HiLetgo GD3300

The HiLetgo GD3300 is a UART-controlled MP3/WAV playback module.
It accepts microSD cards and supports multiple sample rates (8 kHz to 48 kHz). 
It operates at 3.2 V–5.2 V and has adjustable volume control (30 levels). 
You control it via serial commands (UART, typically 9600 bps) to play, pause, skip tracks, etc