Process String form MQTT with a ESP8266

Using Arduino Programming Questions
1

Hi there, I need your help please.

In my Project I use the RTL_433 program and send the data to a MQTT broker.
I recieve the data with a MQTT Client (Mosquitto) on a ESP8266.
So far, so god, but I don't know how to get the Values I need out of this string.

Here is an example of a String i get:

"{"time":"2019-09-11 14:11:28","model":"inFactory sensor","id":80,""temperature_C":17.33333,"humidit y":66}"

I need the temperature and humidity value and want to send this values to a display.
Do you have any ideas how I can do that ?

I already tried to use some Arduino JSON library examples, but it doesent work.

Thank you for your help.

PS: you can reply in English or German
PS: Du kannst in English oder Deutsch antworten

2

Assuming that that is a C string, not a String, you can use strstr to look for something in the string. temperature_c perhaps. then you know that the actual temperature data you're looking at will appear fifteen characters later so you can pass that address to atof to get the value.

3

Thank you for your quick reply. I did not understand your answer, "Assuming that that is a C string".
I use the Arduino Software for programming the ESP8266. Is it possible to use strstr command, when I write my programing code with the Arduino Software ? If not, is there a similiar command available ?
Do I have some alternative Software to write a sourcecode for an ESP8266 ?

4

Why does the JSON library not work, what errors do you get?

5

I tried an Example Code that uses the JSON library but I get the following error:
invalid digit "9" in octal constant.
But the Variable for the String exaple in this Code is defined as a const char.
Whith the my example String it desent't work.
if I remove the time part of the String I get the following error:
missing terminating " character

/*
JSON Object

This sketch demonstrates how to use various features
of the Official Arduino JSON library, in particular for JSON objects.

This example code is in the public domain.
*/

#include <Arduino_JSON.h>

//const char input[] = "{"result":true,"count":42,"foo":"bar"}";
const char input[] = "{"time":"2019-09-11 14:11:28","model":"inFactory sensor","id":80,""temperature_C":17.33333,"humidit y":66}";

void setup() {
Serial.begin(9600);
while (!Serial);

demoParse();

demoCreation();
}

void loop() {
}

void demoParse() {
Serial.println("parse");
Serial.println("=====");

JSONVar myObject = JSON.parse(input);

// JSON.typeof(jsonVar) can be used to get the type of the var
if (JSON.typeof(myObject) == "undefined") {
Serial.println("Parsing input failed!");
return;
}

Serial.print("JSON.typeof(myObject) = ");
Serial.println(JSON.typeof(myObject)); // prints: object

// myObject.hasOwnProperty(key) checks if the object contains an entry for key
if (myObject.hasOwnProperty("result")) {
Serial.print("myObject["result"] = ");

Serial.println((bool) myObject["result"]);
}

if (myObject.hasOwnProperty("count")) {
Serial.print("myObject["count"] = ");

Serial.println((int) myObject["count"]);
}

if (myObject.hasOwnProperty("count")) {
Serial.print("myObject["count"] = ");

Serial.println((double) myObject["count"]);
}

if (myObject.hasOwnProperty("foo")) {
Serial.print("myObject["foo"] = ");

Serial.println((const char*) myObject["foo"]);
}

// JSON vars can be printed using print or println
Serial.print("myObject = ");
Serial.println(myObject);

Serial.println();
}

void demoCreation() {
Serial.println("creation");
Serial.println("========");

JSONVar myObject;

myObject["hello"] = "world";
myObject["true"] = true;
myObject["x"] = 42;

Serial.print("myObject.keys() = ");
Serial.println(myObject.keys());

// JSON.stringify(myVar) can be used to convert the json var to a String
String jsonString = JSON.stringify(myObject);

Serial.print("JSON.stringify(myObject) = ");
Serial.println(jsonString);

Serial.println();

// myObject.keys() can be used to get an array of all the keys in the object
JSONVar keys = myObject.keys();

for (int i = 0; i < keys.length(); i++) {
JSONVar value = myObject[keys*];*

  • Serial.print("JSON.typeof(myObject[");*
    _ Serial.print(keys*);_
    _     Serial.print("]) = ");_
    _     Serial.println(JSON.typeof(value));_
    _     Serial.print("myObject[");_
    _ Serial.print(keys);
     Serial.print("] = ");
     Serial.println(value);
     Serial.println();
     }
     Serial.println();
     // setting a value to undefined can remove it from the object*
    * myObject["x"] = undefined;
     // you can also change a value*
    * myObject["hello"] = "there!";
     Serial.print("myObject = ");
     Serial.println(myObject);
    }*_
6

Please use code tags when posting code. The JSON is not valid, a comma is ill positioned (right after "80") and the quotes are not escaped. Try to replace:

const char input[] = "{"time":"2019-09-11 14:11:28","model":"inFactory sensor","id":80,""temperature_C":17.33333,"humidit y":66}";

with:

const char input[] = "{\"time\":\"2019-09-11 14:11:28\",\"model\":\"inFactory sensor\",\"id\":80\",\"temperature_C\":17.33333,\"humidit y\":66}";

Look carefully at the differences.

7

Moreover, using the JSON library for this little thing is overkill. Here it is old school:

const char input[] = "{\"time\":\"2019 - 09 - 11 14: 11: 28\",\"model\":\"inFactory sensor\",\"id\":80,\"temperature_C\": 17.33333, \"humidity\": 66}";

void setup() 
{
Serial.begin(115200);
char *ptr=strstr(input,"temperature_C");
float tempC=atof(&ptr[15]);
Serial.print("Temperature: ");
Serial.println(tempC);
}

void loop() 
{
}