#define TRIG_PIN 9
#define ECHO_PIN 10
#define RED_LED_PIN 3 // Define the pin for the red LED

void setup() {
  Serial.begin(9600); 
  pinMode(TRIG_PIN, OUTPUT); 
  pinMode(ECHO_PIN, INPUT);
  
  pinMode(RED_LED_PIN, OUTPUT); // Set red LED pin as OUTPUT
}

void loop() {
  long duration;
  float distance;

  // Trigger the ultrasonic pulse
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Read the pulse duration
  duration = pulseIn(ECHO_PIN, HIGH);

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

  // Print the distance to the Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Check if the distance is less than 20 centimeters (20 cm)
  if (distance < 20) {
    digitalWrite(RED_LED_PIN, HIGH); // Turn on the red LED
  } else {
    digitalWrite(RED_LED_PIN, LOW); // Turn off the red LED
  }

  delay(1000); // Delay for 1 second before the next reading
}