An integrated Android Auto retrofit system for the retracting Volvo Road and Traffic Information (RTI) navigation screen. Using a Raspberry Pi 4, custom microcontrollers, custom PCB routing, and 3D-printed mechanical enclosures, this project aims to replace the legacy navigation unit with a modern infotainment hub running LineageOS (Android).

Warning

Status: This setup faces display quality limitations when driving the original Volvo LCD screen directly due to its low resolution (typically 400x234). Replacing the internal screen panel with a high-resolution LCD while retaining the retractable motor housing is highly recommended.

🛠️ System Architecture

The retrofit consists of three key layers working in unison: vehicle bus integration (LIN), screen power/command control (RTI Serial), and the core computer (Raspberry Pi 4).

graph TD
    %% Vehicles Inputs
    SWM[Steering Wheel Module - LIN Bus] -- "LIN Frame ID 0x20" --> ATtiny[ATtiny84 Steering Controller]
    CEM[Central Electronic Module - LIN] -- "LIN Keep-Alive Ping" --> ATtiny
    
    %% ATtiny Processing
    ATtiny -- "RC-6 MCE IR Protocol (Bit-banged)" --> Pi_IR[Raspberry Pi GPIO 24 / IR Input]
    
    %% Pi Processing
    subgraph Raspberry Pi 4 [Raspberry Pi 4 - LineageOS]
        Pi_IR --> KM[KeyMapper / Input Dispatcher]
        KM -- "Volume Up Trigger > 5s LIN Idle" --> SD[OS Shutdown Command]
        Hotspot[Init Services] -- "Auto-start on Boot" --> AP[Wi-Fi AP: VolvoC70_AndroidAuto]
    end
    
    %% Screen Control
    ATmega[Arduino Screen Controller] -- "2400 Baud Serial Control" --> Screen[Volvo RTI Retractable Screen]
    Pi_Video[Raspberry Pi HDMI] -- "VGA / RGBS Video Signal" --> VideoMux[Video Mux] --> Screen
    
    classDef hardware fill:#f9f,stroke:#333,stroke-width:2px;
    classDef software fill:#bbf,stroke:#333,stroke-width:2px;
    class SWM,CEM,ATtiny,ATmega,Screen,VideoMux hardware;
    class KM,SD,Hotspot,AP software;

📁 Repository Structure

📁 Arduino/: Microcontroller firmware written for the Arduino ecosystem.
- LIN_to_IR/: Decodes Steering Wheel Module (SWM) buttons from the LIN bus and outputs RC-6 Mode 6A IR commands to control Android. Monitors LIN inactivity to signal shutdown.
- RTI_Control/: Drives the serial protocol of the Volvo retractable screen, sending commands to raise the screen, set brightness, and keep it active.
- IR_remote_test/: Test firmware for verifying RC-6 IR signal generation.
📁 Kicad/: Schematic, PCB layout, footprints, and Gerber files for a custom Raspberry Pi shield designed to host the MCP2004 LIN transceiver, video muxing, and power routing.
📁 CAD/: SolidWorks 3D CAD design files (.SLDASM, .SLDPRT) and 3D-printable .STL files for the custom mechanical Pi enclosure (case_top & case_bottom).
📁 Raspberry/: Configuration scripts and mapping files for LineageOS/Android, including custom ir-keytable mappings and key event hooks.
📁 Photos/: High-quality hardware builds, installation logs, and system diagrams.

⚙️ Detailed Module Breakdown

1. Steering Wheel Integration (`Arduino/LIN_to_IR`)

The ATtiny84 intercepts steering wheel buttons from the Steering Wheel Module (SWM) on LIN frame 0x20. These button actions are translated into bit-banged RC-6 Mode 6A (MCE Remote) signals and fed directly to the Raspberry Pi.

Button Map & Command Codes

When buttons are pressed, the ATtiny transmits the corresponding Microsoft MCE remote scancodes:

Button	LIN Frame Trigger	Active Button Code	MCE Scancode	Action on LineageOS
UP	`d0 & 0x01`	`1`	`0x800f041e`	Navigate Up
DOWN	`d0 & 0x02`	`2`	`0x800f041f`	Navigate Down
LEFT	`d0 & 0x04`	`3`	`0x800f0420`	Navigate Left
RIGHT	`d0 & 0x08`	`4`	`0x800f0421`	Navigate Right
ENTER	`d1 & 0x08`	`5`	`0x800f0422`	Select / OK
BACK	`d1 & 0x01`	`6`	`0x800f0423`	Back / Exit
Volume Up (Shutdown)	LIN Silent > 5s	`7`	`0x800f0410`	Trigger Soft Shutdown

Smart Power-down (Car-Off Detection)

To avoid battery drain, the system implements automated shutdown:

The ATtiny monitors LIN traffic. Since the car's Central Electronic Module (CEM) continuously polls the LIN bus when the ignition is on, active communication indicates the vehicle is running.
If no LIN serial data is detected for 5 seconds, the ATtiny assumes the car is off, changes state, and sends the MCE code 0x800f0410 (KEY_VOLUMEUP) 3 times to guarantee receipt.
Android intercepts this key and shuts down cleanly via the command line (reboot -p).

2. Retractable Screen Serial Driver (`Arduino/RTI_Control`)

The Volvo RTI screen requires continuous serial commands at 2400 baud over a single communication line to stay awake and raised. The screen controller script performs this keep-alive task.

Display Modes: Configurable via display mode hex codes (RGB: 0x40, PAL: 0x45, NTSC: 0x4C, Screen Off/Retract: 0x46).
Brightness Control: Employs a 16-level hex sequence (0x20 to 0x2F / 0x6E) to adjust the backlighting dynamically.

3. Raspberry Pi Customization (`Raspberry`)

Key Event Remapping

To receive the direct-wired IR signal from the ATtiny, the Pi utilizes ir-keytable with a custom mapping profile:

Configuration File: Raspberry/rc-rc6-mce.toml

Command KeyMapper Setup:

# Enable accessibility service for KeyMapper
adb shell settings put secure accessibility_enabled 1
adb shell settings put secure enabled_accessibility_services io.github.sds100.keymapper/.system.accessibility.MyAccessibilityService

# Map the Volume Up trigger to execute:
reboot -p

Wi-Fi Hotspot Auto-start at Boot

To establish wireless Android Auto on boot, a custom init script starts the Wi-Fi hotspot automatically on startup:

Boot script (/system/bin/start_hotspot.sh):

#!/system/bin/sh
while [ "$(getprop sys.boot_completed)" != "1" ]; do
    sleep 1
done
sleep 5
cmd wifi start-softap VolvoC70_AndroidAuto wpa2 123456789

Init configuration (/system/etc/init/start_hotspot.rc):

service start_hotspot /system/bin/sh /system/bin/start_hotspot.sh
    class main
    user root
    group root system wifi
    oneshot
    disabled

on property:sys.boot_completed=1
    start start_hotspot

📷 Gallery & Renderings

System Overview Diagram

Prototype Hardware

README.md

VolvoRTI — Android Auto Retrofit for Volvo RTI