Grohe Dial

A local-first smart dial for GROHE Blue Home.

✔ Bluetooth Low Energy  ·  ✔ No Cloud  ·  ✔ Open Source  ·  ✔ Off-the-Shelf Hardware

Why it's different  ·  Hardware  ·  Quick start  ·  Architecture  ·  Roadmap

Grohe Dial replaces the phone app for the one thing you actually do ten times a day: pour water. Turn the knob to choose an amount, press to pour, watch a ring fill in real time. No phone, no app, no cloud round-trip — just a knob on your counter that does one thing perfectly.

GROHE publishes no protocol specification for the Blue Home appliance it talks to. The BLE protocol this firmware speaks was independently reverse-engineered from scratch — see Reverse engineering below — and re-implemented here as real, hardware-validated ESP-IDF C++ firmware, not a hobby sketch.

Why it's different

🔒 Local-first Talks to the appliance directly over Bluetooth Low Energy. No cloud, no vendor account, no internet connection required — ever. Unplug your router and it still pours.	🎛️ Built for the knob A round UI designed from zero around a rotary encoder — not a touchscreen app squeezed into a circle. Smooth animations, a live progress ring, one button.
💵 Real hardware, real price One off-the-shelf ESP32-C3 module, about $25, complete out of the box. No custom PCB to design, no BOM to source, no reflow oven.	🔓 Actually open MIT-licensed firmware, a from-scratch protocol write-up with a confidence rating on every field, and every non-obvious design decision explained in ARCHITECTURE.md.

See it in action

_{UI concept mockups — the frozen spec this firmware implements pixel-for-pixel. More in Screenshots.}

Hardware

Everything runs on one off-the-shelf board. No board design, no soldering, no BOM.

Module	VIEWE UEDX24240013-MD50E-B
Price	≈ $25 (at time of writing — check the listing for current pricing)
MCU	ESP32-C3 · 160 MHz · Wi-Fi + BLE 5
Display	1.28″ round IPS, 240×240, GC9A01 driver
Input	Integrated rotary encoder with push button
Assembly	Plug in USB-C. That's the whole bill of materials.

Tip

This is genuinely the entire parts list. If you can plug in a USB-C cable, you already have everything you need to build one.

Full GPIO pinout (for the board revision this firmware targets)

Function	GPIO
LCD SCLK	1
LCD MOSI/SDA	0
LCD CS	10
LCD DC	4
LCD Backlight	8
LCD Reset	none (module has no reset line)
Encoder Phase A	7
Encoder Phase B	6
Button	9

See components/board/include/board/board_config.hpp for the source of truth.

The enclosure

The module above is a bare circular board. Grohe Dial hides it inside a small 3D-printed stand — from the outside, it looks like a finished product sitting next to the tap, not a dev board on a breadboard.

No soldering. No custom PCB. Print it, drop the module in, plug in a cable.

Print files, print settings, and assembly steps live in hardware/enclosure/.

Architecture

flowchart LR
    subgraph Dial["Grohe Dial firmware"]
        direction TB
        Enc(["Rotary encoder"]) --> Ctrl["Dial controller"]
        Ctrl --> UI["Round UI — LVGL"]
        Ctrl --> BLE["BLE client"]
    end
    BLE <-->|"Bluetooth LE<br/>authenticated, HMAC-signed"| Appliance(["GROHE Blue Home"])
    Dial -.->|"optional, HTTPS"| HA(["Home Assistant"])

Loading

One composition root wires together small, single-purpose components — BLE, display, encoder, UI, time sync — with dependencies pointing strictly one way. The full component map, the BLE protocol/state-machine write-up, and the reasoning behind every non-obvious decision live in docs/ARCHITECTURE.md.

