What does analogWrite() do in Arduino?

 analogWrite() makes an Arduino pin output a PWM (pulse-width modulated) signal that behaves like an “analog” level to things like LEDs and DC motors.

What it actually does

• Outputs a square wave that switches HIGH/LOW quickly.

• You set a value (usually 0–255) that controls the duty cycle (how long it stays HIGH each cycle).

  • analogWrite(pin, 0) → always OFF (0% duty)

  • analogWrite(pin, 255) → always ON (100% duty)

  • analogWrite(pin, 128) → ~50% duty

What it’s used for

• LED dimming (brightness follows duty cycle)

• Motor speed control (with a driver/MOSFET)

• Generating a basic PWM control signal (e.g., for some devices)

Important notes

• It only works on PWM-capable pins (marked with ~ on many boards).

• It does not output a true analog voltage by itself.
  If you want a real DC voltage, you need:

  • a low-pass RC filter, or

  • a DAC pin (some boards like Due/Zero have DAC), or

  • an external DAC.

PWM frequency depends on the board

• Uno/Nano (ATmega328P): typically ~490 Hz on most PWM pins, ~980 Hz on a couple pins (because different timers).

• Other boards (Mega, Leonardo, SAMD, etc.) can differ.

Tiny example

int led = 9; // PWM pin
void setup() { pinMode(led, OUTPUT); }
void loop() {
  analogWrite(led, 64);  // ~25% brightness
  delay(1000);
  analogWrite(led, 192); // ~75% brightness
  delay(1000);
}