The project itself is very simple: getting push notifications via MQTT when a wireless doorbell sounds. But as [Robin Reiter] points out, as the “Hello, world!” program is a time-honore… ...

Designed by Namnam in Vietnam, the ESP32 Modbus gateway is built to communicate with PLCs and industrial sensors over Modbus ...

As for the MQTT implementation, it’s a bit clunky in my opinion. You connect with your token as your username, and the way data is associated with a particular device is via the MQTT topic.