Project status

Area	Status
BLE pairing, reconnect, authenticated dispense/stop	✅ Hardware-validated
Round UI — progress ring, animations, display sleep	✅ Hardware-validated
SNTP time sync	✅ Hardware-validated
Water types — Still / Sparkling / Medium	✅ Still & Sparkling validated · Medium implemented, unconfirmed on the physical appliance
Firmware version/build metadata	✅ Implemented, build-verified
OTA firmware updates	⛔ Built, hardware-tested, then fully reverted — see ROADMAP.md
Home Assistant integration	🔜 Planned, always optional

See docs/ROADMAP.md for the complete milestone-by-milestone history, and its "v1.0 Release Criteria" section for what "done" means for this project. Nothing here is claimed as validated unless it's actually been run on real hardware.

Quick start

Note

Requires ESP-IDF v5.3 or newer (with the IDF Component Manager, bundled by default) and the board above.

. $IDF_PATH/export.sh
idf.py set-target esp32c3
idf.py build flash monitor

Important

Real appliance/Wi-Fi credentials are never committed. Copy the two *_local.hpp.example files under components/grohe_ble/ and components/time_service/ to their non-.example names and fill in your own values before building against a real appliance.

Expect a boot log that looks like this:

I (536) app: Grohe Dial
I (546) app: Firmware: v1.0.0-dev
I (546) app: Commit: ba1155f (main)
I (536) main_task: Started on CPU0

Full implemented/planned feature list

Implemented:

• BLE communication with the appliance (NimBLE), including automatic reconnect with backoff after a dropped or failed connection
• Authenticated dispense (HMAC-signed commands, ported from the reverse-engineered protocol)
• Stop dispense mid-pour
• Three water types: Still / Medium / Sparkling
• Rotary-encoder-driven round UI (amount, water type, live progress ring, connection/time status)
• Display sleep (backlight-only inactivity timeout)
• SNTP time synchronization (a one-shot Wi-Fi connection at boot; not a runtime dependency for anything else)
• Firmware version/build metadata embedded in every build, logged at boot

Planned:

• Optional Home Assistant integration — configuration, diagnostics, and appliance status (CO₂, filter, firmware version); never required for basic dispensing

Roadmap

Phase	Status
Hardware bring-up, display, input	✅ Shipped
BLE client foundation, reverse-engineered protocol	✅ Shipped
Dispense, stop, water types	✅ Shipped
Time sync, dispense UI, display sleep	✅ Shipped
Firmware version/build metadata	✅ Shipped
OTA firmware updates	⛔ Reverted
Debugging & flashing tooling	🚧 In progress
Home Assistant integration	🔜 Planned

docs/ROADMAP.md is organized as one section per milestone (M0 through M13), each with its own scope and, once complete, a hardware-validation summary — the authoritative history of how this firmware got to where it is today.

Reverse engineering

The BLE protocol this firmware speaks — service/characteristic layout, authenticated command format, response codes — was independently reverse-engineered from the official mobile app's own behavior and traffic, first in the companion grohe_blue_ble project, then documented and re-implemented from scratch as production firmware here.

This repository is the production firmware and the primary project. grohe_blue_ble remains useful on its own as a protocol reference and a Python research toolkit for anyone exploring the appliance further, but this firmware does not depend on it at build or run time.

This repository does not contain decompiled app code. What it does contain is docs/ARCHITECTURE.md: this firmware's own protocol write-up, including a per-field evidence/confidence table for every piece of appliance state it relies on. The original packet captures and reverse-engineering evidence notes live in grohe_blue_ble's own documentation.

Screenshots

UI concept

_{Design mockups, not live screen captures — the frozen spec this firmware implements. See docs/ui/ for the complete set, including the full dispense-lifecycle breakdown.}

Hardware

_{More hardware, assembly, and wiring photos are welcome — see CONTRIBUTING.md if you'd like to add yours.}

Disclaimer

This project is an independent open source project and is not affiliated with, endorsed by, or sponsored by GROHE AG.

Contributing

Issues and pull requests are welcome — see CONTRIBUTING.md for build instructions, coding style, and how to propose a change. Found a security issue instead? See SECURITY.md.

License

MIT