MOS Transistor Application in IRF520 Module

				
					int pwmPin = 9;        // PWM control pin
int buttonPin = 2;     // Button pin (connected to GND, using pull-up resistor)

int lowSpeed = 85;     // Low speed
int mediumSpeed = 170; // Medium speed
int highSpeed = 255;   // High speed

int currentSpeed = 0;  // Current speed level (0 = Off, 1 = Low, 2 = Medium, 3 = High)
int lastButtonState = HIGH; // Last button state
int buttonState;       // Current button state

void setup() {
  pinMode(pwmPin, OUTPUT);
  pinMode(buttonPin, INPUT_PULLUP); // Enable internal pull-up resistor
  analogWrite(pwmPin, 0); // Initial state: Off
}

void loop() {
  // Read button state
  buttonState = digitalRead(buttonPin);
  
  // Detect button press (falling edge)
  if (buttonState == LOW && lastButtonState == HIGH) {
    // Debounce delay
    delay(50);
    // Confirm button state again
    if (digitalRead(buttonPin) == LOW) {
      changeSpeed(); // Switch speed
    }
  }
  
  lastButtonState = buttonState;
}

void changeSpeed() {
  // Switch to next speed level (cycle: Off -> Low -> Medium -> High -> Off...)
  currentSpeed = (currentSpeed + 1) % 4;
  
  // Set PWM output according to current speed level
  switch(currentSpeed) {
    case 0:
      analogWrite(pwmPin, 0);        // Off
      break;
    case 1:
      analogWrite(pwmPin, lowSpeed);   // Low speed
      break;
    case 2:
      analogWrite(pwmPin, mediumSpeed); // Medium speed
      break;
    case 3:
      analogWrite(pwmPin, highSpeed);   // High speed
      break;
  }
  
  // Wait for button release to avoid continuous triggering
  while(digitalRead(buttonPin) == LOW) {
    delay(10);
  }
  delay(50); // Post-release debounce delay
}