Three robotic bat cars in unison

/* Title: INSTRUCTOR-SPORTSWOMAN (MONITOR-DEPORTISTA FEMENINA)
 * Voice, songs, movements advertised. MP3 player + SD
 * Valid for a series of BAT CAR robots connected by bluetooth. Change only the MACs
 * Configuere also where you find  the simbol ◄
 * Includes anofficial Real Madrid's melody (of basketball)
 * Spirals and circles
 * Reprogrammed and improved by engineer Jose Romaní. Vigo, Septiembre 2019.
 * Based on a BAT CAR robot manufactured by a detached chinese company.
 * Special buzzer melody for final stop and other modes
 * This code does not permit remote control by buttons through infrared
 */

//============================================================================
//  Comprehensive Experiment
//=============================================================================
//#include "./IRremote.h"
//==========================================
#include <SoftwareSerial.h> //first slave (peripheral) HC-06 or HM-10(BLE) of each robot
const int RX = 13; //excepcionally changed the usual order and number of pins
const int TX = 12;
SoftwareSerial Monitor(RX, TX); //"Monitor" in Spanish. "Instructor" in English
//==============================================
//for connect a robot to the following. Slave modules HM-10
String MAC_sportswoman = "606405CFC91F"; //◄ modify if necessary
//first slave (second robot) MAC "606405CFC91F", second slave (third robot): "90E2028DCE49" ) 
//Change depending on the slave (peripheral) module

unsigned int Connected = 3; //◄ = 1  Modify if necessary
//Put Connected = 3 in case of last robot of the group (not connected to another robot)
//===========================================================
//MP3
bool speaker = false; //◄ true, "speaker = false;" if the robot does not have a MP3 player
#include <DFRobotDFPlayerMini.h> //if there is not a MP3 player , is not necessary this line
SoftwareSerial serialMP3(SDA, SCL); //if there is not a MP3 player, is not necessary this line
DFRobotDFPlayerMini playerMP3; //if there is not a MP3 player, is not necessary this line
int music = 1; //for playing the first song
unsigned int volume = 30;  //0-30
//===========================================================
#define run_car        '1'
#define back_car       '2'
#define left_car       '3'
#define right_car      '4'
#define stop_car       '0'
#define back_left_car  '5'
#define back_right_car '6' 
#define circles        '7' //for potencimetre

//==============================
//Car running status enumeration
//==============================
enum {
  enSTOP = 0,
  enRUN,
  enBACK,
  enLEFT,
  enRIGHT,
  enTLEFT,
  enTRIGHT,
  enBACK_LEFT,
  enBACK_RIGHT,
  enCIRCLES //for potenciometre
} enCarState;

//==============================
//Speed control
//==============================
int control = 175;//PWM control speed

//==============================
//Set motor port
//==============================
int Left_motor_back = 9; 
int Left_motor_go = 5; 
int Right_motor_go = 6; 
int Right_motor_back = 10; 
int Right_motor_en = 8; 
int Left_motor_en = 7; 

//==============================
//Bluetooth protocol related
//==============================
int incomingByte = 0;       // Store Received Data(byte)
String inputString = "";         // Store Received Data(String)
boolean newLineReceived = false; // Previous data end flag
boolean startBit  = false;  // Protocol start flag
String returntemp = ""; // Store return data

/*Set BUZZER port*/
int BUZZER = 3;
int buzzerState = HIGH; // set the BUZZER (mute)
                        // Generally, you should use "unsigned long" for variables that hold time
                        // The value will quickly become too large for an int to store
unsigned long previousMillis = 0;   // (me)will store last time back buzzer was updated
                                    // constants won't change:
const long intervalBack = 50;  // interval at which back buzzer sounds (milliseconds)
const long intervalOff = 200;  // interval buzzer is off (milliseconds)
boolean atras = false;   // indicates the robot has gone towards back
#include "Buzzer.h" //include buzzer sounds
Buzzer buzzer(BUZZER); //buzzer object


