MQTT 協定與 Modbus 通訊的遠端監控與控制系統架構

MQTT 協定與 Modbus 通訊的遠端監控與控制系統架構

這張圖片展示了一個結合 MQTT 協定與 Modbus 通訊的遠端監控與控制系統架構（主要透過 Node-RED 進行資料整合）。

系統包含三個核心部分，其運作功能說明如下：

1. ESP32 終端設備（硬體控制層）

• 硬體端： 圖片右上角是一塊 ESP32 開發板，連接到麵包板上的 LED 燈（或透過 IC 擴充的燈號輸出）。

• MQTT 訂閱與發布：

  • 接收控制： ESP32 訂閱（Subscribe）了主題 alex9ufo/ledcontrol。當收到控制指令時，硬體會據此切換 LED 的開關狀態。

  • 狀態回報： 當 LED 狀態改變或需要定時回報時，ESP32 會將當前狀態發布（Publish）到主題 alex9ufo/ledstatus。

2. MQTT Broker（訊息轉發中心）

• 功能： 位於圖片左上角，扮演中間人角色（Broker）。負責接收來自 Node-RED 或 ESP32 的訊息，並根據定義好的主題（Topic）即時轉發給訂閱該主題的設備，實現硬體端與後端系統的解耦與非同步通訊。

3. Node-RED 與 Modbus 模擬器（核心邏輯與工業通訊整合）

• Node-RED 整合中心：

  • 透過安裝 node-red-contrib-modbus 套件，Node-RED 同時與 MQTT Broker 和 Modbus 設備進行資料交換。

  • 控制流程： Node-RED 收到來自 Modbus 端的寫入指令後，會將其轉換並發布至 alex9ufo/ledcontrol 來控制 ESP32；反之，它也會訂閱 alex9ufo/ledstatus 來接收 ESP32 的狀態。

• ModbusSim（Modbus RTU/TCP 模擬器）：

  • 模擬工業自動化中常見的 PLC 或控制器設備。

  • 它與 Node-RED 之間透過本機 TCP 網路（127.0.0.1:502）進行連線。

  • Modbus coils Read / Write： Node-RED 會去讀取（Read）或寫入（Write）ModbusSim 中的線圈（Coils）或暫存器狀態，從而讓傳統的工業 Modbus 設備能夠與現代的 MQTT 物聯網架構（ESP32）進行雙向連通。

總結運作情境

這套架構的功能主要是將工業級的 Modbus 協定與物聯網的 MQTT 協定進行橋接。例如：你可以透過操作 ModbusSim 模擬器（模擬中控室的 PLC 燈號開關），讓 Node-RED 偵測到變化後透過 MQTT 去點亮遠端的 ESP32 LED 燈；同理，遠端 ESP32 的狀態也可以即時同步回傳，寫入 ModbusSim 的暫存器中顯示。

WOKWI程式

#include <WiFi.h>

#include <PubSubClient.h>

// 1. Wi-Fi 與 MQTT 設定 (Wokwi 專用模擬 Wi-Fi)

const char* ssid = "Wokwi-GUEST";

const char* password = "";

const char* mqtt_server = "mqttgo.io";

const int mqtt_port = 1883;

// MQTT 主題定義

const char* topic_control = "alex9ufo/ledcontrol";

const char* topic_status = "alex9ufo/ledstatus";

// 2. 定義 8 個 LED 的 GPIO 腳位

const int ledPins[8] = { 25, 26, 27, 2 ,4, 5, 18, 19};

WiFiClient espClient;

PubSubClient client(espClient);

// Wi-Fi 連線函式

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(".");

  }

  Serial.println("");

  Serial.println("WiFi connected");

  Serial.print("IP address: ");

  Serial.println(WiFi.localIP());

}

// 3. 核心：接收 MQTT 訊息的 Callback 函式

void callback(char* topic, byte* payload, unsigned int length) {

  // 將接收到的 payload 轉換為 C++ String 格式

  String message = "";

  for (int i = 0; i < length; i++) {

    message += (char)payload[i];

