//Initialize pins for the ultrasonic sensor
int echoPin = 6;  // Echo pin number
int trigPin = 7;  // Trigger pin number
int speakPin = 8; // Speaker pin number

void setup() {
  Serial.begin(9600);         // Starting Serial Terminal
  pinMode(trigPin, OUTPUT);   // Setting the Trigger Pin as an output to send the wave
  pinMode(echoPin, INPUT);    // Setting the Echo pin as an input to receive the wave
  pinMode(speakPin, OUTPUT);
}

void loop() {
  float duration, cmDist;      // Distance variables
  
  digitalWrite(trigPin, LOW);  // Turn wave off
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH); // Turn wave on
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);  // Turn wave off
  
  //Use the following functions to calculate the distance in cm
  duration = pulseIn(echoPin, HIGH);
  cmDist = microsecondsToCentimeters(duration);
  
  /*
  Set up a condition where the serial monitor will print "Far: " 
  if the cmDist is greater than 20 cm, otherwise 
  serial monitor prints "Close: ". These should be followed
  by the cmDist follows:
  */
  if(cmDist < 100) {
    tone(speakPin, 2000, 1);
  } else {
    tone(speakPin, 0, 1);
  }
  
}

//Converts the duration calculated by distance sensor to cm
float microsecondsToCentimeters(long microseconds) {
  return microseconds / 29.0 / 2.0;
}