Скачать или смотреть Working with MQTT

MQTT CLI client mosquito as publisher and subscriber
MQTT broker mosquito and iot.eclipse.org:1883
Arduino IDE
Python simple application for publishing and subscribing with writing to SQLite DB (paho library)
Java simple application for publishing and subscribing with writing to MySQL RDBMS

Links:
MQTT topics best practices:
https://www.hivemq.com/blog/mqtt-esse...
Best practices to limit application payloads:
https://www.thethingsnetwork.org/foru...
Choose proper payload size
https://iot.stackexchange.com/questio...
Link to Python project:
https://github.com/andriy-l/Store_MQT...
Link to Java project:
https://github.com/andriy-l/sensorsan...