Styjun

#include <ArduinoJson.h>
#include <SimpleDHT.h>

String input = ""temperature":"26";
SimpleDHT11 dht11;
byte temperature = 0;
int err = SimpleDHTErrSuccess;

void loop {

 StaticJsonBuffer<512> dataBuffer;

 if (err = dht11.read(2, &temperature, NULL)) == simpleDHTErrSuccess) 
 Serial.print((int) temperature);
 JsonObject& dataRoot = dataBuffer.parseObject(input);

 *long Temperature = dataRoot[String("temperature")];
 *Temperature = (long)temperature;
 *dataRoot[String("temperature")] = Temperature;

 String output;
 dataRoot.printTo(output);

I have here a snippet of Arduino code used to format a DHT11 temperature sensor readings in JSON, to allow for live streaming of the data on a web client. This was obtained from this project I am using for inspiration https://www.twilio.com/blog/2018/07/watch-iot-sensors-esp32-javascript-nodejs-twilio-sync.html.

I am instead attempting to pull data from a Myoware muscle sensor. The amplitude value I am wanting can simply be queried like so:

int sensorValue = analogRead(A0);

I need help in understanding how the parseObject function works and what the purpose of the 'input' string is. All I want is for my sensor's value to be fed to the client side which displays it in a graph. The three lines I have asterisked are particularly confusing.

Thanks!

The method parseObject() allocates and populate a JsonObject (that you can work with) from a JSON string.

The "JsonObject" in your code example is named dataRoot and is defined with

JsonObject& dataRoot = dataBuffer.parseObject(input);

where dataBuffer comes from StaticJsonBuffer<512> dataBuffer; which is the entry point for using the ArduinoJson library, and

where input has the value of the JSON string ""temperature":"26"" which follows the standard JSON attribute-value pair format (you need a JSON string to work with and then send it to the client side).

After JsonObject& dataRoot = dataBuffer.parseObject(input); is executed, you get dataRoot as an object with a property named temperature and you can access this property with dataRoot[String("temperature")]

So the three lines:

 long Temperature = dataRoot[String("temperature")];
 Temperature = (long)temperature;
 dataRoot[String("temperature")] = Temperature;

are used to update the value of the temperature attribute with whatever is read from the sensor.

A bit confusing in the example code is the fact that the name of the JSON attribute is temperature and also the name for the variable to hold the temperature read from sensor is also temperature. They are different things.