物联网入门之MQTT协议（一）

发布于 2025-07-28 17:00:54

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文章被收录于专栏：kali blog

MQTT是一种基于发布/订阅模式的“轻量级”通讯协议，该协议构建于TCP/IP协议上，MQTT最大优点在于，用极少的代码和有限的带宽，为连接远程设备提供实时可靠的消息服务。

PART.1
安装
我们首先在官网根据系统类型下载安装包。这里我们以Centos7为例。
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wget https://www.emqx.com/zh/downloads/enterprise/v5.5.1/emqx-enterprise-5.5.1-el7-amd64.rpm
接下来，执行下面命令进行安装。
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yum install emqx-enterprise-5.5.1-el7-amd64.rpm -y
# 源码安装
mkdir -p emqx && tar -zxvf emqx-enterprise-5.5.5-el7-amd64.tar.gz -C emqx
启动
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./emqx/bin/emqx start
访问ip:18083然后输入初始账号admin public登录。
登录后效果
PART.2
MQTT开灯/关灯
在esp8266中写入代码
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#include <ESP8266WiFi.h>
#include <PubSubClient.h>

// GPIO 5 D1
#define LED 5

// WiFi
const char *ssid = "mousse"; // Enter your WiFi name
const char *password = "qweqweqwe";  // Enter WiFi password

// MQTT Broker
const char *mqtt_broker = "broker.emqx.io";
const char *topic = "esp8266/led";
const char *mqtt_username = "emqx";
const char *mqtt_password = "public";
const int mqtt_port = 1883;

bool ledState = false;

WiFiClient espClient;
PubSubClient client(espClient);

void setup() {
    // Set software serial baud to 115200;
    Serial.begin(115200);
    delay(1000); // Delay for stability

    // Connecting to a WiFi network
    WiFi.begin(ssid, password);
    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.println("Connecting to WiFi...");
    }
    Serial.println("Connected to the WiFi network");

    // Setting LED pin as output
    pinMode(LED, OUTPUT);
    digitalWrite(LED, LOW);  // Turn off the LED initially

    // Connecting to an MQTT broker
    client.setServer(mqtt_broker, mqtt_port);
    client.setCallback(callback);
    while (!client.connected()) {
        String client_id = "esp8266-client-";
        client_id += String(WiFi.macAddress());
        Serial.printf("The client %s connects to the public MQTT broker\n", client_id.c_str());
        if (client.connect(client_id.c_str(), mqtt_username, mqtt_password)) {
            Serial.println("Public EMQX MQTT broker connected");
        } else {
            Serial.print("Failed with state ");
            Serial.print(client.state());
            delay(2000);
        }
    }

    // Publish and subscribe
    client.publish(topic, "hello emqx");
    client.subscribe(topic);
}

void callback(char *topic, byte *payload, unsigned int length) {
    Serial.print("Message arrived in topic: ");
    Serial.println(topic);
    Serial.print("Message: ");
    String message;
    for (int i = 0; i < length; i++) {
        message += (char) payload[i];  // Convert *byte to string
    }
    Serial.print(message);
    if (message == "on" && !ledState) {
        digitalWrite(LED, HIGH);  // Turn on the LED
        ledState = true;
    }
    if (message == "off" && ledState) {
        digitalWrite(LED, LOW); // Turn off the LED
        ledState = false;
    }
    Serial.println();
    Serial.println("-----------------------");
}

void loop() {
    client.loop();
    delay(100); // Delay for a short period in each loop iteration
}

线路连接。
接着，我们利用mqtt工具连接服务器，便可以实现开灯/关灯操作。