#define trigPin 13
#define echoPin 12
#define buzzer 2
#define ledPin 3

long duration;
int distance;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(buzzer, OUTPUT);
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Trigger the ultrasonic pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the echo
  duration = pulseIn(echoPin, HIGH);

  // Calculate distance (cm)
  distance = duration * 0.034 / 2;

  // Print for testing
  Serial.println(distance);

  // If object is close, turn on LED & buzzer
  if (distance < 20) {
    digitalWrite(ledPin, HIGH);
    digitalWrite(buzzer, HIGH);
  } else {
    digitalWrite(ledPin, LOW);
    digitalWrite(buzzer, LOW);
  }

  delay(100);
}