// constants won't change
const int TRIG_PIN1  = 6; // Arduino pin connected to Ultrasonic Sensor 1's TRIG pin
const int ECHO_PIN1  = 7; // Arduino pin connected to Ultrasonic Sensor 1's ECHO pin

const int TRIG_PIN2  = 8; // Arduino pin connected to Ultrasonic Sensor 2's TRIG pin
const int ECHO_PIN2  = 9; // Arduino pin connected to Ultrasonic Sensor 2's ECHO pin

const int TRIG_PIN3  = 10; // Arduino pin connected to Ultrasonic Sensor 3's TRIG pin
const int ECHO_PIN3  = 11; // Arduino pin connected to Ultrasonic Sensor 3's ECHO pin

const int BUZZER_PIN = 3;  // Arduino pin connected to Piezo Buzzer's pin
const int DISTANCE_THRESHOLD = 50; // centimeters

// variables will change
float duration_us1, distance_cm1;
float duration_us2, distance_cm2;
float duration_us3, distance_cm3;

void setup() {
  Serial.begin(9600);          // initialize serial port
  pinMode(TRIG_PIN1, OUTPUT);  // set arduino pin to output mode
  pinMode(ECHO_PIN1, INPUT);   // set arduino pin to input mode

  pinMode(TRIG_PIN2, OUTPUT);
  pinMode(ECHO_PIN2, INPUT);

  pinMode(TRIG_PIN3, OUTPUT);
  pinMode(ECHO_PIN3, INPUT);

  pinMode(BUZZER_PIN, OUTPUT); // set arduino pin to output mode
}

void loop() {
  // Sensor 1
  digitalWrite(TRIG_PIN1, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN1, LOW);
  duration_us1 = pulseIn(ECHO_PIN1, HIGH);
  distance_cm1 = 0.017 * duration_us1;

  // Sensor 2
  digitalWrite(TRIG_PIN2, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN2, LOW);
  duration_us2 = pulseIn(ECHO_PIN2, HIGH);
  distance_cm2 = 0.017 * duration_us2;

  // Sensor 3
  digitalWrite(TRIG_PIN3, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN3, LOW);
  duration_us3 = pulseIn(ECHO_PIN3, HIGH);
  distance_cm3 = 0.017 * duration_us3;

  // Buzzer control logic based on the distances from all three sensors
  if (distance_cm1 < DISTANCE_THRESHOLD || distance_cm2 < DISTANCE_THRESHOLD || distance_cm3 < DISTANCE_THRESHOLD){
    digitalWrite(BUZZER_PIN, HIGH); // turn on Piezo Buzzer
    tone(3, 262, 250);}
  else{
    digitalWrite(BUZZER_PIN, LOW);  // turn off Piezo Buzzer
  }
  // print the values to Serial Monitor
  Serial.print("distance1: ");
  Serial.print(distance_cm1);
  Serial.print(" cm, distance2: ");
  Serial.print(distance_cm2);
  Serial.print(" cm, distance3: ");
  Serial.print(distance_cm3);
  Serial.println(" cm");

  delay(500);
}