* 1: EQ Button. When it is playing USB/SD music, short press this button to switch between 5 kinds of EQ sound effects.
* 2: Continuous loop by default after power-on for USB/SD mode. Press this key to switch for single cycle.
* 3: STOP Button. Press this button to stop playing for USB/SD playing mode, and it will play from the first song when you press it again.
* 4: REC Button-recording button. Long press this button when USB/SD is working to record the sound of MIC port. Recording time depends on the capacity of your U disk or SD card used. When a U disk with recording files is used, press this button to switch to recording file and play recordings.
* 5: In BT/USB/SD mode, short press this button for the next song, and long press for volume +. In FM radio mode, short press the button for the next radio station, and long press it for volume +. In AUX mode, long press the button for volume +.
* 6: In BT/USB/SD mode, short press this button for the previous song, and long press for volume -. In FM radio mode, short press the button for the previous radio station, and long press for volume -. In AUX mode, long press the button for volume -.
* 7: In USB/SD mode, short press this button to stop playing. In FM radio mode, short press the button for automatic radio station search.
* 8: MODE button. Short press to switch between AUX/USB/SD/BT/FM modes. Long press the button when playing a recording file to delete the currently playing recording file.
* 9: U disk socket.
* 10: SD card slot.
* 11: LCD screen. It can display the names of Chinese and English songs. You can copy songs and the corresponding lyrics files to your U disk, and it can display the lyrics of the played songs synchronously.
* 12: FM radio antenna interface. To achieve an ideal receiving effect, it is recommended to use an antenna of 800mm/31.5" long and 22# wire in diameter.
* 13: Electric quantity display interface: (Power supply symbol does not light when the detection voltage is lower than 5.8V. One grid will flash with voltage of 5.8V-9.5V; one grid is always on with voltage of 9.5V-10.5V; two grids are always on with voltage of 10.5V-11.5V; three grids displayed when the voltage is 11.5V or above. Note that the maximum detection voltage should not exceed 22V.
* 14: AUX external signal input.
* 15: MIC recording port.
* 16: Left and right channel audio output.
* 17-18. The main board power interface should be plugged in the positive and negative directions. It should be noted that if there is a 78m05 component pasted with position 18, it means that it can work with 12V. If there is 78m05 element not pasted with position 18, it means that 5V power supply can only be used (note that it cannot be higher than 5.5V, otherwise the circuit will be damaged).
* 19: Reserved data control expansion port is used for high-level and low-level control with an power amplifier.
* 20: Reserved interface for optical fiber and coaxial function.