Pinout, Function and working of Arduino Uno R3

The Arduino Uno R3 is a great starting point for your projects. It is the most popular board in the Arduino family. It has two variants one consists of a 28-pin DIP Microcontroller while the other consists of 32 lead Quad Flat Package Microcontroller. The microcontroller on the Arduino Uno R3 is the Atmega328P, which contains everything needed to support the microcontroller.

Arduino Uno R3 Board Layout

It has a Type-B USB connector on the left side of the board. It is used for powering the board as well as programming the Microcontroller. Arduino Uno is similar to Arduino Nano but extended version.

Arduino Uno R3 Board Layout main components

DC jack-It consists of a 2.1 mm DC jack which is used to provide an external power supply.

Memory-It consists of 32 KB ISP flash memory with read-while-write capabilities, 2 KB SRAM(Static RAM), 1 KB of EEPROM, and 23 general-purpose I/O pins.

Voltage Regulator-The voltage regulator is used to convert any input voltage to 5V. The primary work of a voltage regulator is to control the voltage level in the Arduino Board.

Crystal Oscillator– The Crystal oscillator has a frequency of 16MHz. It is used to provide the clock signal to the microcontroller. It provides the basic timing and control to the board. 

RESET ButtonThe Reset button is used to reset the board. 

ICSP header– ICSP stands for “In-Circuit Serial Programming.”

These pins are used to program the Arduino board’s firmware.

Arduino uno dimensions


Specifications Of Arduino Uno R3

The specifications table of Arduino Uno R3 are as follows:-

MISOMaster In Slave Out (Input or Output)
SCKClock (from Master to Slave)
MOSIMaster Out Slave In (Input or Output)
RESETReset (Active LOW)
Operating Voltage5V
Input Voltage6V – 20V (limit)7V – 12V (recommended)
Clock Speed16 MHz
Flash Memory32 KB (2 KB of this used by bootloader)
Digital IO Pins24 (of which 6 can produce PWM)
Analog Input Pins6
Communication protocolUART x 1, SPI x 1, I2C x 1
DC Current per I/O Pin20 mA
DC Current for 3.3V Pin50 mA
ICSP Header2
Power SourcesPower Jack, USB port, Vin pin
Length68.6 mm
Width53.4 mm
Weight25 g

Arduino Uno R3 Pinout Description

Now, let us assume some basic numbering the RX is Pin 1, TX is Pin 2, D2 is Pin 3, and so on.

Arduino uno pinout and function explaination

On the other hand, NC is Pin 19, IOREF is Pin 20, etc. Overall, there are 32 pins on the Arduino UNO Board.

Pin NumberPin NameDescriptionAlternative Functions
1RX / D0Digital IO Pin 0Serial RX PinGenerally used as RX
2TX / D1Digital IO Pin 1Serial TX PinGenerally used as TX
3D2Digital IO Pin 2
4D3Digital IO Pin 3Timer (OC2B)
5D4Digital IO Pin 4Timer (T0/XCK)
6D5Digital IO Pin 5Timer (OC0B/T1)
7D6Digital IO Pin 6
8D7Digital IO Pin 7
9D8Digital IO Pin 8Timer (CLK0/ICP1)
10D9Digital IO Pin 9Timer (OC1A)
11D10Digital IO Pin 10Timer (OC1B)
12D11Digital IO Pin 11SPI (MOSI) Timer (OC2A)
13D12Digital IO Pin 12SPI (MISO)
14D13Digital IO Pin 13SPI (SCK)
16AREFAnalog Reference
17SDA / D18Digital IO Pin 18I2C Data Pin
18SCL / D19Digital IO Pin 19I2C Clock Pin
19NCNot Connected
20IOREFVoltage Reference
21RESETReset (Active LOW)
235V+5V Output from regulator or +5V regulated Input
26VINUnregulated Supply
27A0Analog Input 0Digital IO Pin 14
28A1Analog Input 1Digital IO Pin 15
29A2Analog Input 2Digital IO Pin 16
30A3Analog Input 3Digital IO Pin 17
31A4Analog Input 4Digital IO Pin 18 I2C (SDA)
32A5Analog Input 5Digital IO Pin 19 I2C (SCL)

Table of the pins of the ICSP Connector

Arduino ICSP pins
MISOMaster In Slave Out (Input or Output)
SCKClock (from Master to Slave)
MOSIMaster Out Slave In (Input or Output)
RESETReset (Active LOW)

How to power up Arduino Uno R3

There are two ways to power up the Arduino UNO board

1) Using the Type-B USB Connector

2) Another way is to provide an unregulated supply in the range of 6V to 20V to the Vin pin(Pin number 26) or DC jack of the Arduino UNO.

power up arduino uno

Different Memories Of Arduino Uno

Different memories of Arduino Uno are as follows:-

  1. 32KB of flash memory.
  2. 2KB of SRAM.
  3. 1KB of EEPROM.

Input and Output Pins of Arduino UNO

input and output pins of Arduino Uno digital and anloug

Digital Input Output Pins

From the 32 pins, 22 pins are associated with input and output. D0 – D13 are associated with I/O pins.

It can be configured as per your application by using pinMode(), digitalRead(), and digitalWrite() functions.

 I/O pins are capable of sourcing or sinking 20mA of current. It also consists internal pull-up resistor.

The value of the internal pull-up resistor will be in the range of 20KΩ to 50KΩ.

Analog Input Output Pins

It also has 6 Analog Input Pins (A0 to A5).

All of these analog input pins can be read using analogRead() function.

The Digital IO pins numbered 3, 5, 6, 9, 10, and 11 are capable of producing 8-bit PWM Signals.

PWM Pins

pwm pins of arduino uno

PWM stands for “PULSE WIDTH MODULATION”. The digital pins 3,5,6,9,10, and 11 are the PWM Pins. They have an additional feature PWM that’s why it is called PWM Pins. 

GND Pins

There are 5 GND pins available on the board. 

Communication Interfaces Pins available on Arduino UNO

Serial, I2c and SPI Communication Interfaces pins available on Arduino UNO

Arduino UNO supports 3 diffrent types of communication interfaces:-

  • Serial
  • I2C
  • SPI

The digital IO pins 0 and 1 are used as Serial RX and TX pins which are used to receive and transmit data.

The pins A4 and A5 have alternative functions and they can be configured as SDA (A4) and SCL (A5) to support I2C or I2C or Two Wire Interface (TWI) communication.

The digital IO Pins 10, 11 12, and 13 can be configured as SPI pins 


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