This is a direct, local controller for Midea-UART-compatible mini-splits.
An ESP32-C6 replaces a compatible Smart Kit / Wi-Fi dongle, speaks the indoor
unit's Midea UART protocol, and exposes a standard Matter thermostat. The
Senville SENA/18HF with its SEN20-ACK1T-style Smart Kit port is the reference
build for this guide; other compatible Midea-built and rebranded units are
covered in Which mini-splits are supported.
No Home Assistant. No cloud account. No MQTT. No Wi-Fi password in source code.
I wrote this as the guide I wanted before opening the indoor unit.
Jump to: Shopping list | Wiring | Compatibility | Build and flash | Matter pairing | Troubleshooting
Your Matter controller gets current temperature, target temperature, and Off / Auto / Cool / Heat / Dry / Fan Only controls. The same Room Air Conditioner endpoint also exposes fan speed and vertical/horizontal swing. State changes from the handheld remote are reported back through Matter.
The Midea UART protocol has no dependable compressor-running signal. Heat or Cool therefore reports as active when selected; Auto, Off, Dry, and Fan-only appear idle.
This project is for Midea-UART-compatible indoor units: units with the low-voltage Smart Kit / Wi-Fi-dongle port that carries the Midea air-conditioner protocol at 9600 8N1. It is not a universal mini-split controller.
The intended, first-use target is the Senville SENA/18HF family. The bundled MideaUART package's compatibility list is explicitly incomplete, but names Midea, Electrolux, Qlima, Artel, Carrier, Comfee, Inventor, and Dimstal/Simando as supported brands. Many of those brands sell Midea-built units under their own names, so the indoor unit electronics and Smart Kit port matter more than the badge.
| Situation | Expectation |
|---|---|
| Midea-built indoor unit with the same UART Smart Kit dongle/port | Likely compatible; verify wiring and test safely. |
| A rebranded unit from one of the package's listed brands | Plausibly compatible, but not a guarantee for every model or production year. |
| A port that is actual USB, a wired-wall-thermostat bus, or another proprietary connector | Not supported by this wiring or firmware. Do not connect it until you have confirmed it is the Midea UART Smart Kit port. |
Mode, fan-speed, and swing hardware vary by indoor unit. Matter exposes the standard controls, but an option your particular head lacks may be ignored or reported differently by the unit. Start with Off, Cool, Heat, and setpoint changes; then try fan speed and each swing direction one at a time.
┌──────────────┐ Matter over Wi-Fi ┌──────────────┐ 5 V UART ┌──────────────┐
│ Matter │ ◀──────────────────────────▶ │ ESP32-C6 │ ◀─────────▶ │ Midea IDU │
│ controller │ BLE only while pairing │ ESP-Matter │ │ Smart Kit │
└──────────────┘ └──────┬───────┘ └──────────────┘
│ 3.3 V ↔ 5 V
┌──────▼───────┐
│ TXS0108E │
└──────────────┘
The Smart Kit jack looks like USB-A, but is not USB. It carries a 5 V UART link at 9600 baud. A Matter controller commissions the C6 over Bluetooth Low Energy, then passes it Wi-Fi credentials. Those credentials are stored in C6 flash and are never placed in the firmware source.
These are typical US Amazon-style prices for one controller as of August 2026; listings and multipack sizes change often. The per-build column is the useful number if a kit leaves parts over.
| Part | Buy / use | Typical purchase | Per build |
|---|---|---|---|
| Seeed Studio XIAO ESP32-C6 | One board; 4 MB flash is sufficient. | $6–12 | $6–12 |
| TXS0108E breakout | One 3.3 V ↔ 5 V UART level-shifter board. Multipacks are common. | $5–8 | $1–3 |
| Sacrificial USB-A male cable, at least 3 ft | Cut one end off, identify its conductors with a meter, and use it for the Smart Kit port. Most builders already have one. | Free | Free |
| 100–220 µF radial electrolytic capacitor | 16 V minimum; 25 V preferred. | $5–8 kit | $0.20–0.50 |
| 0.1 µF (100 nF) ceramic capacitor | 25 V minimum; 50 V preferred. | $4–7 kit | under $0.10 |
| 22 AWG stranded hookup wire and heat-shrink | Short leads make the UART happier. | $5–10 | $1–2 |
| Multimeter | Required to verify the Smart Kit 5 V and pin orientation. | $12–25 | — |
Expect roughly $14–28 in controller parts, excluding tools and an enclosure. The capacitor kits cost more up front, but the rest of the parts are useful for later builds.
The TXS0108E handles the 3.3 V ↔ 5 V UART connection between the XIAO and the indoor unit.
Disconnect power to the indoor unit before opening it. Work only on the low-voltage Smart Kit connector; do not touch mains wiring or outdoor-unit terminals.
Never plug the XIAO into a computer over USB-C while it is connected to a powered mini-split Smart Kit port. Both connections provide 5 V and can back-feed one another. Use USB-C only for flashing and recording the Matter QR code. Unplug USB-C completely before connecting the controller to the mini-split; from then on, the Smart Kit port is its only power source.
On the XIAO ESP32-C6, the UART uses D6 / GPIO16 for TX and D7 / GPIO17 for RX.
Indoor Smart Kit port TXS0108E ESP32-C6
───────────────────── ──────── ─────────
+5 V ────────┬────────────────────▶ VCCB
└───────────────────────────────────────────────────▶ XIAO 5V / VBUS
│
100–220 µF + 0.1 µF
│
GND ─────────────────────────────▶ GND ─────────────────────────▶ XIAO GND
Unit TX ───────────────────────────▶ B2 A2 ─────────────────▶ D7 / GPIO17 (RX)
Unit RX ◀─────────────────────────── B1 A1 ◀───────────────── D6 / GPIO16 (TX)
VCCA ◀───────────────────── XIAO 3V3
OE ◀───────────────────── XIAO 3V3
The two capacitors connect in parallel between XIAO 5V / VBUS and GND.
