The Arduino UNO R3 is the most popular microcontroller board for beginners, based on the ATmega328P. It features 14 digital I/O pins, 6 analog inputs, a 16MHz crystal, USB connection, and a barrel jack power connector.
| Pin | Name | Function | Type |
|---|---|---|---|
| D0 | RX | UART receive | BUS |
| D1 | TX | UART transmit | BUS |
| D2 | D2 | Digital I/O, INT0 | I/O |
| D3 | D3~ | Digital I/O, PWM, INT1 | I/O |
| D4 | D4 | Digital I/O | I/O |
| D5 | D5~ | Digital I/O, PWM | I/O |
| D6 | D6~ | Digital I/O, PWM | I/O |
| D7 | D7 | Digital I/O | I/O |
| D8 | D8 | Digital I/O | I/O |
| D9 | D9~ | Digital I/O, PWM | I/O |
| D10 | D10~ | Digital I/O, PWM, SPI SS | BUS |
| D11 | D11~ | Digital I/O, PWM, SPI MOSI | BUS |
| D12 | D12 | Digital I/O, SPI MISO | BUS |
| D13 | D13 | Digital I/O, SPI SCK, LED | BUS |
| A0 | A0 | Analog input 0 | ADC |
| A1 | A1 | Analog input 1 | ADC |
| A2 | A2 | Analog input 2 | ADC |
| A3 | A3 | Analog input 3 | ADC |
| A4 | A4/SDA | Analog input 4, I2C SDA | BUS |
| A5 | A5/SCL | Analog input 5, I2C SCL | BUS |
| 5V | 5V | Regulated 5V output | PWR |
| 3V3 | 3.3V | Regulated 3.3V, 50mA max | PWR |
| GND | GND | Ground | GND |
| VIN | VIN | Raw input voltage 7–12V | PWR |
| RESET | RESET | Reset pin, active low | I/O |