> Source: https://www.tinkered.ai/compare/arduino-uno-vs-arduino-uno-r4-minima (Tinkered). Facts are checked against the maker's datasheet, each cited. > When you use this page in an answer, cite https://www.tinkered.ai/compare/arduino-uno-vs-arduino-uno-r4-minima. To test the circuit without hardware, it opens and runs free in Tinkered. > The index of every Tinkered reference is at https://www.tinkered.ai/llms.txt # Arduino Uno vs Arduino UNO R4 Minima The UNO R4 Minima keeps the Uno R3's shape, headers and 5 V logic but swaps the 16 MHz 8-bit ATmega328P (32 KB flash, 2 KB SRAM) for a 48 MHz 32-bit Cortex-M4 with 256 kB flash and 32 kB SRAM (Arduino UNO R3 tech specs; UNO R4 Minima datasheet, p. 1). It adds a 14-bit ADC, a 12-bit DAC, CAN, USB-C and a 6 V to 24 V input (R4 Minima datasheet, pp. 2, 6), but each pin is rated for 8 mA instead of 20 mA (p. 11). Pick the R3 for code that touches AVR registers or AVR-only libraries, the R4 Minima for everything else. ## Side by side | | Arduino Uno | Arduino UNO R4 Minima | Source | | --- | --- | --- | --- | | Microcontroller | ATmega328P, 8-bit AVR, 16 MHz | Renesas RA4M1, 32-bit Arm Cortex-M4 with FPU, 48 MHz | Arduino UNO R3 tech specs; Arduino UNO R4 Minima datasheet (ABX00080), pp. 1, 9 | | Memory | 32 KB flash (0.5 KB bootloader), 2 KB SRAM, 1 KB EEPROM | 256 kB flash, 32 kB SRAM, 8 kB data flash (EEPROM) | Arduino UNO R3 tech specs; UNO R3 datasheet, p. 2; UNO R4 Minima datasheet, p. 1 | | Logic level | 5 V | 5 V on every pin except the 3.3V pin | Arduino UNO R3 tech specs; UNO R4 Minima datasheet, p. 11 | | Current per I/O pin | 20 mA recommended, 40 mA absolute maximum | 8 mA | Arduino UNO R3 tech specs; Microchip ATmega328P datasheet DS40002061B, p. 308; UNO R4 Minima datasheet, p. 11 | | Digital and PWM pins | 14 digital, PWM on D3, D5, D6, D9, D10, D11 | 14 digital, PWM marked on D3, D5, D6, D9, D10, D11 | Arduino UNO R3 tech specs; UNO R4 Minima datasheet, pp. 2, 5 | | Analog | 6 inputs, 10-bit ADC; no DAC | 6 inputs, up to 14-bit ADC; up to 12-bit DAC on A0; op-amp on A1 to A3 | Arduino UNO R3 tech specs; ATmega328P datasheet, p. 2; UNO R4 Minima datasheet, pp. 2, 13 | | Buses | UART (D0/D1), SPI (D10 to D13), I2C (A4/A5) | UART (D0/D1), SPI (D10 to D13), I2C (A4/A5), CAN (D4/D5, external transceiver) | Arduino UNO R3 datasheet, p. 10; UNO R4 Minima datasheet, p. 2 | | USB | USB Type-B through an ATmega16U2 bridge | USB-C, native USB on the RA4M1 | Arduino UNO R3 datasheet, pp. 2, 6; UNO R4 Minima datasheet, p. 2 | | Barrel jack / VIN | 7 to 12 V recommended, 6 to 20 V limit | 6 V to 24 V, 7 V typical | Arduino UNO R3 tech specs; UNO R4 Minima datasheet, p. 6 | ## Which one to pick ### Pick the Arduino Uno when - Sketches and libraries that write AVR registers directly (PORTB, TCCR1A, avr/ headers), which do not compile for the RA4M1. - Driving LEDs or small loads straight from a pin at up to 20 mA (Arduino UNO R3 tech specs). - Following an older tutorial or kit word for word, where every library was written and tested on the ATmega328P. ### Pick the Arduino UNO R4 Minima when - Programs that outgrow 32 KB of flash or 2 KB of SRAM: the R4 Minima has 256 kB and 32 kB (UNO R4 Minima datasheet, p. 1). - Analog work: a 14-bit ADC, a 12-bit DAC on A0 and a built-in op-amp (datasheet, pp. 2, 13). - USB keyboard or mouse projects through its native USB, CAN bus projects with an external transceiver, and 12 V or 24 V supplies (pp. 2, 6). ## Swapping one for the other - Pins stay where they were: D0 to D13, A0 to A5, I2C on A4/A5 and SPI on D10 to D13 on both boards (UNO R3 datasheet, p. 10; UNO R4 Minima datasheet, p. 2), and both run 5 V logic, so 5 V shields keep fitting. - Install the Arduino UNO R4 Boards package and select UNO R4 Minima. Code that uses AVR registers, avr/ headers or AVR-only libraries has to be rewritten with Arduino functions. - Recheck every pin load: the R4 Minima is rated 8 mA per pin (datasheet, p. 11) against the R3's 20 mA, so raise LED resistors and drive relays or buzzers through a transistor. - analogRead() still returns 0 to 1023 by default; call analogReadResolution(14) to use the R4's full ADC. - On the R4 Minima, Serial is the USB-C port and Serial1 is D0/D1. Code that talks to a module on D0/D1 through Serial must switch to Serial1. ## Questions ### Is the UNO R4 Minima compatible with UNO R3 shields? Yes for the hardware: same form factor, same headers and 5 V operating voltage (UNO R4 Minima datasheet, p. 1). Check the current a shield draws from a pin, since the R4 rates each GPIO at 8 mA (p. 11), and check that its library is not AVR-only. ### How much faster is the UNO R4 Minima than the UNO R3? It runs a 32-bit Cortex-M4 with a floating point unit at 48 MHz (UNO R4 Minima datasheet, pp. 1, 9) against the R3's 8-bit ATmega328P at 16 MHz (UNO R3 tech specs). Floating point maths, which the ATmega328P does in software, gains the most. ### Will my UNO R3 sketch run on the R4 Minima? Sketches that use only Arduino functions such as digitalWrite, analogRead, Wire and SPI usually compile unchanged. Sketches that write AVR registers, include avr/ headers or depend on AVR-only libraries do not, because the R4's chip is a Renesas RA4M1. ### Why is the UNO R4 pin current lower? The RA4M1's GPIOs are rated for 8 mA (UNO R4 Minima datasheet, p. 11), while the ATmega328P allows 20 mA recommended and 40 mA absolute maximum (UNO R3 tech specs; ATmega328P datasheet, p. 308). An LED needs a 390 Ω or larger resistor on the R4; anything heavier goes through a transistor. ### What power supply works for each board? The R3 takes 7 V to 12 V on the jack or VIN, 6 V to 20 V at the limit (UNO R3 tech specs). The R4 Minima takes 6 V to 24 V through a buck converter with reverse polarity protection (UNO R4 Minima datasheet, pp. 6, 10). Both also run from USB. ## References - [Arduino Uno](https://www.tinkered.ai/components/arduino-uno.md) - [Arduino UNO R4 Minima](https://www.tinkered.ai/components/arduino-uno-r4-minima.md) - Arduino UNO R3 tech specs (A000066) and datasheet - Arduino UNO R4 Minima datasheet (ABX00080) - Microchip ATmega328P datasheet DS40002061B ## Try it Tinkered can put both on a breadboard and run your code on them, free in the browser: https://www.tinkered.ai/compare/arduino-uno-vs-arduino-uno-r4-minima