/*Set LED port*/
int LED = 11;  // Show Bluetooth Remote Control(light on)

/*Ultrasonic Sensor*/
int Echo = A1;  // Set Echo port
int Trig = A0;  // Set Trig port
int Distance = 0;

/*Line Walking*/
const int SensorRight = A3;   	// Set Right Line Walking Infrared sensor port
const int SensorLeft = A2;     	// Set Left Line Walking Infrared sensor port
int SL;    // State of Left Line Walking Infrared sensor
int SR;    // State of Right Line Walking Infrared sensor

//State
int g_carstate = enSTOP; //  1:front 2:back 3:left 4:right 0:stop // State of vehicle running state
int g_modeSelect = 0;  // 0:remote control mode(default); 1:line walking mode ; 2: obstacle avoidance mode; 3: tracking
int g_AllState = 0;  // 0:Busy, 1:Mode selection 

/*Format string initialization*/ //Valora si borrar estas dos funiciones
int serial_putc( char c, struct __file * )
{
  Serial.write( c );
  return c;
}

void printf_begin(void)
{
  fdevopen( &serial_putc, 0 );
}

//----------------------------------------------------------------
//prepares for a connection and once the second module is on, connects automatically
void connect2Modules() //HM-10s
{
while (Connected == 1) //Wait till answare is ok. 
  {
    Monitor.print("AT");
    delay(100); //change delay according to response speed
    if (Monitor.available())
    {
      String resp1 = Monitor.readString();
      if (resp1.equals("OK"))
        Connected = 2;
    }
  }
while (Connected == 2)
  {
    Monitor.print("AT+CON" + MAC_sportswoman); //Connect HM-10 central to HM-10 peripheral MAC
    delay(100); //Wait for the response
    if (Monitor.available())
    {
      String resp2 = Monitor.readString(); //Read response
      if (resp2.equals("OK+CONNA"))
        Connected = 3; 
    }
  } 
}
//-----------------------------------------------------------------

void setup()
{ 
  //set a slave bluetooth module (managed by the app, or by another master for 2º,3º,etc robot) on this serial port
  Serial.begin(115200);  // Set Bluetooth baud rate. Must match the one of the module
  //HC-06 or HM-10. They have to be set up to 115200 baud rate

  analogReference(DEFAULT); //to 5 volts. To use as 5V output. This is not a normal use
  
  //Initialize MP3
  if (speaker) serialMP3.begin(9600); //inicializes softwareserial with the MP3 player
  if (speaker) playerMP3.begin(serialMP3); //inicialices the object player
  if (speaker) playerMP3.volume(volume); //0 to 30
  if (speaker) playerMP3.loopFolder(music); //first song 
  music++;
  
  //Initialize motor drive for output mode
  pinMode(Left_motor_go, OUTPUT);
  pinMode(Left_motor_back, OUTPUT); 
  pinMode(Right_motor_go, OUTPUT); 
  pinMode(Right_motor_back, OUTPUT); 
  pinMode(Right_motor_en, OUTPUT); 
  pinMode(Left_motor_en, OUTPUT); 

  pinMode(BUZZER, OUTPUT);// Set buzzer as output
  digitalWrite(BUZZER, buzzerState);   // set buzzer mute
  buzzer.init(); //initialize buzzer sounds
  
  pinMode(LED, OUTPUT);// Set led as output
  digitalWrite(LED, HIGH); //On led


  pinMode(Echo, INPUT);    // Set Ultrasonic echo port as input
  pinMode(Trig, OUTPUT);   // Set Ultrasonic trig port as input

  pinMode(SensorRight, INPUT); // Set Right Line Walking Infrared sensor as input
  pinMode(SensorLeft, INPUT); // Set left Line Walking Infrared sensor as input
  
  Monitor.begin(115200); // HC-05 master
 
  connect2Modules();
  
  digitalWrite(Left_motor_en, HIGH); // set left motor enable
  digitalWrite(Right_motor_en, HIGH); // set right motor enable

  //Initialize state
  g_carstate = enSTOP; // stop 
  g_modeSelect = 0;    // remote mode

