Bluetooth audio for BMW with CAN-bus support for steering wheel buttons control. Supported cars should be E90, E91, E92, E93, E82, E81, (also probably 5, 7-series, maybe E46).

Features:

• Next / Previous - (CAN-bus) steering buttons
• OTA over Wi-Fi (hold Volume Down and Previous Song buttons on the steering to go into Dwonload mode)
  
• Other possibilities that you can develop:
  • autmoatically enable heated seats if ambient tempreture is low)
  • display car info on your phone, if you make an app ;)

Hardware thingies (BOM):

• ESP8266 - (Wemos D1 mini) ($3) (they usually come with the black sockets)
• BK3254 (BT4.1 A2DP audio) - with UART enabled firmware (the ebay ones should be ok) ($2)
• MCP2515 board with some transciever ($2)
• https://oshpark.com/shared_projects/qK7vXqp4
• Audio jack PJ-320D
• (optional) resistors (2x2.2k & 2x3.3k) for level shifting for longetivity of ESP8266. You can replace them with short wire if you're on a brave side.
  
  

Solder the stuff together.

Installation:

• clone the repository and also run download_libraries.bat from /lib folder :/
• Import project to https://platformio.org/platformio-ide and flash ESP8266 using USB cable (for the first time).
• Power it with 5V cigarette charger or get Wemos power shield from ebay.
• Find K-CAN ("chasis" CAN-bus) - twisted green (CAN HIGH) and orange (CAN LOW) cables behind the radio and splice it and connect to MCP2515.
  

Some info regarding K-CAN - it is @100kbps

• https://us.autologic.com/news/bmw-instrument-cluster-lights-and-the-k-bus-failure
  
• https://www.newtis.info/tisv2/a/en/e82-123d-cou/repair-manuals/61-general-vehicle-electrical-system/2EAqiv9
• For CAN messages, refer to https://github.com/dzid26/opendbc-BMW-E8x-E9x/blob/master/bmw_e9x_e8x.dbc.

Photos: