About the command "String msg ="{xxxx}";

[jmguilbert]

Hello and thank you for your often quick and helpful responses.
I need to better understand a command you use in the "temperature" example on a DIY sensor.
This is the one I would like to adapt to other sensors:
String msg = "{"model":"ESP32TEMP","id":"" + NodeId + "","tempc":" + String(temp) + "}";

1- I understand that this line sends a message to OMG so that it translates the sensor data into MQTT.

• the "temp" variable comes from float.
  But where does “tempc” come from?
  Is this a “topic” that OMG can recognize?
  If so, what other topics could we use?
  For example to send a weight collected by HX711.

2- More generally, could you direct me to a doc so that I can learn how to form a "String msg" by myself without disturbing you.

A big thank you from France.
Jean Marc.

[1technophile]

But where does “tempc” come from?

tempc is the key used by OMG to understand that this is a temperature in Celsius

All the properties used in the Theengs decoder could be used, example:
https://github.com/theengs/decoder/blob/121e69989bdfa5831b2f91d181bb838b8e115097/src/devices/XMTZC05HMKG_json.h#L39

In your case it could be:

String msg = "{"model":"ESP32WGHT","id":"" + NodeId + "","weight":" + String(weight) + "}";

[jmguilbert]

Many thanks.