YM 初擊/進擊創客

MQTT(2) 發布 JSON 訊息

參考這篇，宣告儲存訊息的 Json 字串變數(msgStr)，再將 Json 字串變數(msgStr) 以 .toCharArray 轉為字元陣列格式儲存，以此格式發布

String msgStr = "";// 儲存訊息的字串變數

char json[25];// 儲存字元陣列格式的訊息字串

==========loop()==========

loop(){

...

// 建立MQTT訊息（JSON格式的字串）

msgStr = msgStr + "{\"temp\":" + (19 + random(10)) + ",\"humid\":" + 20 + "}";

. // 把String字串轉換成字元陣列格式

msgStr.toCharArray(json, 25);

// 發布MQTT主題與訊息

client.publish(topic, json);

// 清空MQTT訊息內容

msgStr = "";

..

}

Arduino to CharArray

https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/tochararray/

Description

Copies the String’s characters to the supplied buffer.

Syntax

myString.toCharArray(buf, len)

Parameters

myString: a variable of type String.

buf: the buffer to copy the characters into. Allowed data types: array of char.

len: the size of the buffer. Allowed data types: unsigned int.

EXP1/模擬數據以 Json 格式 MQTT 發布，Node-Red 接收展示

使用的 Public MQTT Server：broker.hivemq.com:1883

發布主題：ymiot/1101A/810000/testAll

將 4 個感測器模擬資料以 Json 字串由 MQTT 發布

Json 字串：{"sensor1":666,"sensor2":0,"sensor3":30,"sensor4":78}

1.1 電路

1.2 實作

1.2.1 積木程式設計

連線到 http://easycoding.tn/tuniot/demos/code/
或離線版 TUNIOT(執行資料夾中 demo/code/index.html)

完成之積木程式

randomSeed(analogRead(0));

msgString = msgString + "{\"sensor1\":" + simulatedData1 + ",\"sensor2\":" + simulatedData2 + ",\"sensor3\":" + simulatedData3 + ",\"sensor4\":" + simulatedData4 + "}";
msgString.toCharArray(msgJson, 100);
client.publish(pubTopic, msgJson);
msgString = "";

儲存積木檔(.xml)，儲存 Arduino 程式碼(.ino)

1.2.2 DEMO

1.2.3 Node-Red 流程設計

Flow

dashboard 元件

儀表板網頁布局

元件設定

let a = msg.payload;

let sensor1value = a.sensor1;

msg.payload = sensor1value;

return msg;

let a = msg.payload;

let sensor2value = a.sensor2;

msg.payload = sensor2value;

return msg;

let a = msg.payload;

let sensor1value = a.sensor3;

msg.payload = sensor3value;

return msg;

let a = msg.payload;

let sensor1value = a.sensor4;

msg.payload = sensor4value;

return msg;

1.2.4 Node-Red DEMO

1.2.5 Node-Red 訂閱多主題

DEMO

Flow

將每個儀表板元件設定完成後，可以觀看整個儀表板網頁的布局(layout)

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