Debounce Example

dfrobot_debounce.ino

/*
 * Adapted from the [completely broken] DFRobot example sketches
 *  by Luke Tuthill:
 * https://www.dfrobot.com/blog-662.html
 *
 * 
 * This sketch shows how to debounce a button. Sometimes, when you press
 *  a button, it's not perfect - sometimes it 'bounces' up and down slightly,
 *  and registers multiple presses.
 *
 * We can fix this by ignoring all input from the button for a certain duration
 *  after the button is pressed, in this case, 50ms.
 */


// Attach the button to pin 2
int BUTTON = 2;

// Attach an LED_PIN to pin 3
int LED_PIN = 13;

// The delay (in ms) to ignore button bounces after press
long DEBOUNCE_DELAY = 50;



// Variable to store the LED_PIN state
int ledState = HIGH;

// The last button state; what the button
//  was _last time_ we checked
int lastButtonState = LOW;

// The time in milliseconds that the button was last pressed
long lastDebounceTime = 0;


void setup() {
    // Setup pin modes
    pinMode(BUTTON, INPUT);
    pinMode(LED_PIN, OUTPUT);

    // Set initial LED_PIN state
    digitalWrite(LED_PIN, ledState);

    // Begin serial connection to show values
    Serial.begin(9600);
}

void loop() {
    // Get the value of the button, HIGH or LOW
    int state = digitalRead(BUTTON);

    // Print it to the serial terminal
    Serial.println(state);

    // If the current time minus the last time that the button
    //  is pressed is greater than the delay we have set
    if ((millis() - lastDebounceTime) > DEBOUNCE_DELAY) {

        // Get the time in milliseconds, and store it in lastDebounceTime
        lastDebounceTime = millis();

        // If the button's state is different to what it was before:
        if (state != lastButtonState) {

            // Save the new button state
            lastButtonState = state;

            // If the button is on, switch the LED's state.
            if (state == HIGH) {

                /*
                 * The ! before the variable here is called a 'not',
                 *  and it means:
                 *  - If ledState is a 1, return 0
                 *  - If ledState is a 0, return 1
                 * This is then fed back into ledState, so
                 *  ledState will become the opposite of what
                 *  it was before - known as 'inverting'.
                 */

                ledState = !ledState;
            }
        }
    }

    // Set the LED to ledState
    digitalWrite(LED_PIN, ledState);
}