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# Arduino UNO R4 Minima

The UNO form factor with a 48 MHz Arm Cortex-M4, 5 V I/O, USB-C and a 6 to 24 V barrel jack.

Source page: https://www.tinkered.ai/components/arduino-uno-r4-minima
Datasheet: https://docs.arduino.cc/resources/datasheets/ABX00080-datasheet.pdf

## In short

The Arduino UNO R4 Minima is an UNO-shaped board with a Renesas RA4M1, a 48 MHz Arm Cortex-M4 with 256 kB flash and 32 kB SRAM, and 5 V I/O that keeps UNO shields working (Arduino ABX00080 datasheet, p. 1). Power it from USB-C at 5 V or 6 to 24 V on the barrel jack or VIN (p. 6), wire parts to D0 to D13 and A0 to A5 as on an UNO R3, and keep each pin under 8 mA (p. 11).

The UNO R4 Minima (SKU ABX00080) is the first UNO with a 32-bit microcontroller. Its Renesas RA4M1 runs an Arm Cortex-M4 with a floating point unit at 48 MHz, with 256 kB of flash, 32 kB of SRAM and 8 kB of data flash used as EEPROM (UNO R4 Minima datasheet, pp. 1, 9): eight times the flash and sixteen times the SRAM of the earlier UNO (p. 5). The operating voltage stays at 5 V, so shields designed for previous UNO revisions keep working (p. 1).

The headers match the UNO R3: 14 digital I/O, six marked for PWM (D3, D5, D6, D9, D10, D11), and six analog inputs A0 to A5 (p. 2). The analog side is a clear upgrade, with an ADC of up to 14 bits, a DAC of up to 12 bits on A0 and an op-amp on A1 to A3 (pp. 2, 13). The board adds a CAN controller on D4/D5 (it needs an external transceiver), a USB-C port with native USB, an SWD debug connector and the usual ICSP header (pp. 2, 14).

The Minima is the bare version of the R4: no Wi-Fi module, no LED matrix and no Qwiic connector, which the UNO R4 WiFi adds. Power comes from USB-C or from 6 V to 24 V on the barrel jack or VIN through an ISL854102 buck converter, with Schottky diodes for reverse polarity and overvoltage protection (pp. 2, 10). The main thing to plan around is current: each RA4M1 GPIO is rated for 8 mA (p. 11).

## 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 |

## Specifications

| Spec | Value | Source |
| --- | --- | --- |
| Microcontroller | Renesas RA4M1 (R7FA4M1AB3CFM#AA0), Arm Cortex-M4 with FPU at 48 MHz | Arduino UNO R4 Minima datasheet (ABX00080), pp. 1, 9 |
| Memory | 256 kB flash, 32 kB SRAM, 8 kB data flash (EEPROM) | Arduino UNO R4 Minima datasheet, p. 1 |
| I/O voltage | 5 V on every pin except the 3.3V pin | Arduino UNO R4 Minima datasheet, p. 11 |
| VIN / barrel jack | 6 V to 24 V, 7 V typical | Arduino UNO R4 Minima datasheet, p. 6 |
| USB-C input | 4.8 V to 5.5 V; about 4.7 V reaches the MCU after the Schottky drop | Arduino UNO R4 Minima datasheet, pp. 6, 10 |
| Current per GPIO | 8 mA | Arduino UNO R4 Minima datasheet, p. 11 |
| Digital I/O | 14 pins, PWM marked on D3, D5, D6, D9, D10, D11 | Arduino UNO R4 Minima datasheet, pp. 2, 5 |
| Analog | 6 inputs A0 to A5, up to 14-bit ADC; up to 12-bit DAC on A0; op-amp on A1 (+), A2 (-), A3 (out) | Arduino UNO R4 Minima datasheet, pp. 2, 13 |
| Buses | 1 UART (D0/D1), 1 SPI (D10 to D13, ICSP), 1 I2C (A4/A5, SDA/SCL), 1 CAN (D4/D5, external transceiver) | Arduino UNO R4 Minima datasheet, p. 2 |
| Operating temperature | -40 °C to +85 °C | Arduino UNO R4 Minima datasheet, p. 6 |
| 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 Minima datasheet (ABX00080) |
| Dimensions | 68.58 × 15.5 × 53.34 mm | Tinkered component registry |
| Weight | 22 g | Tinkered component registry |

