Ultrasonic with LED blink code

 const int trigPin = 9;

const int echoPin = 8;

const int ledPin = 13;

long duration;

int distance;

void setup() {

  pinMode(trigPin, OUTPUT);

  pinMode(echoPin, INPUT);

  pinMode(ledPin, OUTPUT);

  Serial.begin(9600);

}

void loop() {

  // Send ultrasonic pulse

  digitalWrite(trigPin, LOW);

  delayMicroseconds(2);

  digitalWrite(trigPin, HIGH);

  delayMicroseconds(10);

  digitalWrite(trigPin, LOW);

  // Read echo time

  duration = pulseIn(echoPin, HIGH);

  // Convert time to distance (in cm)

  distance = duration * 0.034 / 2;

  // Print distance to Serial Monitor

  Serial.print("Distance: ");

  Serial.print(distance);

  Serial.println(" cm");

  // If object is closer than 20 cm, blink LED

  if (distance <= 20) {

    digitalWrite(ledPin, HIGH); // LED ON

    delay(200);

    digitalWrite(ledPin, LOW);  // LED OFF

    delay(200);

  } else {

    digitalWrite(ledPin, LOW);  // LED stays OFF

  }

  delay(100);

}