Interrupt based Button sketch with debounce for Arduino Interrupts Tutorial.

Arduino_Interrupts_Button_Interrupt_Debounce.ino

int ledPin = 13;
int buttonPin = 2;

int ledToggle;
int previousState = HIGH;
unsigned int previousPress;
volatile int buttonFlag;
int buttonDebounce = 20;

void setup() 
{
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(2), button_ISR, CHANGE);
}

void loop() 
{
  if((millis() - previousPress) > buttonDebounce && buttonFlag)
  {
    previousPress = millis();
    if(digitalRead(buttonPin) == LOW && previousState == HIGH)
    {
      ledToggle =! ledToggle;
      digitalWrite(ledPin, ledToggle);
      previousState = LOW;
    }
    
    else if(digitalRead(buttonPin) == HIGH && previousState == LOW)
    {
      previousState = HIGH;
    }
    buttonFlag = 0;
  }
}

void button_ISR()
{
  buttonFlag = 1;
}