Arduino is an amazing tool for physical computing — it’s an open source microcontroller board, plus a free software development environment. Use it to make cool interactive objects that can sense inputs from switches, sensors, and computers — and then control motors, lights, and other physical outputs in the real world.
The Uno is compatible with all current shields and code, and comes assembled — simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery.
The Arduino Uno board is based on the ATmega328 (datasheet). It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. The Uno differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter.