// Ultrasonic Sensor Pins and Threshold Distance
int TrigPin = 3; // Trigger Pin of Ultrasonic Sensor
int echoPin = 2; // Echo Pin of Ultrasonic Sensor
int Proximity_Indicator_LED_Pin = 12; // The LED turns on as the obstacle approaches closer 
int Threshold_Distance_in_cm = 3; // Threshold Distance in centimeters

// Variables to store time and distance
long Time_Elapsed_to_Receive_Echo; // Time in microseconds
int Distance_in_cm; // Distance of the Obstacle in cm

void setup() 
{
  pinMode(TrigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(Proximity_Indicator_LED_Pin, OUTPUT);
  Serial.begin(9600); // Start Serial Terminal
}

void loop() 
{
  // Trigger the sensor
  digitalWrite(TrigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(TrigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(TrigPin, LOW);
  
  // Measure the duration of the pulse
  Time_Elapsed_to_Receive_Echo = pulseIn(echoPin, HIGH); // Time in microseconds
  Distance_in_cm = microsecondsToCentimeters(Time_Elapsed_to_Receive_Echo);
  
  // Print the distance to the Serial Monitor
  Serial.print(Distance_in_cm);
  Serial.print(" cm");
  Serial.println();
  
  // Control the LED based on distance
  if (Distance_in_cm <= Threshold_Distance_in_cm)
  {
    digitalWrite(Proximity_Indicator_LED_Pin, HIGH); // Turn on LED
  }
  else
  {
    digitalWrite(Proximity_Indicator_LED_Pin, LOW); // Turn off LED
  }
  
  // Short delay before the next measurement
  delay(100);
}

// Convert microseconds to centimeters
int microsecondsToCentimeters(long microseconds) 
{
  return (microseconds * 0.0343) / 2; // Convert duration to distance in cm
}