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Node-RED

Installation files

Caution

  • This Router App has been tested on a router with firmware version 6.3.10. After updating the router firmware to a higher version, check whether a newer version of the Router App has also been released and update it accordingly for compatibility.
  • The Node-RED Router App requires Node.js to be installed first — see the Node-RED Dependency and Extensions section.
  • This Router App is only compatible with v3 and v4 platform routers.

Node-RED Router App Description

Node-RED is a flow-based programming tool for wiring together hardware devices, APIs, and online services in new and interesting ways.

The Node-RED Router App for Advantech routers allows Node-RED to run on v3 and v4 routers as a Router App. This lets you use the router as a Node-RED device.

Node-RED provides a browser-based editor that makes it easy to wire together flows using the wide range of nodes in the palette that can be deployed to its runtime in a single click. The lightweight runtime is built on Node.js, taking full advantage of its event-driven, non-blocking model. This makes it ideal for running at the edge of the network (in a router) as well as in the cloud. JavaScript functions can be created within the editor using a rich text editor. A built-in library allows you to save useful functions, templates, or flows for reuse. The flows created in Node-RED are stored as JSON, which can be easily imported and exported for sharing with other users or devices.

Tips

For more information and full documentation see: http://nodered.org/

An example of the Node-RED editor running in an Advantech router
An example of the Node-RED editor running in an Advantech router

Caution

Flow definitions are automatically included in the router report, so you do not need to attach them separately when you send the report to Support. The report does not contain data declared by the node as confidential (credentials).

Node-RED Dependency and Extensions

Tips

Install the Node.js Router App before Node-RED. Node.js is required for Node-RED to work — it is a separate Router App, and it can also be used as a standalone JavaScript server for other purposes.

You can also install other Node-RED Router Apps. These add more nodes to Node-RED. The following extension Router Apps are available:

  • AWS
  • Azure
  • BACnet
  • Bluetooth
  • Dashboard
  • dnp3
  • Filesystem
  • FTP
  • GPSd
  • gzip
  • KNX
  • LwM2M
  • Modbus
  • OPC UA
  • PLC - EtherNet/IP
  • PLC - Melsec
  • Splunk event collector

Each of these additional node packages is a separate Router App with its own page, listed under Node-RED in the sidebar.

Tips

The Node-RED module MQTT Broker was removed. For MQTT broker features on Advantech routers, use the separate MQTT Broker Router App, which is more powerful and has more functions.

Caution

Always use the latest published versions of all Node-RED modules together. Correct operation cannot be guaranteed when versions are mixed.

Node.js required by Node-RED and additional node Router Apps
Node.js required by Node-RED and additional node Router Apps

Node-RED Router App

After you upload the Router App to the router, it is accessible in the Customization section in the Router Apps item of the router's web interface. Click the title of the Router App to see the Router App menu as shown below:

Node-RED Router App menu
Node-RED Router App menu

The Information section provides the Log page with the Node-RED logging messages. In the Configuration section, you can enable automatic start of Node-RED on any port or access the flow editor. The Return item in the General section returns to the router's main web interface.

Node-RED Configuration

Node-RED Router App configuration — run Node-RED
Node-RED Router App configuration — run Node-RED
ItemDescription
Enable Automatic StartEnables Node-RED.
Web access portEnter the port where you want to run the Node-RED HTTP server. The flow editor and all other web-accessible parts (e.g., HTTP in node or Dashboard nodes) communicate on this port. The default port is 1880.
Log levelChoose the severity of the information you want to see in the log. See the Node-RED Status (Log) section for details.
Flow files FS pathSpecify the path where the flow definitions will be stored. See the Flow Files Path section for details. The default value is /var/data/node-red.
Web static files FS pathSpecify the path from which the Node-RED web server serves files. See the Web Static Files FS Path section for details.
Enables flow webeditorUncheck this option on production routers to prevent end users from accessing the flow editor. See the Flow Webeditor section for details.
Flow webeditor URL pathThe path part of the URL through which a user can access the flow editor. See the Flow Webeditor section for details.
Dashboard UI URL pathThe path part of the URL through which a user can access the Dashboard web GUI. See the Flow Webeditor section for details.

