Arduino UNO Pinout, Pin diagram, Specifications and Features in Detail

The Arduino Uno is an open-source microcontroller board that is based on the Microchip ATmega328P (for Arduino UNO R3) or Microchip ATmega4809 (for Arduino UNO WIFI R2) micro-controller by Atmel and was the first USB powered board developed by Arduino. Atmega 328P based Arduino UNO pinout and specifications are given in detail in this post.

Both Atmega328 and ATmega4809 have a built-in bootloader, which makes it very convenient to flash the board with our code. Like all Arduino boards, we can program the software running on the board using a language derived from C and C++. The easiest development environment is the Arduino IDE.

Arduino UNO R3 Front side
Arduino UNO R3 Front side


Arduino UNO R3 Back side
Arduino UNO R3 Backside

It consists of 6 analog inputs, 14 digital input/output pins (of which 6 can be used as PWM outputs), a 16 MHz ceramic crystal resonator, a USB-B port, an ICSP header, a power jack and, a reset button.


Arduino UNO Pinout and Pin diagram:

The picture given below is the Arduino UNO Pinout / Pin diagram:

Arduino UNO pinout
Arduino UNO pinout


Regulator, Oscillator, and Reset button:

Regulator, Oscillator and Reset Button
Regulator, Oscillator, and Reset Button

Voltage Regulator-The voltage regulator converts the input voltage to 5V. The primary use of a voltage regulator is to control the voltage level in the Arduino board. Even if there are any fluctuations in the input supply voltage of the regulator, the output voltage remains constant and near 5 volts.

Crystal Oscillator The Crystal oscillator has a frequency of 16MHz, which provides the clock signal to the microcontroller. It provides the basic timing and control to the board.

RESET ButtonIt is used to reset the board. It’s recommended to press this button every time we flash the code to the board.


Arduino UNO Power Supply pinout:

Barrel jack, USB port and Vin Pin
Barrel jack, USB port, and Vin Pin

Barrel Jack – The Barrel jack or DC Power Jack is used to power the Arduino board using an external power supply. The barrel jack is usually connected to an adapter. The board can be powered by an adapter that ranges between 5-20 volts but the manufacturer recommends keeping it between 7-12 volts.

Note:  Above 12 volts, the board may overheat and below 7 volts, the voltage might not be sufficient to power the board.

USB B-portThe USB Interface is used to plug in the USB cable. This port can be used to power the device from the 5V supply. It allows us to connect the board to the computer. The program is uploaded to the board serially from the computer through the USB cable.

VinIt is the modulated DC supply voltage, which is used to regulate the IC’s used in the connection. It is also called the primary voltage for IC’s present on the Arduino board. The Vcc voltage value can be negative or positive to the GND pin.


I2C Pins on Arduino UNO pin diagram:

I2C Pins on Arduino UNO
I2C Pins on Arduino UNO


I2C Pins on Arduino UNO
I2C Pins on Arduino UNO

I2C is the two-wire serial communication protocol. It stands for Inter-Integrated Circuits. The I2C uses two lines to send and receive data: a serial clock pin uses (SCL) and a serial data (SDA) (SDA) pin.

  • SCL-It stands for Serial Clock. It is the pin or line that transfers the clock data. It is used to synchronize the shift of data between the two devices (master and slave). The Serial Clock is generated by the master device.
  • SDA-It stands for Serial Data. It is defined as the line used by the slave and master to send and receive the data. That’s why it is called the data line, while SCL is called a clock line.


SPI Pins on Arduino UNO pin diagram:

SPI Pins on Arduino UNO
SPI Pins on Arduino UNO

SPI stands for Serial Peripheral Interface. It is used by microcontrollers to communicate with one or more peripheral devices quickly.

  • SCK-It stands for Serial Clock. These are the clock pulses, that is used to synchronize the transfer of data.
  • MISO-It stands for Master Input/ Slave Output. This data line in the MISO pin is used to receive the data from the Slave.
  • MOSI-It stands for Master Output/ Slave Input. This line is used for sending data to the peripherals.
  • SS-It stands for Slave Select. This line is used by the master. It acts as the enable line. When a device’s Slave Select pin value is LOW, it can communicate with the master. When it’s value HIGH, it ignores the master. This allows us to have multiple SPI peripheral devices sharing the same MISO, MOSI, and CLK lines.