  }

 

  Serial.print("Message arrived on topic [");

  Serial.print(topic);

  Serial.print("]: ");

  Serial.println(message);

  // 檢查訊息是否以 "led" 開頭，且長度足夠 (例如 led1on 最短 6 字元)

  if (message.startsWith("led") && message.length() >= 6) {

   

    // 取得 LED 編號 (索引從第 3 個字元開始，到找到 "on" 或 "off" 之前)

    int stateIdx = -1;

    if (message.indexOf("on") != -1) stateIdx = message.indexOf("on");

    else if (message.indexOf("off") != -1) stateIdx = message.indexOf("off");

    if (stateIdx != -1) {

      // 擷取中間的數字字串並轉為整數

      int ledNum = message.substring(3, stateIdx).toInt();

      String action = message.substring(stateIdx); // "on" 或 "off"

      // 檢查編號是否在 1 到 8 之間

      if (ledNum >= 1 && ledNum <= 8) {

        int pinIdx = ledNum - 1; // 陣列索引從 0 開始

        String statusPayload = "";

        if (action == "on") {

          digitalWrite(ledPins[pinIdx], HIGH); // 點亮 LED

          statusPayload = "LED" + String(ledNum) + "ON";

        } else if (action == "off") {

          digitalWrite(ledPins[pinIdx], LOW);  // 熄滅 LED

          statusPayload = "LED" + String(ledNum) + "OFF";

        }

        // 4. 即時回報狀態到 alex9ufo/ledstatus

        if (statusPayload != "") {

          client.publish(topic_status, statusPayload.c_str());

          Serial.print("Published status: ");

          Serial.println(statusPayload);

        }

      }

    }

  }

}

// MQTT 重新連線函式

void reconnect() {

  while (!client.connected()) {

    Serial.print("Attempting MQTT connection...");

    // 隨機產生 Client ID 避免重複衝突

    String clientId = "ESP32Client-";

    clientId += String(random(0xffff), HEX);

   

    if (client.connect(clientId.c_str())) {

      Serial.println("connected");

      // 連線成功後重新訂閱控制主題

      client.subscribe(topic_control);

      Serial.print("Subscribed to: ");

      Serial.println(topic_control);

    } else {

      Serial.print("failed, rc=");

      Serial.print(client.state());

      Serial.println(" try again in 5 seconds");

      delay(5000);

    }

  }

}

void setup() {

  Serial.begin(115200);

 

  // 初始化 8 個 LED 腳位為輸出模式，預設關閉 (LOW)

  for (int i = 0; i < 8; i++) {

    pinMode(ledPins[i], OUTPUT);

    digitalWrite(ledPins[i], LOW);

  }

  setup_wifi();

  client.setServer(mqtt_server, mqtt_port);

  client.setCallback(callback); // 設定收到訊息時的處理函式

}

void loop() {

  if (!client.connected()) {

    reconnect();

  }

  client.loop(); // 維持 MQTT 連線與處理底層通訊

}

Data Addresses	Read	Write Single	Write Multiple
Discrete Output Coils 0xxxx	FC01	FC05	FC15

const coils = msg.payload;

let messagesToPublish = [];

for (let i = 0; i < 8; i++) {

    let ledNumber = i + 1;

    let stateStr = (coils[i] === true) ? "on" : "off";

    let customPayload = "led" + ledNumber + stateStr;

   

    messagesToPublish.push({

        topic: "alex9ufo/ledcontrol",

        payload: customPayload

    });

}

return [messagesToPublish];

// 確保進來的是陣列

if (!Array.isArray(msg.payload)) {

    return null;

}

const rawArray = msg.payload;

let resultArray = [false, false, false, false, false, false, false, false];

rawArray.forEach(str => {

    if (typeof str === 'string' && str.startsWith("LED")) {

        let stateIdx = -1;

        if (str.indexOf("ON") != -1) stateIdx = str.indexOf("ON");

        else if (str.indexOf("OFF") != -1) stateIdx = str.indexOf("OFF");

