MQTT (Message Queuing Telemetry Transport) is a protocol proposed by IBM and Eurotech. The introduction in MQTT Official Website:
MQTT is a machine-to-machine (M2M)/”Internet of Things” connectivity protocol. It was designed as an extremely lightweight publish/subscribe messaging transport.We can say MQTT is a protocol designed for IoT. MQTT is based on TCP/IP and transmits/receives data via publish/subscribe.
Please refer to the figure below:
In the operation of MQTT, there are several roles:
Publisher: Usually publishers are the devices equipped with sensors (ex. Ameba). Publishers uploads the data of the sensors to MQTT-Broker, which serves as a database with MQTT service.
Subscriber: Subscribers are referred to the devices which receive and observe messages, such as a laptop or a mobile phone.
Topic: Topic is used to categorized the messages, for example the topic of a message can be “PM2.5” or “Temperature”. Subscribers can choose messages of which topics they want to receive.
Open the MQTT example “File” -> “Examples” -> “AmebaMQTTClient” -> “MQTT_Basic”
Please modify some WiFi-related parameters.
And some information related to MQTT:
The “mqttServer” refers to the MQTT-Broker, we use the free MQTT sandbox “test.mosquitto.org” for testing.
“clientId” is an identifier for MQTT-Broker to identify the connected device.
“publishTopic” is the topic of the published message, we use “outTopic” in the example. The devices subscribe to “outTopic” will receive the message.
“publishPayload” is the content to be published.
“subscribeTopic” is to tell MQTT-broker which topic we want to subscribe to.
Upload and Execution
Next, compile the code and upload it to Ameba. Press the reset button, then open the serial monitor
After Ameba is connected to MQTT server, it sends the message “hello world” to “outTopic”.