Configuration items

Run and Access the Node-RED Engine

After uploading the Router App to the router, follow these steps to run Node-RED on the router:

  1. In the router app menu, go to Configuration → Node-RED and check Enable Automatic Start. Press the Apply button. Node-RED starts and runs continuously whenever the router is running, including after reboots, until you clear the check box and press Apply again. You can see its status information on the Log page — the "Started flows" row indicates a fully started Node-RED engine. You can also enable or disable the flow editor to restrict end-user access.

  2. Click the Flows menu item to access the flow editor, or manually enter the address https://<router_ip>:<port_number>/<webadmin_path>. HTTPS is mandatory because the communication is encrypted.

    Tips

    The Node-RED UI may take 30 seconds or longer to start (depending on the router model, the number of installed nodes, and the flow size). Wait if the login page does not load immediately.

    Node-RED login in the router
    Node-RED login in the router

  3. Log in using the same credentials used for the router administration (e.g., user root). Because PAM authentication is used, you can log in with the credentials of any defined user. Users can be managed in Administration → Users in the router's web interface.

Admin and User profiles have the same settings when authenticating to Node-RED and therefore have the same rights. For a different authentication process, refer to the documentation: https://nodered.org/docs/security

Flow Files Path

You can specify the path where the flow definitions will be stored. This is the GUI equivalent of the flowFile option in the settings.js file without the file name. The default path is /var/data/node-red. Setting this path to /opt/myapp/flows lets you package a flow as a standard Router App and install it later. See the How to Distribute Your Own Flows to the Routers section for more details.

Web Static Files FS Path

There is a Web static files FS path field on the Node-RED configuration page. This is the GUI equivalent of the httpStatic option in settings.js. It is the path from which the Node-RED web server serves files. It is useful for static web files (e.g., images) or for downloading collected data as a file. See Example 3: Ping Statistics for both use cases.

Caution

Distinguish between the URI for local files (writing, storing data) and the URI for web access (reading for user access, downloading data).

Flow Webeditor

You can customize access to the Node-RED GUI. You can prohibit user access to the Node-RED flow editor on production routers by unchecking Enables flow webeditor. When there is a Dashboard GUI for a running flow, the admin can set a custom URL path for access. Setting Dashboard UI URL path to / makes the GUI available at e.g. https://192.168.1.1:1880/. For convenient development in this case, a developer can set Flow webeditor URL path to e.g. /admin to avoid a conflict between the Dashboard and webeditor paths — the webeditor is then accessible at https://192.168.1.1:1880/admin.

Node-RED Status (Log)

You can choose various log levels on the Node-RED configuration page. The following options are available: None, Fatal, Error, Warning, Info (the default), Debug, and Trace.

The log messages are visible on the Log page in the Status section of the router app interface. The page shows various information, such as software parts and versions used (Node-RED version, Node.js version, etc.), the settings file, the user directory, the flow JSON file, and more. These can be accessed or edited via SSH. Information about the start/stop of flows and error details is also shown. You can download the messages and save them as a text file by clicking the Save Log button. The versions of all other nodes are listed on the Licenses page of the Node.js Router App.

Node-RED status: version information and log
Node-RED status: version information and log

Available Nodes and Version

Node-RED Version

For more information about the software versions, see the Log page in the Node-RED Router App or the Licenses page in the Node.js Router App. The current Router Apps contain Node-RED version 3.0.2 and Node.js version 18.15.0.

Available Nodes

Advantech ships Node-RED and all related nodes in Router App packages and other additional router software. The main Node-RED Router App contains Node-RED itself and the following commonly used nodes:

Other nodes are available in separate Router Apps, each documented on its own page listed under Node-RED in the sidebar. The figure below shows a complete overview of the nodes available in the Node-RED UI.

List of available nodes in main Node-RED Router App
List of available nodes in main Node-RED Router App

Caution

Router firmware version 6.2.1 or later is required for the watch node to work correctly.

For any other node that Advantech does not provide as a part of the Router Apps, you can try to prepare it for the router yourself (see the Building the Custom Nodes for Node.js/Node-RED section) or send a request to cellular.info@advantech.com.

Router Nodes

Advantech provides custom router nodes to access router-specific features. The list of available router-related nodes is in the table below. Click a node in the Node-RED UI to see more detailed documentation.

