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Hardware Setup

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github-actions[bot] edited this page May 28, 2026 · 1 revision

Hardware Setup

Components

Component Details
Microcontroller Arduino Uno (ATmega328P, 16 MHz)
Display SH1107 64×128 OLED (GME64128-02), I2C address 0x3C
Buttons 5-way navigation switch (UP/DOWN/LEFT/RIGHT/SELECT)
K-Line interface Modified KKL OBD-to-USB cable with FT232 MCU

Pinout

Arduino Uno         Function
────────────────────────────────
GND                 Ground (K-Line and display)
5V                  Power (OLED and FT232)
A4 (SDA)            OLED I2C data
A5 (SCL)            OLED I2C clock
Pin 2 (SoftTX)      K-Line TX → FT232 RXD (Software Serial)
Pin 3 (SoftRX)      K-Line RX ← FT232 TXD (Software Serial)
Pin 4               UP button (active LOW, INPUT_PULLUP)
Pin 5               DOWN button (active LOW, INPUT_PULLUP)
Pin 6               LEFT button (active LOW, INPUT_PULLUP)
Pin 7               RIGHT button (active LOW, INPUT_PULLUP)
Pin 8               SELECT button (active LOW, INPUT_PULLUP)

Hardware UART (pins 0/1) is reserved for USB serial monitoring and programming. The K-Line interface uses Software Serial on pins 2/3 to avoid conflicts.

OLED (SH1107)

SH1107 module     Arduino Uno
──────────────────────────────
VCC           →   5V
GND           →   GND
SDA           →   A4
SCL           →   A5
  • I2C address: 0x3C (default). If unresponsive, try 0x3D and update OLED_I2C_ADDR in src/display/Display.h.
  • Clock: 100 kHz (stable for 5V operation)
  • Resolution: 64×128 px, landscape → 10 columns × 16 rows text grid (6×8 px characters)

Button wiring

All five buttons wire between their Arduino pin and GND. Internal pull-ups are enabled (INPUT_PULLUP), so unpressed = HIGH, pressed = LOW.

  • 50 ms debounce for directional buttons
  • 222 ms timeout on SELECT to prevent accidental re-triggers

K-Line cable modification

The K-Line interface uses a modified KKL OBD-to-USB cable (Autodia K409 or compatible). The FT232R/FT232RQ USB-to-serial chip is repurposed as a level shifter.

Steps:

  1. Open the KKL cable connector and locate the FT232R(Q) chip.
  2. Identify TXD and RXD pins from the FT232 datasheet.
  3. Solder connections to Arduino Software Serial pins:
    • FT232 TXD → Arduino pin 3 (software serial RX)
    • FT232 RXD → Arduino pin 2 (software serial TX)
  4. Cut both PCB traces immediately after the solder points to isolate the FT232 from the OBD lines.
  5. Power the FT232 board from Arduino 5V and GND.
  6. Connect the original K-Line wire and GND from the OBD-9 connector to the FT232 board.

See assets/ in the repository for photos of the modification.

Power

Rail Draw
FT232 board ~50 mA
Arduino Uno ~30 mA
SH1107 OLED ~20 mA
Total ~150 mA

When connected to a car, use a separate power source (USB power bank or 12V buck converter) to avoid ground loop issues through the OBD port.

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