#include <SoftwareSerial.h>
#include <MP3Player_KT403A.h>

const int pinSW1 = 6;
SoftwareSerial mp3(2, 3);

void setup() {
  mp3.begin(9600);
  pinMode(pinSW1, INPUT_PULLUP);
  delay(100);
  SelectPlayerDevice(0x02);
  SetVolume(0x1E);
}

void loop() {
  if (!digitalRead(pinSW1)) {
    SpecifyMusicPlay(1);
    delay(500);
  }
}