I have also a similar project going... a simple IO module aiming for industrial use...
It will basically be the same principle with serial clocking for DI and DO, but I use the 4000 series shiftregisters instead and I put some noice filters and protection on everything that goes in and out... The hardware is still only in the CAD...

But I have played a little with the Mudbus lib code.google.com/p/mudbus/ which is a modbus tcp lib for arduino.
There are some issues...
It doesn't compile with the current version of ethernet lib and there is a bug giving wrong response for register write.

My fixes for these issues are here: git://gitorious.org/mudbus/mudbus.git

I plan to add FC 15 and 16 as soon as possible...
Martin

Hi JagsPaul


I just disover your thread and it looks very interesting for me as I thought about quite a similar project.

I have been a little frightened because I use some arduino module for communication with other SPI equipment ( using SPIbus of arduino one side and USB with proview the other side) and I'm encoutering a lot of disconnection in a real industrial environment (EMF mainly) (so +1 for the chescksum feature...)

Did you take into account the chip manufacturer recommendation concerning board rooting in order to make it more immune to noise (like olimexino does).

What is your plan concerning the AI / AO format (4-20 mA ? +/- 10 V ??) differential intputs ??

Anyway don't hesitate to post any progress, I 'm also very interested in. In the same way, if you need a real "environment test bench" don't hesitate to let me know...

Anyway, congratulations for your work as this could be a nice move for open source industrial solution

Snarf

Hi Martin,

I am very glad to know about your arduino modbus IO card. What you have done for AO & AI card?
For Ethernet what module are you using? Is it wiznet chip?

Actually I also like to port my IO module to modbus tcp, but I would like to use ENC28J60 (microchip) instead of wiznet chip due to low price. If you are interested we can jointly work on this.

jags

hi Snarf,

thanks for your interest on my project. I faced lot of problem with FTDI chip. In my case proview can communicate with arduino only after sending a character through arduino IDE serial monitor (find it on previous post of same topic). I finally decided to use MAX232 chip and PCI to serial or USB to serial converter.

If you place arduino board very close to process node noise will be very less. However I request to proview team to add a checksum component to end of the packet.

My AO is 4 to 20 ma and AI is 0 to 5 volt input.

After finish of the project you can contribute for real industrial environment test.

thanks & reagrds
jags

The tests I have carried out so far is with an Arduino Ethernet card arduino.cc/en/Main/ArduinoBoardEthernet

I have (today) extended the functionality of the "Mudbus" project to include Modbus Functions 15 and 16 (write to multiple coil and multiple registers).So far it is not tested properly and I have had no reviewer looking at it yet... I think I put the Git repo URL somewhere in my last post so have a look...

My plan is to include function code 2 (read discrete inputs) and then we will see... Dee Wykoff, who has written the Mudbus lib has been very positive so far. We'll see if my dirty hacks will reach his QA levels in the future... His code is quite neat...

I will try to focus on price reduction later on when I at least have a card that works. The ethernet chip is of course one of the candidates but I haven't though much about it. I'm willing to help though.

SGS Tomssons old VNQ810-E is probably still a good 24V high side driver although there are newer replacements but VNQ810-E is quite cheap... I have only checked prices in couple of places so far though...

I will use Muratas NFM61R filter on basically every input and output. I have used them in the old days when I made my first designs compatible with the CE mark... They are double inductor and cap in between and they can handle 2A... so you can use them on almost everything in a PLC. Maybe there are more compact ones today, I have to check. the NFM60R is smaller but rated 25VDC which is not enough... be careful when you use filter components and read everything you can find on the subject...

I used to always do 4 layer PCB designs with separate layers for gnd and the 5V... for my first prototype I think I will use two layers only...
For 24V signal inputs I use murata filter and then a voltage divider and a Zener + cap and then a Schmit trigger 74HC14 or something...and then into the shift register that I shift in to the Arduino...

My thought is that I will use an enclosure that is DIN rail mounted, but skip the modularity the Wago and Beckhoff way. They spend a lot of money on the connectors and modular plastic enclosures. My thought is make a series of boxes from 8/8 up to to 32/32 but without any possibility to expand a box. After all, you can just buy one more if you need more signals.
.
The 6 analog inputs of the Arduino can be used with proper buffering and signal conditioning but they are only 10bit... enough for some measurements but not for any high accuracy stuff...

For more demanding tasks I'm convinced that a dedicated AD/DA converter should be used in a separate box without any digital signals.

PWM outputs can be nice but not on the same board as any high resolution ad converters...
Oops it' late....

Hi Siamect

I 'm also testing with an arduino ethernet together with the mudbus library.

I changed this library already so it's compatible with the arduino 1.0 version.

How can I get your modifications to the mudbus library?

For now it's not yet working. I will try it today with a modbus tcp client test application.

Regards


Tim