about this project FM TRANSMITTERThe car FM transmitter allows to transmit music from external devices, eg. Smartphone, tablet or other bluetooth device, connect directly to car radio. You can also play music stored on the pen or TF card by directly connecting the pen or TF card to the device. We can also access the functions of Siri/Google Assistant to answer/reject calls. Battery CollectionThe Bluetooth 5.0 adapter with USB for car cigarette lighter socket (12/24V) has a display that shows the battery voltage in real time, as well as an icon that shows the Bluetooth status (pairing/pairing) and the selected FM frequency. It is very easy to install and adjust. The package includes an instruction manual translated into Spanish that describes all the functions of the device. USB Portable Quick ReadingThe bluetooth car mp3 player has various input and output ports: QC 3.0 USB port for fast charging, pen/floppy disk USB port for playing music, USB Type C PD port for fast charging and an SD card read field. The device can automatically switch the playback mode when the USB or SD card is inserted, long press the M key to switch the mode. Hands-free functionHands-free operation is easy to use, we only need to pair the phone with the device. Pressing the center wheel once, we can answer the call, wearing it twice in a row, if we make an impression when we have an incoming call, we can reject it. If we print twice (no incoming or outgoing call), we will call the latest number, and if we leave this effect, we can access Siri or Google Voice Assistant. Improve Audio QualityNote that this device is an FM transmitter, so there must be a radio in the car. Sound quality depends largely on the FM frequency selected. The cleaner the station, without interference, the cleaner and clearer the sound will be. Continue reading the description section below to learn how to improve sound quality. The suggestions described there can solve most problems.