The Arduino UNO has 14 digital pins, 6 analog pins and a power header, and many of them serve more than one purpose. A pin that works as a plain input in one sketch can also act as a PWM output, a serial line or an interrupt source in another sketch. Knowing which function belongs to which pin helps you avoid wiring mistakes before they cost you an evening of debugging.

This guide covers every pin on the Arduino UNO in the order you will meet them on the board. For each group of pins, we explain what the pins do, how to use them in a sketch, and which electrical limits you need to respect. A diagram at the start and a full reference table at the end are included, so you can use the page both for learning and for quick lookups later.

If you also own a smaller board, the Arduino Nano pinout guide shows how closely it matches the UNO.…