MQTT subscribe gets no data back

I have a channel that has several feeds with live data. I am trying to use a particle Argon and thingspeak MQTT broker to subscribe to this data. I used the example provided and got nothing back from the subscription. I am pasting my code below. If anyone has a working example, that would be great!

#include "MQTT.h"

const long channelID = 10X4XXX;

String ReadAPIKey = "XXXXXXXXX";

String subscribeTopic = "channels/" + String( channelID ) + "/subscribe/fields/field1/"+String(ReadAPIKey);

String MQTTAPIKey = "XXXXXXXXXX";

void callback( char* topic, byte* payload, unsigned int length );

MQTT client( "mqtt.thingspeak.com" , 1883 , callback );

// This function processes the messages relayed by the MQTT broker.

void callback( char* topic, byte* payload, unsigned int length ) {

Serial.println("in callback");

char p[ length + 1 ]; // Leave an extra space to null terminate the string.

memcpy( p, payload, length );

p[ length ] = NULL; // Terminate the string.

}

void setup() {

Serial.println("in void setup");

// Connect to the server.

subscribeMQTT();

}

void loop() {

Serial.println("in void loop");

int timeHour = Time.hour();

if (client.isConnected()){

client.loop();

}

else{

subscribeMQTT();

}

if ( ( timeHour > 23 ) or ( timeHour < 4 ) ){

Particle.publish( "Sleep" );

System.sleep( SLEEP_MODE_DEEP , 7200 );

}

delay(20000);

}

void subscribeMQTT(){

Serial.println("in subscribe MQTT");

if (!client.isConnected()) {

client.connect( " MGSubscribeArgon" , "MGUsername" , MQTTAPIKey , NULL , MQTT::QOS0 , 0 , NULL , true );

Particle.publish( " Connect " );

Serial.println("Connected to broker");

delay( 1000 );

if ( client.isConnected()) {

Serial.println("MQTT connected");

client.subscribe( subscribeTopic );

Particle.publish( "subs" );

}

}

}

Answer 1

[Vinod]

Have you taken a look at this example? It should be possible to modify it for a Particle Argon quite easily.

[Mar Ron]

That IS the example I am using. In the code I posted above, the only part that I deleted was the "strncmp" portion. I deleted it in the above example by mistake, but I eventually just use serial.println() in the callback function to see what is being received. That callback function that is supposed to be called by the receipt of a packet on MQTT subscribe, is never triggered.

Answer 2

[Christopher Stapels]

Can you try connecting with another desktop based broker (MATLAB has one) or MQTTFx to make sure you have all the api keys correct? If you verify that, I have an Argon here at home that I can re verify the code with. Its previously been verified with an photon.

[Mar Ron]

Chris,

I have publish working just fine. So I know I have my keys set up correctly.

[Christopher Stapels]

Publish and subscribe have slightly different requirements, I have found using a different client can be a really good check to make sure everything is correct. I've failed to match the appropriate channel ID for example and the subscription broker just disconnects me without a messge. Unofrtunately its the nature of the protocol.

Ive done pub and sub MQTT on a photon previously so im pretty confident it will work. Have a look a the serial ourput, especially during the subscription method. Do you see all the test messages?

Ill see If I can get a test going on my argon soon, but my first step will be to check the connection with MQTTfx.