Programming the Arduino UNO R4 WiFi's LED Matrix

As soon as I held it in my hands, I couldn't wait to get started with the Arduino UNO R4 WiFi and its LED matrix! This little board has a ton of cool features, but the built-in display instantly makes it more charismatic, expressive, and "alive". Here's how to bring yours to life!

The UNO R4 WiFi product page already links to a pretty good official getting-started guide, but I got a bit confused by the separate page for the LED matrix – which talks about the UNO R4 Core and links to a somewhat inscrutable GitHub repo – so I'll clear that up first as we take the first steps.

UNO R4 Core?

To be clear: both new UNO R4 boards run on a Renesas RA4M1 processor, which enables the CAN interface, DAC, and so forth. But despite what the LED matrix page suggests, you don't need to go and download a separate Core and install it somehow from that repo. Just search for "R4" in the Boards Manager to add the new board definitions in the Arduino IDE, as you normally would, and it should work smoothly!

Browser compatibility: UNO R4 WiFi's LED Matrix online tool

I've just learned about Arduino Labs, which hosts a few experimental projects including a MicroPython editor, a BLE data dashboard, and a cute little "Include" robot. They also have a tool you can use to live-edit the pixels on your LED matrix! Unfortunately, the connection didn't work for me in Firefox (on a MacBook Pro running OS X 11.7.6 with the latest Firefox update), so I switched to Chrome, and it worked like a dream.

...Let's go!

Materials

For this project, you'll need:

• An UNO R4 (preferably the WiFi version)
• A USB-C cable that can interface with your computer
• Optional: a piece of paper, or something else to diffuse the LED matrix

1. Install the Arduino IDE and board definitions

If you don't already have it, grab the Arduino IDE and install it on your machine. If you haven't used the IDE in a while, it may take a moment to get used to version 2. However, I've found that it runs quite smoothly.

In the new IDE, you'll click on the UNO-shaped icon in the left sidebar to toggle the Boards Manager. (You'll also find the Sketchbook and Library Manager here, plus a couple of other tools. However, you can still use the menu bar for all of these functions, if you prefer.) Enter R4 in the search box and install the board definitions – no need to futz around with the "R4 Core" GitHub files.

Now, plug in your UNO and select it from the top dropdown in the IDE window – which should automatically select the port you're plugged into.

2. Dig in! LED matrix examples

With your UNO connected, open the File menu > Examples. You should now see a section near the top, labeled "Examples for Arduino UNO R4 WiFi". The LED_Matrix submenu contains some fun experiments you can run immediately – including a short set of alternating frames and, of course, a tiny Conway's Game of Life. Once you've tried those out (and perhaps modded them), I highly recommend trying out the browser-based LED matrix editor.

3. Live LED matrix editor

Let's start with the LivePreview example sketch. When uploaded onto the board, this one sets up a continuous connection between your Arduino and your browser, via the USB-C cable. Follow the directions at the top of the sketch to get to this editor at https://ledmatrix-editor.arduino.cc, where you can draw images and display them on the LED matrix in real-time!

After drawing a few frames, you can click between them and the UNO will respond. Use the controls at bottom-left to copy or delete frames as desired.

4. LED matrix animations

If you create an animated series of frames, you can download it as a.h header file (like the one I've shared below) and load it onto your Arduino using the PlayAnimation example sketch. Use File > Save As to make a copy of the example sketch, then navigate to the sketch folder and drop your downloaded animation.h file there (replacing the original one). Upload the sketch, and voilà! Custom LED animation.

More info

Curious about the UNO R4 WiFi's sister board, the Minima? Want to know more about both versions? Check out my unboxing video: