This is the UI to a serial mp3 player controlled by an arduino. While the user experience is cluttered by the use of the rotary encoder + button, the wiring is minimalistic.

Hardware used:

• Catalex Serial MP3 Player http://www.da-share.com/misc/catalex-mp3-board-yx5300-chip/
• Arduino Nano
• SSD1306

source code: https://github.com/tobozo/ghetto_blaster