After one of my friends introduced me to the wonders of Home Assistant, I was eager to get started on it myself. I purchased a second-hand mini computer and set up a server to run Home Assistant. Together with two friends, we organized a sort of hackathon where each of us would work on our own projects. I decided to start with something simple: temperature sensors. Since I had limited experience with electrical circuits, messaging protocols, and C++, I quickly realized it was quite challenging. But that's how you learn, right?

After several prototypes, I ended up with a solution I was satisfied with. Then, I used Tinkercad to design a custom case to enclose all the electronics. One of my friends helped me by 3D printing the casings, and the end result looks like this:

I created four identical climate sensors to measure temperature and humidity throughout the apartment. For each sensor, I used a Wemos D1 mini, a small microcontroller capable of connecting to WiFi. I programmed the controller to wake up every 5 minutes and perform a series of tasks.

1. It connects to the WiFi network.
2. It reads the current temperature and humidity from the sensor.
3. It reads the battery voltage.
4. It Publishes the data (temperature, humidity, and battery voltage) to Home Assistant using the MQTT protocol.
5. It enters sleep mode for 5 minutes.

On my Home Assistant dashboard, the data is visualized as shown in the image below:

I also implemented an automation in Home Assistant to monitor the battery voltages of the climate sensors. Whenever one of the sensor's batteries is running low, I receive a push notification informing me which sensor needs to be recharged.