  
  //Initializes the pseudo-random number generator for a delay
  randomSeed(3);//needs an unsigned long int, 3 for example

  printf_begin();
  
  if (speaker) playerMP3.advertise(1); //"monitor" wellcome
  
}

//robot follows a curve in an spiral shape
/*NOVELTY!*/
void spiral(){
  int rightWheel = 200;
  analogWrite(Right_motor_go, rightWheel); //I already do not use digitialWrite HIGH
  for (int leftWheel = 50; leftWheel <= 150; leftWheel += 5)
    {
      analogWrite(Left_motor_go, leftWheel);
      delay(250);
    }
}


void Distance_test()   // Measuring front distance
{
  digitalWrite(Trig, LOW);   // set trig port low level for 2μs
  delayMicroseconds(2);
  digitalWrite(Trig, HIGH);  // set trig port high level for 10μs(at least 10μs)
  delayMicroseconds(10);
  digitalWrite(Trig, LOW);    // set trig port low level
  float Fdistance = pulseIn(Echo, HIGH);  // Read echo port high level time(unit:μs)
  Fdistance = Fdistance / 58;    // Distance(m) =(time(s) * 344(m/s)) / 2     /****** The speed of sound is 344m/s.*******/
                                 //  ==> 2*Distance(cm) = time(μs) * 0.0344(cm/μs)
                                 // ==> Distance(cm) = time(μs) * 0.0172 = time(μs) / 58
  Distance = Fdistance;
}

void forward()     // go ahead 
{
  // right motor go ahead
  digitalWrite(Right_motor_back, LOW);
  analogWrite(Right_motor_go, control); //PWM--Pulse Width Modulation(0~255) control speed. It can be adjusted to control speed.

  // left motor go ahead
  digitalWrite(Left_motor_back, LOW);
  analogWrite(Left_motor_go, control); //PWM--Pulse Width Modulation(0~255) control speed. It can be adjusted to control speed.

}

void brake()         //stop
{
  if (atras == true) {digitalWrite(BUZZER, HIGH); atras = false;}//stops the buzzer
  
  digitalWrite(Left_motor_back, LOW);
  digitalWrite(Left_motor_go, LOW);
  digitalWrite(Right_motor_go, LOW);
  digitalWrite(Right_motor_back, LOW);
}

void left()         //turn left
{
  if (buzzerState == LOW)
  digitalWrite(BUZZER, HIGH);//Avoids buzzer couplings after going backwards
  
  // right motor go ahead
  digitalWrite(Right_motor_back, LOW);
  analogWrite(Right_motor_go, control);//control speed

  digitalWrite(Left_motor_go, LOW);  // left motor stop
  digitalWrite(Left_motor_back, LOW);
}

//I add a rotation towars back from left side
/*NOVELTY!*/
void backLeft()
{
digitalWrite(Right_motor_go, LOW);
digitalWrite(Right_motor_back, LOW);

//digitalWrite(Left_motor_go, LOW);
digitalWrite(Left_motor_back, HIGH);
analogWrite(Left_motor_back, control);

/*NOVELTY!*/
backBeep();   //we make the buzzer sound on back rotation
}

void spin_left()   //Left rotation
{
  //digitalWrite(Right_motor_go, HIGH);	// right motor go ahead
  digitalWrite(Right_motor_back, LOW);
  analogWrite(Right_motor_go, 180);

  digitalWrite(Left_motor_go, LOW);  // left motor back off
  //digitalWrite(Left_motor_back, HIGH);
  analogWrite(Left_motor_back, 180); //has to be enough speed to rotate
}

void right()       //turn right
{
  if (buzzerState == LOW)
  digitalWrite(BUZZER, HIGH);//Avoids buzzer couplings after going backwards
  
  digitalWrite(Right_motor_go, LOW);  // right motor stop
  digitalWrite(Right_motor_back, LOW);

