/*
* Athors: Oulis Evnagelos, Oulis Nikolaos, Katsibras Drosos
* Ultrasonic Sensor HC-SR04 and Arduino
*
*/

// defines pins numbers
const int trigPin = 9;
const int echoPin = 10;
const int response = 6;
const int response1 = 5;
const int id = 2;

// defines variables
long duration;
int distance;

void setup() {
pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
pinMode(response, OUTPUT);
pinMode(response1, OUTPUT);
pinMode(echoPin, INPUT); // Sets the echoPin as an Input
Serial.begin(9600); // Starts the serial communication

// Clears the trigPin
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
}

void loop() {
// 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);

// Calculating the distance
distance= duration*0.034/2;

// Prints the distance on the Serial Monitor
//Serial.print("Distance: ");
//Serial.println(distance);

String park_out;
if (distance < 4){
  park_out = String(id) + "#0"; //parking isn't available.
  digitalWrite(response, LOW);
  digitalWrite(response1, HIGH);
}
else{
  park_out = String(id) + "#1"; //parking is available.
  digitalWrite(response, HIGH);
  digitalWrite(response1, LOW);
}

Serial.println(park_out);

delay(500);
}