       

        if (stateIdx != -1) {

            let ledNum = parseInt(str.substring(3, stateIdx));

            let action = str.substring(stateIdx);

           

            if (ledNum >= 1 && ledNum <= 8) {

                let arrayIndex = ledNum - 1;

                resultArray[arrayIndex] = (action === "ON");

            }

        }

    }

});

msg.payload = resultArray;

return msg;

Node-Red程式

[{"id":"de273b1b8bd36b17","type":"modbus-read","z":"56c70b10b2e55b6e","name":"","topic":"","showStatusActivities":false,"logIOActivities":false,"showErrors":false,"showWarnings":true,"unitid":"1","dataType":"Coil","adr":"0","quantity":"8","rate":"10000","rateUnit":"ms","delayOnStart":false,"enableDeformedMessages":true,"startDelayTime":"","server":"54dde46e.53267c","useIOFile":false,"ioFile":"","useIOForPayload":false,"emptyMsgOnFail":false,"x":150,"y":120,"wires":[[],["eb0999703abe22e8"]]},{"id":"eb0999703abe22e8","type":"function","z":"56c70b10b2e55b6e","name":"function  ","func":"var data=msg.payload.data;\nmsg.payload=data;\nreturn msg;","outputs":1,"timeout":0,"noerr":0,"initialize":"","finalize":"","libs":[],"x":300,"y":120,"wires":[["led_single_topic_fn"]]},{"id":"cceab653f17ba013","type":"function","z":"56c70b10b2e55b6e","name":"Read FC=15","func":"// Define your coil array values\nconst coilValues = msg.payload;\n\nmsg.payload = {\n    \"value\": coilValues,        // Array of booleans to write\n    \"fc\": 15,                   // Function Code 15 (Write Multiple Coils)\n    \"unitid\": 1,                // Modbus Slave/Unit ID\n    \"address\": 16,               // Starting coil memory address\n    \"quantity\": coilValues.length // Number of coils to write\n};\n\nreturn msg;\n","outputs":1,"timeout":"","noerr":0,"initialize":"","finalize":"","libs":[],"x":450,"y":320,"wires":[["baf9113b483f99d0","d135dcbf561bc6db"]]},{"id":"f237104758129409","type":"debug","z":"56c70b10b2e55b6e","name":"debug 5","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":800,"y":340,"wires":[]},{"id":"baf9113b483f99d0","type":"debug","z":"56c70b10b2e55b6e","name":"debug 6","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":620,"y":280,"wires":[]},{"id":"d135dcbf561bc6db","type":"modbus-write","z":"56c70b10b2e55b6e","name":"","showStatusActivities":false,"showErrors":false,"showWarnings":true,"unitid":"1","dataType":"MCoils","adr":"16","quantity":"8","server":"54dde46e.53267c","emptyMsgOnFail":false,"keepMsgProperties":false,"delayOnStart":false,"startDelayTime":"","x":620,"y":340,"wires":[[],["f237104758129409"]]},{"id":"mq_l1","type":"mqtt out","z":"56c70b10b2e55b6e","name":"LED 1-8 MQTT 傳送端 (固定主題)","topic":"alex9ufo/ledcontrol","qos":"1","retain":"false","respTopic":"","contentType":"","userProps":"","correl":"","expiry":"","broker":"7c89942e45b95822","x":780,"y":120,"wires":[]},{"id":"led_single_topic_fn","type":"function","z":"56c70b10b2e55b6e","name":"編碼為單一主題訊息","func":"const coils = msg.payload;\nlet messagesToPublish = [];\n\nfor (let i = 0; i < 8; i++) {\n    let ledNumber = i + 1;\n    let stateStr = (coils[i] === true) ? \"on\" : \"off\";\n    let customPayload = \"led\" + ledNumber + stateStr;\n    \n    messagesToPublish.push({\n        topic: \"alex9ufo/ledcontrol\",\n        