Arduino Uno

Arduino Uno R3 Front
Arduino Uno R3 Front
Arduino Uno R3 Back
Arduino Uno R3 Back

    "Uno" refers one in Italian.  


The Arduino Uno is a ATmega328 based micro controller Board.

It has 14 digital i/o pins ( 6 pins of them can be used as PWM outputs), 6 analog inputs, a 16 MHz oscillator/resonator , an USB connection port, a power jack, an ICSP header(In Circuit Serial Programming (ICSP) is a method of directly programming AVRs, the Parallax Propeller, and PIC microcontrollers), and one reset button.

We have connect it to a computer with a USB cable or power it with a AC-to-DC power adapter or even battery to let it work!

of the Uno board has a resistor pulling the 8U2 HWB line to ground, making it easier to put into DFU (Device Firmware Upgrade) mode.

of the board has the following new features:
  • Addition of SDA(Serial Data Line) and SCL (Side Coupled Linac) pins that are near to the AREF pin and two other new pins placed near to the RESET pin.
  • Stronger RESET circuit.
  • Atmega 16U2 replace the 8U2.



Uno can be powered up by the USB or with an external power supply, i.e, a battery or AC to DC adapter.  

The board can work on an external supply of 6 to 20 volts. If its supplied with less than 7V, the 5V pin may supply less than 5V and the board may be unstable. 

If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.  

The pins related to power are:
  • VIN: You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.
  • 5V: This pin outputs a regulated 5V from the regulator on the board. Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. So its not advisable.
  • 3.3V: A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
  • GND: Ground pins.
  • IOREF: This pin on the Arduino board provides the voltage reference with which the microcontroller operates.


Memory Onboard

  • The ATmega328 has 32 KB (with 0.5 KB used for the bootloader) flash. 
  • It also has 2 KB of SRAM and 1 KB of EEPROM 

Input and Output Pins

Each of the 14 digital pins on the Uno can be used as an input or output, using pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms. In addition, some pins have specialized functions:
  • Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data. These pins are connected to the corresponding pins of the ATmega8U2 USB-to-TTL Serial chip. 
  • External Interrupts: 2 and 3. These pins can be configured to trigger an interrupt on a low value, a rising or falling edge, or a change in value. See the attachInterrupt() function for details. 
  • PWM: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite() function. 
  • SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication using the SPI library. 
  • LED: 13. There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the LED is on, when the pin is LOW, it's off.
  • The Uno has 6 analog inputs, labeled A0 through A5, each of which provide 10 bits of resolution (i.e. 1024 different values). By default they measure from ground to 5 volts, though is it possible to change the upper end of their range using the AREF pin and the analogReference() function.
  • TWI: A4 or SDA pin and A5 or SCL pin. Support TWI communication using the Wire library.
  • Reset. Bring this line LOW to reset the microcontroller. 

Communication Between Arduino or Computer

  • The Arduino Uno has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. 
  • The ATmega328 provides UART TTL (5V) serial communication, which is available on digital pins 0 (RX) and 1 (TX). An ATmega328 on the board channels this serial communication over USB and appears as a virtual com port to software on the computer. 
  • The Arduino software includes a serial monitor which allows simple textual data to be sent to and from the Arduino board. 
  • The RX and TX LEDs on the board will flash when data is being transmitted via the USB-to-serial chip and USB connection to the computer (but not for serial communication on pins 0 and 1).
  • A SoftwareSerial library allows for serial communication on any of the Uno's digital pins.
  • The ATmega328 also supports I2C (TWI) and SPI communication. The Arduino software includes a Wire library to simplify use of the I2C bus.


  • The Arduino Uno can be programmed with the Arduino software. Select "Arduino Uno from the Tools > Board menu (according to the microcontroller on your board).
  • The ATmega328 on the Arduino Uno comes preburned with a bootloader that allows you to upload new code to it without the use of an external hardware programmer. It communicates using the original STK500 protocol.
  • You can also bypass the bootloader and program the microcontroller through the ICSP (In-Circuit Serial Programming) header.
  • You can then use Atmel's FLIP software (Windows) or the DFU programmer (Mac OS X and Linux) to load a new firmware. Or you can use the ISP header with an external programmer (overwriting the DFU bootloader).
  • Download Latest Version Of Arduino IDE

Software Reset

Rather than a physical press of the reset button before an upload, it allows it to be reset by software running on a connected computer.

USB Overcurrent/Power Protection

The Arduino Uno has a resettable polyfuse that protects your computer's USB ports from shorts and overcurrent. If more than 500 mA is applied to the USB port, the fuse will automatically break the connection until the short or overload is removed.


Operating Voltage5V
Input Voltage (recommended)7-12V
Input Voltage (limits)6-20V
Digital I/O Pins14 (of which 6 provide PWM output)
Analog Input Pins6
DC Current per I/O Pin40 mA
DC Current for 3.3V Pin50 mA
Flash Memory32 KB (ATmega328) of which 0.5 KB used by bootloader
SRAM2 KB (ATmega328)
EEPROM1 KB (ATmega328)
Clock Speed16 MHz


Other Reference Links for this Board Digital iVision Labs Recommend You to go through are: