Arduino Basics: Analog Output (PWM)

Arduino boards cannot produce true analog voltages on their digital pins. Instead, they use PWM (Pulse Width Modulation) to simulate analog output. PWM rapidly switches a pin between HIGH and LOW, and the ratio of ON time to OFF time determines the effective voltage.

Using PWM with analogWrite()

• analogWrite(pin, value) sets the PWM output on a pin.
• value ranges from 0 (always LOW, 0V) to 255 (always HIGH, 5V).
• Pins capable of PWM are marked with a ~ on most Arduino boards (e.g., ~3, ~5, ~6, ~9, ~10, ~11 on Arduino Uno).

Example 1: Dimming an LED

int ledPin = 9; // PWM-capable pin
int brightness = 0;
int fadeAmount = 5;

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  analogWrite(ledPin, brightness); // Set LED brightness
  brightness = brightness + fadeAmount;

  // Reverse direction at limits
  if (brightness <= 0 || brightness >= 255) {
    fadeAmount = -fadeAmount;
  }

  delay(30); // Small delay for smooth fading
}

Example 2: Controlling Motor Speed

int motorPin = 3; // PWM-capable pin
int speed = 128;    // Half speed (0–255)

void setup() {
  pinMode(motorPin, OUTPUT);
}

void loop() {
  analogWrite(motorPin, speed); // Control motor speed
  // You can change 'speed' dynamically for acceleration
}

Tips for Using PWM

• Use only PWM-capable pins for analogWrite.
• For LEDs, PWM changes perceived brightness; for motors, it controls speed or power.
• Combine PWM with smoothing circuits (capacitors) if a more stable analog voltage is needed.
• Remember that analogWrite does not produce continuous voltage—it is a digital simulation.

By using PWM, you can add dynamic control to your projects, such as dimming lights, adjusting fan or motor speeds, and creating analog-like behaviors with digital pins.