This bluetooth audio device is based on the RN-52 module. It streams music and provide the song metadata (song title, artist, ...) with A2DP and AVRCP protocols. An arduino pro mini gets the metadata and drive a display (oled i2c or can-bus "Renault's Update List display").
It can handle the HFP protocol to use it as a hands-free phone device.
I added to the PCB a small audio amplifier with a headphone jack to feed my car radio aux input. The 2nd jack is for an external microphone.
The can-bus driver and transceiver (via the arduino pro mini) are intended to drive my Renault's Update List display, but it might be used to interface the car diag connector to display car stats (speed, rpm, ...) and maybe OBD error codes (to be confirmed...).
Everything is open source hardware, so feel free to improve it, if you want!