Publishing a float value with PubSubClient

Projects Programming
1

I am stuck on a problem that should have an easy solution, but that I'm unable to find due to my lack of knowledge programming Arduino.

I am working with a Nano 33 IOT exchanging (publishing and receiving) messages with a MQTT broker (Ubidots in this particular case). When sending an integer value to the broker, I have no problems:

char msg_out[20];
itoa(intvalue,msg_out,10);
mqttclient.publish(topic, msg_out,retain);escribe o pega el código aquí

The problem comes when having to send a float value instead of an integer one. I cannot find any way of sending the string with the float value conversion. Function dtostrf(floatvalue,5,2,msg_out) does not work, and there is no ftoa() function doing something similar to itoa() but with float values.

Any hint about how to proceed ?

Thanks very much for your help

Joan

2 
    bmeInfo.concat( String(x_eData.Temperature, 2) );
    bmeInfo.concat( "," );
    bmeInfo.concat( String(x_eData.Pressure, 2) );
    bmeInfo.concat( "," );
    bmeInfo.concat( String(x_eData.Humidity, 2) );
    bmeInfo.concat( "," );
    bmeInfo.concat( String(x_eData.IAQ, 2) );
    xSemaphoreGive ( sema_eData );
    xSemaphoreTake( sema_MQTT_KeepAlive, portMAX_DELAY );
    if ( MQTTclient.connected() )
    {
      MQTTclient.publish( topicInsideInfo, bmeInfo.c_str() );
    }
    xSemaphoreGive( sema_MQTT_KeepAlive );
    xSemaphoreGive( sema_PublishPM ); // release publish of dust density

The temperature, pressure, humidity and iaq are floats.

3

The dtostrf() function does indeed work as documented. I suspect any difficulty you had was due to Pilot Error.

4

gfvalvo, thanks for your reply. You are right. The dtostrf() DID not work, and now (I don't know why) it does work (?!?). I don't understand what has happened ... but now it works:

dtostrf(t,5,2,msg_out);
if (!mqttclient.publish(pubTopicTemperature, msg_out, retain)) Serial.println("** ERROR 7 Publish");

Independently of this, following idahowalker suggestion, I have tried also:

String myString;
myString.concat(String(h));
if (!mqttclient.publish(pubTopicHumidity, myString.c_str(), retain)) Serial.println("** ERROR 8 Publish");

and this also works.

Thanks very much to both of you for your help. I have spent a complete afternoon trying to see what was going on ...

Definitely, when you are stuck on something like this, better to go out to have a walk to refresh your mind.

Once again, thanks very much.

Joan

5

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