Arduino pins: digital vs analog, explained simply

An Arduino talks to the world through its pins. Getting the pin type right is the first thing that trips up beginners.

Digital pins: on or off

A digital pin has two states: HIGH (usually 5V) or LOW (0V). Use them for anything that is binary:

• Reading: a button pressed or not, a limit switch, a line sensor that says black or white.
• Writing: turning an LED or a relay on and off.

pinMode(2, INPUT);
int pressed = digitalRead(2);   // 0 or 1
digitalWrite(13, HIGH);         // LED on

Analog pins: a range of values

Analog input pins (marked A0, A1, ...) read a voltage between 0 and 5V and turn it into a number from 0 to 1023. Use them for sensors that give a smooth value:

• a light sensor, a potentiometer, many distance sensors.

int value = analogRead(A0);     // 0..1023

PWM: fake analog output

Arduino cannot output a true in-between voltage, but pins marked with ~ can fake it with PWM (rapid on/off pulses). That is how you dim an LED or set motor speed. We cover this in the PWM lesson.

The mistake to avoid

Reading a button with analogRead or a light sensor with digitalRead is the classic beginner bug. Match the pin type to the signal: binary goes digital, smooth goes analog.