เชื่อมต่อกับโบรกเกอร์

Before any messages flow, your device must reach a broker. It is the server that accepts connections and routes every message.

You can use a free public broker like test.mosquitto.org for learning, or run your own private one for real projects.

On ESP boards the popular choice is the PubSubClient library. Install it once, then include it at the top of your sketch.

PubSubClient needs a network client to ride on. You hand it a WiFiClient that has already joined your network.

Tell the client where the broker lives with its address and port. Plain MQTT uses port 1883 by default.

Every connection needs a unique client ID. If two devices share one, the broker kicks the older connection off.

Call connect with your client ID to log in. It returns true when the broker accepts you and false if something is wrong.

Connections die on real networks. Wrap your connect in a loop so the device keeps retrying until it is back online.

You must call client.loop() often inside loop(). It handles keepalive pings and incoming messages behind the scenes.

Private brokers usually want a username and password. Pass them to connect so only trusted devices get in.

Print the result of connect or check client.state() to debug. Clear logs save you from guessing why nothing arrives.

Your ESP32 sketch compiles but never receives messages, even though it connected once. What is the likely cause?

You connected to a broker with PubSubClient: set the server and port, used a unique client ID, and kept the link alive. 🎉