The Arduino UNO R4 Minima and Arduino UNO R4 WiFi that were released a few months ago are now officially available. Yesterday, they were officially launched on the Arduino Store, and the new version brings many possibilities to our DIY world, upgrading from the previous 8-bit MCU to a 32-bit Arm Cortex-M4, with memory increased by 16 times and many other performance enhancements. “The prices are $20 (18 euros) and $27.50 (25 euros) respectively.”

Previously, Arduino released the Portenta C33 board, which is equipped with Renesas Electronics’ ARM Cortex-M33 microcontroller: RA6M5. These two new development boards are equipped with Renesas Electronics’ chip RA4M1. The 32-bit ARM Cortex-M4 runs at 48 MHz, with 32 KB RAM and 256 KB flash memory. The solutions based on Renesas Electronics’ MCUs seem to be increasing.

One very different point is that “most conventional ARM-type MCUs are powered by 3.3V, but the RA4M1 can be powered by up to 5V,” which provides greater compatibility and interchangeability during DIY, which is very nice!

About Peripherals

The data sheet for ATmega328 has less than 300 pages, while RA4M1 has over 1400 pages. The design complexity of the UNO R4 Minima is similar to that of R3, but the UNO R4 WiFi is very dense, mainly because it adds an 8×12 LED matrix and ESP 32-S3-MINI WiFi module, “and it is worth mentioning that it finally changed to a USB TYPE-C interface.”

Communication Interfaces

“RA4M1 integrates two SPI interfaces, two I²C interfaces, and four serial communication interfaces (SCI).” SCI can be UART, I2C master, or simple SPI ports (up to 6 I2C or SPI ports), and it can even be a smart card interface. However, from the Minima schematic, it seems that only one I²C port is connected. Pins A4, A5, D4, and D5 expose the second SPI port, although the board specifications mention only one. A second serial port (Serial1) is also available, but it shares its pins with the SPI port. CAN bus support has also been added.

UNO R4 WiFi has a Qwiic I2C connector that allows easy connection to nodes in the Qwiic ecosystem. Adapter cables can also be compatible with sensors and actuators based on other connectors.

Analog Interfaces

UNO R4 has a 12-bit digital-to-analog converter (DAC) for generating real analog signals rather than PWM-based substitute signals. There is also an operational amplifier, a comparator, and an internal 8-bit DAC, while the analog-to-digital converter (ADC) is 14 bits wide, as opposed to 10 bits wide on the UNO R3. The AnalogWave library has been added, making the use of the DAC much easier. “Generating sine waves, sawtooth waves, or square waves is as simple as calling a library function.” Of course, we can do much more with it. Therefore, in terms of analog functionality, UNO R4 offers much more than the UNO R3.

Software

For the Arduino IDE, switching to the new model controller also means adding software support. New software often introduces issues, so the experience with UNO R4 may take some time to become as smooth as with UNO R3. One good point is that the UNO R4 Minima makes troubleshooting easier, “because it has an SWD interface for strict (serial) debugging.”

WiFi

Let’s take a look at the differences between Arduino UNO R4 WiFi and UNO R4 Minima. First, of course, is the Wi-Fi and Bluetooth LE module, namely Espressif’s ESP32-S3. It communicates with the MCU via serial (Serial2) in AT command mode. Other pins of the Wi-Fi module are exposed as small pads. The module can be reprogrammed, with the required pins accessible on a 2 x 3 header (and at the bottom of the PCB). The new Arduino library WiFiS3 provides high-level software support for this module.

The cloud connectivity feature on UNO R4 Wi-Fi means you can upload data and synchronize certain variables and data between different Arduinos. For example, “one Arduino with a button can turn on an LED on another Arduino wirelessly without any additional single line of code to handle the communication. Everything will be handled behind the scenes.”

LED Matrix

“The 96-pixel (8 × 12) red LED matrix allows users to plot data, create animations, and provide more complex and refined feedback in projects.” The new library provides the ability to display animations on the board. Synchronized web tools for designing animations have also been released.

The matrix uses Charlieplexing to connect 96 LEDs to only 11 GPIO ports (from D28 to D38 in Arduino notation). This means that only a few LEDs can be active at any one time, as the pixels consist of two LEDs connected in reverse parallel and share ports. However, due to the slower speed of the human eye, rapid time multiplexing can deceive the brain into seeing a complete image.

Power Supply

When not powered via USB, the power supply on Arduino UNO R3 is a basic linear voltage regulator. On the UNO R4 board, it has been replaced by DCDC. It supports a wider input voltage range from 6V to 24V. The regulator is also from Renesas Electronics and can provide up to 1.2A of current with an efficiency of about 90%. UNO R4 WiFi also has a connector for powering the real-time clock (RTC).

Conclusion

The Minima and WiFi versions of the Arduino UNO R4 boards look like reliable successors to the UNO R3. They share the same form factor, expansion connectors, and full 5V I/O. “UNO R4 WiFi is somewhat like the UNO R4 Minima with a built-in expansion board. With its Wi-Fi module, LED matrix, and Qwiic connector, it makes building IoT applications easy. UNO R4 is more powerful than UNO R3, with everything richer from memory to peripherals and running speed.”

https://store-usa.arduino.cc/products/uno-r4-wifi?selectedStore=ch

Finally, it is very interesting that the debug connector on the Minima and the CMSIS-DAP debugging capability of the ESP32-S3 module on WiFi are features that many developers have been waiting for since the birth of Arduino, so the Arduino UNO R4 can be seen as a strong step forward.

“Thanks to the Arduino community and early developers who contributed to the new porting libraries over the past few months, providing us with support.”