Build an Urban Air Quality Monitoring System

Using IoT Technologies

Metropolitan cities face their own unique challenges when it comes to air pollution. In this project article, Dhairya details his design of a fully equipped, low-cost urban air quality monitoring system for cities in developing countries, powered by Soracom and AWS IoT Service. It also supports email alerts.

With that in mind, I have developed my Soracom-powered Urban Quality Monitor (SUQM). It is designed specifically for urban environments. Please note that I’ve designed this device with cities in India in mind. Metropolitan areas like Delhi (the urban territory in India containing New Delhi) is one of the most polluted areas in the world when it comes to air pollution. The final system without any enclosure is shown in Figure 1.

So, let’s get started with the project. First, let’s have a look at the project diagram, which is shown in Figure 2. The diagram shows how the flow of data takes place in the whole system. We use various Soracom services—services that come with the SIM card access. The “brain” of our monitoring node will be a Raspberry Pi SBC. You can use any Raspberry Pi, including the Pi Zero W. But I used the Raspberry Pi 3 board for this demo because I didn’t have a mini-HDMI cable with me. But the source code for this project will work identically on any other Pi device that has on-board Bluetooth.

HARDWARE AND SOFTWARE

Let’s have a look at the required components for the project. The hardware components required for this project are pretty straight forward because they are available as a kit. We will be using the Soracom IoT Starter Kit with Raspberry Pi for this project. It is shown in Figure 3 and it contains the following components:

Soracom Global SIM Card: The Soracom Global SIM provides cellular data connectivity and SMS functionality on 2G, 3G, 4G LTE and Cat M1 networks in over 120 countries around the world. It’s fully managed right from your browser on the Soracom User Console (also included as part of the starter kit)

Raspberry Pi Zero W and Official Case: Small, easy-to-use Linux computer that supports a wide variety of programming environments for IoT development.

Huawei 3G USB Modem (MS2131i) and USB OTG Adapter Cable: A great modem that provides 2G and 3G cellular connectivity, designed especially for IoT projects, plus a USB OTG cable to hook it up to the Raspberry Pi

Ultrasonic Range Finder (HC-SR04): This simple yet reliable sensor measures distance using ultrasonic vibrations, and is accurate up to 10′. I love this sensor because I can quickly capture data for easy visualization, just by waving a hand in front of it!

8GB Micro-SD card and Micro-SD card reader: Provides storage for your Raspberry Pi, plus a card reader so you can edit its contents on your computer.

Perma-Proto breadboard and color-coded wires: This is for connecting the Ultrasonic Range Finder to your Raspberry Pi, without soldering anything.

USB-A to Micro-USB cable: To power your Raspberry Pi from your computer or other USB power source

Beyond those kit components, Soracom also provided me with $30 worth of Soracom SIM credits along with $25 worth AWS of credits to use the required AWS services. Apart from the Soracom kits, we will also be using NXP Semiconductor’s Rapid IoT prototyping kit [1]. It is the perfect all in one sensor for our project. It measures all the required values for urban quality monitoring, which includes temperature monitoring (in degrees Celsius), humidity monitoring (in percentage), ambient light monitoring (in lux), pressure monitoring (in kPa) and air quality monitoring (in parts per million or ppm).

On top of this, it has on-chip Bluetooth connectivity, which makes it very easy for our Raspberry Pi SBC to receive the sensor data wirelessly. In addition to the two kits, we will be using a couple additional components including an Android device, for app development and testing and a battery bank to power our device and make in portable.

There several of software components used in this project. The software components used are:

Raspberry Pi OS—Operating system for Raspberry Pi (previously called Raspbian)
Soracom Harvest—Data collection and visualization services for the IoT device
Soracom Funnel—An adapter that transfers data from the device directly to a specific cloud service
Soracom Lagoon—An easy-to-use, personalized dashboarding tool that uses data collected with Soracom Harvest services
AWS IoT Core—A managed cloud service that lets connected devices easily and securely interact with cloud applications and other devices
Android Studio—This will be used for application development and testing.

MONITORING NODE SETUP

Now that we’re aware of the components to be used in the project, let’s get started with building our monitoring system. First, we’ll start by setting up our hardware—or monitoring node. For this, we will have to first set up our Soracom IoT Starter Kit, which includes installation of Raspberry Pi OS, setting up the Pi to support the Huawei 3G Modem (SIM support) and, finally, connecting to the required Soracom services.

The process is quite long and tedious but a very good step-by-step documentation for this is provided by Soracom itself. The link [2] to that document can be found in RESOURCES. Follow it step by step and, if everything goes as planned, by the end of the setup process you will have successfully connected your Raspberry Pi to Soracom Harvest and you will be publishing the ultrasonic sensor data in real time.

