Industrial HMI and Arduinos in MODBUS RTU

In this instructable I will describe an example of communication between an industrial HMI (COOLMAY MT6070H, 150EUROS), an Arduino CLONE DIY (10EUROS) and an Arduino UNO (10EUROS). The network will run under a special and robust and industrial protocol: the MODBUS RTU (no IP or ethernet requested). More informations about this network, here:

https://en.wikipedia.org/wiki/Modbus

I made 2 experiments to explore the skills and the power of this kind of network:

-in the first one: the HMI is the Master, CLONE is Slave1 and UNO is Slave3 (you give the ID you want)

-in the second one: the HMI is the Slave1, CLONE is the Master (with an automation embeded program), UNO remains the Slave3.

Step 1: Very Easy to Connect

What is needed:

-an industrial HMI COOLMAY MT6070H with a modbus connector

-a DIY ARDUINO CLONE

-an UNO

-2 MAX485 shields

-a power supply 24V DC

-2 USB programing cables and an USBasp.

Be carefull to connect together every pinA+ and pinB- and have the same GND for all the devices.

Step 2: The First Experiment: HMI As Master and Arduinos As Slaves

First of all, you need to add some usefull libraries and board to yourArduino IDE:

-hardware: minicore for CLONE board

-SM: state machine library

-SimpleModbus: modbus RTU library in slave or mater mode.

I give too the sketch of the HMI and both arduinos with a tutorial and a french guide on modbus rtu.

Step 3: The Second Experiment: HMI As Slave, CLONE As Master and UNO As Slave

Why this experiment? Because It 's impossible to embed an automation program in this kind of HMI: you can't do this because it does not respect the safety and security rules on systems and machines.

The HMI soft is available here:

http://www.coolmay.com/Download-159-36-41.html

Like the Arduino IDE with the special library inside, you change easyly your device in a Slave or in a Master.

The speed of the communication seems to slower here. So I add some things to earn more speed reaction:

-serial communication in 8O1 instead of 8E1

-state machine for a real time running

-add some additional components in the network:

-120 OHM resistor between A and B

-560 OHM resistor between A and GND

-560 OHM resistor between B and GND

Step 4: Conclusion

Owing to this experiments I will soon try to supervise a 6 axes robot with arduinos as slaves and a PLC (M221 schneider) as a master to control movements sequences.

Others projects will also come soon like a network made with an HMI, a softster (ATS22 schneider) and a Arduin clone.

Thanks to all interesting tutorial and guides and website allover the net. Happy instructables!!!