You obviously didn't follow the link to this article/thread (I posted above) as if you had read it you would have seen the link to the Arduino files that work for me and my IoT students.
Here's a direct link to the Arduino files, but I would encourage you to read the article I posted.
I've just found some code to 'publish' values from a temperature/humidity/pressure (thp) BME280 sensor.
You will have to edit the code to remove all the bits (my variables) you don't need. Hope this helps.
void publish_thp()
{
status = "fail";
if (bitRead(status_register, thp_pos))
status = "good";
StaticJsonDocument<256> doc; // The names in doc["xxx"] have been shortened to fit within the char limit !!!
doc["remote"] = "node" + String(remote_node_ref);
doc["src"] = "ws_pcb"; //Tag for Node-RED to indicate the data-source (e.g. "rf24", "lora", "wsv1", "wsv2")
doc["type"] = "bme280";
doc["sensor_st"] = status;
doc["t"] = temperatureValue;
doc["h"] = humidityValue;
doc["p"] = pressureValue;
doc["base"] = "node98";
doc["ssid"] = WiFi.SSID();
doc["rssi"] = WiFi.RSSI();
char topic[30]; // 30 chars wide
strcpy(topic, mqtt_publish_topic);
strcat(topic, "/");
strcat(topic, thisNodeID);
char buffer[256];
size_t n = serializeJson(doc, buffer);
mqtt_client.publish(topic, buffer, n);
} //------------ End of publish_thp()
To overcome the limit on length of MQTT messages we decided to publish readings in sequence.
E.g. BME280, solar panel data, DS18B20.
void transmit_data_to_mqtt_broker()
{
if (newData == true)
{
publish_thp();
publish_solar();
publish_analog();
newData = false;
}
} //============ End of transmit_data_to_mqtt_broker()
