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# Arduino UNO R4 WiFi

An UNO with a 48 MHz Arm Cortex-M4, an ESP32-S3 for Wi-Fi and Bluetooth LE, and a 12 × 8 LED matrix.

Source page: https://www.tinkered.ai/components/arduino-uno-r4-wifi
Datasheet: https://docs.arduino.cc/resources/datasheets/ABX00087-datasheet.pdf

## In short

The Arduino UNO R4 WiFi is an UNO-shaped board whose main chip, a 5 V Renesas RA4M1 (48 MHz Cortex-M4, 256 kB flash, 32 kB SRAM), is paired with an ESP32-S3-MINI-1 module for 2.4 GHz Wi-Fi and Bluetooth LE (Arduino ABX00087 datasheet, pp. 1, 3). Power it from USB-C or 6 to 24 V on the barrel jack (p. 7), wire 5 V parts to D0 to D13 and A0 to A5 at no more than 8 mA per pin (p. 16), and plug 3.3 V Qwiic boards into the Qwiic port as Wire1 (p. 14).

The UNO R4 WiFi (SKU ABX00087) keeps the UNO form factor and headers but runs two processors. The main one is a Renesas RA4M1: an Arm Cortex-M4 with a floating point unit at 48 MHz, 256 kB of flash, 32 kB of SRAM and 8 kB of EEPROM, fixed at 5 V to stay compatible with UNO shields (UNO R4 WiFi datasheet, pp. 1, 9). Beside it sits an ESP32-S3-MINI-1-N8 module running at 3.3 V, which provides 802.11 b/g/n Wi-Fi on 2.4 GHz and Bluetooth 5 LE, talks to the RA4M1 through a TXB0108 level translator, and by default bridges the USB-C port to the RA4M1 for programming (pp. 2, 3, 9, 11).

On the board you also get a 12 × 8 red LED matrix you can program for text and animations, a Qwiic connector on a second 3.3 V I2C bus, an RTC with a VRTC backup pin, and an OFF pin that switches the board's supply (pp. 6, 12, 14, 19). The analog side matches the Minima: an ADC of up to 14 bits on A0 to A5, a DAC of up to 12 bits on A0 and an op-amp on A1 to A3 (pp. 2, 18). CAN is on D10 (TX) and D13 (RX) and needs an external transceiver (p. 18).

Power arrives through USB-C or 6 V to 24 V on the barrel jack or VIN, stepped down to 5 V by an ISL854102 buck converter; a separate 3.3 V regulator feeds the ESP32-S3 (pp. 7, 15). The RA4M1's GPIOs are rated for 8 mA (p. 16), and the ESP32-S3's own header is 3.3 V and must never meet the RA4M1's 5 V pins (p. 16). In the Arduino core, Wi-Fi goes through the WiFiS3 library and Bluetooth LE through ArduinoBLE.

## Pinout

| Pin | Function | Type |
| --- | --- | --- |
| D0 | UART RX, PWM, Digital · 5 V | bidirectional |
| D1 | UART TX, PWM, Digital · 5 V | bidirectional |
| D2 | PWM, Digital · 5 V | bidirectional |
| D3 | PWM, Digital · 5 V | bidirectional |
| D4 | PWM, Digital · 5 V | bidirectional |
| D5 | PWM, Digital · 5 V | bidirectional |
| D6 | PWM, Digital · 5 V | bidirectional |
| D7 | PWM, Digital · 5 V | bidirectional |
| D8 | PWM, Digital · 5 V | bidirectional |
| D9 | PWM, Digital · 5 V | bidirectional |
| D10 | PWM, SPI CS, Digital · 5 V | bidirectional |
| D11 | PWM, SPI COPI, Digital · 5 V | bidirectional |
| D12 | PWM, SPI CIPO, Digital · 5 V | bidirectional |
| D13 | PWM, SPI SCK, Digital · 5 V | bidirectional |
| SDA | I2C SDA, Digital · 5 V | bidirectional |
| SCL | I2C SCL, Digital · 5 V | bidirectional |
| A0 | ADC, Digital · 5 V | bidirectional |
| A1 | ADC, Digital · 5 V | bidirectional |
| A2 | ADC, Digital · 5 V | bidirectional |
| A3 | ADC, Digital · 5 V | bidirectional |
| A4 | ADC, I2C SDA, PWM, Digital · 5 V | bidirectional |
| A5 | ADC, I2C SCL, PWM, Digital · 5 V | bidirectional |
| BOOT | BOOT | input |
| IOREF | IOREF | power out |
| RESET | Digital · 5 V | input |
| 3V3 | 3.3V · 3.3 V | power out |
| 5V | 5V · 5 V | power out |
| GND | GND | power in |
| GND3 | GND | power in |
| VIN | VIN | power in |
| GND2 | GND | power in |
| AREF | AREF | input |
| OFF | OFF | input |
| GND4 | GND | power in |
| VRTC | VRTC | power in |

