Node-RED with Modbus Tutorial (part 1)

Introduction

This tutorial will guide you through creating a simple example using Node-RED and Modbus via TCP/IP. We will set up a Modbus server, read from and write to registers, and utilize Node-RED for real-time data handling. This is particularly useful for those looking to integrate industrial automation systems or IoT applications.

Step 1: Setting Up Node-RED with Modbus Server

1. Add a Modbus server node to your Node-RED flow:

   • Double-click the node to configure it.
   • Set the port to the default Modbus TCP port, typically 502.
   • Enable a listener to monitor outputs from the server.

2. Inject a trigger:

   • Use an inject node to send an empty string to start the server.
   • Deploy your flow to activate the server.

3. Check for errors:

   • If you encounter issues, verify that the port is not blocked on your system.
   • You can troubleshoot the flow files located in the Node-RED directory.

Step 2: Configuring the Modbus Reader

1. Add a Modbus Flex Getter node:

   • This is preferred over the standard Getter due to its robustness.
   • Connect it to the Modbus server node.

2. Configure the Modbus Flex Getter:

   • Set the function code to 3 (read holding registers).
   • Specify the unit ID, starting address, and the quantity of registers to read.
   • For example, to read 4 registers, your configuration might look like this:

     {
       "unitid": 1,
       "fc": 3,
       "address": 0,
       "quantity": 4
     }
     

3. Deploy the flow and check the output:

   • Use the inject node to trigger a read.
   • You should see the values from the specified registers.

Step 3: Writing Values to Modbus Registers

1. Add a Modbus Flex Writer node:

   • This node allows you to write values to Modbus registers.

2. Configure the Modbus Flex Writer:

   • Set the function code to 16 for writing multiple registers.
   • Specify the unit ID and starting address.
   • Prepare the payload with integer values to write.

3. Use a Join node to create an array:

   • This node can combine multiple values into a single array for writing.
   • Ensure the array length matches the number of values you wish to write.

4. Deploy the flow and test writing values:

   • Inject an array of values (e.g., [1, 2]) to write to the specified registers.
   • Confirm the values by reading the registers again.

Step 4: Implementing Random Number Generation

1. Install the random node:

   • Use the terminal to install the node by navigating to the Node-RED directory.
   • Run the command:

     npm install node-red-contrib-random
     

2. Create a flow to generate random values:

   • Set the random node to generate values from 0 to 65535 (2^16).
   • Configure the inject node to trigger the random number generation every second.

3. Deploy the flow to see random values being generated and written to the Modbus registers in real-time.

Step 5: Enhancing Your Flow

1. Add comments and labels:

   • Clearly label nodes and add comments to explain their purpose.
   • This will make your flow easier to understand for future reference.

2. Test and debug your flow:

   • Ensure all nodes are connected correctly and troubleshoot any issues that arise.

Conclusion

You have successfully created a basic Node-RED flow that interacts with a Modbus server, allowing you to read from and write to registers. By implementing random number generation, you can simulate real-world data inputs. For further learning, consider exploring more advanced Modbus features or integrating actual hardware systems into your flows.