HomeKit-Compatible Setup

This firmware is free and open-source. You flash it yourself, then follow these steps to connect it to WiFi and add it to Apple Home. An Apple Home Hub (Apple TV or HomePod) is required for remote access and automations.

Not certified by Apple: this is not an MFi-certified HomeKit accessory.

1. Connect to Your HVAC Unit

Turn off power to your HVAC unit and open the cover to locate the CN105 connector (usually red, sometimes white).
Plug the CN105 connector into the HVAC unit and Grove connector into the device.
Place the device safely inside the unit if needed, reinstall the cover, and restore power.

The controller mounted inside a ductless mini-split indoor unit with the CN105-to-Grove cable connected

Don't have the cable yet? Grab a ready-made CN105-to-Grove cable, assembled and tested, no crimping required.

2. Connect to WiFi

On first boot (or after 5 minutes without Wi-Fi), the device creates a Wi-Fi access point:

Connect to the Serin-XXXX network (XXXX = last 4 characters of the device's WiFi address, password: serinlabs).
A setup page opens. Enter your home WiFi name and password.
- If it doesn't open automatically, go to http://192.168.4.1 in a browser.
The device saves your credentials and reboots.

Connect over USB instead (Improv Serial)

On a computer using Chrome or Edge, plug the device in over USB to set up Wi-Fi straight from this page — pick your network, enter the password, done. No hotspot needed. (Not available on phones or in Safari/Firefox, which lack Web Serial.)

Web Serial isn't available in this browser — use desktop Chrome or Edge.

3. Add to Apple Home

Option A: Scan QR Code (recommended)

In a browser, open the device's web UI at http://Serin-XXXX.local (XXXX = the suffix from Step 2). If .local doesn't resolve, use http://<device-ip> from your router.
Scan the QR code shown in the HomeKit panel with your iPhone or iPad.

Option B: Manual Setup Code

Open the Home app on your iPhone or iPad.
Tap + > Add Accessory.
Tap More options… and select Mini Split XXXX.
Enter the setup code shown in the web UI's HomeKit panel.

4. Access Web UI

The built-in web UI is reachable at http://Serin-XXXX.local or http://<device-ip>. It provides:

Thermostat control (mode, temperature, fan speed)
Vane control (vertical and wide vane positions)
Diagnostics (compressor frequency, outside temp, error codes)
Settings (device name, poll interval, temperature unit)
Real-time log streaming

5. OTA Updates

Update firmware over the air without USB access:

Check for Updates (easiest): In the web UI, open Settings > Firmware Update and tap Check for Updates. If a newer release is available, tap Install. The device downloads it, verifies the SHA256 checksum, and restarts. No manual download needed.
Manual upload: Upload a firmware .bin in the same Firmware Update section. The browser verifies integrity before uploading.
Via curl:

idf.py build
curl --data-binary @build/mitsubishi-cn105-homekit.bin \
     -H "Content-Type: application/octet-stream" \
     http://<device-ip>/upload

After an OTA update, the device validates WiFi and UART communication before confirming the new firmware. If validation fails, it automatically rolls back.

6. Troubleshooting

WiFi Recovery

Method	Details
Auto hotspot	The device creates a fallback hotspot after 5 minutes without WiFi. It turns off once WiFi reconnects.
Recovery page	Connect to the hotspot, then go to `192.168.4.1` to enter new WiFi credentials.
Button reset	Hold the board button for 10 seconds to erase stored WiFi credentials.

Re-pairing

If you need to re-pair to Apple Home, open the web UI and use the "Reset Pairing" button in the HomeKit panel, then add the device again from the Home app.

For more troubleshooting tips, see the full troubleshooting guide.

Need Help?

Check the troubleshooting guide, browse Discussions for answers, or open an issue on GitHub.

Source Code

The HomeKit-compatible firmware is open source. See the GitHub repository for protocol documentation, project structure, and build instructions.

Disclaimer

This is an independent open-source project. It is not developed, endorsed, or certified by Apple Inc. or Mitsubishi Electric Corporation. Modifying HVAC systems may void warranties and carries risks. Proceed with care. This project is provided as-is, with no warranties or liability.