// https://forum.arduino.cc/t/arduino-debounce-button-logic-controlling-servos/1154479/10

const int buttonPin = 9;

int buttonState;

void loop () {
    int but = digitalRead (buttonPin);
    if (buttonState != but)  {
        buttonState = but;
        delay (20);             // debounce

        if (LOW == but)
            Serial.println ("pressed");
        else
            Serial.println ("released");
    }
}

void setup () {
    Serial.begin (9600);

    pinMode (buttonPin, INPUT_PULLUP);
    buttonState = digitalRead (buttonState);
}