so the SPI protocol will require this 
>unit to be used *only* in the parallel mode with a dedicated strobe.

>To drive 24 relays will use five digital outputs.

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.....

>> <http://lightsosoft.com/sites/default/files/I2C-Relay8-H_040813_1240.pdf>

>This board seems to be I2C only.  That would require I2C support in your 
>PLC.  Does the PLC have that in the software?

<http://www.digital-loggers.com/plchw.html>
I2C Memory Expansion Socket

There is a 32K socketed EEPROM that can be used for non-volatile
storage that's also connected to the I2C bus.  Because it has
a large write-endurance, EEPROM is usually the best place to
store data that's frequently updated.  Other 5V chips a standard
8 pin DIP package such as FRAM, SRAM, Larger EEPROM etc can be
substituted. The pinout is

1 = AO
2 = A1
3 = A2
4 = GND
5 = SBA
6 = SCL
7 = TEST (grounded) 
8 = 5V VCC.  
`
The socket could also be used as an expansion port via an 8-pin
ribbon cable plug.  Although it's a bit inconvenient, this chip
has been located beneath the clock module to gain space for
reprogramming headers.


>> but many other boards are not what they seem to be, or are from across the pond.
>> <http://jap.hu/electronic/relay_module.html>

>Another I2C board.

>> Not sure I grasp "wire three boards serially" but we can spare chip select
>> outputs.

>Normally SPI devices have a serial data input MOSI (master out, slave 
>in) and and serial output MISO (care to guess what this one means?).  If 
>you connect the MISO of the first module to the MOSI of the second 
>module, etc before connecting the MISO of the last module to the MISO of 
>the master module it will form a daisy chain of N * 8 bits.  So the PLC 
>will need to shift out 24 bits before removing the strobe.  But the one 
>SPI relay board has no serial output (MISO) and must be used in 
>parallel.  Then the PLC output will drive all the MOSI (aka data) inputs 
>together as well as a PLC output that will drive all the Clock inputs 
>together.  The Strobe signals will all have to be separate.

>With I2C, you just wire the two outputs to each of the two inputs on all 
>three boards (with a pullup resistor somewhere in the path).  The relay 
>boards will need to have jumpers to set a unique address on the bus. 
>Each byte you wish to send to control a set of relays requires two 
>bytes, one to set the address and one to set the data.

Do you echo krw's concerns on I2C cabling?

>Just a comment, some of the lightsosoft.com documentation isn't so 
>clear.  I'm not sure how to wire up the I2C interface.  This is what 
>they say:

>The specific pins you need for I2C communications are:

>TB19, SD
>TB20, SCL
>TB18, GND
>TB19, 5V

>I could make an educated guess, but why can't they make it     
>clear in the manual *AND* on the board?                        

I have asked such questions about every board I have found so far.

-- 
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

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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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