## Circuit notes

- The RA4M1 runs at 5 V, as do all header pins except the 3.3V pin (UNO R4 Minima datasheet, p. 11). 3.3 V-only modules need a level shifter on their signal lines.
- Each GPIO is rated for 8 mA (p. 11). Size LED resistors for it (about 390 Ω for a red LED at 5 V) and switch relays, motors and LED strips through a transistor or a driver board.
- Power the board from 6 V to 24 V on the barrel jack or VIN, or 5 V over USB-C, and never more than 5 V through USB (pp. 6, 10). On USB alone the MCU sees about 4.7 V because of the protection diode (p. 10), which slightly lowers the ADC's 5 V reference.
- The 3.3V pin is fed from the RA4M1's own USB regulator (VCC_USB), not from the buck converter (p. 11). Keep it to light loads such as one sensor; power heavier 3.3 V circuits from a separate regulator.
- CAN on D4 (TX) and D5 (RX) needs an external CAN transceiver with a 5 V logic side between the board and the bus (p. 2).
- Leave the BOOT pin at the start of the power header unconnected: it is the chip's mode selection input (p. 13).

## Common mistakes

- **Treating pins like an UNO R3's.** The RA4M1's pins are rated for 8 mA (UNO R4 Minima datasheet, p. 11), lower than the classic ATmega328P boards. A 220 Ω LED resistor or a relay coil on a pin is too much: use larger resistors and a transistor for anything heavier.
- **Looking for Wi-Fi, the LED matrix or Qwiic.** Those belong to the UNO R4 WiFi. The Minima has no radio, no matrix and no Qwiic connector: wire I2C parts to A4/A5 or the SDA/SCL header pins.
- **Expecting a DAC on every analog pin.** Only A0 has the DAC (p. 10). analogWrite on other pins gives PWM, and A1 to A3 double as the op-amp's inputs and output (p. 13).
- **Wiring CAN without a transceiver.** D4 and D5 carry the CAN controller's logic signals, not a bus (p. 2). Connect them to a CAN transceiver, and the transceiver to CANH and CANL.
- **Using AVR register code.** Sketches that write PORTB, DDRD or use avr/ headers for speed were written for the ATmega328P. On the R4 use digitalWrite and the core's libraries, or port the code to the RA4M1.

## Questions

### What is the difference between the UNO R4 Minima and the UNO R3?

Same shape, headers and 5 V logic, but the R4 Minima runs a 48 MHz Cortex-M4 with 256 kB flash and 32 kB SRAM against the R3's 16 MHz ATmega328P with 32 kB flash and 2 kB SRAM (UNO R4 Minima datasheet, p. 1; UNO R3 datasheet, p. 2). It adds a 14-bit ADC, a 12-bit DAC, CAN, an op-amp, USB-C and a 6 V to 24 V input (pp. 2, 6). The trade-off is 8 mA per pin (p. 11).

### UNO R4 Minima or UNO R4 WiFi?

Both use the same RA4M1 and 5 V headers. The WiFi model adds an ESP32-S3 module for Wi-Fi and Bluetooth LE, a 12 × 8 LED matrix and a Qwiic connector (UNO R4 WiFi datasheet, pp. 1, 12, 14). Choose the Minima when the project needs none of those.

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

5 V. Every header pin runs at 5 V except the 3.3V supply pin (UNO R4 Minima datasheet, p. 11), so 5 V UNO shields work. 3.3 V-only modules need a level shifter.

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

Install the Arduino UNO R4 Boards package, select UNO R4 Minima 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, then upload again (UNO R4 Minima datasheet, p. 16).

### How much current can an UNO R4 Minima pin drive?

8 mA per GPIO (UNO R4 Minima datasheet, p. 11). That covers an LED with a 390 Ω or larger resistor or a transistor's input, not a relay coil, a motor or a buzzer driven directly.

### What power supply can I use with the UNO R4 Minima?

6 V to 24 V on the barrel jack or VIN, 7 V typical, or 5 V through USB-C (UNO R4 Minima datasheet, p. 6). A 9 V or 12 V adapter is fine, and the input is protected against reverse polarity by Schottky diodes (p. 10).

## 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 WiFi](https://www.tinkered.ai/components/arduino-uno-r4-wifi.md): same job: an Arduino board

## Try it

Tinkered simulates the Arduino UNO R4 Minima 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.