Arduino Uno R3

Overview

The Arduino Uno R3 is the world's most widely used open-source microcontroller development board and the de facto entry point for electronics education globally. Based on Microchip's ATmega328P 8-bit AVR microcontroller running at 16MHz with a 16MHz ceramic resonator, it offers 32KB of Flash (0.5KB used by the bootloader), 2KB of SRAM, and 1KB of EEPROM in a form factor that has defined the Arduino shield ecosystem for over a decade.

The R3 revision introduced three significant improvements over earlier Unos: an improved ATmega16U2 USB interface chip replacing the earlier ATmega8U2, an expanded female header adding a 3.3V reference voltage and RESET pin for shield compatibility, a 500mA polyfuse protecting the USB power rail, and automatic power-source selection switching between USB and external DC power. These changes solidified the Uno as the reference platform for Arduino shield design.

Fourteen digital I/O pins (D0–D13) cover the primary GPIO needs. Six of those pins (D3, D5, D6, D9, D10, D11) support PWM output via the ATmega's hardware timers. Six analog input pins (A0–A5) provide 10-bit ADC readings. Hardware serial (UART on D0/D1), SPI (D10–D13), and I2C (A4/A5) cover the standard communication protocols. An ICSP header provides direct AVR programming access for bootloader burning or high-speed firmware flashing.

The Uno R3 is powered by either the USB-B connector (5V from the host) or a 7–12V DC barrel jack regulated to 5V internally. It is the recommended starting board for the Arduino IDE, fully supported by the Arduino C++ framework, and compatible with thousands of libraries and shields for motors, displays, sensors, Ethernet, GSM, and more.