payload: customPayload\n    });\n}\n\nreturn [messagesToPublish];","outputs":1,"timeout":"","noerr":0,"initialize":"","finalize":"","libs":[],"x":500,"y":120,"wires":[["mq_l1"]]},{"id":"mqtt_in_status","type":"mqtt in","z":"56c70b10b2e55b6e","name":"訂閱 ledstatus","topic":"alex9ufo/ledstatus","qos":"1","datatype":"auto-detect","broker":"7c89942e45b95822","nl":false,"rap":true,"rh":0,"inputs":0,"x":120,"y":200,"wires":[["join_node_correct"]]},{"id":"join_node_correct","type":"join","z":"56c70b10b2e55b6e","name":"Join 收集8條","mode":"manual","build":"array","property":"payload","joiner":"\\n","joinerType":"str","accumulate":false,"timeout":"50","count":"8","x":330,"y":200,"wires":[["function_convert_correct"]]},{"id":"function_convert_correct","type":"function","z":"56c70b10b2e55b6e","name":"Function 轉換布林陣列","func":"// 確保進來的是陣列\nif (!Array.isArray(msg.payload)) {\n    return null;\n}\n\nconst rawArray = msg.payload;\nlet resultArray = [false, false, false, false, false, false, false, false];\n\nrawArray.forEach(str => {\n    if (typeof str === 'string' && str.startsWith(\"LED\")) {\n        let stateIdx = -1;\n        if (str.indexOf(\"ON\") != -1) stateIdx = str.indexOf(\"ON\");\n        else if (str.indexOf(\"OFF\") != -1) stateIdx = str.indexOf(\"OFF\");\n        \n        if (stateIdx != -1) {\n            let ledNum = parseInt(str.substring(3, stateIdx));\n            let action = str.substring(stateIdx);\n            \n            if (ledNum >= 1 && ledNum <= 8) {\n                let arrayIndex = ledNum - 1;\n                resultArray[arrayIndex] = (action === \"ON\");\n            }\n        }\n    }\n});\n\nmsg.payload = resultArray;\nreturn msg;","outputs":1,"timeout":"","noerr":0,"initialize":"","finalize":"","libs":[],"x":560,"y":200,"wires":[["debug_correct_out","cceab653f17ba013"]]},{"id":"debug_correct_out","type":"debug","z":"56c70b10b2e55b6e","name":"正確輸出布林陣列","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":790,"y":200,"wires":[]},{"id":"54dde46e.53267c","type":"modbus-client","name":"local","clienttype":"tcp","bufferCommands":true,"stateLogEnabled":true,"queueLogEnabled":false,"failureLogEnabled":false,"tcpHost":"127.0.0.1","tcpPort":"502","tcpType":"TCP-RTU-BUFFERED","serialPort":"/dev/ttyUSB","serialType":"RTU-BUFFERD","serialBaudrate":"9600","serialDatabits":"8","serialStopbits":"1","serialParity":"none","serialConnectionDelay":"100","serialAsciiResponseStartDelimiter":"","unit_id":1,"commandDelay":1,"clientTimeout":1000,"reconnectOnTimeout":false,"reconnectTimeout":2000,"parallelUnitIdsAllowed":false,"showErrors":false,"showWarnings":true,"showLogs":true},{"id":"7c89942e45b95822","type":"mqtt-broker","name":"mqttgo","broker":"mqttgo.io","port":1883,"clientid":"","autoConnect":true,"usetls":false,"protocolVersion":4,"keepalive":60,"cleansession":true,"autoUnsubscribe":true,"birthTopic":"","birthQos":"0","birthRetain":"false","birthPayload":"","birthMsg":{},"closeTopic":"","closeQos":"0","closeRetain":"false","closePayload":"","closeMsg":{},"willTopic":"","willQos":"0","willRetain":"false","willPayload":"","willMsg":{},"userProps":"","sessionExpiry":""},{"id":"dd649eb72b4bcf6f","type":"global-config","env":[],"modules":{"node-red-contrib-modbus":"5.45.2"}}]