Arduino Pinout Reference
A mobile-friendly Arduino Uno R3 pinout reference for makers — digital pins, PWM pins, analog inputs, SPI, I2C, UART, power pins and quick wiring notes.
⚠️ Safety Note: Arduino Uno logic is normally 5 V. Do not connect 5 V Arduino outputs directly to 3.3 V-only boards such as Raspberry Pi or ESP8266 without level shifting.
🔌 Arduino Uno R3 visual pinout
POWER / RESET / ANALOG SIDEDIGITAL I/O SIDE
D0RX / UART
D1TX / UART
D2INT0
D3~PWM / INT1
D4GPIO
D5~PWM
D6~PWM
D7GPIO
D8GPIO
D9~PWM
D10~SS / PWM
D11~MOSI / PWM
D12MISO
D13SCK / LED
ATmega328P
Arduino UNO R3
USB / Power
A0ADC0
A1ADC1
A2ADC2
A3ADC3
A4SDA / ADC4
A5SCL / ADC5
VINInput
GNDGround
GNDGround
5VRegulated
3.3VOutput
RSTReset
AREFADC Ref
PWM
Analog / ADC
I2C
SPI
UART
Power
Search Pin / Function
Filter Group
Quick filters:
| Pin | Name | Group | Use / Notes |
|---|---|---|---|
| D0 | RX | UART | Serial receive. Avoid using during USB serial upload/debug. |
| D1 | TX | UART | Serial transmit. Connected to USB serial interface. |
| D2 | INT0 | DIGITAL | Digital I/O, external interrupt 0. |
| D3 | PWM / INT1 | PWM | PWM output and external interrupt 1. |
| D4 | Digital I/O | DIGITAL | General digital input/output. |
| D5 | PWM | PWM | PWM output and digital I/O. |
| D6 | PWM | PWM | PWM output and digital I/O. |
| D7 | Digital I/O | DIGITAL | General digital input/output. |
| D8 | Digital I/O | DIGITAL | General digital input/output. |
| D9 | PWM | PWM | PWM output and digital I/O. |
| D10 | SS / PWM | SPI | SPI SS chip select, also PWM output. |
| D11 | MOSI / PWM | SPI | SPI MOSI, also PWM output. |
| D12 | MISO | SPI | SPI MISO and digital I/O. |
| D13 | SCK / LED | SPI | SPI clock and built-in LED pin. |
| A0 | ADC0 | ANALOG | 10-bit analog input, can also be digital I/O. |
| A1 | ADC1 | ANALOG | 10-bit analog input, can also be digital I/O. |
| A2 | ADC2 | ANALOG | 10-bit analog input, can also be digital I/O. |
| A3 | ADC3 | ANALOG | 10-bit analog input, can also be digital I/O. |
| A4 | SDA / ADC4 | I2C | I2C data line and analog input. |
| A5 | SCL / ADC5 | I2C | I2C clock line and analog input. |
| VIN | VIN | POWER | External input before regulator. Commonly used with 7–12 V supply. |
| 5V | 5V | POWER | Regulated 5 V rail. Use carefully when powering external modules. |
| 3.3V | 3.3V | POWER | 3.3 V output for small modules. |
| GND | GND | GND | Ground reference for power and signals. |
| AREF | AREF | ADC | External analog reference input for ADC. |
📋 Common Arduino Uno Interfaces
🟢 PWM Pins
PWM outputsD3, D5, D6, D9, D10, D11
analogWrite()0–255
🟠 I2C
SDAA4
SCLA5
R3 headerSDA/SCL duplicate
🟣 SPI
SSD10
MOSID11
MISOD12
SCKD13
📚 Maker Notes
Digital vs analog A0–A5 are analog inputs, but they can also be used as digital pins when needed.
5 V logic warning Arduino Uno outputs 5 V logic. Use a level shifter for 3.3 V-only boards and sensors.
Pin current limit Do not drive motors, relays or high-power LEDs directly from Arduino pins. Use a transistor, MOSFET or driver module.
UART pins during upload D0 and D1 are used by USB serial. Connected circuits on these pins can disturb upload or serial monitor.
Arduino Pinout Reference
This Arduino pinout reference helps you quickly identify the Uno R3 digital pins, PWM pins, analog inputs, I2C pins, SPI pins, UART pins and power header pins while wiring sensors, displays, relays, modules and breadboard circuits.
Arduino Uno Pinout Quick Summary
Arduino Uno R3 has 14 digital I/O pins, 6 analog input pins, 6 PWM-capable digital pins, UART on D0/D1, I2C on A4/A5 and SPI on D10–D13.
❓ Frequently Asked Questions
PWM is available on digital pins D3, D5, D6, D9, D10 and D11. These pins are marked with a tilde symbol on many Arduino boards.
I2C uses A4 as SDA and A5 as SCL. On Uno R3, the SDA/SCL header near AREF is connected to the same I2C bus.
SPI uses D10 as SS, D11 as MOSI, D12 as MISO and D13 as SCK. SPI is also available through the ICSP header.
Yes. A0 to A5 can be used as digital inputs or outputs when they are not being used for analog measurement.
Usually yes for digital inputs because 3.3 V is normally read as HIGH by a 5 V Uno, but always check the sensor output and use safe wiring.
Do not connect Uno 5 V outputs directly to Raspberry Pi GPIO. Raspberry Pi GPIO is 3.3 V only and needs level shifting.
AREF is the analog reference input. It can be used when you need a specific ADC reference voltage instead of the default reference.
D0 and D1 are used for serial communication with the USB interface. External circuits on these pins can interfere with uploading sketches or using Serial Monitor.