Slide 1: Setting up an IoT

Session 3: MQTT and Cayenne

Uli Raich

Formally CERN, Geneva, Switzerland

Slide 2: The Network Layers

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

Slide 3: Accessing the WiFi network

Slide 4: Accessing the WiFi network from Micropython

Slide 5: MQTT

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

Slide 6: MQTT Demo

Slide 7: The Micropython library

Slide 8: A MQTT example using umqtt.simple

Slide 9: Sending dummy temperature data

Slide 10: Receiving commands

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

Slide 11: Subscribe a callback

Slide 12: Callback result

Slide 13: Controlling a LED

In order to control a LED through MQTT we now simply interpret the payload:

• Message “LED on”
• Message “LED off”

Slide 14: Changed Callback

Slide 15: Missing functions in IoT

• MQTT broker should be globally reachable
• GUI to easily visualize sensor measurements
• GUI elements to easily control actuators
• GUI should be accessible through a WEB interface
• GUI should be accessible through smart phone app

Slide 16: Cayenne functionality

• MQTT broker is accessible at mqtt.mydevices.com
  
  
• Supplies GUI

Slide 17: Signing up for Cayenne

Sign up at
https://mydevices.com/cayenne/signup

Slide 18: Cayenne Start

Slide 19: Cayenne Doc

You find the documentation at

https://mydevices.com/cayenne/docs/intro

Contains short introductory video clips, information of Cayenne on Raspberry Pi and Arduino but also how to use Cayenne on any device.

Pointers to the Cayenne MQTT Libraries and their API

Slide 20: Installing Cayenne on the Raspberry PI

Slide 21: Installing Cayenne on the Raspberry Pi manually

Slide 22: Register your Controller Single Board Computers

Slide 23: Run Cayenne on the Arduino

Slide 24: Basic Arduino Sketch for the Arduino

Slide 25: Cayenne Credentials

Slide 26: Cayenne network layers

The Cayenne credentials are integrated into the MQTT topic string

Value and units are integrated into the payload string

Slide 27: Cayenne and Python

This falls under “bring your own thing” !

Having a look at the Arduino sketch you can see that it uses the

Arduino Cayenne C++ library.

Cayenne MQTT libraries are available in

• C, C++
• Python
• Java

Slide 28: Cayenne and Micropython

The Python Cayenne Client library depends on the Eclipse Paho MQTT library

Micropython uses its own, stripped down “umqtt” (micro mqtt) library

such that the standard Cayenne Client does not work on Micropython

but …

The Python Cayenne Client is Open Source and can be adapted to umqtt, which is what I did for you.

The adapted Client library uses the same API as the original one,

which means that the example programs work unchanged.

Slide 29: The Cayenne Client

When creating a Cayenne Client Class it

• Initializes its internal variables
• Checks if the OLED display is connected and if yes, initializes it
• The Cayenne Client has has a begin method which
• Connects to WiFi
• Connects to the Cayenne MQTT broker at mqtt.mydevices.com
• Subscribes to commands send by Cayenne
• Displays its internal state on the OLED display

Slide 30: The code to connect to Cayenne

Slide 31: Connecting to Cayenne

Slide 32: The empty Cayenne dashboard

-- Uli Raich - 2019-05-14

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