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

This is what Cayenne supplies

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

and probably a few other languages

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

Slide 33: Send dummy measurement

Slide 34: Dummy temperature in Cayenne

Slide 35: Dummy temperature parameters

Slide 36: Fix widget to dashboard

Slide 37: Dummy temperature history

Cayenne keeps measurement values which can be plotted as a history plot

or downloaded for further evaluation

Slide 38: A custom widget

Slide 39: A gauge widget

Slide 40: Dummy temperature gauge on the dashboard

Slide 41: Gauge value ranges

Slide 42: It's hot!

Slide 43: Several dummy measurements

Now we want to send a dummy temperature and a dummy humidity value.

How do we distinguish?

They use different communication channels!

Slide 44: Sending temperature and humidity: the code

Slide 45: Dashboard with temperature and humidity

Slide 46: Other measurements

We have seen that we can send temperature with

• client.celsiusWrite(channel,temp)

And relative humidity with

• Client.humidityWrite(channel,hum)

Which other types of measurements can we send?

Slide 47: Measurements implemented in the Cayenne Client

Slide 48: How to control a device?

Cayenne supplies only 2 control widgets:

• a push button
• A slider

Slide 49: Cayenne Slider

We can define the range for the slider in the above case: 0..255

Slide 50: Slider on the dashboard

Slide 51: A Cayenne Button

Slide 52: Dashboard with button

Slide 53: How to receive commands

We must define a callback function, which is called

whenever the user of the Cayenne dashboard

changes a setting on the push button or slider

The callback takes a message parameter which is a tuple of

• Cayenne topic
• Cayenne payload

Slide 54: Cayenne command message

Please compare the command message with our credentials and try to find out

to which channel this command has been addressed. Can you find the values as well?

Remember: we defined the push button on channel 3 and the slider in channel 2!

Slide 55: Exercises!

More on how to interpret this message in the next session

-- Uli Raich - 2019-05-14

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