/* HCSR04UltrasonicDistanceSensorv1
 * 
 * Basic sketch to learn how the HC-SR04 sensor works
 * The sketch works but because it uses delay() would be harder to integrate with other components or sensors.
 * 
 * pins used
 * pin 7 to Trig Pin
 * pin 6 to Echo pin
 */


//const int is a constant integer that cannot have it's value changed.
const int triggerPin = 7;
const int echoPin = 6;

//An unsigned long is needed because the numbers produced can be much larger 
//than an int can hold (max value 32,767)
unsigned long duration;  //time taken for echo
int distance;   //in mm


void setup() {
  Serial.begin(9600);
  Serial.println("HCSR04UltrasonicDistanceSensorv1...");
  Serial.println(" ");//Blank line
  //pinMode set for OUTPUT...sending HIGH of LOW
  pinMode(triggerPin, OUTPUT);  //sends signal
  //pinMode set for INPUT, we will receive an incoming HIGH or LOW on this pin
  pinMode(echoPin, INPUT);      //receives signal
}

void loop() {
  
  // Clears the trigPin condition, just in case it had been left HIGH
  //Same as turing the LED off in the blink sketch
  digitalWrite(triggerPin, LOW);
  
  //A tiny delay 2 millionths of a second
  delayMicroseconds(2);
  
  // Sets the trigPin HIGH (ACTIVE) for 10 microseconds
  //same as turing the LED on in the blink sketch
  digitalWrite(triggerPin, HIGH);
  
  //pin stays HIGH (5v) for 10 microseconds to trigger a pulse
  delayMicroseconds(10);
  
  //Pin taken LOW (0v) after pulse triggered ready for next pulse
  digitalWrite(triggerPin, LOW);
  
  // Reads the echoPin, returns the sound wave travel time in microseconds
  //Pulse in HIGH waits for the echoPin to go HIGH (5v) and then starts a timer until it goes LOW
  //At that point the HC-SR04 has received it's set of echos
  duration = pulseIn(echoPin, HIGH);
  
  // Calculating the distance
  // Speed of sound wave divided by 2 as the sound travels to and from the object
  distance = duration * 0.34 / 2; 
  
  // Displays the distance on the Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" mm");
  
  //wait 1 second before runing the code again
  delay(1000);
}