Session 3: MQTT and Cayenne

Uli Raich

Formally CERN, Geneva, Switzerland

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The WeMos D1 mini has a built-in WiFi interface

In order to communicate with other IoT nodes we must therefore

connect to the WiFi network first

On top of WiFi we will run a TCP session

On top of TCP we will run the MQTT protocol

On top of MQTT we have dedicated topics and payloads imposed by Cayenne

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MQTT (Message Queuing Telemetry Transport: a publish-subscribe based

message protocol running of top of TCP.

A processor can subscribe to messages of a certain “topic” and/or it can push its

results on a certain topic

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Receiving commands is a bit more tricky! We must:

• Write a callback function and register it with the MQTT client
• This function takes 2 arguments:
• The topic
• The payload
• Subscribe to the topic
• Wait forever. The callback function will be executed when a message with the
  topic we subscribed to, will arrive

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