Using Node-RED on MCUs

Could Node-RED generate code for MCUs? I asked backed in March 2020. As you may know, I am a big fan of Node-RED. It provides an elegant low-code/no-code solution for IoT but requires a single-board computer to run, like a Raspberry Pi 4B.

My question received an answer at the Node-RED Con 2022 with the Moddable presentation. The Moddable SDK implements JavaScript on MCUs and thus allows to run a Node-RED flow on them.

Supported hardware includes ESP32, Raspberry Pi Pico W, among other options, and proprietary boards like the Moddable Two, built around an ESP32 and a 320x240 touch display, which I ordered.

The project relies on different components:

The flow is designed with Node-RED.
Node-RED MCU Edition exports it to JavaScript.
Moddable translates the JavaScript project into C++ code.
Moddable calls the tool-chain of the board to build and link, upload and launch the project.
Moddable opens an optional debugger.

Configure

Installation includes four parts: the required tools; the Moddable SDK; the tool-chain for the targeted board; and the Node-RED MCU plug-in.

As I am using a non-production PC, I opted for a MacBook.

Required tools for macOS 13.2 include Xcode 14.2 and CLT 14.2.
The xs-dev utility installs the Moddable SDK and related utilities, including a debugger and a simulator.
The same xs-dev utility can also be used to install the tool-chain for the targeted board, ESP32 or Raspberry Pi Pico.
The node-red-mcu-plugin installs the front-end Node-RED MCU and Node-RED MCU Edition runtime. Edit the settings.js file and restart Node-RED.

Although I faced some issues during the installation, support from Moddable was great and the process ultimately succeeded.

Given the complexity of the project, a container would have been really great to get everything configured at once. Alas, there is no official container, but a user is sharing his own configuration. I haven't tested it yet.

Use

Node-RED now includes a new pane, MCU, with two parts: on top, the selection of the flows to consider for the MCU; below the choice of the targeted board and different options.

The different options include UI support, SSID and password for WiFi, and parameters for the screen.

First test

The first test is a minimal example with an inject node and a debug node.

The xsbug shows the input and output messages.

WiFi and MQTT

The flow connects to a MQTT broker, subscribes to the test/in thread, extracts the value from the message, performs some calculations and publishes the result to the test/out thread.

The first question was: How to connect to a WiFi network? The Options pane include dedicated fields to enter the SSID and password. They could also be mentioned on the Arguments field.

I wanted to use JSONata to perform the calculation, but Moddable doesn't support it. I had to use the function node instead.

GPIO

The built-in LED on the Raspberry Pi Pico W is not attached to a GPIO of the RP2040 but instead to the WiFi CYW43439 radio on WL_GPIO0. Suggested answer was to specify 32 as GPIO.

I also attached an LED to GPIO15. Selecting GPIO15 on the Raspberry Pi GPIO node displays 10, but the LED does blink.

On the Moddable 2 board, built-in LED is available on pin GPIO2 and backlight PWM is on pin GPIO18.

SPI and I²C buses

I haven't tested SPI and I²C buses yet.

Pre-configured sensors are available and can be installed with the following command.

Dashboard on MCU

One of the greatest and possibly most popular features of Node-RED is the dashboard. The video from the Node-RED Con 2022 shows at 2:19:41 a Node-RED dashboard running on an MCU.

I ordered the recommended Moddable Two board to test this feature. The board is built around an ESP32 and features a 2.4" displays with capacitive touch.

The versions of the dashboard displayed on the Moddable 2 screen, the browser and the similator look very similar. The Moddable 2 board takes default GMT as timezone, while the browser uses the correct locale format.

The UI Support should be Enabled and Screen Pixel Format set to rgb565le. Optional Screen rotation can be set to 90°, 180° or 270°.

Specific parameters need to be mentioned on the Arguments field, otherwise a stack overflow occurs.

Conclusion

Yes, Node-RED now generates code for MCUs!

I really like the new ability to use the same dashboards on a MCU-powered board. The Node-RED MCU implementation already supports a long list of nodes and new ones are added.

Targeting MCUs with Node-RED might not be the most optimised solution, especially when displaying a dashboard, but this approach speeds up the development on interfaces for MQTT and GUI.