#include <SoftwareSerial.h>

SoftwareSerial softSerial(5, 4); //TX_BT --> D5 / RX_BT --> D4

const int TRIGGER = 6;
const int ECHO   =  7;
const int BUZZER =  8;

long duration;
float distance;

int flag = 0;

void setup() {

  Serial.begin(9600);
  softSerial.begin(9600);
  pinMode(BUZZER, OUTPUT);
  pinMode(TRIGGER, OUTPUT);
  pinMode(ECHO, INPUT);
}

// 36 CM = EMPTY
// 30 CM = 20%  = 1
// 24 CM = 40%  = 2
// 18 CM = 60%  = 3
// 12 CM = 80%  = 4
//  6 CM = 100% = 5

void loop() {
  US();

  // 30 CM = 20%  = 1
  if (distance > 24 && distance <= 400) {
    Serial.println("1");
    softSerial.println("1");
    flag = 0;
    delay(3000);
  }

  // 24 CM = 40%  = 2
  else if (distance > 18 && distance <= 24) {
    Serial.println("2");
    softSerial.println("2");
    flag = 0;
    delay(3000);
  }

  // 18 CM = 60%  = 3
  else if (distance > 12 && distance <= 18) {
    Serial.println("3");
    softSerial.println("3");
    flag = 0;
    delay(3000);
  }

  // 12 CM = 80%  = 4
  else if (distance > 6 && distance <= 12) {
    Serial.println("4");
    softSerial.println("4");
    flag = 0;
    delay(3000);
  }

  //  6 CM = 100% = 5
  else if (distance > 0 && distance <= 6) {
    Serial.println("5");
    softSerial.println("5");
    flag = 0;
    delay(3000);
  }

  else {
    if (flag == 0) {
      softSerial.println("00");
      flag = 1;
    }
  }
  delay(100);
}// end of LOOP


void US() {
  digitalWrite(TRIGGER, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIGGER, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIGGER, LOW);
  duration = pulseIn(ECHO, HIGH);
  distance = (duration / 2) / 29.1;
  Serial.println(distance);
}