The serial signals cross: unit TX goes to ESP RX, and ESP TX goes to
unit RX. Smart Kit +5 V powers both the TXS0108E 5 V side and the XIAO's
5V / VBUS input. Never connect it to the XIAO 3V3 pin. Do not also plug
USB-C power into the XIAO unless the two supplies are isolated.
Before powering up, meter the Smart Kit port's 5 V and GND. Many Midea ports use USB-style data positions for RX/TX, but verify against the original dongle or indoor-board markings rather than trusting wire colors.
mideamatter/
├── main/ # Matter thermostat and Midea UART bridge
├── components/ # ESP-IDF component wrappers
├── CMakeLists.txt # native ESP-IDF / ESP-Matter project root
├── sdkconfig.defaults # ESP32-C6 and Matter configuration
├── README.md # this guide
└── libraries/
└── MideaUART/ # bundled Midea protocol library
The firmware uses native ESP-IDF and ESP-Matter plus the bundled MideaUART
protocol implementation. It compiles MideaUART directly for the indoor-unit
frame protocol, polling, status parsing, and control commands; this project
does not reimplement that protocol. The code in main/hvac/ is the
ESP32-C6 UART and state bridge, while main/matter/ maps that state to Matter
thermostat, fan-speed, and swing controls.
There is no Arduino runtime, HomeSpan, Home Assistant, or cloud dependency.
Install Espressif's ESP-IDF 6.x and a compatible checkout of ESP-Matter. From the project root, load the supplied environment helper:
cd mideamatter
. ./env.sh
idf.py build
idf.py -p /dev/cu.usbmodemXXXX flash
idf.py -p /dev/cu.usbmodemXXXX monitorenv.sh defaults to ESP-IDF at ~/.espressif/v6.0.2/esp-idf and ESP-Matter
at ~/esp/esp-matter. If yours are elsewhere, set ESP_IDF_EXPORT and/or
ESP_MATTER_PATH before sourcing it.
The supplied partition table reserves a 3.8 MB application partition, so use a 4 MB XIAO ESP32-C6. The build has no Arduino or PlatformIO step.
- With the mini-split not connected, power the XIAO from USB-C and open the ESP-IDF monitor at 115200 baud after flashing.
- On first boot, the log prints a manual pairing code, a Matter QR payload, and a QR-code URL. Open that URL in a browser, then print or save the QR code. You need it after USB-C is disconnected.
- Disconnect USB-C completely. Do not connect it again while the Smart Kit port is connected and powering the XIAO.
- Connect the controller to the mini-split Smart Kit port. That port now provides its only power.
- In your Matter controller, choose Add Accessory and scan the saved or printed Matter QR code (or enter the recorded manual code). The controller passes Wi-Fi credentials to the C6 over BLE; they are stored in device flash, never in this project or firmware image.
- Rename the thermostat and assign it to the right room.
For a new home or Wi-Fi network during development, run idf.py erase-flash,
flash again over USB-C only, and record the pairing code before reconnecting
the mini-split.
- Flash over USB-C and record or print the Matter QR code.
- Disconnect USB-C completely.
- With the mini-split unplugged, wire the level shifter and inspect every lead.
- Reconnect the mini-split, then connect ESP ground and UART wires.
- Wait a few seconds for MideaUART to discover the indoor unit.
- Pair from the saved/printed QR code, then test Cool, Heat, Off, and one setpoint change at a time.
- Test the handheld remote and check that the Matter controller follows it.
constexpr int HVAC_UART_RX_PIN = 17; // XIAO D7
constexpr int HVAC_UART_TX_PIN = 16; // XIAO D6
constexpr uint32_t HVAC_UART_BAUD = 9600;The mini-split target range is 17–30 °C. Your Matter controller may display that range in Fahrenheit, depending on its unit preference.
After the controller has joined Wi-Fi, open http://<controller-IP>/ from a
device on the same local network to view a rolling live log. This avoids
connecting computer USB power while the Smart Kit port powers the XIAO. The log
is kept only in RAM and is cleared on reboot. Do not expose this page to the
internet; it is intended only for local troubleshooting.
A Matter thermostat has separate heat and cool thresholds in Auto mode. The Midea indoor unit has one Auto target. This firmware maps Midea's target to the middle of Matter's required 2.5 °C comfort band:
Matter Auto: heat ───── 2.5 °C ───── cool
│
Midea Auto: target
Changing either Matter Auto threshold sends the midpoint to the mini-split. Heat and Cool are direct one-target mappings.
| Problem | What to check |
|---|---|
| Firmware is too large | Confirm the XIAO has 4 MB flash and use the supplied partition table. |
| Board resets | Check the Smart Kit 5 V rail and capacitor polarity; use a separate supply only if that rail sags. |
| Pairs but has no unit data | Re-check shared ground, crossed TX/RX, VCCA, VCCB, and OE. |
| Unit ignores commands | Verify Smart Kit pin orientation. |
| Serial link unstable | Keep UART wires short and re-check the TXS0108E power and OE wiring. |
| Matter controller says “No Response” | Check Wi-Fi and that its hub/controller is online. |
| No pairing code | Run idf.py erase-flash, flash again, and reopen the monitor at 115200. |
- Matter controllers decide how to present fan speed, swing, Dry, and Fan Only. The endpoint reports standard Matter clusters, but an individual controller may choose not to put every control on its main thermostat screen.
- This uses the indoor-unit temperature sensor, not a remote room sensor.
- This single-app partition has no OTA application slot; update by USB.