MBox part 2 Software

14 Jan 2014

In the previous post I've described the component used to build the MBox.
In this one I'll shortly describe the software.
I've release it on github: MBox.

First some more details about hardware:

  • I've removed the multifunction button from the mp3 board cause I didn't want to use it. All interaction is performed using the keypad.
  • I've removed also the two LEDs cause I needed some more free pins for the keypad. Also cause they are useless ones the board is enclosed into the MBox case.
  • The keypad is connected to digital pins 2 to 8. You also need to build a pull up resistors circuits as one like in the data sheet.

I've started by downloading this source code and remove all the unnecessary parts. Than I've introduced some libraries:

  • The standard arduino SD library (you will find it under libraries directory of you arduino sdk installation) in order to support FAT 16 and 32.
  • Keypad library for interaction with the keypad.

The files config.h and config.cpp contain the whole configuration and initialization methods for the SPI, VS1053b(audio decoder) and keypad.

Directory Structure:
The SD card should contains 12 directories numbered from 0 to 11. Inside any directory the player expects to find files named with a consecutively number, starting by 0, plus an extensions: ".mp3" or ".wav". Here an example of a data structure:

├── 0
|   ├── 0.mp3
|   ├── 1.wav
|   └── 2.wav
├── 1
|   ├── 0.mp3
|   ├── 1.mp3
|   ├── 2.mp3
|   └── 3.mp3

The current directory and file number are stored respectively into dirN and fileN. At any iteration of the method play() the player checks if the current file exists. If yes it starts playing else restart the play list from the beginning.
It reads file data into a 32 byte buffer and transfer to the mp3 chip.
The audio decoder chip signals with a high DREQ pin, that it can receive data. For more details read the VS1053b data sheet
During the time when the audio decoder chip is busy and it cannot receive any further data we can read the status of the keypad buttons. This is done into the method AvailableProcessorTime().
If a button is pressed the current playing song is stopped by setting the playStop variable to 0.
If the button is associated to the current play list then it simply increment the fileN variable in order to point to the next file.
If the button is associated to a different play list then the new play list number is saved into dirN and the variable fileN is reset to 0.

Hope the code itself is simple and self explaining.