I'm looking for a way to play mp3's through headphones, controlled by an Arduino Uno, but using only a few pins. I know that the popular mp3 player shield needs five (specific) pins to function (www.sparkfun.com/products/10628), but I would like to play mp3's in an application where I need those pins, most importantly the PWM pins, for other functions. So I have only one PWM pin left, and 3 other non-PWM pins. Does anyone know of a solution where only a few pins are sufficient, like a mp3 player that can be controlled over a serial connection? I found this audio shield, which works that way and only needs three pins, but it is to synthesize sound rather than to play pre-recorded sounds (www.ginsingsound.com). Any help appreciated!