... memory function:volume,FM frequency TF card,USB,AUX Decoder Board with FM radioStrang decoder: TF card,USB,AUX MP3 Decoder Board, pcb board ... audio, multimedia speaker, subwoofer, amplifier, electronic products and so on.-Key function: last songs, next songs, volume control, Play/pause, ... standby mode when you press this button. SD card decoder board: SW-005 TF card,USB,AUX Decoder Board with FM radio