Bumpy is a DIY mp3 player based on ATMEGA32U4 @ 8MHz and VS1003 for mp3 decoding IC. It’s powered from a Li-Ion battery and Max1555 manages battery charging. TPS2112APW is used to automatically switch between USB and battery power. The design is full open source and materials costs about $58 USD for a single board.
Bumpy is a small homemade mp3 player, with features similar to an iPod shuffle. The entire design is open-source, from the firmware to the circuit board to the 3D-printed case. Bumpy plays .mp3 files off of a micro-SD card. You can load files onto the card then plug it into Bumpy, or plug Bumpy into your computer: it will show up like a flash drive (though it’s a bit slower).
Bumpy – a DIY MP3 Player based on ATMEGA32U4 – [Link]