The Debounce Circuit

Here is the circuit connection with your Arduino board



Here is the code:

// constants won't change. They're used here to set pin numbers:
const int buttonPin = 6;  // the number of the pushbutton pin
const int ledPin = 7;    // the number of the LED pin

// Variables will change:
int ledState = HIGH;        // the current state of the output pin
int buttonState;            // the current reading from the input pin
int lastButtonState = LOW;  // the previous reading from the input pin

// the following variables are unsigned longs because the time, measured in
// milliseconds, will quickly become a bigger number than can be stored in an int.
unsigned long lastDebounceTime = 0;  // the last time the output pin was toggled
unsigned long debounceDelay = 50;    // the debounce time; increase if the output flickers

void setup() {
  pinMode(buttonPin, INPUT);
  pinMode(ledPin, OUTPUT);

  // set initial LED state
  digitalWrite(ledPin, ledState);
}

void loop() {
  // read the state of the switch into a local variable:
  int reading = digitalRead(buttonPin);

  // check to see if you just pressed the button
  // (i.e. the input went from LOW to HIGH), and you've waited long enough
  // since the last press to ignore any noise:

  // If the switch changed, due to noise or pressing:
  if (reading != lastButtonState) {
    // reset the debouncing timer
    lastDebounceTime = millis();
  }

  if ((millis() - lastDebounceTime) > debounceDelay) {
    // whatever the reading is at, it's been there for longer than the debounce
    // delay, so take it as the actual current state:

    // if the button state has changed:
    if (reading != buttonState) {
      buttonState = reading;

      // only toggle the LED if the new button state is HIGH
      if (buttonState == HIGH) {
        ledState = !ledState;
      }
    }
  }

  // set the LED:
  digitalWrite(ledPin, ledState);

  // save the reading. Next time through the loop, it'll be the lastButtonState:
  lastButtonState = reading;
}

// End of the code


Explanations:

For the following piece of code, the function millis() always log the present time. When the reading changes, it logs the present time.
When the state doesn't change for a certain amount of time, it enters the IF Statement that follows.

  if (reading != lastButtonState) {
    // reset the debouncing timer
    lastDebounceTime = millis();
  }



If you comment out the following piece of code, it won't work as good as keeping them there.
    if (reading != buttonState) {
      buttonState = reading;

If you remove this part, the loop() function wll always read the pin value and keep toggling the LED instead of just running it for once. This makes the LED state unpredictable.


Here is the demonstration