ESPHome Features

The ESPHome build makes the heat pump a native Home Assistant device. The unit arrives as a climate entity, its vanes as selects, and every reading you turn on as its own sensor. Nothing leaves your network and no account is involved.

Anything tagged YAML generator is not in the flashed build. Adopt the device first, then build a config that includes it and push that over Wi-Fi. Everything else is there the moment Home Assistant finds the device.

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What lands in Home Assistant

Adopting the device creates one Home Assistant device with these entities under it. Entity IDs take the name you adopt it under, so a unit adopted as living-room gives you climate.living_room.

Entity	Domain	What it gives you
The unit itself	climate	Mode, target temperature, fan speed, and the current room reading in one thermostat card
Vertical Vane	select	Up and down airflow direction
Horizontal Vane	select	Left and right airflow direction
Led	light	The board's onboard RGB LED, yours to drive from Home Assistant. The ESPHome build gives it no status meaning of its own
Button	binary_sensor	The button on the board
Signal dB	sensor	Wi-Fi signal strength, filed under diagnostics
IP and SSID	sensor	The address it took and the network it joined
ESPHome Version	sensor	The ESPHome version it was built against

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Climate control

Auto mode drives a single target by default. Dual setpoint YAML generator splits it into separate heating and cooling thresholds, the way a conventional thermostat handles a deadband.

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Vane control

• Vertical vane: Auto, five fixed positions, and Swing. Ships in the flashed build
• Horizontal vane: five fixed positions, a split setting that throws air both ways, and Swing. Ships in the flashed build
• Swing mode on the climate entity YAML generator adds Home Assistant's own swing control beside the mode and fan pickers, on top of the two selects
• Airflow control YAML generator exposes the Even, Indirect and Direct settings on units that have them

Plenty of units have no horizontal vane. Leave it out of your config and Home Assistant stops showing a control that does nothing.

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Room temperature sensor YAML generator

A wall unit measures the air at ceiling height, right by its own return intake, which usually reads warmer than the part of the room you live in. Feeding it a reading from a thermometer at seating height is the single cheapest comfort improvement available here.

On this build the reading comes from Home Assistant. Any temperature entity it already knows about will do, whichever way that sensor got there: Zigbee, Z-Wave, Bluetooth, or another ESPHome device. Name the entity in the generator and the config wires it to the heat pump.

• Sent on change, at most every 30 seconds, so a chatty sensor does not flood the serial link
• Clamped to 1 to 40°C, the range the unit will accept. Readings outside it are dropped rather than rounded into something wrong
• Automatic fallback: if readings stop arriving for 30 minutes the unit goes back to its own sensor, and picks the remote one up again when it returns
• Fahrenheit sensors are handled by uncommenting the conversion line the generator leaves in place for them

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Heat pump diagnostics YAML generator

The unit reports far more about itself than a thermostat card has room for. Turning on diagnostics adds nine sensors, all of them recorded by Home Assistant like any other, so you get history graphs of what the heat pump is actually doing:

• Compressor frequency, which is the honest measure of how hard the system is working
• Outside air temperature, read from the outdoor unit rather than from a weather service
• Input power and energy use
• Runtime hours and heat pump connection uptime
• Stage, sub mode, and auto sub mode, the internal state that explains why the unit is doing what it is doing

The generator turns these on rather than merely adding them, so they arrive live in Home Assistant instead of sitting in the disabled list waiting to be enabled one at a time.

i-See sensor YAML generator is a separate option, for units fitted with Mitsubishi's infrared occupancy sensor. It reports as a binary sensor you can automate against.

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Extra controls YAML generator

Features that only some units have, each added as its own switch so it can go in a scene or an automation:

• Night mode: reduced fan speed and a dimmed display
• Air purifier: the unit's built-in purifier, on models fitted with one
• Circulator: fan-only circulation with no heating or cooling

There is also an ISU functions option, which exposes the installer settings stored inside the unit. Those are the same codes a technician sets from the service menu, so it is worth being deliberate about what you change.

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Serin Dial YAML generator

The ESPHome build can pair with a Serin Link, a rotary knob display that sits on a desk or nightstand and sets temperature and mode without a phone. The dial reaches the controller directly over encrypted ESP-NOW, so neither your Wi-Fi nor Home Assistant sits in the path, and the dial keeps working while either is down.

• Pair Serin Dial and Forget All Dials arrive as buttons in Home Assistant. Pairing opens a 60 second window
• Serin Dial Linked is a binary sensor, so an automation can tell whether a dial is still reporting
• The dial follows your vane selects, if the config includes them
• Wi-Fi power saving is turned off when this is enabled, because the radio has to stay awake to hear the dial

The Serin Link is still in development. The firmware ships with support for it today.

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Built-in web server

The flashed build includes ESPHome's own web server, so the controller answers in a browser at its address on your network. Mode, temperature, fan and vanes are all there, along with every entity the config defines.

That matters at two moments. Before you adopt the device, it is proof the controller is talking to the heat pump. After you adopt it, it is a way in when Home Assistant is down, restarting, or being upgraded.

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Updates and recovery

• Updates go over Wi-Fi. The USB cable is needed once, for the first flash. After that, Install in the ESPHome dashboard compiles your config and pushes it to the device
• The device introduces itself. The flashed build advertises its own config to the ESPHome dashboard, so it shows up as Discovered with an Adopt button rather than having to be added by hand
• Fallback hotspot. If it cannot reach your network it raises its own access point, named after the device, with the password serinlabs. Join it and a captive portal opens for new credentials
• Credentials over USB. The flash tool can hand the device your Wi-Fi name and password over the same cable it flashed with, so it comes up on your network on first boot

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Building your own config

Everything tagged above comes from the same place. The YAML generator assembles a complete config from the options you pick and hands it back in the browser, with nothing uploaded anywhere.

• It replaces, rather than adds to. The output is a whole config file, meant to take the place of the one the dashboard wrote when you adopted the device
• It carries your keys across. Paste in the config the dashboard generated and it reuses that device's API key and OTA password, which is what keeps Home Assistant from losing the device on the next install
• Bluetooth proxy is one of the options, turning the controller into extra Bluetooth range for Home Assistant. A thermometer reaching Home Assistant that way can then feed the heat pump through the remote sensor above
• Fahrenheit compatibility covers units that work natively in Fahrenheit, including the ones with a non-standard mapping

Open the YAML generator

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Supported boards

Board	Status
M5Stack NanoC6 (ESP32-C6)	Supported, flashable from the browser
M5Stack Atom S3 Lite (ESP32-S3)	Supported, flashable from the browser
Other ESP32 boards	Compile it yourself

The two boards above are the ones the browser flasher and the generator cover. The component underneath is ordinary ESPHome, so another ESP32 can run it, but you would write that board's own section yourself, starting with the two UART pins the CN105 cable lands on.

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Source code

Everything in this build is open source. The heat pump component is echavet's MitsubishiCN105ESPHome, and the configuration that packages it for these boards is in Serin-Labs/serin-cn105, alongside the fragments this site's generator assembles. The Serin Dial component lives in serin-link-core. What each build is made of is listed on the licenses page.

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