#include <SoftwareSerial.h>
#define ARDUINO_RX 5//should connect to TX of the Serial MP3 Player module
#define ARDUINO_TX 6//connect to RX of the module
SoftwareSerial mySerial(ARDUINO_RX, ARDUINO_TX);
static int8_t Send_buf[8] = {0} ;

#define CMD_SEL_DEV 0X09
#define DEV_TF 0X02
#define CMD_PLAY_W_VOL 0X22
#define CMD_PLAY 0X0D
#define CMD_PAUSE 0X0E
#define CMD_PREVIOUS 0X02
#define CMD_NEXT 0X01


void setup()
{
    mySerial.begin(9600);
          Serial.begin(9600);
      delay(500);//Wait chip initialization is complete
      sendCommand(CMD_SEL_DEV, DEV_TF);//select the TF card 
      delay(200);//wait for 200ms
      sendCommand(CMD_PLAY_W_VOL, 0X1E01);//play the first song with volume 30 class
}
String str;
void loop() {
if(Serial.available())
{
str = Serial.readStringUntil('\n');


if(str == "2")
{
sendCommand(CMD_PLAY_W_VOL, 0X1E02);//play the second track with volume 30 class
Serial.println("Second sound track.");
}
if(str == "3")
{
sendCommand(CMD_PLAY_W_VOL, 0X1E03);//play the third track with volume 30 class
Serial.println("Third sound track.");
}
if(str == "4")
{
sendCommand(CMD_PLAY_W_VOL, 0X1E04);//play the forth track with volume 30 class
Serial.println("Forth sound track.");
}
if(str == "ps")
{
sendCommand(CMD_PAUSE, 0X0E);//pause the playing track
Serial.println("Pause");
}
if(str == "pl")
{
sendCommand(CMD_PLAY, 0X0D);//play it again
Serial.println("Play");
}
if(str == "pr")
{
sendCommand(CMD_PREVIOUS, 0X02);//play previous track
Serial.println("Playing previous track.");
}
if(str == "nx")
{
sendCommand(CMD_NEXT, 0X01);//play next track
Serial.println("Playing next track.");
}
 }
}


void sendCommand(int8_t command, int16_t dat)
{
  delay(20);
  Send_buf[0] = 0x7e; //starting byte
  Send_buf[1] = 0xff; //version
  Send_buf[2] = 0x06; //the number of bytes of the command without starting byte and ending byte
  Send_buf[3] = command; //
  Send_buf[4] = 0x00;//0x00 = no feedback, 0x01 = feedback
  Send_buf[5] = (int8_t)(dat >> 8);//datah
  Send_buf[6] = (int8_t)(dat); //datal
  Send_buf[7] = 0xef; //ending byte
  for(uint8_t i=0; i<8; i++)//
  {
    mySerial.write(Send_buf[i]) ;
  }
}

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Description of our code:

*no specific libraries need to be downloaded for this code

The first part of our code is just defining everything such as our commands and getting the code ready for execution. Then we get into the void setup which is setting the data rate of our serial monitor as well as initializing the external parts of the Arduino such as the chip. Then we get into the commands themselves. All of these commands are put into a loop so that the user can click and listen to the audio cue as many times as needed. Those strings are then used to play the audio once they are typed. Finally, the last part of our project is the buffers. Buffers are what you save your arrays of data on. These are basically acting as cabinets that are holding all of our two-dimensional data that the code is working based on. It takes the data on our Micro SD card and arranges it. 

Mistakes to watch out for:

A mistake that we realized that caused the speakers to not play the command was the Arduino RX and TX pins. Whilst connecting these please be careful that the RX on the serial mp3 player is connected to the TX on the Arduino Uno(whatever button you set it to for us the RX was hole 5 and the TX was hole 6 ).