1. Call function (support call) 2. Function keys: PLAY, +, -, PREV, , valid at high level 1.8V. The key functions are introduced as follows: PLAY: play/pause (short press); the call (incoming call, short press); hang up (call, short press); reject (call, long press for 1S); call back (double click); re-pair (long press) 2.5S); clear the pairing list (long press 5S) +: Volume up (short press, long press to keep volume up) -: Volume down (short press, long press to keep volume down) PREV: Previous song (short press) : song (short press) LED light: pairing state, double lights flash alternately; pairing is successful, single light flashes USB sound card function Always in pairing when there is no connection, no standby Control the mute pin MUTE of the external power amplifier (with sound: output high 1.8V, no sound: output low level) Support AAC, -X decoding color: blue Material: PCB Package Contents: 1 x Audio Module Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.