NodeDescription
get configGets a router configuration (both firmware and all Router App configurations).
set configSets a router configuration (both firmware and all Router App configurations).
binary inDigital input node for the router. Sends a message with payload 0 or 1 to the node output when the pin changes state.
binary outDigital binary output node for the router.
signal ledDirectly controls the signal LED on the router.
hw monitoringMonitors the hardware parameters. You can select between the temperature in degrees Celsius and the supply voltage in volts.
sms receiverReceives an SMS sent to the router.
sms senderSends an SMS from the router.
xbus subscriberSubscribes to messages from XBus.
xbus publisherPublishes messages to XBus.

Router nodes

Advanced Topics

File Locations

Files related to Node-RED are organized in the router as follows:

/usr/lib/node_modules — Node.js looks for node modules in this folder and its subfolders. One of the subfolders is node-red with the Node-RED installation.

/usr/lib/node_modules/node-red/settings.js — File with Node-RED configuration and authentication configuration.

/usr/lib/node_modules/node-red/nodes — Node-RED looks for nodes in this folder. You can put third-party nodes directly into this folder.

/var/log/module-nodered — Node-RED writes its logs to this file. The log is rotated (maximum size 1 MB; the history length depends on the configured log level).

/var/data/node-red/flows.json — This file contains the definition of your flows. The path part is configurable — see the Flow Files Path section.

/var/data/node-red/flows_cred.json — This file contains the credentials (confidential data) of your flows. The file is encrypted. The path part is configurable — see the Flow Files Path section.

/var/data/node-red/context — Node-RED stores persistent flow and global variables here.

How to Distribute Your Own Flows to the Routers

There are several ways to distribute your flows to other routers.

You can use the export/import functions in the flow editor and perform the deployment. This method is especially useful during development. However, it is too tedious for production routers and cannot be automated.

Alternatively, you can copy the files with flow definitions directly over SFTP. The path to those files can be set in the Configuration (Flow files path item). The default path is /var/data/node-red. The main file is called flows.json. After uploading the file, restart Node-RED.

If your flows contain confidential data (for example, a password in an FTP node), you also need to add the file flows_cred.json. This file is encrypted. To decrypt this file, the router needs the secret from the router where the flows were created. The secret is generated during the first launch of Node-RED, or you can choose your own. This option is not accessible via the GUI. The secret can be found in the /opt/nodered/etc/setting file under the MOD_NODERED_CREDSECRET item. If you are running a bulk router installation, you are probably loading a prepared configuration. If you prepare the configuration on the router where the flows are developed, the Node-RED secret is distributed with it.

The best way to distribute flows to multiple routers is to create your own Router App. This way, you can install and update your Node-RED application exactly like other Router Apps. One simple trick is needed — set the storage folder for flows (Flow files path item in Configuration) to a path under /opt (for example /opt/myapp/flows).

After that, prepare the myapp folder with subdirectories flows and etc. Place the flow definitions in flows (see above). The etc folder should contain text files name and version with the name and version of your application. Compress everything using the tar command:

tar -czf myapp.v3.tgz myapp

More information about creating Router Apps/User Modules can be found in the Extending Router Functionality application guide.

Your own Router App can also be used for distributing your own nodes (see the Building the Custom Nodes for Node.js/Node-RED section for details on how to prepare your own node). The finished node can then be compressed with the other files into a .tgz file. You need to create a symbolic link to the node on the router, for example /usr/lib/node_modules/node-red/nodes/mynode → /opt/myapp/nodes/mynode. Use the script /opt/myapp/etc/install for creating the symbolic link and /opt/myapp/etc/uninstall for deleting it. Make sure these scripts are executable.

Example of the install script:

Example of the uninstall script:

#!/bin/sh

rm -f /usr/lib/node_modules/node-red/nodes/mynode

/opt/nodered/etc/init restart

There are other ways to get your flows to Node-RED, for example, the Node-RED REST API, but this topic is beyond the scope of this document.

Persistent Variable Storage

The persistent storage for variables is defined in the Node-RED configuration. When you add an item of the flow or global type, you can choose whether it should be stored in memory or in the filesystem. If the variable is stored in the filesystem, it survives a router reboot. Items are physically stored in /var/data/node-red/context.

Persistent storage
Persistent storage

Node "router"

The router node is added to the global context. See the Node.js Router App manual for more information about this node. You can use this node to obtain router data, such as a serial number. The example below shows how to get the serial number into the message payload.

Router node
Router node

Alternatively, the router node can be used in the function node, like this:

let router = global.get('router')
msg.payload = router.productName

Building the Custom Nodes for Node.js/Node-RED

Caution

Advantech is not responsible for the consequences caused by customer-built nodes, and it provides no support for the instructions in this section.

