Forums

Output boards, SPI vs I2C

Started by David Lesher March 24, 2017
On 28 Mar 2017 18:59:51 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

>On 2017-03-28, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >> On 03/27/2017 07:07 PM, Martin Riddle wrote: >>> On 27 Mar 2017 18:41:59 GMT, Jasen Betts <jasen@xnet.co.nz> wrote: >>> >>>> 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. >>>> >>> >>> 74HC138 Mux, 3 to 8 >>> >>> Cheers >>> >> >> Using a 4017 is pretty gnarly--how do you avoid !CS glitches? If you >> had a '595 buffered SIPO register on there, every time you hit its chip >> select, its output register gets loaded with whatever garbage is in the >> shift reg at the time. > >the 4017 has an enable pin but that means using 3 outputs to drive it. > >is the '138 guaranteed glitch free? > >> Since that would require that each shift register be loaded with the >> correct data at nearly all times, you might as well daisy chain them and >> use one chip select. > >yeah, if your interface parts support that, it seems the best way to go. > >> Cheers >> >> Phil Hobbs >>
Never had a problem using a standard MUX like the 138. If I need a park position I leave one output free and set the Mux to that. Cheers
I've been looking at other PLC controller offerings, and thus
far the <http://www.digital-loggers.com/plchw.html> comes out
ahead; it does a lot of what we need in a package with a good
price. Alternatives I've found either cost far more or require
lots of integration. (I've just been pointed at the Siemens Logo
line and am looking into it now.)

The Digital Logger has other things we don't need but we can
ignore them.  It does not have one important item, wired
Ethernet.

I'm pondering how that could be added outboard. What we need is
really a terminal server: serial from the PLC on the one side,
and TCP/IP on the other. You can buy such in a shiny box for
say $100  <http://www.antaira.com/products/STE-501C?gclid=CIDYyKbRiNMCFdyEswod5E8AnQ>
or less for boxless <http://www.mouser.com/ds/2/224/XPort_DS-220314.pdf>
The latter requires making a PCB, worrying about power, etc.
Any alternatives you're aware of?


-- 
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
On 4/3/2017 1:49 PM, David Lesher wrote:
> I've been looking at other PLC controller offerings, and thus > far the <http://www.digital-loggers.com/plchw.html> comes out > ahead; it does a lot of what we need in a package with a good > price. Alternatives I've found either cost far more or require > lots of integration. (I've just been pointed at the Siemens Logo > line and am looking into it now.) > > The Digital Logger has other things we don't need but we can > ignore them. It does not have one important item, wired > Ethernet. > > I'm pondering how that could be added outboard. What we need is > really a terminal server: serial from the PLC on the one side, > and TCP/IP on the other. You can buy such in a shiny box for > say $100 <http://www.antaira.com/products/STE-501C?gclid=CIDYyKbRiNMCFdyEswod5E8AnQ> > or less for boxless <http://www.mouser.com/ds/2/224/XPort_DS-220314.pdf> > The latter requires making a PCB, worrying about power, etc. > Any alternatives you're aware of?
Why don't you just get a controller that includes Ethernet to start with? I haven't seen where you explain why you are only looking at PLC controllers rather than generic CPU boards. From how you have explained your needs so far, there is nothing in a PLC that you will use that is different from a CPU board. From what I can see, you would do well with a Raspberry Pi or a Beagle Bone Black type board. Ethernet included and tons of support (metric tons even). So what do you get with a PLC that you don't get with one of the *many* CPU boards? -- Rick C
rickman <gnuarm@gmail.com> writes:


>Why don't you just get a controller that includes Ethernet to start with?
The controllers we have seen are 6-12X the price of this approach.
>I haven't seen where you explain why you are only looking at PLC >controllers rather than generic CPU boards.
>From how you have explained your needs so far, there is >nothing in a PLC that you will use that is different from a CPU >board. From what I can see, you would do well with a Raspberry >Pi or a Beagle Bone Black type board. Ethernet included and >tons of support (metric tons even).
This controller has value-added in integration, packaging, input protection and such. They have done things we will not have to ourselves. We looked at Beagles but want to avoid the issues with supporting a Linux device. (& that would be far more overkill.)
>So what do you get with a PLC that you don't get with one of the *many* >CPU boards?
I've not found an Arduino case/touchscreen/AD/input protection/ etc that we can plug in and fly with. Suggestions? -- 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
On 4/3/2017 10:59 PM, David Lesher wrote:
> rickman <gnuarm@gmail.com> writes: > > >> Why don't you just get a controller that includes Ethernet to start with? > > The controllers we have seen are 6-12X the price of this approach. > >> I haven't seen where you explain why you are only looking at PLC >> controllers rather than generic CPU boards. > >>From how you have explained your needs so far, there is >> nothing in a PLC that you will use that is different from a CPU >> board. From what I can see, you would do well with a Raspberry >> Pi or a Beagle Bone Black type board. Ethernet included and >> tons of support (metric tons even). > > This controller has value-added in integration, packaging, input > protection and such. They have done things we will not have to > ourselves. > > We looked at Beagles but want to avoid the issues with > supporting a Linux device. (& that would be far more overkill.) > >> So what do you get with a PLC that you don't get with one of the *many* >> CPU boards? > > I've not found an Arduino case/touchscreen/AD/input protection/ etc > that we can plug in and fly with. Suggestions?
The first problem is I don't know what your requirements are. The second problem is I usually get paid for this sort of thing. When you say things like you "want to avoid the issues with supporting a Linux device", that makes me think there are many more issues to deal with that you haven't explained. The term "input protection" is entirely vague. There can potentially be a huge list of such requirements that you need to detail before anyone can try to find hardware for you. -- Rick C