Compose-5000: Connect to an MQTT Broker using Compose

The following software and accounts are required for this tutorial:

1. In SmartWorks, Create New Space > AnythingDB > Things > New Thing > Create.

   

   After the Thing is created, a property is created to receive data from Compose and be stored on SmartWorks.

2. Select Properties (+) > Create.

   

   

   

3. Create Properties to be attributed to this object:

   

   

4. To set the MQTT credentials on SmartWorks, select Interfaces > MQTT Create Credentials > Set Username and Password > Save.

   

1. Clear existing clients that are connected to the session:

   cld_all  = mqttclientinfo('clientids');
   if ~isempty(fieldnames(cld_all))
   	cellfun(@mqttdestroy,{cld_all(:).clientids}, 'uniformoutput', 0);
   end

2. Compose has a useful capability to return a response when the client receives a CONNACK (connect and response messages) from the server. For this, you must write the callback function:

   function connect_mqtt_callback(clientid, rc, Mqttmessageinfo)
   if rc == 0;
   	printf('CONNACK return message for clientid %s: %s\n', clientid, Mqttmessageinfo);
   else
   	printf('Failed to connect broker with clientid %s: %s\n', clientid, Mqttmessageinfo);
   end
   end

3. Declare all the necessary arguments to be used on the MQTT functions, such as host, port, credentials, and topic attributes:

   host = 'mqtt.swx.altairone.com';
   port = 1883;
   space = 'demo-models';
   thing_id = '01HE682NDWSZ0F61JSFE0ZB6TE';
   property = 'obj1';
   topic = ['spaces/' space '/things/' thing_id '/properties'];
   user = 'cmodel@demo-models';
   password = 'cmodel';

4. Set a client to get the ID and send the message using that ID. This is the first step to set an MQTT connection. For this tutorial, the code below is used to set a client, using the callback function to advise if the connection was established:

   clientid = mqttclient(host, 'port', port, 'username', user, 'password', password ...
   			, 'keepaliveduration', 5, 'on_connect', 'connect_mqtt_callback');

   In this case, a simple sinusoidal wave signal is generated to be sent to the client.

   Note: Cells are used to be better manipulated further in the publishing section:

   t = [0:0.1:10];
   time = num2cell(t);
   amplitude = num2cell(sin(t));

5. Create a loop to send the sinusoidal data individually. SmartWorks requires JavaScript Object Notation (JSON) format on the data. For that, a function is used to manipulate the data individually, accessing each cell member of the sinusoidal wave. Finally, a plot is created, having 0.5 seconds as a pause condition, to see what is the data that is sent:

   for i = 1:length(t)
   	msg = jsonencode(struct(property, struct('amplitude', num2str(time{i}), 'time', num2str(amplitude{i}))));
   	[mid, rc, msginfo] = mqttpublish(clientid, topic, msg, 2, true);
   	pause(0.5);
   	if rc == 0
   		printf('Publishing to MQTT broker %s\n', host)
   		printf('Send message %s with ID:%s, to topic: %s\n',num2str(amplitude{i}),num2str(mid), topic)
   	end
   	stem(t(i),amplitude{i});
   	hold on;
   end

   It is possible to see that the data sent from Compose is being received on SmartWorks using the MQTT protocol.

   

   

1. Clear existing clients that are connected to the session:

   cld_all  = mqttclientinfo('clientids');
   if ~isempty(fieldnames(cld_all))
   	cellfun(@mqttdestroy,{cld_all(:).clientids}, 'uniformoutput', 0);
   end

2. Compose has a useful capability to return a response when the client receives a CONNACK (connect and response messages) from the server. For this, you must write the callback function:

   function connect_callback(clientid, rc, Mqttmessageinfo)
   	if rc == 0;
   		printf('CONNACK return message for clientid %s: %s\n', clientid, Mqttmessageinfo);
   	else
   		printf('Failed to connect broker with clientid %s: %s\n', clientid, Mqttmessageinfo);
   	end
   end

   It is possible to have a callback function to receive a message when the client subscribes to the broker:

   function subscribe_callback(clientid, mid, grand_qos)
   	printf('message id: %s\n', num2str(mid));
   end

3. Get the message from the broker, in this case from SmartWorks. This is the last callback function in this model:

   function msg_callback(clientid, topic, msg)
   	data = jsondecode(msg);
   	printf('amplitude: %s\ntime: %s', data.obj1.amplitude, data.obj1.time);
   end

   Note: A JSON function is used to decode the data, as the message from SmartWorks has that format.
4. Declare all the necessary arguments to be used on the MQTT functions, such as host, port, credentials, and topic attributes:

   host = 'mqtt.swx.altairone.com';
   port = 1883;
   space = 'demo-models';
   thing_id = '01HE682NDWSZ0F61JSFE0ZB6TE';
   property = 'obj1';
   topic = ['spaces/' space '/things/' thing_id '/properties/' property]

5. Set a client to get the ID and send the message using that ID. This is the first step to set an MQTT connection. For this tutorial, the code below is used to set a client, using the callback function to advise if the connection was established:

   clientid = mqttclient(host, 'port', port, 'username', user ...
   			,'password', password, 'keepaliveduration',5 ...
   			,'on_connect','connect_callback' ...
   			,'on_subscribe','subscribe_callback' ...
   			,'on_message','msg_callback');

6. With all the setup done, subscribe to the broker and receive all the messages that are sent to the IoT platfom:

   [mid1, rc1, msginfo1] = mqttsubscribe(clientid, topic, 0);

   Considering that Compose is subscribed to the topic, if any message is sent from one device to that topic, Compose receives it:

   

   It is possible to see that the data sent from SmartWorks is being received on Compose using the MQTT protocol.