NetMF MP3 Player Part 1

For one of my class projects the students build an NetMF MP3 player using a Netduino, MP3 shield, MicroSD card and some code. The first step is to learn about files, and directories by enumerating the contents of the MicroSD card.

public static void Main()
 {
    string[] musicFiles = Directory.GetFiles(@"\SD");

    foreach (string musicFile in musicFiles)
    {
       Debug.Print(musicFile);
    }
}

The NetMF implementation of GetFiles doesn’t support wildcards (unlike the full .Net Framework) so the list of files has to be manually filtered.

public static void Main()
{
   string[] musicFiles = Directory.GetFiles(@"\SD");

   foreach (string musicFile in musicFiles)
   {
      if (filePath.IndexOf(".mp3") != -1)
      {
         Debug.Print(musicFile);
      }
   }
}

The code above displayed
\SD\01 Pride (In the Name of Love).mp3
\SD\02 New Year’s Day.mp3
\SD\03 With or Without You.mp3
\SD\04 I Still Haven’t Found What I’m Looking For.mp3
\SD\05 Sunday Bloody Sunday.mp3
\SD\06 Bad.mp3
\SD\07 Where the Streets Have No Name.mp3
\SD\08 I Will Follow.mp3
\SD\09 The Unforgettable Fire.mp3
\SD\10 Sweetest Thing [The Single Mix].mp3
\SD\11 Desire.mp3
\SD\12 When Love Comes to Town.mp3
\SD\13 Angel of Harlem.mp3
\SD\14 All I Want Is You.mp3

For this project Directory.GetFiles was used (rather than Directory.EnumerateFiles) because the list files on the MicroSD will be used in other parts of the application.

The parsing and processing of file paths is important and can if done wrong can introduce hard to find issues(e.g. directory traversal attacks)

Debug.Print(musicFile .Substring( 0, musicFile.LastIndexOf(".mp3")));

Updating the code to use the built in System.IO.Path functionality

public static void Main()
{
   string[] MusicFiles = Directory.GetFiles(@"\SD");

   foreach (string musicFile in MusicFiles)
   {
      if (Path.GetExtension(musicFile) == ".mp3" )
      {
         Debug.Print(Path.GetFileNameWithoutExtension(musicFile));
      }
   }
}

The next step is to load and play the MP3 files using a provided library.

Freaduino MP3 Music Shield

For code club one of the projects I had been considering was an MP3 player with a simple user interface (UI) based on a joystick providing track next/previous , volume up/down, and pause/play. I looked for suitable Arduino shields which had Netduino driver support. I narrowed the list down to (Prices as at April 2014) these VS1053 based shields

For Code Club I purchased 5 of the Elecfreaks Freaduino shields as the price and on-board joystick made it ideal for our application. The Freaduino MP3 Shield wiki page indicated that the following pins were used by the SPI bus

D10 – Used for SPI Chip Select.
D11 – Used for SPI MOSI.
D12 – Used for SPI MISO.
D13 – Used for SPI SCK.

I initially tried the NetduinoVS1053 library from SoftElectoTech but found that no sound was produced. I tried different pin configurations, format and bitrate music files but nothing worked. I then had a look at the shield schematic and noticed that D11/D12/D13 were not connected to the VS1053, only D10 which is used for chip selected on the MicroSD card socket was connected.

I soldered some jumpers to the board and connected the SPI pins on the ICSP socket to the D11,D12 & D13 on the edge connector and the shield now works. It would be good if elecfreaks could make the pins the SPI bus uses configurable using jumpers or similar.

Modified Freaduino Music Shield

Modified Freaduino Music Shield

The library needs to be initialised with the following pins

Player = newVs1053B(Pins.GPIO_PIN_A1, Pins.GPIO_PIN_A3, Pins.GPIO_PIN_A2, Pins.GPIO_PIN_A0);

The joystick operations can be handled with Interrupts with the following configuration

InterruptPort volumeDownButton = newInterruptPort(Pins.GPIO_PIN_D7, false, Port.ResistorMode.PullUp, Port.InterruptMode.InterruptEdgeLow);

InterruptPort volumeUpButton = newInterruptPort(Pins.GPIO_PIN_D3, false, Port.ResistorMode.PullUp, Port.InterruptMode.InterruptEdgeLow);

InterruptPort nextSongButton = newInterruptPort(Pins.GPIO_PIN_D4, false, Port.ResistorMode.PullUp, Port.InterruptMode.InterruptEdgeLow);

InterruptPort previousSongButton = newInterruptPort(Pins.GPIO_PIN_D6, false, Port.ResistorMode.PullUp, Port.InterruptMode.InterruptEdgeLow);

InterruptPort playStopButton = newInterruptPort(Pins.GPIO_PIN_D5, false, Port.ResistorMode.PullUp, Port.InterruptMode.InterruptEdgeLow);

volumeUpButton.OnInterrupt += new NativeEventHandler(volumeUpButton_OnInterrupt);

volumeDownButton.OnInterrupt += new NativeEventHandler(volumeDownButton_OnInterrupt);

nextSongButton.OnInterrupt += new NativeEventHandler(nextSongButton_OnInterrupt);

previousSongButton.OnInterrupt += new NativeEventHandler(previousSongButton_OnInterrupt);

playStopButton.OnInterrupt += new NativeEventHandler(playStopButton_OnInterrupt);

I could now play MP3 files off the SD card on my Netduino Plus 2 but couldn’t adjust the volume or change the track being played. Using an interrupt based approached for the UI also highlighted some problems with the driver code which I will discuss in a future post.