USB power and compatibility - The device uses a USB power input. Power can come from a portable power bank or USB charger via the mobile data cable. It can also operate from a 3.7V lithium battery with a USB 5V supply. High quality sound - Built-in 2W mono amplifier (5V input to 3W output) connected directly to the speaker. For best results, use a 4 ohm, 3W speaker. Features a gold-plated 3.5 mm headphone jack for headphones or external audio. Media playback and indicators - Supports MP3 playback with auto play on power up; red LED updates during playback. Media formats and modes - Supports U-Disk playback (tested up to 32 GB) and TF card playback (tested up to 16 GB). Use the standard TF card mode; if no TF card is present, it automatically switches to U-Disk. When both TF card and U-Disk are installed, playback mode can be set manually. See the main operating instructions for details. TF card and U-Disk playback with easy wiring - Supports TF card and U-Disk playback modes. No soldering required for wiring thanks to the terminal clamp design; modular construction makes it easy to modify.