Hardware

To complete this tutorial you need the following components.

Components	Buy	Price	Quantity
Sparcore	Sparkcore Store	$39,00	1
Push button	Component packs	$0.35	1
Led	Component packs	$0.35	1
10K Ohm resistor	Resistor kit	$0.25	1

Software

In order to connect Spark Core to the internet follow the official Getting started guide, access to the Sparkcore IDE and add and the following libraries.

Library	Notes
mqtt.h mqtt.cpp	This is a fork of the Kitard MQTT library setting the max packet size to 512 bytes (needed for Lelylan to work). Add the two files to your project using the Sparkcore IDE (click the '+' button in the upper right corner).

Be sure that files will not be imported twice and if you change filenames (mqtt.h and mqtt.cpp), remember to change import statement too.

Hardware Setup

This schema represents the led, resistor and pushbutton setup. With this setup each time you press the button, the LED is turned on and off.

Lelylan Setup

Open Lelylan Dashboard and create a new device by following 3 simple steps (if you are new to Lelylan, you can sign up for free).

1) Set a meaningful name (e.g. bedroom light).

2) Choose the device type. For this tutorial choose Basic Light.

What is a type? A type defines what a device is by defining its properties, functions and statuses. For this tutorial you do not need to now more about.

3) Choose "Connect with MQTT" as connectivity option.

In this tutorial we'll use MQTT, a publish subscribe protocol for the Internet of Things.

4) Get the Device ID and Device Secret.

Once the device is created, click the settings link (placed under the device name) and get the device ID and device secret. You'll need them in the next section.

Code

Once the (virtual) device is defined on Lelylan you need to make it communicate with Arduino. Copy the sketch below and change the following variables: deviceId, deviceSecret, outTopic, inTopic and clientId. It will not take more than one minute.

You are done

Access Lelylan Dashboard and control your connected light from mobile, tablet and desktop. If any problem occours, let @lelylan know.

Code Explained

To better understand how the Arduino sketch works, follows a brief description of what most important sections do.

Device Settings

The deviceId and deviceSecret are used to authenticate the physical object (Arduino) with Lelylan. To get the device credentials open the Dashboard, select the desired device, click on settings and copy the Device ID and the Device Secret.

Lelylan uses MQTT, a publish subscribe protocol for the Internet of Things. To make Lelylan communicate with Arduino you need to set two topics: one receiving messages from Lelylan (inTopic) and one sending messages to Lelylan (outTopic). These topics are unique and identified by the device id.

Finally, you need to set the MQTT client id, a random string not longer than 23 bytes.

JSON Payloads

Every message exchanged with Lelylan is made up by a list of properties where each of them contains the property ID and the property value. For the type "basic light" we only have the status property with ID 518be5a700045e1521000001 accepting the values on and off.

MQTT Signatures

To open the communication with Lelylan you need to initialize the MQTT client settings by defining the MQTT server address, the MQTT server port, a callback function (called every time a message is received from Lelylan) and the ethernet client.

Led and Button Pins

Here we define the pins used to connect the led and the button. If you have followed the Fritzing diagram you don't need to change anything. If you use different pins, remember to change these values.

Led and Button Logics

Here we define the variables you need to make the button work correctly. If you are new to push buttons check out this switch tutorial.

Spark Core Setup

Here the Spark Core opens the connection with the Lelylan MQTT server, and set the led and button pin mode.

During the MQTT connection phase the client set the deviceId as username and the deviceSecret as password. If the credentials are missing or not valid, the connection will be rejected.

To keep the connection alive after temporary loss of internet connection we check if the client is connected. When not, the Spark Core reconnects to Lelylan MQTT server. This is why the lelylanConnection method is also defined into the loop function (see below).

Spark Core Loop

Here we define the loop function where we use a pushbutton as a switch. Each time you press the button the led is turned on or off. To make it work we need to add a debounce, otherwise everytime you press the button a single press would be recognized as multiple press.

Once the push button is pressed (the led status changes) we publish a message to Lelylan with the updated led status.

Publish Messages to Lelylan

To let Lelylan know when the led is turned on or off, you need to publish a message to the MQTT out topic with the updated properties.

Receive Messages from Lelylan

When a user updates a device property using Lelylan Dashboard a message is published to the topic devices/<DEVICE-ID>/get (in topic) and it's received from Spark Core through the callback function. We check it the received message turns on or off the light and once the led status is updated, a confirmation message must to be sent back to Lelylan to confirm that the physical changes were successfully applied (if not, the device will keep being pending).

Troubleshooting

If any problem occours check out the following points. If still not working mail or tweet us.

• Message Size - Using Lelylan your messages are usually bigger than 128 bytes. For this reason we forked the original PubSubClient setting the max packet size to 512 bytes.

Get inspired

Did you like this tutorial? You could be interested in the following ones.

If you want to learn more check out the Lelylan Dev Center and Lelylan Lab.

Social

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Thanks

This article is brought to life from the following people. Mail or Tweet us for any idea that can improve the project.