How to Build a Bi‑directional MQTT Sensor Network with Node.js

1. Project Background

Company collaborates with a third party to develop a sensor project that can be controlled via computer or mobile phone. Because edge terminals connect to the public network wirelessly and cannot obtain a fixed IP, conventional HTTP communication is infeasible, so MQTT is chosen for bidirectional communication between the cloud platform and edge terminals.

2. Terminology

2.1 Cloud Platform

Software system deployed in the cloud for managing data and devices, interacting with edge terminals to acquire data or issue commands.

2.2 Edge Terminal

Computing device at the network edge that connects to the cloud platform and downstream to analyzers and sensors.

2.3 Analyzer

Device that receives data, connecting to edge terminals or, via wired mode, receiving sensor data from various sources.

2.4 Sensor

Device that connects to the edge terminal via wired or wireless mode to transmit parameters, or connects to the analyzer via wired mode.

3. Network Architecture

4. Code Implementation

4.1 Server Implementation

First install Node.js and the Aedes MQTT broker; installation steps are widely available.

Create a file named "server.js".

const aedes = require('aedes')();
const aedesServer = require('net').createServer(aedes.handle);
const port = 1883;

aedesServer.listen(port, function () {
    console.log('服务启动并开始监听端口：', port);
});

// Listen for client connections
aedes.on("client", (client) => {
    console.log("客户端连接成功:", client.id);
});

// Listen for client disconnects or missing heartbeat
aedes.on("clientDisconnect", (client) => {
    console.log("客户端断开连接:", client.id);
});

// Listen for published topics
aedes.on("publish", function (packet, client) {
    if (client) {
        console.log("监听客户端发过来的消息", packet.topic, packet.payload.toString());
    }
});

// Server publishes messages periodically
setInterval(() => {
    aedes.publish({
        topic: "serverMsg",
        payload: "服务器发消息",
        qos: 1,
        retain: false,
        dup: false,
        cmd: "publish"
    }, (err) => {
        if (err) {
            console.log("发布失败");
        }
    });
}, 20000);

4.2 Client Implementation

Create a file named "client.js".

The client uses mqtt.connect to establish a long‑lived connection with the server.

In practice the client may occasionally disconnect and reconnect; stability needs verification.

var mqtt = require('mqtt');

var client = mqtt.connect('mqtt://192.168.70.220:1883', {
    clientId: 'nodejs-mqtt-client'
});

client.on('connect', function () {
    console.log('连接上MQTT服务器');
    client.subscribe('serverMsg', { qos: 1 });
});

setInterval(() => {
    client.publish('topic1', 'hello mqtt client', { qos: 1 });
}, 20000);

client.on('message', function (topic, message) {
    console.log('接受服务器消息:', '主题：', topic, '消息：', message.toString());
});

4.3 Result Presentation

Two timers achieve bidirectional communication.

Server side:

Client side: