MQTT Discovery with a NodeMCU and Home Assistant
Back in November 2020, I kicked off a fascinating journey into the world of MQTT and Home Assistant, laying the groundwork for making some awesome smart devices. Let me remind you how I clearly depicted how to create a simple MQTT switch in Home Assistant. No doubt, that step-by-step guide works like a charm, but let's face it, who loves manual work anyway?
If there is anything I dread doing repeatedly, it's looking for a way to automate it. Luckily, Home Assistant doesn't disappoint - with its impressive and pretty handy MQTT discovery feature.
In this post, we'll go on a journey together! I'll reveal some tricks and hacks I've used to make the most of MQTT discovery. Also, you'll get a bonus: I'll share my Arduino program in case you're eyeing this for your projects. Sounds exciting, right?
Here is a quick rundown of the topics we'll cover:
- What is MQTT Discovery?
- How can you use MQTT Discovery on a NodeMCU?
Let's roll up our sleeves and dive right in! I believe that you will find this feature as enthralling as I have!
What is MQTT Discovery?
At its core, MQTT Discovery is simply the means to guide your MQTT broker (we use Mosquitto running inside of Home Assistant in this example) to the topics it needs to pay attention to. Sounds like a breeze, yes? Well, it is.
In one of my previous posts, I offered some valuable insight into how you can manually instruct Mosquitto to tune into a certain topic. Works perfectly, but when you have more than a handful of devices, it's safe to say the thrill wears off pretty fast.
The beauty of MQTT Discovery lies in its easy automation. Your MQTT device (an Arduino in our scenario) shoots a message to a discovery topic on the MQTT broker. This message tells it which topic to pay heed to for messages. As a result, your MQTT device pops up on the broker's radar without you breaking a sweat over manual configuration. Basically, your MQTT broker will always be in-the-know about all devices that have declared their presence - and this requires zero effort from you!
Home Assistant has an in-built discovery topic which I use quite often - MQTT discovery topic. I primarily use my MQTT devices as plant sensors, and currently, my device houses three sensors. Each sensor has a unique 'state' and logically, each requires its very own discovery topic. In my case, my discovery topics are: - homeassistant/sensor/plant_sensor_1/temperature/config - homeassistant/sensor/plant_sensor_1/humidity/config - homeassistant/sensor/plant_sensor_1/moisture/config
Imagine having to register each of these sensors manually for each MQTT device. The drudgery will not only be tiring, but you'd spend more time on configuration than genuinely enjoying the functionalities of your smart devices! With MQTT Discovery, all I do is connect the Arduino to a power source and voila! The MQTT broker instantly recognizes it and its various attendant sensors. Talk about convenience!
How can you use MQTT Discovery on an NodeMCU?
So how does it look like when you're coding MQTT Discovery on your Arduino or NodeMCU? Surprisingly, it bears a lot of similarity to the manual coding in Home Assistant. Except for a tiny twist: instead of setting up each sensor in Home Assistant, you're doing it in your Arduino program and then shipping it to Home Assistant.
I'll skip the technicalities on a few things for now:
- Wi-Fi setup in your Arduino program
- Reading Sensor data in your Arduino program
- Sending MQTT sensor data to Home Assistant
Each of these topics is worthy of its own blog post! But worry not, they're all included in the code sample for a complete picture. Enough chit-chat, let's dive into some code!
Sending the discovery message
There are two major prerequisites to sending the discovery message:
- Active Wi-Fi connection
- A correctly configured Pubsub client
You can get all the juicy details on this in the full code sample provided later. I've organized the discovery messages into functions for tidiness and to prevent intermingling with the main Arduino program.
Here's a sneak peek of the discovery message for the temperature sensor of a particular device: