Register a new device in Homeassistant via MQTT


The example that we are going to be looking at is a light hooked up to an ESP8266 module (which comes with native support for mqtt) and turn that light on & off via Homeassistant.

I make heavy use of Docker since it’s the easiest way I know to get started with running Homeassistant and mqtt locally.

This is how you do it!

Getting Started

Folder structure

We are going to store the Homeassistant configuration in the following directory:

$ mkdir config/hass

Homassistant configuration file

In config/hass/configuration.yaml, we are going to store the following configuration which will be picked up when Homeassistant gets booted:


  broker: mqtt
  discovery: true

  - name: "Terrace Lamps"
    platform: mqtt
    command_topic: "home/terrace/light"
    payload_on: "1"
    payload_off: "0"

In here we are specifying two important things:

  • We are telling Homeassistant to create a connection with an mqtt server. The endpoint is the DNS record mqtt via the broker property, which is setup for us automatically when using docker-compose. If we were to use something else, we’d have to setup the DNS record ourselves, use a service discovery provider or punch in the IP address.

The default_config has been left blank on purpose and it’s mandatory for this example to work.

docker-compose file

Our docker-compose.yml file should look like this:

version: '3'
    image: eclipse-mosquitto

    image: homeassistant/home-assistant
    - "8123:8123"
      - ./config/hass:/config
    - mqtt

This configuration file tells docker that we want two containers:

  • One that runs mqtt based on the image eclipse-mosquitto
  • Another one that runs Homeassistant based on the image homeassistant/home-assistant

Firing things up

We can bring up both services with docker-compose like so:

$ docker-compose up

The output is somewhat lengthy but we’re interested in a couple of lines in specific which I’m going to selectively paste below:

hass_1  | 2020-01-09 00:55:46 INFO (MainThread) [homeassistant.setup] Setting up mqtt
hass_1  | 2020-01-09 00:55:46 INFO (MainThread) [homeassistant.setup] Setup of domain mqtt took 0.0 seconds.

We can see that Homeassistant is setting up the connection with our mqtt broker. Further, we can see the logs of the mqtt server acknowledging the connection from the Homeassistant container:

mqtt_1  | 1578531346: New connection from on port 1883.
mqtt_1  | 1578531346: New client connected from as auto-71016E2B-550B-AE4D-523E-A9DA0D25BD25 (p2, c1, k60).

Last, we see that Homeassistant is configuring the light that we have defined in the configuration.yaml file:

hass_1  | 2020-01-09 00:55:46 INFO (MainThread) [homeassistant.components.light] Setting up light.mqtt

Homeassistant will look through the items in that configuration.yaml configuration file and find our Terrace Lamps and map it to the home/terrace/light topic on mqtt. It also specifies the payloads for when we want to turn the thing on ("1") or off ("2"). How we handle those signals is up to the ESP8266 module that will also be listening on the topic home/terrace/light.

Accessing the GUI

Homeassistant will be listening on http://localhost:8123.
Follow the setup instructions and find the Terrace Lamps widget waiting for you on the dashboard.

You will notice that the lamps are turned off by default. You can tweak this configuration but that’s out of the scope of this article.

What we’re going to do, though, is to monitor the commands that Homeassistant will be sending to the topic on mqtt so that we can proceed later on with the implementation on the ESP8266 module for our lights.

Subscribing to the topic

Homeassistant has a tool for listening on a mqtt topic directly from the GUI. You can find that under Developer Tools -> MQTT -> Listen to a topic. Punch in the topic that we’re interested in, which is home/terrace/light and then click on the START LISTENING button.

On another tab, go to Homeassistant’s dashboard and try turning the Terrace Lamps on and off; you should see the 0s and 1s coming on the Developer Tools tab.

Another way to do this is directly from your terminal using docker:

$ docker-compose exec mqtt mosquitto_sub -t home/terrace/light

In here we subscribe to the topic directly using the mosquitto_sub tool, passing the topic that we’re interested in using the -t flag.


Registering a new device in Homeassistant via mqtt is rather trivial. There are many more settings that you can look into, though, since Homeassistant offers also in its API a way to register configuration settings for each device in the network but that’s topic for another article.

Happy hacking!

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