The official way to build and install a node is to use the npm command. However, the router is an embedded device with limited resources, and some nodes require a complex build environment and high performance because they contain code in languages other than JavaScript. Advantech provides the npm tool as a standalone Router App. You can install it on the router, but its usage is limited.

Another way is to prepare a node on a PC with Linux and then copy it to the router. The process is straightforward, but in some cases, your PC needs the same major version of Node.js as the router.

Tips

During installation, you may encounter two kinds of nodes: those written in JavaScript only and those written in JavaScript and other language(s). Some node authors provide prebuilt binaries so you can install the latter type just as easily as pure JavaScript nodes. However, if you see the message

WARN install No prebuilt binaries found

in the npm output, you need to compile the binaries; the following section describes one way to do this.

Preparing JavaScript Only Nodes on PC

These nodes need only the NPM package manager. Install NPM via your distribution repository. For example, for deb-based distributions:

apt-get install npm

For rpm-based distributions:

dnf install npm

(or yum install npm)

Now you can prepare the desired node:

npm --global-style install NODE

where NODE is a node name as found on www.npmjs.org or flows.nodered.org.

Once finished, you can see a node_modules folder with the desired node folder inside. Copy the node folder to the router at /usr/lib/node_modules/node-red/nodes (e.g., via FTP/SFTP), restart Node-RED, and the node(s) should appear in the palette. A better approach is to place it in /opt and create a link from the mentioned folder so that it is not overwritten during firmware upgrades. You can also pack the resulting node into a .tgz file as a standard Router App.

Preparing Nodes Using Other Languages on PC

Some nodes have parts written in languages other than JavaScript. These nodes require the GYP meta-build system and a build environment relevant to the language.

On most distributions, the GYP package is installed as an NPM dependency, so you do not need to install it separately.

For C/C++, the most common languages, you can use the same toolchains as for building Router Apps. See the Environment Setup chapter in the Developing Router Apps Guideline to learn how to install them.

When you have installed all prerequisites, invoke the following commands for the v3 platform:

export CC="/opt/toolchain/gcc-conel-armv7-linux-gnueabi/bin/armv7-linux-gnueabi-gcc"
export CXX="/opt/toolchain/gcc-conel-armv7-linux-gnueabi/bin/armv7-linux-gnueabi-g++"
npm --arch=arm --global-style install NODE

Or for the v4 platform:

export CC="/opt/toolchain/gcc-conel-aarch64-linux-gnueabi/bin/aarch64-linux-gnueabi-gcc"
export CXX="/opt/toolchain/gcc-conel-aarch64-linux-gnueabi/bin/aarch64-linux-gnueabi-g++"
npm --arch=arm64 --global-style install NODE

where NODE is again the actual node name. Then copy the node as described above.

Caution

Bindings to other languages can use a version-dependent API, so while building, we strongly recommend using the same Node.js major version as on the router.

Installing Nodes Directly on Router

The npm tool installs nodes physically to /usr/lib/node_modules on the system partition.

Tips

Applications installed in the system partition are deleted when you update the router firmware.

Caution

If the /usr/lib folder fills the entire storage, the router may stop working, and a factory reset might not resolve the issue. Do not install too many applications in this folder.

You can manage nodes with the installed npm Router App on the router. A common command is:

npm install -g <node_name>

For example:

npm install -g node-red-contrib-combine

This installs the node to the main node modules folder /usr/lib/node_modules. Node-RED can find palette nodes in this location. The system partition (including /usr/lib/node_modules) is replaced during a firmware update, so nodes installed there are lost. To keep the nodes, install them to /opt (the Router App storage, which a firmware update does not erase) and create a symbolic link to them from /usr/lib/node_modules/node-red/nodes.

Installation with npm tool on the router
Installation with npm tool on the router

The npm tool requires an Internet connection.

Caution

Only nodes provided by Advantech as Router Apps are supported. Node.js/Node-RED nodes installed with the npm tool are not supported.

Flow Examples

You can import the following examples to Node-RED as JSON code. To import an example to the Node-RED UI, copy the JSON code provided in the example. Import the code via the top right menu in the Node-RED UI by choosing Import → Clipboard.

Top right menu — import from clipboard
Top right menu — import from clipboard

Paste the JSON code into the input field, as shown in the figure below.

