System overview
BlueBus emulates a CD changer on the I-Bus to provide:- Bluetooth audio streaming via A2DP with AAC codec support
- Hands-free telephony using the factory microphone
- Metadata display on original vehicle screens
- Full integration with vehicle controls and systems
The hardware is compatible with BMW vehicles from 1994-2010 using the I-Bus architecture, including E38, E39, E46, E52, E53, E83, E85, E86, and R50/R52/R53 MINI models.
Core specifications
Microcontroller
| Specification | Value |
|---|---|
| Model | PIC24FJ1024GA606 |
| Architecture | 16-bit |
| Clock Speed | 16 MHz |
| Flash Memory | 1 MB |
| Features | USB bootloader support, EEPROM storage |
Bluetooth module
| Specification | Value |
|---|---|
| Model | Microchip BM83 |
| Bluetooth Version | 5.0 |
| Profiles | A2DP, AVRCP, HFP |
| Codec Support | AAC |
| Paired Devices | Up to 8 devices |
Audio performance
| Specification | Value |
|---|---|
| DAC Model | PCM5122 |
| Output Level | 2.1V RMS (line-level) |
| Signal-to-Noise Ratio | 113 dB |
| Audio Outputs | Analog, S/PDIF digital |
| Amplifier | PAM8406 (5W Class-D/Class-AB) |
Power requirements
Input voltage
Operates from vehicle 12V supply via I-Bus connector
Power management
Automatic sleep mode when vehicle ignition is off
Interfaces
I-Bus connection
- Transceiver: Melexis TH3122.4
- Protocol: BMW I-Bus (low-speed K-bus variant)
- Connection: Direct to vehicle I-Bus via diagnostic connector or CD changer harness
USB interface
- Controller: FTDI FT231XS (USB to UART)
- Purpose: Firmware updates and configuration
- Connector: USB Type-B or Micro-USB (depending on hardware version)
Audio outputs
Analog output
Line-level 2.1V RMS output for DSP analog input
S/PDIF output
Digital audio via DIT4096 encoder for DSP digital input
Hardware versions
The BlueBus project includes multiple hardware revisions:- v1: Initial production hardware with core functionality
- v2: Current production hardware with improved audio chain and expanded features
All hardware versions support firmware updates via USB, ensuring compatibility with the latest features and improvements.
Environmental specifications
| Specification | Value |
|---|---|
| Operating Temperature | -20°C to +70°C (typical automotive range) |
| Storage Temperature | -40°C to +85°C |
| Humidity | Non-condensing |
| Mounting | Inside vehicle cabin |
Configuration storage
Settings are stored in non-volatile EEPROM and persist across power cycles:- Audio settings (DAC gain, DSP input source, volume offsets)
- Telephony settings (HFP mode, microphone gain)
- Comfort settings (auto-lock speed, blinker count)
- UI preferences (language, temperature units)
- Navigation preferences (auto-zoom, map mode)
Supported display units
The hardware communicates with various BMW display units:| Unit | Description | Display Type |
|---|---|---|
| BMBT | Board Monitor (Navigation) | Full graphical menus |
| MID | Multi-Information Display | 24-character single line |
| CD53 | Business CD Radio | 11-character single line |
| MIR | Multi-Information Radio | Single line display |
The hardware automatically detects the installed display unit and adapts its output accordingly.