RC Car with type-C Car Camera and arduino nano Ultrasonic and buzzer and led

#define echoPin   10
#define trigPin   9
#define ledPin    4

long duration;
int distance;
int flag = 0;

//----------------------------------
int alertDistance = 20; // 20 CM
//----------------------------------

void setup() {
  Serial.begin(9600);
  Serial.println("Serial COM Test");
  pinMode(ledPin, OUTPUT);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  digitalWrite(ledPin, 1);

}

void loop() {
  US();
  if (distance < alertDistance) {
    digitalWrite(ledPin, 0);
  }
  else {
    digitalWrite(ledPin, 1);
  }
  delay(50);
}


void US() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2;
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
}