Sorry for the longer than expected hold, I have been busy with personal business and another small project which is finishing up now. I'll be posting that here in the near future.

Anyways, during the hold I have been thinking about this project more and have done some work regarding it. I have decided to change the structure of this project yet again. The new plan is to use the newly released Raspberry Pi Zero in place of the previous one. The Zero will significantly reduce the cost, size, and complexity of this project. To further reduce size, I am also going to be putting all the hardware onto a single board soldered directly to the Pi. There will no longer be a need for a separate module with its own microcontroller and supporting hardware.

A small and cheap TFT LCD (like this one) will replace the expensive and bulky LCD currently in use. It will be controlled directly by the Pi, and allow for more detailed information to be shown.

Complex power management circuitry has also been made redundant after some minor changes I have made to my car. I purchased a good, basic cigarette lighter USB adaptor, which will always remain plugged in. I then modified my car's cigarette lighter jack so that it will only be powered while the car is on. I used a cheap fuse tap to tap off of a fuse that was only powered when the key is set to ACC or higher, and spliced the output to the cigarette lighter. Fortunately, no disassembly was required to get to my car's center console wiring, making the whole process very easy. Because the whole device will only be powered when the car is on, the Pi's filesystem will need to be made read-only to prevent SD card corruption.

Otherwise, basic functionality to going to stay mostly the same. Still using bluetooth and FM radio for music transmission, car statistic display will still exist, etc. The buzzer may or may not be removed, it depends on how well it cooperates with the Pi. I will be posting updates here more often now, since I have time to work on this project again.