esp32 emqx

### ESP32 EMQX MQTT连接配置教程 #### 连接准备 为了使ESP32能够成功连接到EMQX MQTT Broker，需先完成必要的硬件和软件准备工作。确保已安装Arduino IDE，并添加了ESP32开发板支持。此外，在Arduino IDE中还需安装`PubSubClient`库用于处理MQTT协议通信[^1]。 #### WiFi连接设置 WiFi连接是建立MQTT通信的前提条件之一。下面展示了一个简单的WiFi连接函数，该函数会尝试连接指定名称和密码的无线网络： ```cpp #include <WiFi.h> const char* ssid = "your_SSID"; const char* password = "your_PASSWORD"; void setup_wifi() { delay(10); Serial.println(); Serial.print("Connecting to "); Serial.println(ssid); WiFi.begin(ssid, password); while (WiFi.status() != WL_CONNECTED) { delay(500); Serial.print("."); } randomSeed(micros()); Serial.println(""); Serial.println("WiFi connected"); Serial.println("IP address: "); Serial.println(WiFi.localIP()); } ``` 此段代码实现了基本的WiFi客户端功能，即以Station模式连接至特定SSID的Wi-Fi热点[^2]。 #### MQTT初始化与回调注册 接下来定义MQTT服务器的相关参数以及创建一个`PubSubClient`对象实例来管理订阅发布操作。同时还需要设定当收到消息时触发的动作——这里通过重写默认的消息到达事件处理器实现自定义逻辑。 ```cpp #include <PubSubClient.h> #include <WiFi.h> // Update with your network credentials const char* ssid = "your_SSID"; const char* password = "your_PASSWORD"; // Define the MQTT broker settings const char* mqtt_server = "broker.emqx.io"; // Public test server provided by EMQX #define MQTT_PORT 1883 WiFiClient espClient; PubSubClient client(espClient); void callback(char* topic, byte* payload, unsigned int length) { Serial.print("Message arrived ["); Serial.print(topic); Serial.print("] "); for (int i=0;i<length;i++) { Serial.print((char)payload[i]); } Serial.println(); // Handle message according to its content or topic here... } void reconnect() { // Loop until we're reconnected while (!client.connected()) { Serial.print("Attempting MQTT connection..."); // Attempt to connect if (client.connect("ESP32_Client")) { // Client ID can be customized as needed. Serial.println("connected"); // Once connected, publish an initial message and subscribe to topics of interest client.publish("outTopic", "hello world"); client.subscribe("inTopic"); } else { Serial.print("failed, rc="); Serial.print(client.state()); Serial.println(" try again in 5 seconds"); // Wait before retrying delay(5000); } } } void setup() { pinMode(LED_BUILTIN, OUTPUT); // Initialize the LED pin digitalWrite(LED_BUILTIN, LOW); // Turn off initially Serial.begin(115200); setup_wifi(); // Connect to Wi-Fi first. client.setServer(mqtt_server, MQTT_PORT); client.setCallback(callback); } void loop() { if (!client.connected()) { reconnect(); } client.loop(); // Publish a message every few seconds static long lastMsg = 0; const long interval = 5000; // Interval between messages (ms) if (millis() - lastMsg > interval) { lastMsg = millis(); String msg = "Hello from ESP32!"; Serial.print("Publish message: "); Serial.println(msg); client.publish("outTopic", msg.c_str()); // Toggle onboard LED each time a new message is sent out digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN)); } } ``` 上述程序展示了完整的流程：从启动WiFi模块直至向指定主题发送测试字符串为止；同时也包含了接收来自其他设备发布的通知后的响应机制[^3]。