#define BUTTON_PIN 21 

//Variable Will Change
int lastState = HIGH; //The previous state from the input pin 
int currentState; //The current reading from the input pin


void setup() {
  Serial.begin(115200);
  pinMode (BUTTON_PIN, INPUT_PULLUP);
}

void loop() {
  //Read the state of the switch/button
  currentState = digitalRead(BUTTON_PIN);

  if (lastState == LOW && currentState == HIGH)
  Serial.println ("The state change from LOW to HIGH");

  //Save the last state
  lastState =currentState;
}