Presentation

The Uno Arduino is based on the ATmega328 microcontroller.
It has 14 digital inputs/outputs (6 of which can be used as PWM outputs), 6 analog inputs, a 16 MHz quartz oscillator, a USB connection, a power outlet, an ICSP connector, and a reset button.
It contains everything you need to control the microcontroller, just connect it to a computer with a USB cable and it's easy to use.
The Uno differs from all previous Arduino models in that it does not use the USB-to-Series FTDI converter. Instead, it has an Atmega8U2 programmed as a USB-to-serial converter.

The Arduino Uno is based on the ATmega328 microcontroller, it replaces the Arduino Duemilanove model.

It has 14 digital inputs/outputs (6 of which can be used as PWM outputs), 6 analog inputs, a 16 MHz quartz oscillator, a USB connection, a power outlet, an ICSP connector, and a reset button.

It contains everything you need to control the microcontroller, just connect it to a computer with a USB cable and it's easy to use.

The Uno differs from all previous Arduino models in that it does not use the USB-to-Series FTDI converter. Instead, it has an Atmega8U2 programmed as a USB-to-serial converter.

SMD version:

The ATMEGA328 is surface welded.

Rev3 (R3) version:
 

1.0 Pinout: 2 pins (SDA and SSL) are added next to the AREF pin and 2 pins (IOREF and a reserve) are added next to the RESET. These pins will be added on the next shields.

Improved reset circuit.

ATMEGA 16U2 replaces ATMEGA 8U2.
 

Package

The Arduino Uno is available in two versions, DIP and SMD.

The functionalities are identical it is only the package of the ATmega328 microcontroller that changes (see pictures)
Features & Features

•     Microcontroller: ATmega328
•     Nominal supply voltage: 5V
•     Supply voltage (recommended): 7-12V
•     Supply voltage (limits): 6-20V
•     Digital inputs/outputs: 14 (of which 6 can be used as PWN outputs)
•     Analog Inputs: 6
•     DC Current per I/O Pin: 40 mA
•     DC Current for 3.3V Pin: 50 mA
•     Flash Memory: 32 KB (ATmega328) of which 0.5 KB used by bootloader
•     SRAM: 2 KB (ATmega328)
•     EEPROM: 2 KB (ATmega328)
•     Clock frequency: 16 MHz

What is the Arduino?

Arduino is an electronic prototyping opensource platform that consists of components and software that is easy to use.
Who is Arduino for?
The Arduino kit is designed for artists, designers, amateurs and anyone interested in creating interactive objects.
How to use the Arduino?

The Arduino can detect its environment by adding sensors that can be connected to its input pins.

All you have to do is retrieve this information and process it by programming the ARduino using the free Arduino development software. You can then control outputs that will act on other elements such as LEDs, displays, motors and many others.
Examples of construction with Arduino kits

Documentation

Documentation Arduino UNO : https://www.arduino.cc/en/Guide/ArduinoUno