## Specifications

| Spec | Value | Source |
| --- | --- | --- |
| Main microcontroller | Renesas RA4M1 (R7FA4M1AB3CFM#AA0), Arm Cortex-M4 with FPU at 48 MHz, 5 V | Arduino UNO R4 WiFi datasheet (ABX00087), pp. 1, 9 |
| Memory (RA4M1) | 256 kB flash, 32 kB SRAM, 8 kB EEPROM | Arduino UNO R4 WiFi datasheet, p. 1 |
| Wireless module | ESP32-S3-MINI-1-N8, 3.3 V: Wi-Fi 4 (802.11 b/g/n, 2.4 GHz), Bluetooth 5 LE | Arduino UNO R4 WiFi datasheet, pp. 2, 3, 9 |
| VIN / barrel jack | 6 V to 24 V, 7 V typical | Arduino UNO R4 WiFi datasheet, p. 7 |
| USB-C input | 4.8 V to 5.5 V; about 4.7 V reaches the RA4M1 after the Schottky drop | Arduino UNO R4 WiFi datasheet, pp. 7, 15 |
| Current per GPIO | 8 mA (RA4M1 pins) | Arduino UNO R4 WiFi datasheet, p. 16 |
| LED matrix | 12 × 8 red LEDs, driven from RA4M1 pins | Arduino UNO R4 WiFi datasheet, p. 12 |
| Analog | 6 inputs A0 to A5, 14-bit ADC; up to 12-bit DAC on A0; op-amp on A1 (+), A2 (-), A3 (out) | Arduino UNO R4 WiFi datasheet, pp. 2, 18 |
| Buses | UART on D0/D1, SPI on D10 to D13, I2C on A4/A5 (Wire) and Qwiic (Wire1, 3.3 V), CAN on D10 (TX) / D13 (RX) | Arduino UNO R4 WiFi datasheet, pp. 2, 14, 18 |
| Operating temperature | -40 °C to +85 °C | Arduino UNO R4 WiFi datasheet, p. 7 |
| Logic level | 5 V | Tinkered component registry |
| Clock speed | 48 MHz | Tinkered component registry |
| Flash | 256 KB | Tinkered component registry |
| RAM | 32 KB | Tinkered component registry |
| GPIO pins | 20 | Tinkered component registry |
| ADC channels | 6 | Tinkered component registry |
| ADC resolution | 14 bits | Tinkered component registry |
| PWM channels | 6 | Arduino UNO R4 WiFi datasheet (ABX00087) |
| Bluetooth | BLE 5.0 | Tinkered component registry |
| Dimensions | 68.58 × 14.5 × 53.34 mm | Tinkered component registry |
| Weight | 25 g | Tinkered component registry |

## Circuit notes

- D0 to D13 and A0 to A5 are 5 V pins driven by the RA4M1 (UNO R4 WiFi datasheet, p. 16). 3.3 V-only modules need a level shifter there, or a Qwiic connection.
- The Qwiic connector is a second I2C bus at 3.3 V, Wire1 in code, separate from Wire on A4/A5 (p. 14). Do not plug a 5 V I2C module into it.
- The small header near the RESET button exposes the ESP32-S3's own UART and boot pins at 3.3 V (p. 10). Never connect those to the RA4M1's 5 V pins (p. 16).
- Each RA4M1 GPIO is rated for 8 mA (p. 16): about 390 Ω or more for an LED at 5 V, and a transistor or driver for relays, motors and LED strips.
- Feed 6 V to 24 V into the barrel jack or VIN, or 5 V over USB-C, never more than 5 V through USB (pp. 7, 12). Pull the OFF pin to GND to switch the board's supply off, and put a coin cell on VRTC to keep only the RTC running (p. 19).
- CAN is on D10 (TX) and D13 (RX), the same pins as SPI's CS and SCK (p. 18). Add an external CAN transceiver, and do not use SPI on those pins at the same time.

## Common mistakes

- **Using ESP32 Wi-Fi code.** The UNO R4 WiFi is programmed as an RA4M1 board, with the ESP32-S3 acting as its modem. Use the WiFiS3 library, not ESP32's WiFi.h, HTTPClient or WebServer, and not WiFiNINA.
- **Plugging a 5 V module into Qwiic.** The Qwiic connector runs at 3.3 V (UNO R4 WiFi datasheet, p. 14). Put 5 V I2C modules on A4/A5 or the SDA/SCL pins, and remember a Qwiic board is reached through Wire1, not Wire.
- **Wiring CAN to D4/D5.** The datasheet's summary mentions D4/D5, but the WiFi board's pinout puts CAN TX on D10 and CAN RX on D13 (p. 18), through an external transceiver.
- **Drawing too much from a pin.** RA4M1 pins are rated for 8 mA (p. 16). A 220 Ω LED resistor, a relay coil or a motor on a pin overloads it; use a larger resistor or a transistor.
- **Expecting Bluetooth Classic.** The ESP32-S3 module provides Bluetooth 5 LE (p. 9). Serial Bluetooth apps that need Classic SPP will not pair; use ArduinoBLE and a BLE app instead.

## Questions

### UNO R4 WiFi vs UNO R3: what changed?

The 16 MHz ATmega328P with 32 kB flash and 2 kB SRAM (UNO R3 datasheet, p. 2) becomes a 48 MHz Cortex-M4 with 256 kB flash and 32 kB SRAM (UNO R4 WiFi datasheet, p. 1), still at 5 V. The R4 WiFi adds an ESP32-S3 for Wi-Fi and Bluetooth LE, a 12 × 8 LED matrix, Qwiic, a 14-bit ADC, a 12-bit DAC, CAN and USB-C (pp. 2, 3, 12, 14). Pins are rated for 8 mA (p. 16).

### Is the UNO R4 WiFi 5 V or 3.3 V?

The headers are 5 V, set by the RA4M1 (UNO R4 WiFi datasheet, p. 16). The ESP32-S3 module and the Qwiic connector run at 3.3 V (pp. 2, 14); a TXB0108 level translator links the ESP32-S3 to the RA4M1 on the board (p. 2). Wire 5 V parts to the headers and 3.3 V Qwiic boards to the Qwiic port.

### Which library do I use for Wi-Fi on the UNO R4 WiFi?

WiFiS3, which ships with the Arduino UNO R4 Boards package: WiFiClient, WiFiSSLClient, WiFiUDP and WiFiServer go through the ESP32-S3 modem. For Bluetooth LE use ArduinoBLE. The radio is 802.11 b/g/n on 2.4 GHz with Bluetooth 5 LE (UNO R4 WiFi datasheet, p. 3).

### Why won't my UNO R4 WiFi upload?

Select UNO R4 WiFi in the Arduino UNO R4 Boards package and use a USB-C cable that carries data. If a sketch has locked up the board, double-tap the reset button right after power-up to enter the bootloader and upload again (UNO R4 WiFi datasheet, p. 20). USB goes through the ESP32-S3 bridge by default (p. 11), so its firmware must be intact; Arduino's firmware updater restores it.

### How do I show something on the UNO R4 WiFi LED matrix?

Include Arduino_LED_Matrix.h, create an ArduinoLEDMatrix object, call begin(), then load a frame or render a bitmap of 8 rows by 12 columns. The matrix is 12 × 8 red LEDs driven from RA4M1 pins (UNO R4 WiFi datasheet, p. 12), so it needs no wiring.

### What power supply does the UNO R4 WiFi need?

6 V to 24 V on the barrel jack or VIN, 7 V typical, or 5 V through USB-C (UNO R4 WiFi datasheet, p. 7). The input has Schottky diodes for reverse polarity and overvoltage protection (p. 15).

## Related parts

- [Arduino Uno](https://www.tinkered.ai/components/arduino-uno.md): same job: an Arduino board
- [Arduino Mega 2560](https://www.tinkered.ai/components/arduino-mega.md): same job: an Arduino board
- [Arduino Nano V3](https://www.tinkered.ai/components/arduino-nano-v3.md): same job: an Arduino board
- [Arduino Nano R4](https://www.tinkered.ai/components/arduino-nano-r4.md): same job: an Arduino board
- [Arduino UNO R4 Minima](https://www.tinkered.ai/components/arduino-uno-r4-minima.md): same job: an Arduino board

## Try it

Tinkered simulates the Arduino UNO R4 WiFi in the browser: wire it on a 3D breadboard, run your real code on the board, and measure it. Free to start at https://www.tinkered.ai.