  //digitalWrite(Left_motor_go, HIGH); // left motor go ahead
  digitalWrite(Left_motor_back, LOW);
  analogWrite(Left_motor_go, control); //PWM--Pulse Width Modulation(0~255) control speed
}

//I add a rotation backwards from the right
/*NOVELTY!*/
void backRight()
{
//digitalWrite(Right_motor_go, LOW);
digitalWrite(Right_motor_back, HIGH);
analogWrite(Right_motor_back, control);

digitalWrite(Left_motor_go, LOW);
digitalWrite(Left_motor_back, LOW);

backBeep(); //we make the buzzer sound on back rotation
}

void spin_right()        //Right rotation
{
  
  digitalWrite(Right_motor_go, LOW);  // right motor back off
  analogWrite(Right_motor_back, 180); // has to be enough speed to rotate

  digitalWrite(Left_motor_back, LOW);
  analogWrite(Left_motor_go, 180); // has to be enough espeed to rotate
}

/*NOVELTY!*/
void circle ()
{
  int slow;
  // right motor back off
  digitalWrite(Right_motor_back, LOW);
  analogWrite(Right_motor_go, control); // PWM--Pulse Width Modulation(0~255) control speed

  // left motor go ahead
  digitalWrite(Left_motor_back, LOW);
  slow = (int)(control * 2 / 3);//without decimals
  analogWrite(Left_motor_go, slow); // PWM--Pulse Width Modulation(0~255) control speed   
  //speed of left wheel is two thirds of right wheel
}


//beep with interruptible delay 
/*NOVELTY!*/
void backBeep()
{ //empieza la bocina a sonar a intervalos:
  unsigned long currentMillis = millis();
  
  if (atras == false){
        buzzerState = LOW;
        previousMillis = currentMillis; //la cuenta de intervalo comienza
        atras = true;
  }
  
  if ((currentMillis - previousMillis >= intervalBack) && (buzzerState == LOW)){ 
   
    // if the interval sounding has past 
    previousMillis = currentMillis;
    buzzerState = HIGH; //switch off
  }
  
  if (currentMillis - previousMillis >= intervalOff){
    //if interval off (a multiple of intervalBack) has past, switch on buzzer
    buzzerState = LOW; //switch on buffer
    previousMillis = currentMillis;
  }
  
  digitalWrite(BUZZER, buzzerState); //it presents the state buzzer has to have
}


void back()          //back off 
{
  digitalWrite(Right_motor_go, LOW); //right motor back off
  //digitalWrite(Right_motor_back, HIGH);
  analogWrite(Right_motor_back, control); // PWM--Pulse Width Modulation(0~255) control speed

  digitalWrite(Left_motor_go, LOW); //left motor back off
  //digitalWrite(Left_motor_back, HIGH);
  analogWrite(Left_motor_back, control); // PWM--Pulse Width Modulation(0~255) control speed
  backBeep(); //makes buzzer sound
}


/*NOVELTY!*/
/*Real Madrid's party melody*/
void madrid() 
{
  //2 spaced sounds
  digitalWrite(BUZZER, LOW);
  delay(75);
  digitalWrite(BUZZER, HIGH);
  delay(400);
  
  
  digitalWrite(BUZZER, LOW);
  delay(75);
  digitalWrite(BUZZER, HIGH);
  delay(400);

  //3 sounds
  digitalWrite(BUZZER, LOW);
  delay(50);
  digitalWrite(BUZZER, HIGH);
  delay(200);
  

  digitalWrite(BUZZER, LOW);
  delay(50);
  digitalWrite(BUZZER, HIGH);
  delay(200);
  
  digitalWrite(BUZZER, LOW);
  delay(75);
  digitalWrite(BUZZER, HIGH);
  delay(400); 
  
  //another 4 sounds
  digitalWrite(BUZZER, LOW);
  delay(50);
  digitalWrite(BUZZER, HIGH);
  delay(200);

  digitalWrite(BUZZER, LOW);
  delay(50);
  digitalWrite(BUZZER, HIGH);
  delay(200);
  
  digitalWrite(BUZZER, LOW);
  delay(50);
  digitalWrite(BUZZER, HIGH);
  delay(200); 

  digitalWrite(BUZZER, LOW);
  delay(75);
  digitalWrite(BUZZER, HIGH);
  delay(400); 

