KEY : Button control terminal (4 button functions, additional resistance required)
MUTE: Mute control terminal (output high level 3.3V when muting, output low level during playback)
VCC: Positive 5V power supply (Lithium battery 3.7V power supply requires short circuit diode)
GND: negative power supply
L: Left channel output
R: Right channel output
Control terminal: used to control the power amplifier board. When muting, MUTE outputs a high level of 3.3V, and outputs a low level during playback.
KEY button control: This function requires additional connection of resistors and buttons.
Volume power off function: The default output is 100% volume. Press the button to control the volume increase and decrease. If the control volume is less than 15%, the volume output will be 15% after re-powering; if the control volume is greater than 15%, the original volume will remain unchanged after power-on.