Import nodes via JSON
Import nodes via JSON

After the import, the JSON code turns into the desired flow of nodes.

Example 1: User LED Turn On and Off

This is a simple first Node-RED flow to try with Router nodes. Import the following JSON code to get the flow:

The flow uses two inject nodes from the input nodes list and one signal led node from the Router nodes list. Double-click a node to see or edit its parameters.

Example 1 — user LED flow
Example 1 — user LED flow

Click the red Deploy button in the upper right corner. Now the flow is running. Click the small rounded button in front of the ON node (indicated by the orange arrow in the figure). The USR LED on the router turns on, as shown in the figure below. You can turn it off by clicking the OFF node (sends boolean false to the signal-led node).

Example 1 — user LED turned on
Example 1 — user LED turned on

Example 2: HTTP Endpoint

This example is taken from the Node-RED documentation examples:

https://cookbook.nodered.org/http/create-an-http-endpoint

Import the JSON code from the link above. It creates the nodes shown in the following figure — an HTTP endpoint that responds to GET requests with static content (such as an HTML page).

Example 2 — imported nodes to deploy
Example 2 — imported nodes to deploy

The flow uses the "HTTP in" (where the URL is defined), "template" (where the HTML page is defined), and "HTTP response" nodes. Next, click the red Deploy button in the upper-right corner. This makes the flow live.

When you enter the URL defined in the "HTTP in" node into the web browser (in this case, https://<ip-address-of-the-router>:<configured-port>/hello), you see the defined HTML page as the response:

Example 2 — HTTP response
Example 2 — HTTP response

Example 3: Ping Statistics

This example demonstrates how to use the Web static files FS path option in Node-RED configuration. It pings the www.advantech.com domain, stores the results in a file, shows them in a chart, and enables download of the collected data file.

First, add the path /var/data/node-red/static to the Node-RED configuration as seen in the figure:

Example 3 — Web static file FS path configuration
Example 3 — Web static file FS path configuration

Next, create the folder structure so the given path exists. Log in to the router (via SSH) and run this command:

mkdir /var/data/node-red/static

Alternatively, connect to the router via FTP and create the folder /var/data/node-red/static. Then download the button image from https://upload.wikimedia.org/wikipedia/commons/8/8d/Download_alt_font_awesome.svg and upload it to the router as /var/data/node-red/static/download.svg. Alternatively, download it directly on the router, for example, with the command:

curl https://upload.wikimedia.org/wikipedia/commons/8/8d/Download_alt_font_awesome.svg \
  -o /var/data/node-red/static/download.svg

Copy this JSON code and import it as the Node-RED flow:

Caution

This example requires the Node-RED Dashboard module to be installed.

The following flow of nodes appears:

Example 3 — ping statistics flow
Example 3 — ping statistics flow

Deploy the flow with the red button in the upper right corner. Now you can access the ping statistics at:
https://<router_ip>:<port_number>/<dashboard_path>

Example 3 — ping statistics chart and download
Example 3 — ping statistics chart and download

The page shows a chart with ping statistics in milliseconds (the router must be connected to the Internet) and a button for downloading the /var/data/node-red/static/pings.dat file. Web static files FS path is used when writing (saving ping results to the data file), reading (viewing the statistics page with the button image), and downloading the data file.

Node-RED Bluetooth Examples

Example 4: Reading from Supported BLE Sensor in Node-RED

This example demonstrates how to use three RuuviTags for temperature and humidity monitoring.

Example 4 — RuuviTag
Example 4 — RuuviTag
Example 4 — status
Example 4 — status

Advantech offers a specialized node for RuuviTag sensors that handles data decoding. You can connect a RuuviTag to the BLE scanner node to get the measured values. The sensors propagate data via the manufacturer data advertising item.

Copy this JSON code and import it as the Node-RED flow:

Caution

This example requires the Bluetooth, Node-RED Bluetooth, and Node-RED Dashboard Router Apps to be installed.

Example 4 — Bluetooth Router App
Example 4 — Bluetooth Router App

The data are collected continuously. The Switch node splits the data from three different sensors by their addresses into three Dashboard sections. You can see the result at https://<ip-address-of-the-router>:<configured-port>/ui.

Example 4 — Presentation of the environment conditions with Dashboard UI
Example 4 — Presentation of the environment conditions with Dashboard UI

You can find more Bluetooth examples in the Bluetooth Router App documentation. Those examples are not for Node-RED, but they can clarify some other aspects of using Bluetooth with Advantech routers.