  //2 sounds
  digitalWrite(BUZZER, LOW);
  delay(50);
  digitalWrite(BUZZER, HIGH);
  delay(200);
  
  digitalWrite(BUZZER, LOW);
  delay(75);
  digitalWrite(BUZZER, HIGH);
  delay(200); 
}


//buzzer sounds for 1s to wait mode selection
void BeepOnOffMode()
{
  buzzer.playRttl(PROGRAM_FINISHED_RTTL);
  digitalWrite(BUZZER_PIN, HIGH);  //mute
}

/*Bluetooth receive*/
/*with improvements*/
void Bluetooth(void)
{
  if (newLineReceived)
  {
    
    //Determine if mode selection or not
    if (inputString[1] == 'M' && inputString[2] == 'O' && inputString[3] == 'D' && inputString[4] == 'E')
    {
      if (inputString[6] == '0') //stop
      {
        Monitor.print("$MODE 0#"); //send instruction to slave module
        g_carstate = enSTOP;
        g_modeSelect = 4; //4: no mode. It is necessary to select another mode
        g_AllState = 0; //0:Busy, 1:Mode selection
        if(speaker) playerMP3.pause(); //off MP3 player mini
        BeepOnOffMode();
        restartMusic();   
      }
      else
      {
        switch (inputString[5])//the fifth bit in the string (0:remote control mode(default); 1:line walking mode)
        {
          case '0': Monitor.print("$MODE0#");
                    g_modeSelect = 0; control = 175; break;              
          case '1': Monitor.print("$MODE1#");
                    g_modeSelect = 1; control = 100; break;
        }
        g_AllState = 0;
        BeepOnOffMode();
      }
    }
    else
      {
        if (g_modeSelect == 0)
          { 
            unsigned long pastTime; pastTime = 0; //initial time
            pastTime = millis();  
            switch (inputString[1]) //Direction
            {
              case run_car:   // stops the buzzer in case it has stayed on
                              if (atras == true) {digitalWrite(BUZZER, HIGH); atras = false;}
                              g_carstate = enRUN;
                              if (speaker) playerMP3.stopAdvertise(); //avoids overlaps
                              if (speaker) playerMP3.start(); //avoids ramdom breaks
                              if(speaker) playerMP3.advertise(2); //play "Adelante"
                              Monitor.print("$1#"); //to send the order to the following robot  
                              break; 
                              
