Warning
The MQTT server used here is public and data sent will be publicly accessible. Be aware of the data you share.
The aim of this exercise is to get hands-on with the MQTT protocol by connecting Cordelia-I module to a public MQTT server without any encryption or authentication.
MQTT - Message Queuing Telemetry Transport is a lightweight application layer protocol based on a publish/subscribe messaging mechanism. This protocol was designed for resource constrained and unreliable networks with limited bandwidth and high latency. These characteristics make MQTT suitable for low-power, low-bandwidth IoT applications. Inherently, the MQTT protocol offers some degree of assurance of delivery thereby offering the robustness necessary for industrial machine-to-machine communication.
MQTT was originally developed by IBM and the version 3.1.1 is an OASIS standard that is open and royalty-free. It is based on client-server architecture where every client connects to a server (broker) over TCP resulting in a star topology. Once connected, the clients send and receive messages using the publish/subscribe mechanism.
Data transfer in MQTT takes place based on publish/subscribe mechanism. The clients connected to the broker can publish messages under certain topics. The clients can also subscribe to topics that are of interest to them. When a client publishes a message on a topic, the broker forwards the message to any client that has subscribed to the topic. This mechanism enables bi-directional communication with an extremely low overhead (2-byte header).
For this hands-on exercise, we will use a publicly available version of the Eclipse Mosquitto MQTT server/broker. This server is provided as a service for the community to do testing, but it is also extremely useful for testing.
Warning
Being publicly hosted, it is possible that the mosquitto broker is not always online and available. In case the this server is not available at the time of your testing, you can use the server from EMQX instead. When using the EMQX broker, the hostname/endpoint address will be "broker.emqx.io". All the other parameters will remain the same.
For this exercise, we will use MQTT explorer tool as the client. MQTT Explorer is a comprehensive MQTT client that provides a structured overview of your MQTT topics and makes working with devices/services on your broker dead-simple. Follow the instructions here to install this tool.
In this step, we will connect to the Mosquitto broker over TCP. In this case the connection is neither mutually authenticated nor encrypted.
Open the MQTT explorer tool. In the start-up page add the parameters of the MQTT broker/server.
- Click on the "+ connections" button.
- Give a unique name to this connection. For example, "mosquitto".
- Enter the host name. This is the address of the MQTT broker/server "test.mosquitto.org"
- Click on advance button. In the advanced view,
- Delete the default topic "#" in order to prevent receiving all messages published to this public server.
- Delete the default topic "$SYS/#"
- Type in a new topic name "cordelia/+".
- Click on add to subscribe to this topic by default on successful connection.
- Click on "BACK" button to return to the default view.
- Finally, click on the "CONNECT" button to connect to the broker.
You can now test the connection by publishing the data to a topic that this client has subscribed to. To do this, in the data view,
- Type in the name of the topic. It should start with the prefix "cordelia/". For example, "cordelia/banana".
- Type in the payload. Let us use a JSON formatted payload. For example,
{"test": 8} - You should be able to see the data you published in the received list
Congratulations! You have now sent your first MQTT packet.
Important
Perform a "Factory Reset". Please note that the reset will typically take 60 seconds. Please wait for at least this time. The PC tool will not show any reaction during that duration, please be patient. Do not power-off or hard reset the EV-board during this time.
Open the WLAN settings tab in the WE UART terminal. In order to connect the Cordelia-I module to your WiFi network,
- Type in the SSID of your WiFi network.
- Choose the correct security type.
- Type in your password.
- Finally click on "Connect".
On successful connection, you will receive a "connect" event as well as an "ipv4_acquired" event.
-> AT+wlanconnect=your_ssid,,WPA_WPA2,your_password,,,
<- OK
<- +eventwlan:connect,your_ssid,0x34:0x31:0xc4:0x4a:0xeb:0x5f
<- +eventnetapp:ipv4_acquired,192.168.178.100,192.168.178.1,192.168.178.1
Congratulations! Your module is now connected to the internet via your WiFi network. You can confirm this by checking the fact that the "mode" and "status" LEDs are now switched on.
In this step, we configure the Cordelia-I module to connect to the public Mosquitto Broker and send/receive data. The on-board MQTT client on the Cordelia-I module needs to be configured. These parameters are stored in the "user settings" of the module. In the WE UART terminal, use the "Custom command/input" section in the "General" tab to configure the user settings.
💡 You could use the "Set up module with dummy parameters" button. This will configure the following user settings parameters necessary for this connection:
- MQTT Broker address.
- MQTT port.
- Flags to indicate the type of server used for this connection.
- Set the client ID (Replace "your_client_id" with a meaningful name).
- Set topic strings to subscribe and publish.
-> AT+set=MQTT,iotHubEndpoint,"test.mosquitto.org"
<- OK
-> AT+set=MQTT,iotHubPort,1883
<- OK
-> AT+set=MQTT,flags,"url"
<- OK
-> AT+set=MQTT,clientId,"your_client_id"
<- OK
-> AT+set=SUBTOPIC0,name,"cordelia/+"
<- OK
-> AT+set=PUBTOPIC0,name,"cordelia/apple"
<- OK
[Optional] You could configure additional topics to publish,
-> AT+set=PUBTOPIC1,name,"cordelia/banana"
<- OK
-> AT+set=PUBTOPIC2,name,"cordelia/orange"
<- OK
-> AT+set=PUBTOPIC3,name,"cordelia/kiwi"
<- OK
Now that the module is configured, Go to the "IoT Operations" tab and click on "Connect" button. On successful connection, you will the module will generate a "CONNACK" event.
-> AT+iotconnect
<- OK
<- +eventmqtt:info,"CONNACK",0
To exchange data, use the "Publish data" section in the "IoT Operations" tab. Here type in the payload in the text box and click on "Publish custom payload" button to send the data. Alternatively, use the "Generate and publish random payload" button to send random data.
-> AT+iotpublish=0,"{"RandomString":"oUykIeOvzm","Number1":104,"Number2":575}"
<- OK
<- +eventmqtt:recv,cordelia/apple,qos0,"{"RandomString":"oUykIeOvzm","Number1":104,"Number2":575}"
Since we publish to the same topic, you should be able to see the data on the MQTT explorer client.
Congratulations on completing this exercise!