Example 5: Reading from and Writing to Unsupported BLE Sensor in Node-RED

This example shows how to use a sensor that has no specialized decoding node. It uses Xiaomi Flower Care to control the greenhouse environment.

Example 5 — Xiaomi Flower Care
Example 5 — Xiaomi Flower Care
Example 5 — status
Example 5 — status

The sensor propagates data via the service characteristics.

Copy this JSON code and import it as the Node-RED flow:

This example requires the Bluetooth and Node-RED Bluetooth Router Apps to be installed.

Example 5 — nodes
Example 5 — nodes

The data are checked every 5 minutes. Because there is no specialized node for this sensor, the data are processed with general nodes. You need to know the GATT services and characteristics for this — consult the sensor vendor for this information. The following tables list only the information needed for this example:

Service UUIDService short UUIDUsage
0000fe95-0000-1000-8000-00805f9b34fbfe95device discovery
00001204-0000-1000-8000-00805f9b34fb1204data

Characteristics for the 1204 service:

Characteristic UUIDRead/WriteUsage
00001a00-0000-1000-8000-00805f9b34fbwritemode control
Write the 2-byte sequence 0xa01f to read realtime data from the next characteristic.
00001a01-0000-1000-8000-00805f9b34fbreadrealtime data
The data are Little Endian encoded. Bytes 00–01 contain the temperature in 0.1°C as uint16, bytes 03–06 brightness in lux as uint32, byte 07 moisture in % as uint8, and bytes 08–09 conductivity in µS/cm as uint16.
00001a02-0000-1000-8000-00805f9b34fbreadbattery and FW
The first byte contains the battery level as a percentage.

The BLE scanner scans until it finds a sensor with the specific service. This example assumes only one sensor, so there are no address checks and duplicates are allowed. Real-time data are read with a slight delay so that the sensor can change the mode. Next, they are decoded with the general function node.

The flow controls the greenhouse environment via Modbus devices (e.g., watering with a Modbus-controlled water valve or fertilizing with a Modbus-controlled dispenser) according to measured values. It also turns the user LED on the router on or off according to the sensor battery level.

You can find more Bluetooth examples in the Bluetooth Router App documentation. Those examples are not for Node-RED, but they can clarify some other aspects of using Bluetooth with Advantech routers.

Node-RED Modbus Examples

Caution

The Node-RED Modbus Node Module is required for these examples.

The Modbus Server is only a helper part of the examples below. You can install its node on another router or use a different Modbus server (e.g., a simulator on a PC). Make sure that the communication configuration of the client in the example matches that of the server.

Before trying Examples 6–9, add the Modbus Server node to the flow and configure the Modbus Client, which the Modbus nodes use to connect.

Copy this JSON code and import it as the Node-RED flow:

The following node appears:

Modbus Flex Server
Modbus Flex Server

Example 6: Writing to the User-Defined Modbus Server

This example flow writes to the holding registers of the Modbus TCP server.

Copy this JSON code and import it as the Node-RED flow:

The following flow of nodes appears:

Example 6 — write voltage nodes
Example 6 — write voltage nodes

Writing is triggered every time the voltage changes in the router's power supply. Since the registers can store numbers between 0 and 65535 and the voltage on the router can range from +9 to +48 V DC (depending on the router model) with three-digit precision, the number is multiplied by 1000 before storing.

Voltage is written to address 0 using the Modbus-write node. The node configuration uses Modbus function code 6, which writes a single value to a specified address in the holding registers. After the voltage changes again, the old value in the register is overwritten.

Example 7: Reading from the User-Defined Modbus Server

This example flow reads the value written in Example 6 from the Modbus TCP server.

Copy this JSON code and import it as the Node-RED flow:

The following flow of nodes appears:

Example 7 — read voltage nodes
Example 7 — read voltage nodes

Press the button to read the value from the Modbus holding registers. The node configuration uses Modbus function code 3, which reads a specified number of holding registers from the starting address. In this case, the configuration reads one register from address 0. Since the stored value in the register was multiplied by 1000, it is divided before displaying to restore three-digit precision.

Example 8: Writing a Sequence to the User-Defined Modbus Server

This example flow writes a sequence of values. It demonstrates how to modify Example 6 to write values to the registers in a different way.

