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• Shift to WiFi/MQTT Communication

  Tim S • 07/07/2025 at 19:46 • 0 comments

  As I've gotten deeper into home-assistant, I decided I wanted to change how my desktop control panel communicated with the PC, and other smart-home things. 

  I have reworked a lot of the code so that it no longer relies on serial communication; instead, it uses the WiFiManager library to let the user specify an SSID and password, along with some MQTT configuration. Once a connection is established to the WiFi, it tries to connect to the MQTT broker. Assuming both of those things are successful, instead of sending serial messages in response to inputs, it sends messages to topics in MQTT.

  As an added bonus, since I'm connected to WiFi anyway, it can just sync the time with NTP instead of relying on periodic serial messages to update the clock.

  Since I want to use it with Home Assistant, the first thing it communicates over MQTT is a discovery message. This lets Home Assistant identify the device, and know what inputs to expect. In this case, five timestamp sensors (one for each button), and one generic sensor that stores the last action taken via the dial. Then in Home Assistant I can listen for changes on those sensors, and perform automations accordingly.  For my setup, one of the buttons triggers an automation to toggle the lights in my office, and another toggles the fan (both are operated via smart switches).

  The remaining buttons I wanted to continue to use to trigger hotkeys on my PC. To enable this, I wrote a simple background service in python. The service, much like the device, connects to the MQTT broker and sends a discovery message. This one, however, provides several virtual "buttons" which can be pressed manually or via automations in Home Assistant. From there it is fairly trivial to set up automations to respond to changes in one of the timestamp sensors by "pressing" the appropriate virtual button.

  For the most part, the change in functionality is pretty minimal. The clock display got a minor update in the process (to include day/month), and the device can be plugged into any USB power supply, instead of needing to use a port on the PC itself. But it means that re-binding the buttons to new behaviors isn't going to require code changes/re-programming the device, just some changes to HA automations. 

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