1. Call function (support call)2. Function keys: PLAY, VOL+, VOL-, PREV, , valid at high level 1.8V. The key functions are introduced as follows:PLAY: play/pause (short press); answer the call (incoming call, short press); 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)VOL+: Volume up (short press, long press to keep volume up)VOL-: 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 flashesUSB sound card functionAlways in pairing when there is no connection, no standbyControl the mute pin MUTE of the external amplifier (with sound: output high 1.8V, no sound: output low level)Support AAC, APT-X decodingcolor: blueMaterial: PCBPackage Contents:1 x Audio ModuleOnly 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.