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:

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:

• Required software:

  • Node.js 6+ (https://nodejs.org/en/download/ )

  • PostgreSQL (https://www.postgresql.org/download/ )

  • The Cloud Foundry CLI (https://github.com/cloudfoundry/cli#downloads )

  • Request (https://www.npmjs.com/package/request )

  • Modbus (https://www.npmjs.com/package/modbus )

  • Docker (https://docs.docker.com/engine/installation/ )

• Required hardware:

  • Raspberry Pi 3 (model B)

  • A power adapter (2A/5V)

  • A microSD card (8 GB+) and an SD adapter

  • An Ethernet cable for a wired network connection

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

4. 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.

5. Create the /home/pi/hub

6. 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”
      }
   }

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

   

8. 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

9. Create the /home/pi/sensor

10. 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”
      }
   }

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

    

12. 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

# Build an image from a Dockerfiledocker build -t modbus-hub .## Run container in foregrounddocker run --privileged -it --rm --name modbus-hub-container modbus-hub## Run container in background# docker run --privileged -d  --rm --name modbus-hub-container modbus-hub## Fetch the logs of a container# docker logs -f modbus-hub-container## Stop running container# docker stop modbus-hub-container

# Build an image from a Dockerfiledocker build -t modbus-sensor .## Run container in foregrounddocker run -p 1502:1502 --privileged -it --rm --name modbus-sensor- container modbus-sensor## Run container in background# docker run -p 1502:1502 --privileged -d  --rm --name modbus- sensor-container modbus-sensor## Fetch the logs of a container# docker logs -f modbus-sensor-container## Stop running container# docker stop modbus-sensor-container

var http = require('http');var querystring = require('querystring'); 
var Pool = require('pg').Pool;var pool = new Pool({ 
 user: 'user', 
 database: 'database', 
 password: 'password', 
 host: 'host', port: 5432});
//ensure table exists in dbpool.query('CREATE TABLE IF NOT EXISTS "sensor-logs" (id serial NOT 
NULL PRIMARY KEY, data json NOT NULL)', function (err, result) {
 if (err) console.log(err);});
http.createServer(function (req, res) { 
 req.on('data', function (chunk) {  var data = querystring.parse(chunk.toString()); 
  console.log(data);
  //save in db  pool.query('INSERT INTO "sensor-logs" (data) VALUES ($1)', 
[data], function (err, result) {     if (err) console.log(err);   });});req.on('end', function () {  res.writeHead(200, 'OK', {'Content-Type': 'text/html'}); 
  res.end('ok')});}).listen(process.env.PORT || 8080);

# Build an image from a Dockerfiledocker build -t modbus-receiver . # Run container in foregrounddocker run -p 8080:8080 -it --rm --name modbus-receiver-container modbus-receiver # Run container in background# docker run -p 8080:8080 -d  --rm --name modbus-receiver-container modbus-receiver # Fetch the logs of a container# docker logs -f modbus-sensor-container # Stop running container# docker stop modbus-receiver-container