              case back_car:  // stops the buzzer in case it has stayed on
                              if (atras == true) {digitalWrite(BUZZER, HIGH); atras = false;} 
                              g_carstate = enBACK;
                              // stops the buzzer in case it has stayed on 
                              if (speaker) playerMP3.stopAdvertise(); //avoids overlaps
                              if (speaker) playerMP3.start(); //avoids ramdom breaks
                              if(speaker) playerMP3.advertise(3); //play "Atrás"
                              Monitor.print("$2#"); //to send the order to the following robot  
                              break; 
              case left_car:  Monitor.print("$3#");
                              // stops the buzzer in case it has stayed on
                              if (atras == true) {digitalWrite(BUZZER, HIGH); atras = false;}
                              if (speaker) playerMP3.stopAdvertise(); //avoids overlaps
                              if (speaker) playerMP3.start(); //avoids ramdom breaks
                              if(speaker) playerMP3.advertise(14);
                              while ((millis()- pastTime) < 850) //waits 850ms with interruptible delay
                              {
                                int x; x = x+0;
                              }
                              //delay(850); 
                              g_carstate = enLEFT;  break;
              case right_car: Monitor.print("$4#");
                              // stops the buzzer in case it has stayed on 
                              if (atras == true) {digitalWrite(BUZZER, HIGH); atras = false;}
                              if (speaker) playerMP3.stopAdvertise(); //avoids overlaps
                              if (speaker) playerMP3.start(); //avoids ramdom breaks
                              if(speaker) playerMP3.advertise(15);
                              while ((millis()- pastTime) < 850) //waits 850ms with interruptible delay
                              {
                                int x; x = x+0;
                              } 
                              //delay(850); 
                              g_carstate = enRIGHT; break;
              case stop_car:  Monitor.print("$0#");
                              // stops the buzzer in case it has stayed on
                              if (atras == true) {digitalWrite(BUZZER, HIGH); atras = false;}
                              g_carstate = enSTOP; break; 
              case back_left_car: Monitor.print("$5#"); 
                              // stops the buzzer in case it has stayed on
                              if (atras == true) {digitalWrite(BUZZER, HIGH); atras = false;}
                              if (speaker) playerMP3.stopAdvertise(); //avoids overlaps
                              if (speaker) playerMP3.start(); //avoids ramdom breaks
                              if(speaker) playerMP3.advertise(13); 
                              while ((millis()- pastTime) < 1400) //waits 1400ms with interruptible delay
                              {
                                int x; x = x+0;
                              }
                              //delay(1400); 
                              g_carstate = enBACK_LEFT; break;
              case back_right_car: Monitor.print("$6#");
                              // stops the buzzer in case it has stayed on
                              if (atras == true) {digitalWrite(BUZZER, HIGH); atras = false;}
                              if (speaker) playerMP3.stopAdvertise(); //avoids overlaps 
                              if (speaker) playerMP3.start(); //avoids ramdom breaks
                              if(speaker) playerMP3.advertise(12);
                              while ((millis()- pastTime) < 1400) //waits 1400ms with interruptible delay
                              {
                                int x; x = x+0;
                              }
                              1; 
                              //delay(1400); 
                              g_carstate = enBACK_RIGHT; break;
              case circles:   Monitor.print("$7#");
                              g_carstate = enCIRCLES; break;
            }
            if (inputString[3] == '1') //Left rotation and madrid melody
            { 
              if (speaker) playerMP3.stopAdvertise(); //avoids overlaps
              if (speaker) playerMP3.start(); //avoids ramdom breaks
              if(speaker) playerMP3.advertise(5); //play "Giro a la izquierda" (Spanish) 
              Monitor.print("$--1#"); //send the instruction to slave robot
              spin_left();
              madrid();
              brake();
            }
            else if (inputString[3] == '2') //Right rotation and madrid melody
            {
              if (speaker) playerMP3.stopAdvertise(); //avoids overlaps
              if (speaker) playerMP3.start(); //avoids ramdom breaks
              if(speaker) playerMP3.advertise(6);  //play "Giro a la derecha" (Spanish)
              Monitor.print("$--2#"); //send instruction to slave module
              spin_right();
              madrid();
              brake();
            }
            else if (inputString[3] == '3') //Circle
            {
              Monitor.print("$--3#"); //send instruction to slave module
              if(speaker) playerMP3.advertise(10);
              circle();
              delay(2000);
              brake();
            }
            else if (inputString[3] == '4')
            {
              Monitor.print("$--4#"); //send instruction to slave module  
              if (speaker) playerMP3.advertise(11); //advertise "spiral" 0011.mp3 in folder ADVERT              
              delay(950);
              spiral();
              brake();
            }
          }
        if (inputString[5] == '1') //next song/stop
        {
          if (speaker) playNextSong(); //next song/stop. The function does not belongs to the library
        }
        if (inputString[5] == '2')
        {
          Monitor.print("$_ _ 2#"); //send instruction to slave module
          if(speaker) playerMP3.advertise(4); //"Hala Madrid" reproduction (Spanish)
          madrid();
        }
        if (inputString[7] == '1') //speed up
          {
            Monitor.print("$_ _ _ 1#"); //send instruction to slave module
            control += 20; //or 50
            if (control > 255)
            {
              control = 255;
            }
          }
        if (inputString[9] == '1') //speed reduction
          {
            Monitor.print("$_ _ _ _ 1#"); //send instruction to slave module
            control -= 20; //or 50
            if (control < 50)
            {
              control = 100;
            }
          }
        if (inputString[1] == 'D' && speaker)
        playerMP3.volumeDown();
        if (inputString[1] == 'U' && speaker)
        playerMP3.volumeUp();
        if (inputString[8] == 'P') //button hands begging emoticon
          { //We can add more functions to the button like stopping for example
            Monitor.print("$- - - -P#"); //send message to other robots
            if(speaker) playerMP3.advertise(16); //"Perdón, no era así el ejercicio. Me equivoqué" (advertise in Spanish)
          }
      }
   inputString = "";   // clear the string
   newLineReceived = false;
  }
}


