Send dummy measurement

Dummy temperature in Cayenne

Dummy temperature parameters

Fix widget to dashboard

Dummy temperature history

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

or downloaded for further evaluation

A custom widget

A gauge widget

Dummy temperature gauge on the dashboard

Gauge value ranges

It's hot!

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!

Sending temperature and humidity: the code

Dashboard with temperature and humidity

Other measurements

We have seen that we can send temperature with

• client.celsiusWrite(channel,temp)

• Client.humidityWrite(channel,hum)

Measurements implemented in the Cayenne Client

How to control a device?

Cayenne supplies only 2 control widgets:

• a push button
• A slider

Cayenne Slider

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

Slider on the dashboard

A Cayenne Button

Dashboard with button

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

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!

Exercises!

More on how to interpret this message in the next session

Changed Callback

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

Cayenne functionality

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

Signing up for Cayenne

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

Cayenne Start

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

Installing Cayenne on the Raspberry PI

Installing Cayenne on the Raspberry Pi manually

Register your Controller Single Board Computers

Run Cayenne on the Arduino

Basic Arduino Sketch for the Arduino

Cayenne Credentials

Cayenne network layers

The Cayenne credentials are integrated into the MQTT topic string

Value and units are integrated into the payload string

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

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.

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

The code to connect to Cayenne

Connecting to Cayenne

The empty Cayenne dashboard

Controlling a LED

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

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

Callback result

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

Sending dummy temperature data

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

Subscribe a callback

Accessing the WiFi network

Setting up an IoT

Session3: MQTT and Cayenne

Uli Raich

Formally CERN, Geneva, Switzerland

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

Accessing the WiFi network from Micropython

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

MQTT Demo

The Micropython library

A MQTT example using umqtt.simple

Slide 1: Title

-- Uli Raich - 2019-05-14

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