M18:
KEY:Button control terminal (4 button functions, need to add additional resistant)
MUTE:Mute control terminal (output high level 3.3V when mute, low level when playing)
VCC:Positive power supply 5V (short circuit diode required for 3.7V lithium battery power supply)
GND:Power negative
L:Left channel output
R:Right channel output
M28:
5V:Power positive 5V
GND:Power negative
VBAT:Lithium battery positive electrode 3.7-4.2V
L:Left channel output
R:Right channel output
AGND:Audio frequency
M38:
5V: power supply positive 5V
GND: negative power supply
VBAT: Lithium battery positive electrode 3.7-4.2V
L + / L-: Left channel output (directly connected to the speaker)
R + / R-: right channel output (directly connected to the speaker)
