DIY Digital Shift Knob: WearOS Smartwatch in an Audi A4

Category: Automotive · DIY Maker · Reverse Engineering · WearOS
Read time: ~12 minutes

A broken smartwatch, a 3D printer, and a 2001 Audi A4. That’s what I used to create something that Tom’s Hardware and Tweakers.net (the biggest tech portal in the Netherlands) decided to cover without me even asking.

The Digital Smartwatch Shift Knob is a TicWatch Pro 3 GPS embedded inside my car’s shifter, running a WearOS app built from scratch that reads gears via the accelerometer, and even hides a media controller that no passenger will ever notice.

Here is everything: the hardware, the code, the physics, the mistakes, and what’s coming in V2.

As seen on

Table of Contents

1. The Project Nobody Expected: Saving Hardware from the Trash

The battery on my TicWatch Pro 3 GPS was completely dead. The logical option would be to throw it away. But, as a true DIY and electronics enthusiast, I decided to open the case before giving up.

What I found inside completely changed my plans. The AMOLED screen was still flawless, and the motherboard housed an IMU (Inertial Measurement Unit) sensor containing a high-precision accelerometer and gyroscope. I looked at the classic manual shifter of my 2001 Audi A4 B5 and the question was inevitable: What if I put this watch inside the shift knob to read the gears?

2. The Video Showing It All in Action

Before we dive into the math of the code and the plastic engineering, check out the final result working in the real world:

3. Hardware Extraction and Adaptation (Electronic Frankenstein)

The first major hurdle was turning a wristwatch into a reliable automotive component. The TicWatch motherboard and screen were carefully extracted using precision rotary tools.

The Battery Problem

A car in the summer reaches extremely high temperatures. Leaving a degraded lithium battery inside a shift knob under the blazing sun is asking for a fire. The solution was to bypass it—I completely removed the original battery. I used a buck converter (step-down) to draw power directly from the Audi’s 12V electrical system. The shift knob is powered continuously and safely as soon as the ignition is turned on.

4. The Brain of the Shift Knob: The WearOS Algorithm (Phase 1)

No wires connected to the clutch. No mechanical sensors. I developed a custom WearOS app from scratch called GearDetector. The system uses the smartwatch’s native accelerometer to read the exact angular position of the shifter in real time.

The Math of Shifting Gears and the Physics of Movement

I set a deadzone of 0.8G. If the tilt variation exceeds this margin, the code calculates the coordinates and determines the gear. However, an IMU sensor reads tilt based on gravity’s stationary G-vector. On hills or during hard braking, the sensor gets “tricked”.

To solve this and apply dynamic calibration, I implemented an Exponential Low-Pass Filter. The mathematical formula used in the code to smooth out the sensor noise was:

x = (0.7 × previous_x) + (0.3 × new_reading)

With this filter, sudden braking generates a quick G-force spike, but the system “ignores” the jolt and keeps the correct gear locked on the screen.

5. 3D Printing and Critical Tolerances

I designed the outer shell in Fusion 360 to hug the motherboard to the millimeter. The tolerances had to be extremely tight to ensure the glass display wouldn’t pop out during the normal jolts of spirited driving. The current prototype was printed in PLA for quick fit testing, preserving the original metal thread of the Audi shifter.

6. Phase 2: The Hidden Controls Nobody Expected

The Reddit community asked, and I delivered. I added Bluetooth touch gestures (AVRCP profile) for media control directly on the screen:

Swipe Right: Skips to the next track on Spotify.
Swipe Left: Goes back to the previous track.
Touch and Hold: Play/Pause.

I also created a Debounce Logic (Screen Lock): while the accelerometer detects a gear transition, touch is ignored, preventing accidental inputs. It is literally a hidden controller.

Update: Challenge accepted! I coded an invisible touch Spotify controller into my Audi gear shift.
by
u/Desmontei in
Audi

7. How the World Reacted: Going Viral and Press Coverage

The organic response was overwhelming. The project not only dominated TikTok and Reddit (r/Audi, r/3Dprinting), but also caught the attention of international media in over 10 countries.

Posts from the 3dprinting
community on Reddit

“An electronics, automobile, and DIY enthusiast has turned an old smartwatch into an interactive gear shift display… The vibe coded WearOS app prevented the old smartwatch from becoming eWaste.”
— Tom’s Hardware (USA)

Among the outlets that spontaneously covered the project are:

🇺🇸 Tom’s Hardware and Android Authority — two of the largest tech portals in the world
🇳🇱 Tweakers.net — the biggest tech site in the Netherlands
🇷🇺 iXBT.com and The Geek — tech leaders in Russia
🇪🇸 Motor.es and Modernet Digital — Spanish automotive and tech press
🇭🇷 Autonet Bug.hr — the largest automotive portal in Croatia
🇹🇷 TeknolojiMAG — featured in Turkish press
🇮🇳 Techlusive — coverage in India
🇺🇿 Zamin.uz — published in 8 languages in Uzbekistan
🇵🇹 Hotnews.pt — One of the biggest tech sites in Portugal

The project sparked valuable technical debates in the global community that are already shaping the development of V2.

8. Technical Specifications (V1 Summary)

Donor Hardware	TicWatch Pro 3 GPS (Motherboard + OLED Display)
Base Software	WearOS (Custom GearDetector App)
Sensors	Native Accelerometer and Gyroscope
Power Supply	Direct 12V via Buck Converter (Battery removed)
3D Printing	Material: PLA \| High tolerance
Media Control	Bluetooth AVRCP via Gestures (with debounce)