Make Your Own Cheap Portable MP3 Player (Part 1) | Bluetooth, USB, AUX, SD Card, FM - YouTube
No knowledge of circuits or basic electonics - MP3 player, how to make direct connection without charging the battery, what voltage adapter does it require to run : r/PCB
How to Build Your Own Portable DIY MP3 Player
DIY Pocket MP3 Player | Hackaday
DIY Portable Music Player Kits - CDM Create Digital Music