Flexit-Button-controller

ESP32-C5 button panel for the Flexit Tradition-S ventilation unit. Replaces or parallels the original 5-button control panel with an isolated emulator that adds Wi-Fi (2.4 GHz + 5 GHz) and MQTT for smart-home integration.

The ESP32-C5 is currently one of the few cheap ESP modules with dual-band Wi-Fi 6, which lets the panel live on either band depending on your home network and signal coverage.

What it does

The board exposes 5 channels, each mirroring one button + indicator LED on the original Flexit Tradition-S panel:

• 5 button outputs drive AQY212S solid-state opto-couplers in parallel with on-board tactile switches. A short pulse on a channel looks electrically identical to a finger press, in galvanic isolation from the Flexit unit.
• 5 LED inputs read the indicator-LED state back from the panel net.

You get three ways to interact with the panel:

1. The physical tactile buttons on the PCB (works without firmware).
2. A self-served web UI (Wi-Fi setup, manual trigger, live LED dots, pulse tuning, MQTT setup).
3. MQTT — subscribe to LED state changes, publish to fire buttons.

Hardware

• Module: ESP32-C5-Mini (USB-C, dual-band Wi-Fi 6, 4 MB flash, no PSRAM)
• Isolation: 5x AQY212S solid-state relays (LED-driven MOSFET output, ~3 ms switching)
• Connector to Flexit: Micro-MaTch 2x6 (J1), carrying 5 button signals + 5 LED signals + 5 V supply + GND, mating with the cable on the back of the original Flexit panel.
• PCB: KiCad files under PCB/ (Gerbers/BOM/positions for the fab in PCB/production/).

Pin mapping (set in FW/ESP32-C5-Flexit/src/main.cpp)

Channel	Trigger out	LED in
1	IO4	IO5
2	IO3	IO6
3	IO2	IO7
4	IO1	IO8
5	IO0	IO9

Trigger outputs idle LOW and pulse HIGH for ~300 ms (configurable from the UI) to emulate a press. LED inputs are read with INPUT_PULLDOWN; the Flexit drives them HIGH when an indicator is lit.

Build & flash

Requires PlatformIO (pip install platformio or the VSCode extension).

cd FW/ESP32-C5-Flexit
pio run                       # compile
pio run -t upload             # flash via USB-C
pio device monitor -b 115200  # serial log

The C5 enumerates as /dev/ttyACM* (built-in USB Serial JTAG, no driver needed).

First-time setup

1. Power the ESP32-C5 over USB-C, or via the J1 connector once mounted.
2. With no saved Wi-Fi, the board comes up as an access point:
   • SSID: Flexit-Setup
   • Password: fibonacci
3. Join that AP and open http://192.168.4.1/ (also reachable as http://flexit.local/ via mDNS when on the same LAN).
4. In the Wi-Fi section, enter your home SSID + password and click Save & reboot. The board joins your network and is then reachable on its STA IP, or via flexit.local.

Wi-Fi credentials are stored in the ESP32 NVS and survive a reflash. Forget & reboot to AP wipes them.

Web interface

Section	What it does
Knapper	5 trigger buttons + 5 live LED indicators (polled every 400 ms).
Pulse duration	Length of the simulated button press (20–2000 ms, default 300 ms). Useful if a Flexit function requires a long-press.
MQTT	Broker host/port, optional user/password, base topic, heartbeat republish interval, live connection status, MAC-derived client ID.
Wi-Fi	SSID + password, Save & reboot into STA, Forget clears creds. Banner at top shows current STA/AP state, RSSI, IP.

Everything except Wi-Fi changes applies live without reboot.

MQTT

When the board is in STA mode (joined to your Wi-Fi) and a broker host is configured, it connects to the broker and stays connected with auto-reconnect and a Last Will. With base topic flexit (default — configurable in the UI):

Topic	Direction	Payload	Notes
flexit/led/1..5/state	publish	ON / OFF	Retained. Sent on every transition; also republished periodically if heartbeat > 0.
flexit/sw/1..5/trigger	subscribe	any (optional <ms>)	Any payload triggers a pulse on that channel. A numeric payload overrides the configured pulse duration for that single trigger.
flexit/status	publish	online / offline	LWT, retained.

Client ID is flexit-<MAC> (12 hex chars from the chip's eFuse MAC) — globally unique per ESP32. Use it in your broker's ACL.

Home Assistant example

mqtt:
  binary_sensor:
    - name: "Flexit LED 1"
      state_topic: "flexit/led/1/state"
      payload_on: "ON"
      payload_off: "OFF"
    # ... repeat for 2..5
  button:
    - name: "Flexit button 1"
      command_topic: "flexit/sw/1/trigger"
    # ... repeat for 2..5

Repo layout

.
├── FW/ESP32-C5-Flexit/      PlatformIO project (Arduino framework)
│   ├── src/main.cpp         Firmware
│   └── src/index_html.h     Embedded web UI (single page)
├── PCB/                     KiCad schematic + PCB design
│   └── production/          Gerbers, BOM, positions for fab
└── knappepanel_flexit.kicad_pro

Notes & quirks

• The board has 5 on-board tactile switches in parallel with the opto outputs, and 5 indicator LEDs on the LED nets, so it doubles as a stand-alone bench panel.
• ESP32-C5 boot prints MSPI Timing: Failed to allocate dummy cacheline for PSRAM memory barrier! — harmless, the C5-Mini has no PSRAM but the SDK looks for it.
• Verified against a Flexit Tradition-S. Other Flexit models with a different button matrix or LED drive scheme may need pin or polarity changes (see LED_ACTIVE_HIGH in src/main.cpp).

License

No license set yet — treat as "all rights reserved" until one is added. Open an issue if you'd like a specific one (MIT / Apache-2.0 / CC-BY-SA for the hardware, etc.).