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IIoT edge development - Using Modbus

Alena Traukina, Jayant Thomas, Prashant Tyagi, Kishore Reddipalli

January 21, 2019

Alena Traukina, Jayant Thomas, Prashant Tyagi, Kishore ReddipalliJanuary 21, 2019

Editor's Note: The Industrial Internet of Things (IIoT) promises to provide deep insight into industrial operations and enhance efficiency of connected machines and systems. Large-scale IIoT applications rely on layered architectures to collect data from a broad range of sensors, move data reliably and securely to the cloud, and perform analysis required to deliver that insight and efficiency. In Industrial Internet Application Development, the authors provide a detailed examination of the IIoT architecture and discuss approaches for meeting the broad requirements associated with these systems. 

 

Adapted from Industrial Internet Application Development, by Alena Traukina, Jayant Thomas, Prashant Tyagi, Kishore Reddipalli.

Chapter 3. IIoT Edge Development (Continued)
By Alena Traukina, Jayant Thomas, Prashant Tyagi, Kishore Reddipalli

Industrial M2M protocols – Modbus

In this section, we will try to build a simple IoT application for sending data from a sensor simulator module to a receiver device (a PC or a cloud), using a Raspberry Pi hub and the Modbus protocol:


Data flow from a sensor simulator to a receiver device

For devices with limited hardware resources, it makes sense to use the Modbus protocol for serial communication. While simple, it has several open and proprietary implementations that vary in functionality.

Note that this protocol can be used on the transport layer, but, in our example, we are going to use Modbus TCP, working on the application level.

In the following table, you can find a more detailed description of the protocol to understand whether it is suitable for your needs:

Key Value
Open source Yes*
The OSI layer Transport or an application
Data types Integer, float, string, Boolean
Limitations • No support for large binary objects

• The master node regularly polls each device for data modifications*

• Maximum 254 devices addressed on a single data link*

• Only contiguous transmissions are allowed
Possible operations Read and write registers and coils, diagnostics
Latency High
Usage SMS, GPRS, wireline, wireless, mesh communication
Security No
Compression No

Table 4: The Modbus protocol specifications

The values marked with * are not applicable to all implementations of the Modbus protocol.

For building the application, we will need the following:

Preparing an SD card

To prepare an SD card, follow the sequence of actions as described:

  1. Download the latest Raspbian LITE image (available at https://raspberrypi.org/downloads/raspbian/).

  2. Connect your SD card to a computer and use Etcher (https://io/) to flash the Raspbian .img file to the SD card.

  3. Enable SSH:

    cd /Volumes/boot
    touch ssh

 

  1. To enable Wi-Fi, create conf with the following content:


   network={
      ssid="YOUR_SSID"
      psk="YOUR_WIFI_PASSWORD"
   }

To create a file in a Linux console, you can use the GNU nano editor. It is pre-installed in most Linux distributives. All you need is to run the nano FILE_NAME command and follow the displayed instructions.

  1. Create the /home/pi/hub

  2. Create the /home/pi/hub/package.json file with the following content:


   {
      "name": "hub",
      "version": "1.0.0",
      "description": "",
      "main": "index.js", "scripts": {
         "start": "node index.js",
         "test": "echo \"Error: no test specified\" && exit 1"
      },
      "author": "",
      "license": "ISC", "dependencies": {
         "modbus": "0.0.16",
         "request": "^2.81.0"
      }
   }

  1. Create the /home/pi/hub/index.js file with the following content, replacing REMOTE-SERVER-ADDRESS.com and REMOTE-SENSOR-ADDRESS with real values:

  1. Create a /home/pi/hub/Dockerfile file with the following content:


   FROM hypriot/rpi-node:boron-onbuild
   RUN apt-get update && apt-get install -y libmodbus5

  1. Create the /home/pi/sensor

  1. Create the /home/pi/sensor/package.json file with the following content:


   {
      "name": "sensor",
      "version": "1.0.0",
      "description": "",
      "main": "index.js", "scripts": {
         "start": "node index.js",
         "test": "echo \"Error: no test specified\" && exit 1"
      },
      "author": "",
      "license": "ISC", "dependencies": {
         "modbus": "0.0.16"
      }
   }

  1. Create the /home/pi/sensor/index.js file with the following content, replacing REMOTE-HUB-ADDRESS.com with a real value:

  2. Create the /home/pi/sensor/Dockerfile file with the following content:


   FROM hypriot/rpi-node:boron-onbuild
   RUN apt-get update && apt-get install -y libmodbus5

Continue reading on page two >>

 

 

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