Lesson 6: PWM & Analog Outputs

By the end of this lesson, you will:

• • Understand PWM (Pulse Width Modulation) principles
• • Use analogWrite() for analog output control
• • Control LED brightness and motor speed
• • Create smooth fading and dimming effects

Key Concepts:

• • PWM frequency and duty cycle
• • Arduino PWM pins and limitations
• • RGB LED color mixing
• • Servo motor control basics

Key PWM Concepts:

• Duty Cycle: Percentage of time the signal is HIGH
• Frequency: How fast the switching occurs (typically 490Hz or 980Hz)
• Average Voltage: Effective voltage based on duty cycle

PWM Value Examples:

• 0: Always LOW (0V average)
• 64: 25% duty cycle (1.25V average)
• 128: 50% duty cycle (2.5V average)
• 192: 75% duty cycle (3.75V average)
• 255: Always HIGH (5V average)

LED Brightness Control

One of the most common uses of PWM is controlling LED brightness. Here's a complete example that gradually fades an LED in and out:

Wiring Diagram

Wiring: Connect the LED's long leg (anode) to pin 9 through a 220Ω resistor, and the short leg (cathode) to GND.

// LED Fading Example
const int ledPin = 9;  // PWM pin
int brightness = 0;    // LED brightness
int fadeAmount = 5;    // How much to change brightness

void setup() {
  Serial.begin(9600);
}

void loop() {
  // Set LED brightness
  analogWrite(ledPin, brightness);
  
  // Print current brightness
  Serial.print("Brightness: ");
  Serial.println(brightness);
  
  // Change brightness for next iteration
  brightness = brightness + fadeAmount;
  
  // Reverse direction at the ends
  if (brightness <= 0 || brightness >= 255) {
    fadeAmount = -fadeAmount;
  }
  
  delay(30);  // Small delay for smooth fading
}

RGB LED Control Code

🔌 RGB LED Wiring Instructions

Before running the RGB LED code, you need to connect an RGB LED properly:

Common Cathode RGB LED Wiring:

• Red pin → 220Ω resistor → Digital pin 9
• Green pin → 220Ω resistor → Digital pin 10
• Blue pin → 220Ω resistor → Digital pin 11
• Common cathode (longest pin) → GND

Alternative: Use Built-in RGB LED

If your expansion board has a built-in RGB LED, check its pin connections and modify the pin numbers in the code accordingly.

RGB LED Wiring: Red → Pin 9, Green → Pin 10, Blue → Pin 11 (each with 220Ω resistor)

Here's an example that cycles through different colors on an RGB LED:

📋 Copy

// RGB LED Color Cycling
const int redPin = 9;    // Red LED pin
const int greenPin = 10; // Green LED pin
const int bluePin = 11;  // Blue LED pin

void setup() {
  Serial.begin(9600);
  Serial.println("RGB LED Color Demo");
}

void loop() {
  // Red
  setColor(255, 0, 0);
  Serial.println("Red");
  delay(1000);
  
  // Green
  setColor(0, 255, 0);
  Serial.println("Green");
  delay(1000);
  
  // Blue
  setColor(0, 0, 255);
  Serial.println("Blue");
  delay(1000);
  
  // Purple
  setColor(255, 0, 255);
  Serial.println("Purple");
  delay(1000);
  
  // Off
  setColor(0, 0, 0);
  Serial.println("Off");
  delay(1000);
}

// Function to set RGB color
void setColor(int red, int green, int blue) {
  analogWrite(redPin, red);
  analogWrite(greenPin, green);
  analogWrite(bluePin, blue);
}