Playing MP3 files on a Serial MP3 Player board from Catalex (YX5300 chip)
Buy the MP3 module on http://www.dx.com/p/uart-control-serial-mp3-music-player-module-for-arduino-avr-arm-pic-blue-silver-342439#.VfHyobPh5z0
Documentation and some Arduino code examples:
(Spanish) http://joanruedapauweb.com/blog/index.php/2017/02/07/arduino-serial-mp3-player-yx5300-es/
(Chinese)(Catalex_YX5300_Docs.zip files) http://pan.baidu.com/s/1hqilpB2
(English) http://www.da-share.com/misc/catalex-mp3-board-yx5300-chip/
(French) https://andrologiciels.wordpress.com/arduino/son-et-arduino/mp3/catalex-mp3-serie/
(Polish) http://www.jarzebski.pl/arduino/komponenty/modul-mp3-z-ukladem-yx5300.html