This mp3 player actually is the second version that I've made. The circuit is quite simple. It is based on Atmega16 for processor and VS1003 for decoder.
The code is from another open source project. In the original code it supported a LCD screen, but in my edition it is deleted. From my point of view, music is for listen, not for look.
The control is quite simple, only 7 buttons without any lable on housing. It can be held in hand and the buttons can be recognized by it's relative position.
The housing is made of aluminum.