Vdo breakout

VDO Breakout

A 4-gauge breakout board for VDO automotive instruments (e.g. Vision Black), with fused 12 V distribution, sender signal routing, and PWM dimming for LED backlighting.

Overview

VDO gauges (e.g. Vision Black) terminate in 4–5 individual spade connectors, not a single harness plug: 2 or 3 for the gauge (12v power, ground, and usually a sender/sense) plus 2 for the bulb (Light+, Light−). Wiring these directly in a custom dash in place is tedious.

This board consolidates those spade connections into four gauge ports (Molex Micro-Fit) plus dedicated power and signal headers — one harness per gauge instead of a handful of loose spades.

LED backlighting does not dim with a stock rheostat alone. An ATtiny402 reads the vehicle dimmer input and PWM-switches the shared Light− return via an IRLML2502 MOSFET so LED backlights track the dash lighting level.

flowchart LR
  Rheostat["Vehicle rheostat"] --> ADC["ATtiny402 ADC"]
  ADC --> PWM["PWM output"]
  PWM --> MOSFET["Q1 MOSFET"]
  MOSFET --> LightMinus["Gauge Light−"]
  Ign12V["Ignition 12V"] --> Gauges["4× gauge connectors"]
  Gauges --> SenseHeader["Signals header"]

Features

• Individual Molex Micro-Fit 3.0 connectors for each gauge (J3–J6)
• Power input protection with mini blade fuse + 15 V TVS
• Single connector for all 4 gauge sender signals (J2)
• Rheostat input on power connector (J1)
• ATtiny402 PWM dimming on shared Light− (enables LED backlighting with rheostat-following brightness)
• UPDI programming header (J7); KiCad sources + production files in hardware/

Gauge connectors J3–J6

Molex 43650-0515 (one per gauge). PCB silk: L− L+ GND 12V S^N

J3 = Gauge 1 … J6 = Gauge 4.

Power J1

Molex 43650-0300

Dimming

Rheostat-following dimming on J1 pin 1 only works when the vehicle dimmer is wired high-side — the rheostat sits between the lighting supply and the bulbs. Brightness increases as voltage on pin 1 rises.

If the stock dimmer is low-side (between bulbs and ground), do not connect it to J1 for dimming. The voltage is inverted (full brightness ≈ 0 V, dimmest ≈ supply voltage) and indistinguishable at 0 V, where both full brightness and lights-off read ~0 V.

For low-side vehicles, add a separate potentiometer near the board, wired as a high-side divider between the lighting supply and J1 pin 1 (with GND on J1 pin 2), to dim the gauge backlights independently of the stock dash dimmer.

Signals J2

Molex 43650-0400

Program J7

2.54 mm pin header

Building the board

• Open design: hardware/VDO Breakout.kicad_pro (KiCad 10)
• BOM: hardware/production/bom.csv (LCSC part numbers included)
• Gerbers: hardware/production/VDO_Breakout.zip
• Pick-and-place: hardware/production/positions.csv

Open items:

• Fuse rating (F1) is not specified in the BOM — choose based on total gauge load.
• LDO is listed as HT75xx; confirm 5 V variant when ordering.

Firmware

PlatformIO project in firmware/. The ATtiny402 reads the vehicle dimmer on PA6 (ADC) and PWM-switches gauge Light− on PA1.

Two build profiles: ATtiny402 (incandescent fade timings) and ATtiny402_LED (faster fades for LED backlights). Program via UPDI on J7 — see the firmware README for build and flash instructions.

Repository layout

hardware/     KiCad schematic, PCB, and production outputs
firmware/     ATtiny402 dimming firmware (PlatformIO)

License

• Hardware (hardware/): CC BY-NC-SA 4.0 — non-commercial use; derivatives must use the same license.
• Firmware (firmware/): MIT

See LICENSE.md for details.

Disclaimer

This is an automotive electrical project. Use at your own risk. Verify all wiring against your vehicle and gauge documentation before connecting power.