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 replaces 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 two key layers working in unison: the ATtiny84 Controller (vehicle bus decoding + screen motor control) and the core computer (Raspberry Pi 4 running Android).

graph TD
    %% Vehicles Inputs
    SWM[Steering Wheel Module - LIN Bus] -- "LIN Frame ID 0x20" --> ATtiny[ATtiny84 Controller]
    CEM[Central Electronic Module - LIN] -- "LIN Keep-Alive Ping" --> ATtiny
    
    %% ATtiny Processing & Control
    ATtiny -- "RC-6 MCE IR Protocol (Bit-banged)" --> Pi_IR[Raspberry Pi GPIO 24 / IR Input]
    ATtiny -- "2400 Baud Serial Control" --> Screen[Volvo RTI Retractable Screen]
    
    %% 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
    
    %% Video Routing
    Pi_Video[Raspberry Pi HDMI] -- "HDMI Video Signal" --> Screen
    
    classDef hardware fill:#f9f,stroke:#333,stroke-width:2px;
    classDef software fill:#bbf,stroke:#333,stroke-width:2px;
    class SWM,CEM,ATtiny,Screen hardware;
    class KM,SD,Hotspot,AP software;

📁 Repository Structure

📁 Arduino/: Microcontroller firmware written for the Arduino ecosystem.
- LIN_to_IR/: The unified controller firmware. Decodes Steering Wheel Module (SWM) buttons from the LIN bus, outputs RC-6 Mode 6A IR commands to control Android, and drives the Volvo screen motor serial interface (automatic opening/closing, toggle, and car power state detection).
- RTI_Control/: Legacy screen-only driver firmware (retains original standalone serial protocol testing logic).
- 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 hosting the MCP2004 LIN transceiver, video routing, and power control.
📁 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 & Screen Integration (`Arduino/LIN_to_IR`)

The ATtiny84 is the central hardware coordinator. It decodes steering wheel buttons from the LIN bus (0x20), controls the screen's extension motor via serial commands, and signals the Raspberry Pi using IR commands.

Core Behaviors & Logic

Startup Extension: The screen automatically opens upon startup (ignition on).
Manual Screen Toggle: Pressing BACK + ENTER at the same time toggles the screen between fully open and fully closed states.
Manual Sleep Command: Pressing RIGHT + ENTER at the same time sends a Volume Down IR command to put the Raspberry Pi to sleep.
Smart Power-down (Car-Off Detection): The ATtiny monitors LIN traffic. If no LIN communication is detected for 5 seconds, the system automatically retracts the screen and sends a Volume Up IR command 3 times to trigger a clean Raspberry Pi OS shutdown.

Button Map & Command Codes

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

Input / Combo	LIN Frame Trigger	Active Button Code	MCE Scancode	Action on LineageOS / Hardware
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
BACK + ENTER	Both buttons held	`8`	None (Local)	Toggles Screen Motor (Open/Close)
RIGHT + ENTER	Both buttons held	`9`	`0x800f0411`	Send Sleep / Volume Down

2. Retractable Screen Serial Driver

The Volvo RTI screen housing requires continuous serial packets at 2400 baud over a single communication line to stay awake and raised.

Display ON sequence: 0x4C (NTSC), 0x2F (max brightness), 0x83 (execute).
Display OFF sequence: 0x46 (OFF), 0x00 (min brightness), 0x83 (execute).
Keep-Alive Periodicity: The ATtiny84 continuously writes these 3-byte command packets at a non-blocking 100ms interval (one byte every 100ms) to ensure smooth operation without blocking LIN bus reception.

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