#define TRIG_PIN 18
#define ECHO_PIN 19
#define LED_PIN 23
#define BUZZER_PIN 32

float measureDistance(){
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  long duration = pulseIn(ECHO_PIN, HIGH);
  float distance = duration*0.034/2;
  return distance;
}
void setup() {

  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN,OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}

void loop() {
  float distance = measureDistance();

  if ( distance < 50 ){
    digitalWrite(LED_PIN, LOW);
    tone(BUZZER_PIN, 500);
  }

  else {
    digitalWrite(LED_PIN, HIGH);
    noTone(BUZZER_PIN);
  }

  Serial.print("Distance : ");
  Serial.print(distance);
  Serial.println(" cm.");
  delay(250);
}