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Once connected, sharing a reading is one call. You publish a value to a topic and the broker delivers it to subscribers.

Pick a descriptive topic path like home/garden/soil. Good names make a growing system easy to read and route.

The basic form takes a topic and a message. Both are simple strings, so MQTT does not care what is inside the payload.

A payload is a plain byte string. You decide its meaning, whether it is a number, a word, or structured data.

Sensor readings are often floats. Turn them into a string first with dtostrf or String() before you publish.

To bundle several values, format the payload as JSON. One message can carry temperature and humidity together.

Publishing thousands of times a second wastes power and bandwidth. Add a sensible interval so messages stay useful.

Use millis() instead of delay to publish every few seconds. Your device stays responsive while it waits.

Add a retain flag so the broker stores the most recent value. New dashboards then show data the instant they connect.

Give each measurement its own topic, like .../temp and .../humidity. Clean separation keeps subscribers simple.

The publish call returns true on success. Log it, or watch with a desktop MQTT client, to be sure data left the board.

You want a new dashboard to immediately show the last temperature, even before the sensor publishes again. What helps?

You learned to publish sensor data: convert values to strings, pick clear topics, time sends with millis, and retain the latest. 🎉