GND and VCC are 12V power supply Using TI amp TPA6132,better sound quality GND and BAT are powered by a 3.7V lithium battery With call function,CSR8645 low power consumption, power on the boot,the default volume of the largest OUTL,AGND,OUTR for the balanced output,can be directly connected headphones,amplifiers,audio and other input devices COM is the common side of the for key,the other end of the for key are then VOL+,VOL-, PREV,NEXT,PLY for M + and M- is the positive and negative of the microphone Can be connected at the same for time two mobile phones (the only way: boot automatically back to the chain of the final match the phone, the penultimate pair of mobile phone to be manually connected) Size:3.3x2.9cm/1.3x1.14inch Note: Please allow 1-3mm error due to manual measurement. pls make sure you do not mind before you bid Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you! Package Includes: 1x CSR8645 Amplifier board