How to Transfer Data from Modbus to MQTT

Open Automation Software can be used to transfer data from Modbus TCP, Modbus RTU, and Modbus ASCII devices to a MQTT broker, locally or over a network. This guide walks you through downloading and installing OAS, configuring a Modbus connector, a MQTT connector, and finally publishing the tag using the MQTT connector.

For this guide on how to transfer data from a Modbus device to a MQTT broker you will need:

• A Modbus device connected to your workstation

1 - Download and Install OAS

If you have not already done so, you will need to download and install the OAS platform.

Fully functional trial versions of the software are available for Windows, Windows IoT Core, Linux, Raspberry Pi and Docker on our downloads page.

On Windows, run the downloaded setup.exe file to install the Open Automation Software platform. For a default installation, Agree to the End User License Agreement and then click the Next button on each of the installation steps until it has completed.

If you'd like to customize your installation or learn more, use the following instructions:

• Windows Installation
• Linux Installation
• Raspberry Pi Installation
• Docker Installation

The OAS Service Control application will appear when the installation finishes on Windows.

Click on each START SERVICE button to start each of the three OAS services.

2 - Configure OAS

Configure OAS is the main application used to configure local and remote OAS instances.

1. From your operating system start menu, open the Configure OAS application.

2. Select the Configure > Tags screen.

   Important

   If this is the first time you have installed OAS, the AdminCreate utility will run when you select a screen in the Configure menu. This will ask you to create a username and password for the admin user. This user will have full permissions in the OAS platform.

   For further information see Getting Started - Security.

3. If this is the first time you are logging in, you will see the AdminCreate utility. Follow the prompts to set up your admin account. Otherwise, select the Log In menu button and provide the Network Node, username and password.

   

   

3 - Configure Modbus Data Source

In the following steps you will create and configure a Modbus Connector using a Master connection type and an Ethernet TCP connection. It assumes that your device is using the default port 502.

1. Select Configure > Drivers from the top menu.

   

2. Enter a meaningful Driver Interface Name to give this driver interface instance a unique name.

3. Ensure the following parameters are configured:

   • Driver: Modbus
   • Type: Master
   • Connection: Ethernet
   • Ethernet Type: TCP
   • Port: 502

4. Specify the device IP in the IP Address field.

   

5. Click on the ADD DRIVER button on the left hand side to add this driver configuration. Once added, the driver interface name should appear in the list of drivers.

   

4 - Add Data Source Tag

In this section you will create a Tag to represent your data point in the field (for example a temperature sensor). This can then be transferred your desired destination.

1. Select Configure > Tags from the top menu.

   

2. If you want to add a Tag to the root Tags group make sure the Tags node is selected in the tag list and click on the ADD TAG button.

   

   If you want to add a Tag to a Tag Group, select the Tag Group first and then click on the ADD TAG button.

   You can also add Tag Groups by using the ADD GROUP button.

3. Provide a Tag Name such as TemperatureSensor and click the OK button.

   

5 - Assign Modbus as Tag Data Source

You will now set the Tag's data source to the Modbus driver interface that you created previously.

1. Select the Tag that will source data from a Modbus data source.

   

2. Set the Data Source to Modbus.

3. Set the Select Driver Interface drop-down to the ModbusDevice1 interface created previously.

4. Configure the Modbus parameters accordingly based on your device requirements.

   • Device Address: The Modbus station number [default: 1]
   • Memory Type: The Modbus data model table type [Coil Status, Input Status, Input Register, Holding Register]
   • Address: The register to read/write based on the address offset
   • Modbus Data Type: The Input and Holding Register data type
   • Zero Based Address: Whether the Address starts at 0 or 1 [default: true]
   • Word Swap & Byte Swap: Adjust as required for your controller type [default: false]

5. Set the polling rate in seconds by setting the Polling Rate property [default: 1 second].

   

6. Click on the Apply Changes button to apply the changes.

7. Check that the quality status is Good Quality and the data in the Value field is as expected.

   

6 - Configure MQTT Publishing Connector

In the following steps you will create and configure a MQTT Connector to connect and publish tags to a third party broker. For the purposes of this guide, you will connect to the public HiveMQ broker.

1. Select Configure > Drivers from the top menu.

   

2. Enter a meaningful Driver Interface Name to give this driver interface instance a unique name.

3. Ensure the following parameters are configured:

   • Driver: MQTT
   • IP Address: broker.hivemq.com
   • Port: 1883
   • Client ID: OAS_Publisher

   

4. Click on the ADD DRIVER button on the left hand side to add this driver configuration. Once added, the driver interface name should appear in the list of drivers.

   

7 - Publish Selected Tags in MQTT connector

In this step you will select the Tags that you want to publish to the MQTT broker.

1. In the Configure > Drivers screen, select the MQTT driver instance that you created in the previous section (for example MQTT Connector 1).

2. Make sure the Publish Selected Tags checkbox is ticked.

   

3. In the table at the bottom click on the ADD button.

   

4. Select the Tag you want to add in the left hand panel and then ensure the Value property is selected. By default the name of the property will be the full Tag path (e.g. TemperatureSensor.Value). If you want to set your own property name, you can change the Id field to your own custom value.

   

5. The Tag has now been added to the list. You can add other Tags by repeating steps 3 and 4.

   

6. Click on the Apply Changes button.

8 - Verify Messages are Published to MQTT Broker

In this step you will confirm that OAS is successfully publishing your selected Tags to the external MQTT broker. By default, the publishing type is set to Continuous and the interval is 10 seconds.

In this section you will need to use a tool like MQTT Explorer to subscribe to the OAS tags in the HiveMQ broker.

1. Open MQTT Explorer and configure the connection to broker.hivemq.com.

   

2. Click on the ADVANCED button. Add a subscription to oas_tags. Click on the BACK button.

   

3. Click on the CONNECT button to open your connection.

4. Any changes your TemperatureSensor tag value should be published within 10 seconds. You can inspect the message in the side panel.

   

5. Click on the DISCONNECT button when you are done.

9 - Save Changes

Once you have successfully configured your OAS instances, make sure you save your configuration.

On each configuration page, click on the Save button.

If this is the first time you are saving the configuration, or if you are changing the name of the configuration file, OAS will ask you if you want to change the default configuration file.

If you select Yes then OAS will make this configuration file the default and if the OAS service is restarted then this file will be loaded on start-up.

If you select No then OAS will still save your configuration file, but it will not be the default file that is loaded on start-up.