//Car running control
void CarControl()
{
  switch (g_carstate)
  {
    case enSTOP: brake(); break; 
    case enRUN: forward(); break;
    case enLEFT: left(); break;
    case enRIGHT: right(); break;
    case enBACK_LEFT: backLeft(); break; //I added
    case enBACK_RIGHT: backRight(); break; //I added
    case enCIRCLES: circle(); break; //for potentiometre
    case enBACK: back(); break;
    case enTLEFT: spin_left(); break;
    case enTRIGHT: spin_right(); break;
    default: brake(); break;
  }  
}


//line walking mode. Maybe it only works at low speed
void track()
{
  /**************************************************************************************
  Infrared signal back means white undersurface ,returns low level and led lights up.
  Infrared signal gone means black undersurface ,returns high level and led lights off. 
  **************************************************************************************/
  SR = digitalRead(SensorRight);//Right Line Walking Infrared sensor against white undersurface,then LED[L2] light illuminates and while against black undersurface,LED[L2] goes off
  SL = digitalRead(SensorLeft);//Left Line Walking Infrared sensor against white undersurface,then LED[L3] light illuminates and while against black undersurface,LED[L3] goes off

  if (SL == LOW && SR == LOW) // Black lines were not detected at the same time
    {g_carstate = enRUN;   // go ahead
    //if (speaker) playerMP3.advertise(2);
    }
  else if (SL == LOW & SR == HIGH)// Left sensor against white undersurface and right against black undersurface , the car left off track and need to adjust to the right.
    {g_carstate = enRIGHT;
    //if(speaker) playerMP3.advertise(15);
    }
  else if (SR == LOW & SL ==  HIGH) // Rihgt sensor against white undersurface and left against black undersurface , the car right off track and need to adjust to the left.
    {g_carstate = enLEFT;
    //if(speaker) playerMP3.advertise(14);
    }
  else // Black lines were detected at the same time , the car stop.
    {g_carstate = enSTOP; 
    //if(speaker) playerMP3.advertise(1);
    }
    
}
  

/*main loop*/
void loop()
{
  Bluetooth();
  // Switch different mode
  if (g_AllState == 0 && g_modeSelect == 1)
    track();
  CarControl();
}

//Serial read data
void serialEvent() //only checks the serial port each time the loop is finished
{
  while (Serial.available())
  {
    incomingByte = Serial.read();   //One byte by one byte reads 
    if (incomingByte == '$')  // '$' means the start of packet.$#
    {
      startBit = true;
    }
    if (startBit == true)
    {
      inputString += (char) incomingByte;     // The received data constitutes a completed packet.
    }
    if (incomingByte == '#')    // '#' means the end of packet
    {
      newLineReceived = true;
      startBit = false;
    }
  }
}

//--------------------------------------------------------------
//MP3 new function
//to play following song, or at the end, to stop
void playNextSong()
{
  if(music == 0)
  {
    if(speaker) playerMP3.pause(); //stop music
    music++;
  }
  else
  {
    if(speaker) playerMP3.loopFolder(music); //next song
    music++;
    if(music == 4)
    music = 0;
  }
}

//begin again with the first song after final stop (scissors icon button of the app)
void restartMusic()
{
  if (speaker)
  {
  music = 1;
  playerMP3.loopFolder(music);
  music++;
  }
}