Copy this JSON code and import it as the Node-RED flow:

The following flow of nodes appears:

Example 8 — writing sequence nodes
Example 8 — writing sequence nodes

This example focuses on the transformation of measured values. Instead of multiplying the calculated value, it stores the value in single-precision floating-point format, which allows negative values to be preserved. Another way to accurately store negative numbers is to define an offset, add it before storing, and subtract it before displaying. The best practice is to hold the offset in another register and read it when computing.

How does the "float to dec array" function node work? For example, if the float value 12.078 flows in, this node transforms it into an array of length 2 with decimal values ranging from 0 to 65535. This way, the registers use 32 bits of storage.

Values are written to addresses 1 and 2 using the Modbus-write node. The node configuration uses Modbus function code 16, which presets multiple registers from a specified address in the holding registers.

Example 9: Reading a Sequence from the User-Defined Modbus Server

Caution

The Node-RED Dashboard module is required for this example.

This example flow reads the sequence of values written to the registers in Example 8.

Copy this JSON code and import it as the Node-RED flow:

The following flow of nodes appears:

Example 9 — reading sequence nodes
Example 9 — reading sequence nodes

This example focuses on decoding the single-precision floating-point format sequence from the Modbus Server, written in Example 8. The Modbus-read node uses function code 3 to read two holding registers from address 1. The node returns an array of two values that are split, converted from decimal to binary, and joined. The "to float" node then converts the result from binary to float.

This example could end with a debug node, but it adds a chart that displays the voltage over the last 2 minutes as a practical use case. The "inject" node is configured to inject the flow every second. Invalid values are filtered out using the "switch" node.

The chart can be accessed at: https://<ip-address-of-the-router>:<configured-port>/ui

The chart should look like this:

Example 9 — voltage chart
Example 9 — voltage chart

Example 10: Reading Coil Status from a Modbus RTU Relay using the Modbus Protocol

The primary purpose of the Modbus protocol is to facilitate communication in industrial systems. This example demonstrates reading from a Modbus RTU Relay connected to the /dev/ttyS1 serial port.

The relay used in this example: https://www.waveshare.com/modbus-rtu-relay.htm

Copy this JSON code and import it as the Node-RED flow:

The following flow of nodes appears:

Example 10 — reading coil nodes
Example 10 — reading coil nodes

When you press the button, the Modbus Response node reports the coil status. The node configuration uses Modbus function code 1, which reads a specified number of coil statuses from the starting address. In this case, the configuration reads eight coils from address 0 — the only permitted read operation of the hardware. The node returns an array of eight Boolean values.

Example 11: Writing Coil Status to a Modbus RTU Relay using the Modbus Protocol

This example demonstrates how to write to the Modbus RTU Relay, showcasing two different forms of writing: single and multiple values.

The relay used in this example: https://www.waveshare.com/modbus-rtu-relay.htm

Copy this JSON code and import it as the Node-RED flow:

The following flow of nodes appears:

Example 11 — writing coil nodes
Example 11 — writing coil nodes

The flow consists of multiple buttons that set different values on coils inside the Modbus registers when pressed. The "Relay write Coil" node is set up with function code 5, "force single coil," to force the predefined coil (here, the coil on address 0) to take a value from the "inject" node.

The "Relay write Coils" node is set up with function code 15, "force multiple coils," which forces coils from the starting address to the passed values. The "inject" node passes eight values, which the Modbus-write node expects.

Example 12: Reading from a Real Sensor using the Modbus Protocol

This example demonstrates how to read, convert, and display values in the correct format from an actual industrial sensor.

The sensor used in this example: https://www.seeedstudio.com/RS485-Temperature-and-Humidity-Sensor-p-5235.html

Copy this JSON code and import it as the Node-RED flow:

The following flow of nodes appears:

Example 12 — real sensor nodes
Example 12 — real sensor nodes

The flow consists of a button that reads registers from the Modbus device when pressed. The Modbus-read node uses function code 3 to read three holding registers from address 0. The node returns an array of three values that are split, routed, converted, joined, and formatted into an output message.

Example of output:

At Thu Apr 13, 2023, 11:48:04 GMT+0000 (UTC), the temperature was 23.16°C with humidity 37.39%RH and dew point 7.83°C

Resources

For more resources on implementing your own flows, see the Node-RED documentation:

https://nodered.org/docs/