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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


Slide 18: Cayenne Start


Slide 19: Cayenne Doc

You find the documentation at


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


Topic attachments
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