Arduino Uno R4 Minima

The Uno R4 uses the Renesas RA4M1 (ARM Cortex-M4) - a major upgrade from the classic Uno's ATmega328P. 16x the RAM, 8x the flash, and USB DFU support for browser-based flashing from the Playground.

Specs

Firmware setup

PlatformIO

; platformio.ini
[env:uno_r4_minima]
platform = renesas-ra
board = uno_r4_minima
framework = arduino
lib_deps = conduyt

pio run --target upload

Arduino IDE

1. Go to Tools → Board → Boards Manager
2. Search for Renesas and install Arduino Renesas fsp Boards
3. Select Arduino Uno R4 Minima from Tools → Board → Arduino Renesas Boards

Transport

USB serial:

#include <Conduyt.h>

ConduytSerial  transport(Serial, 115200);
ConduytDevice  device("MyDevice", "1.0.0", transport);

void setup() {
  Serial.begin(115200);
  device.begin();
}

void loop() {
  device.poll();
}

Browser flashing (DFU)

The Uno R4 has a USB DFU bootloader, which means it can be flashed directly from Chrome/Edge using WebUSB - no IDE required.

Step by step:

1. Enter DFU mode: double-tap the RESET button quickly (two taps within ~500ms). The "L" LED will start pulsing slowly. If it doesn't pulse, tap faster.
2. Go to the Playground and click Flash
3. Select Arduino Uno R4 and click Flash Arduino Uno R4
4. Chrome prompts you to select a USB device - pick the Arduino DFU device
5. Wait for the progress bar to reach 100%
6. The board automatically reboots into the new firmware

Windows users: if no DFU device appears in the browser prompt, you may need to install WinUSB drivers:

1. Download Zadig
2. Put the board in DFU mode (double-tap RESET)
3. In Zadig, select the Arduino DFU device and install the WinUSB driver

On macOS and Linux, DFU works without additional drivers.

Built-in LED

Pin 13, same as the classic Uno.

Differences from Uno R3

Common issues

• DFU mode not entering: You need two quick taps within ~500ms. A single tap just resets the board. Practice the rhythm - tap-tap.
• Serial port disappears after DFU flash: This is normal. Single-tap RESET to reboot into the new firmware. The serial port reappears.
• Port busy after flash: Wait 2–3 seconds after the board reboots, then reconnect.