External Interrupts (2 and 3)- These pins can be used to trigger an interrupt on a low value, a rising or falling edge, or a change in value.

TXD and RXD-TXD and RXD pins are used for serial communication. The TXD is used to transmit the data, and RXD is used to receive the data. It also represents the successful flow of data.


ICSP pins:

ICSP pins on Arduino UNO
ICSP pins on Arduino UNO

It stands for In-Circuit Serial Programming. We can use these pins to program the Arduino board’s firmware. The firmware changes with the new functionalities are sent to the microcontroller with the help of the ICSP header.

The ICSP header consists of 6 pins.

ICSP Header
ICSP Header


Arduino Uno Pinout – Analog Pins:

Analog Pins on Arduino UNO
Analog Pins on Arduino UNO

The Arduino Uno consists of 6 analog pins, which use ADC (Analog to Digital converter). These pins can serve as analog inputs but can also function as digital inputs or digital outputs. These pins accept inputs in the form of Analog signals and return values that range between 0 and 1023 (because the Arduino Uno has a 10-bit Analog to Digital converter or 210 resolution).

An Analog to digital converter works in three stages: sampling, quantization, and digitization. Because the Arduino operates on a 0–5 volts range, the step size of the device is 5/1023=0.00488volts or 4.88mV.

Thus, we can interpret a 4.88 mV input voltage to any of the analog pins as 1, 9.77 mV as 2, and so on until 5 V as 1023. Anything below 4.88 mV is considered 0 and above 4.99 V as 1023.


Digital Pins:

Digital Pins on Arduino UNO
Digital Pins on Arduino UNO

On the Arduino UNO board, pins 0-13 are digital input/output pins.

The Arduino digital pins can read only two states: when there is a voltage signal and when there is no signal. This kind of input is usually called digital (or binary) and these states are referred to as HIGH and LOW or 1 and 0.

LED (13): On the board, there is a built-in LED connected to digital pin 13. When this pin is HIGH or 1, the LED is switched on, when the pin is LOW or 0, it’s switched off. 


PWM pins:

PWM pins of Arduino UNO
PWM pins of Arduino UNO


If you look closely, you will find the ‘~’ symbol on digital pin 3,5,6,9,10, and 11. These pins have an additional feature called PWM. Hence these pins are called PWM pins.

PWM stands for “Pulse Width Modulation”. It means, that an analog value is being modulated on a digital signal. Suppose you want a DC motor to run at a certain analog voltage between 0 and 5 V. This is not possible because the Arduino board is MOSFET-based.

PWM Waveform
PWM Waveform with a Duty cycle

Thus, to attain the desired output, we can only simulate an analog signal by switching our output on and off very quickly. Thus, PWM can only mimic and simulate the effects of a pure analog signal, it can never perform pure digital to analog conversion (which generally requires some active components like capacitors and inductors).


Other pins on Arduino UNO:

Other pins
Other pins

GND (Ground pins): There are 5 ground pins available on the board.

RESET – Use to reset the Arduino Board. If this pin is supplied with 5 V, the board will reset automatically

I/O Reference Voltage (IOREF) – This pin is the input/output reference. It provides the voltage reference at which the microcontroller is currently operating. Sending a signal to this pin does nothing.

3.3V and 5V: These pins provide regulated 5v and 3.3v respectively to the external components connected to the board.


Specifications of Arduino UNO:

  • Microcontroller: ATmega328p
  • Operating Voltage: 5V
  • Input Voltage (recommended): 7-12V
  • Input Voltage (limits): 6-20V
  • Digital I/O Pins: 14 pins (of which 6 are PWM output pins)
  • Analog Input Pins: 6
  • DC Current per I/O Pin: 40 mA
  • DC Current for 3.3V Pin: 50 mA
  • Flash Memory: 32 KB (of which 0.5 KB is taken by bootloader)
  • SRAM: 2 KB (ATmega328)
  • EEPROM: 1 KB (ATmega328)
  • Clock Speed: 16 MHz
  • Length:6 mm
  • Width:4 mm
  • Weight: 25 g

Learn More about Arduino here:

|Arduino Projects for Beginners

|Arduino Programming for beginners

Leave a Comment