Using a Raspberry Pi 2 or 3, you can make a stereo with gps navigation, touchscreen, MP3 player, FM digital radio (no AM), bluetooth connectivity, and it can monitor the car's OBD2 computer (read and erase check engine light). The basic parts include: Raspberry Pi with sd-card, touchscreen, usb-gps, usb-digital radio reciever (rtl-sdr), bluetooth if your using a Pi 2, amplifier to power speakers, and converter to change the car's voltage to something the Pi would like. Its still being developed, but not much is left to do before its ready. Its 85% - 90% done.
Decided to reinstall Raspbian but with a newer version (Buster) and ended up with some new problems to get past, and I did. Now I'm testing it in my car and working out where to put holes in the side of the stereo for the mounting brackets and where to put the GPS and digital radio antennae. Also I need to make a "face" for the front of the stereo. I'll probably use an old plastic DVD case. Just use the front, flat part and cut holes for the screen, volume knob, and USB port. Also I noticed the sound of alternator whine when the engine is running, so I have to check my negative connection for the amp. Hopefully, I should have pics and video of the finished project soon.
I stopped working on this project for a while, but with COVID 19, I had more time. I finished most of the work on the app itself, except the bluetooth stuff, and now I just need to assemble the parts into something that can fit into the Double-Din stereo slot in my truck. I also need to figure out if the 12 volt switched power coming through the wire harness is enough for all the devices or will I have to put the amplifier on un-switched wire with a relay to make it switched too. I want everything switched. It does not need constant power like a lot of stereos do because they need the power to keep time and your radio stations saved. My stereo gets its time and date from GPS satellites and saves your info on a USB drive.
I also need to make the Raspberry Pi read-only so it can be shut off without shutting down the software. I'm going to move the home folder over to the USB stick that will hold all the media files so it can be written to. I'll probably move the /etc folder there too. Then make all the logs save to a virtual drive that gets erased every time it's shut off.