Seeed xiao rp2040 with dfplayer (mp3 mudule)

Products & Technology RP2040
2

The D6/D7 serial port on the XIAO RP2040 is Serial1 and you should not use Serial.

/*
 * @file Voice Module.ino
 * @brief
 * @n [Get the module here]
 * @n This example Set the voice module volume and playback
 * @n [Connection and Diagram]()
 *
 * @copyright  [DFRobot](https://www.dfrobot.com), 2016
 * @copyright GNU Lesser General Public License
 *
 * @author [carl]([email protected])
 * @version  V1.0
 * @date  2017-11-3
 */
unsigned char order[4] = {0xAA,0x06,0x00,0xB0};


void setup() {
//Serial.begin(115200);
 Serial1.begin(9600);
 volume(0x1E);//Volume settings 0x00-0x1E
}


void loop() {
 play(0x01);//Play the specified audio:0x01-file0001
// Serial1.write(order,4);//order play
 delay(2000);
}

void play(unsigned char Track)
{
 unsigned char play[6] = {0xAA,0x07,0x02,0x00,Track,Track+0xB3};
   Serial1.write(play,6);
}
void volume( unsigned char vol)
{
  unsigned char volume[5] = {0xAA,0x13,0x01,vol,vol+0xBE};
     Serial1.write(volume,5);
 }