# How your controller works

> Understand the Serin Controller hardware, firmware, smart-home apps and optional Serin Link before choosing your setup.

Source: https://serin-labs.com/controller/overview.html
Last updated: 2026-10-27

The Serin Controller sends commands and reads state through the **CN105 port inside one Mitsubishi indoor unit**. The unit still controls its own heating and cooling.

## Understand the connections

![Serin Link connects directly by wireless radio; a compatible room sensor sends readings by Bluetooth; a smart-home platform connects over the home network. The Serin Controller connects to one indoor unit by a CN105 cable carrying power and communication.](https://serin-labs.com/assets/diagrams/controller-connections.svg)

Dashed lines are wireless. [Check sensor compatibility.](https://serin-labs.com/controller/room-sensors.html) Direct Bluetooth in ESPHome requires matching sensor configuration.

Install your chosen firmware before fitting the controller. Serin Link and a smart-home app are optional; you can use either or both.

## Choose how you want to control the unit

- **ESPHome:** connect to Home Assistant.
- **HomeKit-compatible firmware:** connect to Apple Home. This optional, open-source firmware is free to install.
- **Matter-compatible firmware:** connect to Google Home, Alexa, SmartThings, Apple Home or Home Assistant.

Start with [Choose your firmware](https://serin-labs.com/controller/firmware.html) if the board is unflashed.

To use Serin Link without a smart-home app, follow [Serin Link setup](https://serin-labs.com/controller/link.html#link-only). For browser controls, open the [local web interface](https://serin-labs.com/controller/web-interface.html) once the controller has joined Wi-Fi.

## What works locally

The web interface works on your local network. A paired Serin Link can control the unit without a router or internet connection. Neither requires a Serin Labs account or subscription.

Your smart-home platform has its own hub and internet requirements for remote access, voice control and automations. Sensor dependencies are covered in [how temperature control works](https://serin-labs.com/controller/temperature.html).

## More than one indoor unit

Use one controller and cable per indoor unit, with distinct room names. The indoor units' shared outdoor-system limits still apply.