MQTT library PubSubClient - sending float/int/bool data to topics? char convert

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1

I'm new MQTT. I'm looking at an example MQTT sketch from the PubSubClient library. It looks like this:

void callback(char* topic, byte* payload, unsigned int length) {
// handle message arrived
}

EthernetClient ethClient;
PubSubClient client(server, 1883, callback, ethClient);

void setup()
{
Ethernet.begin(mac, ip);
if (client.connect("arduinoClient")) {
client.publish("outTopic","hello world");
client.subscribe("inTopic");
}
}

I'd like to publish ints, bools, and floats instead of the string "hello world" to the topic, but trying this gives me a "invalid conversion from int to char" error:

void setup()
{
int mydata = 4;
Ethernet.begin(mac, ip);
if (client.connect("arduinoClient")) {
client.publish("outTopic", mydata);
client.subscribe("inTopic");
}
}

Does the protocol only take in character strings? I have a feeling I have to do some kind of conversion involving the "&" operator...but I'm not sure.

2

Might've found the answer here:

http://2lemetry.com/2013/04/17/a-simple-example-arduino-mqtt-m2mio/

// publish light reading every 5 seconds
if (millis() > (time + 5000))
{
time = millis();
String pubString = "{"report":{"light": "" + String(lightRead) + ""}}";
pubString.toCharArray(message_buff, pubString.length()+1);
//Serial.println(pubString);
client.publish("io.m2m/arduino/lightsensor", message_buff);
}

In this example, rightRead is an int. The other parts of the message_buff are part of how this particular person is using the data, but the important part is this:

String(lightRead)

So this String() function converts whatever is sent to it as a parameters into a string.

3

Thank you for posting this here is an example built using your string conversion idea

Mqtt_Esp8266_Dhtv2.ino (4.57 KB)