What is PWM? Explain usage of PWM pins with Example

What is PWM?

PWM stands for Pulse Width Modulation. It is a technique used to encode a message into a pulsing signal. PWM is commonly used in various applications, including controlling the brightness of LEDs, the speed of motors, and the generation of audio signals.

How PWM Works

PWM works by varying the width of the pulses in a pulse train. The key parameters in PWM are:

1. Duty Cycle: The percentage of one period in which a signal is active. A 50% duty cycle means the signal is on for half the time and off for the other half.
2. Frequency: The number of times the PWM signal completes a cycle per second, measured in Hertz (Hz).

Usage of PWM Pins

PWM pins are special pins on microcontrollers that can generate PWM signals. These pins are often labeled as PWM or have a tilde (~) symbol next to them.

Example: Controlling LED Brightness with PWM

Let's consider an example using an Arduino to control the brightness of an LED using PWM.

Components Needed:

• Arduino board (e.g., Arduino Uno)
• LED
• Resistor (220 ohms)
• Breadboard and jumper wires

Circuit Setup:

1. Connect the anode (longer leg) of the LED to a PWM-capable pin on the Arduino (e.g., pin 9).
2. Connect the cathode (shorter leg) of the LED to one end of the resistor.
3. Connect the other end of the resistor to the ground (GND) on the Arduino.

Code Example:

// Define the PWM pin
const int ledPin = 9;

void setup() {
  // Set the LED pin as an output
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // Increase brightness
  for (int brightness = 0; brightness <= 255; brightness++) {
    analogWrite(ledPin, brightness);
    delay(10); // Wait for 10 milliseconds
  }
  
  // Decrease brightness
  for (int brightness = 255; brightness >= 0; brightness--) {
    analogWrite(ledPin, brightness);
    delay(10); // Wait for 10 milliseconds
  }
}

Explanation:

1. Setup: The setup() function initializes the LED pin as an output.
2. Loop: The loop() function continuously runs, increasing and then decreasing the brightness of the LED.
   • analogWrite(ledPin, brightness) sets the PWM duty cycle. The brightness value ranges from 0 (0% duty cycle) to 255 (100% duty cycle).
   • The delay(10) function creates a short pause to make the change in brightness visible.

Conclusion

PWM is a versatile technique used in various applications to control devices like LEDs and motors. By varying the duty cycle of the PWM signal, you can control the power delivered to these devices. Using PWM pins on microcontrollers like Arduino makes it easy to implement PWM in your projects.