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Arduino UNO Pins (Diagram) Learn quickly pins function

Arduino UNO Pinout and Board components detail

The Arduino Uno board is an electronic experimental board. Atmega328P is the heart of the Arduino board. This is an open-source platform for creating electronics projects.

I will explain the description of the Arduino UNO Pins and the board in the post. Arduino Uno is a standard board of the company, even though other boards, e.g. micro, Nano, mega, Leonardo, 101. Due and Yen. Arduino also manufactured IoT (Internet of Things), Bluetooth, GSM/3G, Wi-Fi, and motion sensor boards.

Arduino UNO Pinout

Arduino Uno board

The Atmega328P Microcontroller is 8bit with 32k byte internal flash memory. To program the main chip, a 16 MHz crystal is part of the board. The Arduino board requires only 5V DC to operate.

Arduino Uno pinout detail

The Arduino UNO board has 5 analog and 14 digital (PWM) pins. These pins could be GPIO or used for specific signals.

Vin Pin

We use a Vin pin for 7-12 VDC, applied to the board as an external power source. We can use a 9V battery cell for the input supply voltage.

Analog Input Pins

From A0 to A5, Analog input Pins are used for sensor modules, as well as analog output. It contains a 06 ADC (analog-to-digital converter) with a 10-bit resolution. These Arduino pins have the functionality of general-purpose digital in/out pins.


SDA/SCL are data and clock pins. We use it for I²C (inter-integrated-circuit) / TWI (two-wire interface) communication. A Wire library is available to communicate with different devices with the Arduino board.

Serial-UART (SPI Communication)

Pin 0 is used as RX and 1 TX (in fig-A as D0&D1) is used for TTL Serial Communication. RX is to receive data, and TX is to transmit the data.

SPI Communication pins

10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication.


Pins 2 & 3 can use as INT0 & INT1, we can configure them to act as external interrupts for a function written in the program.


Pin # 3, 5, 6, 9, 10, and 11 are used for the PWM function (Pulse Width Modulation). Analogwrite function () is very effective to operate the DC motors and varying led light in many electronic projects.


We use an analog reference pin for the analog-reference function. AREF is used to set external analog input voltage. We cannot use less than o and over 5 volts for the AREF Pin.

Arduino Uno Pinout (GPIO) 

We use 14 digital pins as input or output. From 0 to 13 used as general-purpose digital in/out has internal pull-up resistors that can be high/low to ON/OFF maximum current per pin 40 mA.
As shown in Fig A from D0 to D13 pins. A built-in led function through pin 14 (D13).

PWM (Pulse Width Modulation)

We use digital out as High or Low even with the PWM outputs function. We can use these pins. As analog out/we can control the motor at different speedsDigital write () function used for high/low pins.

USB Communication Interface

For USB/Serial communication, we use mostly two chips, CH341A or Atmega16U.


CH341a has used a USB interface chip for UART communication. It is a standard parallel port, memory parallel port, and synchronous serial (I2C, SPI Communication). We use the CH341A chip in many cheap programmers.


We use the atmega16u Microcontroller for the USB serial communication interface. To program the Microcontroller, an ICSP pin header is available on the board.


LM358 is a dual-channel op-amp IC. The Arduino used it for an auto-voltage selection circuit, but in reality, it operates as an auto-voltage cut-off circuit.


It is a series of chips that set the output voltage from 1.25V to 13.8V with only two external resistors.

DC Power Port

We use this DC power port for the DC input voltage. The board is using a power supply voltage of 5-20Vdc.

USB Type B port

The USB port is used to program the chip and also for the power source. We use the port for a USB connection to the computer. USB cable is used to connect the board and PC.

Reset Button

If you push the Reset button, it will restart the codes even if there is a malfunction happens, just press this button, and it will restart the program.


The red color pin we used for the power source. We can use a 3.3V/5V power supply voltage for our projects, but it could not exceed 50 mA. GND for ground pins.

Arduino uno schematic

To find the Arduino Uno circuit, a more detailed schematic diagram could be helpful.

Arduino UNO Pinout

Arduino Uno board comparison to other Boards

Arduino boards have come in many types versions, as per pins, size, and
function, I will explain mostly the comparison of the Arduino UNO board.

Arduino UNO R3

Digital IO pins 14 (including 6 pins PWM), 
Analog pins 6, 
Microcontroller Atmega328P,
USB to serial communication ATMEGA 8U2 Microcontroller.

Arduino Duemilanove

Duemilanove is an Italian word, meaning the year of manufacture, 2009.

Digital IO pins 14 (6 pins PWM)

ATMEGA 168 Microcontroller.

16kb flash memory, although Uno has 32kb flash memory

FTDI USB serial communication chip.

Arduino Diecimila

After the completion of the 10,000 board, it introduced the Diecimila name. 
The flash memory is 16kb 
FTDI chip for the USB port.
Digital IO pins 14 

Arduino BT (Bluetooth)

Supplied with ATMEGA 168 SMD type in the start but now comes with Atmega 328, added Bluegiga TTI module.

Arduino Mega

ATMEGA 1280 Microcontroller. 

FTDI chip for USB to serial communication.

54 digital IO pins, 

15 pins for the PWM function.

Arduino Lilypad

Using the ATMEGA 32U4 Microcontroller, 
The small size of 9 digital IO pins (4 pins used as an analog pins and 4 for PWM). Micro USB port used for communication.

Arduino Nano

ATMEGA  328 SMD micro-controller
Nano used a mini-B USB port for programming and the power supply voltage. Small in size but has the same 14 digital IO pins, 
6 Pins for the PWM function, and 8 Pins for analog pins.

Arduino mini

Mini is smaller than Nano. 
Atmega 168 (in start), but now uses the Atmega 328 Microcontroller,
14 digital IO pins, including 06 analog pins.


Arduino Uno Pins vary in many Arduino boards, but the main pin's function is similar. We have just simplified it in a concise description.


Ntangi_Roberto said…
This comment has been removed by a blog administrator.
Biplab Koley said…
Really good one.....
Anonymous said…
Reference FIG-A, the SCL/SDA pins above AREF are not associated with the correct A5/A4 pins.

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