#define echoPin 4 // attach pin D2 Arduino to pin Echo of HC-SR04
#define trigPin 3 // attach pin D3 Arduino to pin Trig of HC-SR04
#define beepPin 0 // attach pin D4 Arduino to beep

// defines variables
long duration; // variable for the duration of sound wave travel
int distance; // variable for the distance measurement

//void myTone(byte pin, uint16_t frequency, uint16_t duration)
//{ // input parameters: Arduino pin number, frequency in Hz, duration in milliseconds
//  unsigned long startTime=millis();
//  unsigned long halfPeriod= 1000000L/frequency/2;
//  pinMode(pin,OUTPUT);
//  while (millis()-startTime< duration)
//  {
//    digitalWrite(pin,HIGH);
//    delayMicroseconds(halfPeriod);
//    digitalWrite(pin,LOW);
//    delayMicroseconds(halfPeriod);
//  }
//  pinMode(pin,INPUT);
//}

void setup() {
  pinMode(trigPin, OUTPUT); // Sets the trigPin as an OUTPUT
  pinMode(echoPin, INPUT); // Sets the echoPin as an INPUT
  pinMode(beepPin, OUTPUT); // Sets the beepPin as an OUTPUT
}
void loop() {
  
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2; // Speed of sound wave divided by 2 (go and back)

//  digitalWrite(beepPin, HIGH);
//  delay(distance);
//  digitalWrite(beepPin, LOW);
//  delay(distance);

  if (distance < 3){
    digitalWrite(beepPin, HIGH);
    delay(30);
    digitalWrite(beepPin, LOW);
    delay(20);
  }
  else{
    if (distance < 5){
      digitalWrite(beepPin, HIGH);
      delay(50);
      digitalWrite(beepPin, LOW);
      delay(50);
    }
    else{
      if (distance < 10){
        digitalWrite(beepPin, HIGH);
        delay(50);
        digitalWrite(beepPin, LOW);
        delay(80);
      }
      else{
        if (distance < 20){
        digitalWrite(beepPin, HIGH);
        delay(50);
        digitalWrite(beepPin, LOW);
        delay(120);
      }
        }
    }
  }
 }