Hello guys, you know what an arduino board is. But as a beginner (or) a novice you may face a difficulty in choosing the right board from the wide range of boards in Arduino family.

For you I strongly suggest Arduino UNO–R3 to get started with electronic projects. In this instructable I will be giving you an insight of Arduino UNO .


The arduino UNO is the most used and documented board in the arduino family.

UNO is a great choice for first arduino as it is relatively cheap and very easy to setup and it is the toughest board you can play with. In rare cases even if you mess up with the board you can just change the ATmega 328p microcontroller for few bucks ( around 6$/200 INR) as UNO is a surface mount version with DIP package . It is a huge advantage of arduino UNO.

Step 2: ARDUINO UNO -R3:

"UNO" means one in Italian and it is named to mark the release of Arduino software IDE 1.0

The latest Arduino UNO R3 was released in 2011 and it is the third revision of UNO boards.


So shall we see the specifications of this little board so that you can look forward to use all the cool features described in them.


  • Microcontroller : ATmega328p
  • Operating Voltage : 5V
  • Input Voltage (recommended) : 7-12V
  • Input Voltage (limits) : 6-20V
  • Digital I/O Pins : 14 (of which 6 provide PWM output)
  • Analog Input Pins : 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 : 1 KB (ATmega328)
  • Clock Speed : 16 MHZ


The Arduino UNO is based on ATmega 328p microcontroller and it also has ATmega16U microcontroller.

  1. ATmega 328p: It is the brain of the Arduino and it is a high performance Atmel pico power 8bit AVR RISC based microcontroller which is cable of executing powerful instruction in single clock cycle.
  2. ATmega 16U2: This microcontroller takes care of the USB connection and ICSP bootloader.

Step 4: I/O Pins:

The Arduino UNO has

14 Digital pins(6 PWM) and6 Analog pins

DIGITAL PINS:Pin 0 to Pin 13

In which pin 0 and pin 1 are used to receive and transmit serial data. PWM: 3,5,6,9,10,11

These 6 pins can be used as PWM(Pulse Width Modulation) pins.Using these pins you can control the voltage in turn you can control the brightness of led,speed of the motor or whatever you wish to by varying the voltage.

ANALOG PINS: Pin A0 to Pin A5

The main function of Analog pins is reading the values from Analog sensors.


The Arduino UNO has super convenient power management and buit-in voltage regulation.

Unlike older boards the power source is selected automatically.You can directly power it through USB or external power supply.

The external power supply can be given by

  1. Connecting power source(7-12V DC) to DC power jack (or)
  2. Connecting a battery lead to Vin and Gnd.

NOTE:Don’t try to power it through 5V or 3.3V pins it will damage the on board regulator.

  • 5V and 3.3V pins can be used to provide power to sensors and modules when connecting it to .
  • Arduino IOREF: This pin provides voltage reference with which the microcontroller operates.

Step 6: MEMORY:

ATmega 328p has 32KB of flash memory to store your program and 2KB of SRAM and1KB of EEPROM.


UNO has communication protocols like UART Serial commication,SPI and I2C.


UNO uses digital pin0(RX) and digital pin1(TX) for UART TTL serial communication.


UNO uses A4 or SDA pin and A5 or SCL pin are used for I2C communication with wire library.

  • SCL is the clock signal
  • SDA is the data signal

NOTE:SDA and SCL pins are not extra pins available in UNO for I2C its an copy of pins A4 and A5.





  • MOSI(Master Out Slave In)- The Master line for sending data to the peripherals.
  • MISO(Master In Slave Out)-The slave line for sending data to the master.
  • SCK(Serial Clock)- The clock pulse which synchronise data transmission generated by the master.

Corresponding pins along with SPI library is used for SPI communication.

ICSP headers can be used to program ATmega directly using boot loader.

Step 8: CLOCK:

It has 16MHz clock on board makes it fast and speediest micro controller.


  • It has a reset button to reset the program on chip.
  • A Led on board is mapped to pin 13 for debugging and testing purpose.
  • A power Led to indicate power.
  • Two Led for RX and TX which blinks when the serial communication takes place.

So I hope you have got all the answers you need to know about what is inside an Arduino UNO. So why are you waiting for go grab your arduino board from Amazon, Ebay , Flipkart or from any electronic retail shop near you.

If you already have one tell me what you have done with it in comment box. :-)