/*
  HC-SR04 Ultrasonic Sensor Example.

  Turn the LED on when an object is within 100cm range.

*/

#define trigPin 5 
#define echoPin 18
#define ledPin 2 

//define sound speed in cm/uS
#define SOUND_SPEED 0.034
#define CM_TO_INCH 0.393701

long duration;
float distanceCm;
float distanceInch;

void setup() {
  Serial.begin(115200); // Starts the serial communication
  pinMode(ledPin, OUTPUT);
  pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
  pinMode(echoPin, INPUT); // Sets the echoPin as an Input
}

void loop() {
  // Clears the trigPin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  // Sets the trigPin on HIGH state for 10 micro seconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Reads the echoPin, returns the sound wave travel time in microseconds
  duration = pulseIn(echoPin, HIGH);
  
  // Calculate the distance
  distanceCm = duration * SOUND_SPEED/2;
  
  // Convert to inches
  // distanceInch = distanceCm * CM_TO_INCH;
  
  // Prints the distance in the Serial Monitor
  bool isNearby = distanceCm < 100;
  digitalWrite(ledPin, isNearby);

  Serial.print("Distance (cm): ");
  Serial.println(distanceCm);
  // Serial.print("Distance (inch): ");
  // Serial.println(distanceInch);
  
  delay(1000);
}