We will be using the ultrasonic sensor Python code as the basis for developing our own project code in which we will connect to our Rapid IoT prototyping kit via Bluetooth with Python and sending different sensor data values every 30 seconds.

SORACOM CONSOLE AND AWS IOT CORE

The next step is to set up Soracom Console for our project. We will also set up AWS IoT core because we want to show this data in a mobile app too. Please note that this article only deals with Android app development. First, let’s look at the Soracom Console, which includes the setup of software components Soracom Harvest, Soracom Funnel and Soracom Lagoon.

Soracom Console setup: After you login to your Soracom Console, you will see the homepage where your SIM card is listed. If your device is on and running the demo ultrasonic code, you will see that it shows that the device session is online. The next step is to set up “actions.” You will find an Actions tab beside the Register SIM and Details button. Just press that and select the Change Group option. After that, you will be redirected to a new page. There, create a new group. Choose a name of your liking. Then you will be prompted to select which services to use for this project. Select Harvest and Funnel.

The basic flow goes like this: Our node sends the sensor data to the Soracom Harvest platform and this data is sent to Soracom Lagoon (a dashboard service) and the Soracom Funnel IoT Adapter is used to send this data to AWS IoT. Now, just create the group. The Harvest setup has already been done in the tutorial. So, now we just have to setup the Funnel IoT service to send our data to AWS IoT. The whole step-by-step tutorial is provided in the Soracom tutorial at [2].

Soracom Lagoon setup: Now we will set up the Soracom Lagoon for data visualization. From the homepage of the Console, tap on the menu tab situated on the top left corner, search for Soracom Lagoon and click on it. Then create a username and select the “Free or Maker” account so that you can subscribe successfully to this service. Next, just open the Soracom Lagoon dashboard and create a new dashboard. You will find all the same sensor names that you found in your Harvest data. That’s because it’s a tool that uses Soracom Harvest data as its source.

Now, create a dashboard and insert the graphs and all the visual elements you want on your dashboard. Using the dashboard is very easy, and adding widgets and graphs is even easier. You just have to use the buttons provided on the top right corner. Just hover on them and you will know the functionality of each button. This will finally complete our dashboard. When we start our monitoring system, it will provide almost real time data, with a deficit of 30 seconds—a limitation of the Free or Maker plan. The dashboard I created is shown in Figure 4.

Next, we set up an alert system using Lagoon, which sends an email alert when a particular sensor value goes beyond the programmed threshold. A typical email notification is shown in Figure 5. To set this up, we have to do the following: First, go to the Lagoon console and select any of the graphs. Now from the drop-down menu, press the Edit button. After this, as the menu opens, go to the Alerts tab and create a new alert by setting the threshold value and other parameters. Next, we have to attach a notification to this alert. But, to do so we first need to create a new notification channel. So, from the leftmost menu, go to the Alerting tab and select the Notification Channels tab. Now, create a new channel by pressing on the green New Channel button. Fill in all the required details and select your desired notification source. I’ve used email for this purpose. Finally, just go back to the dashboard and the Alert section and attach the notification channel to the datapoint.

This completes the Soracom console setup for our project. Note that you may also export this data from the Harvest data screen, which stores up to 40 days of data. That could be useful if you would like to store this data locally for further analysis or for training a machine learning model. A machine learning model can easily run on a Raspberry Pi SBC thanks to the latest tflite (TensorFlow Lite) models and TinyML.

AWS IoT Core setup: The next step is to set up the AWS IoT Core for our project. First, create an AWS account and verify your payment method to activate your account. Don’t worry about automatic transactions. You will get to use a majority of the AWS services, with some limits, for free for the first 12 months. Next, sign in as the root user of the account and you will be taken to the AWS management console. After that, go to the IoT Core from the Services tab on top of the screen and you will come to the AWS IoT Core home screen. The home screen of AWS IoT Core is shown in Figure 6. Now, to set up this for our project, just follow the tutorial documentation at [3]—the same document you used while setting up Soracom Funnel earlier.

HARDWARE CODE AND ANDROID APP

Now let’s discuss hardware code. To make it easier to follow, I’ve broken the Python code into small snippets. These snippets, along with descriptions of the purpose of each, are detailed in Listing 1, Listing 2 and Listing 3. Note that this code is written in Python 2, but writing it in Python 3 is pretty straightforward. You just have to change the print statements for the most code.

Next, we move on to the Android app part, which is the final part of our project. We will create a very simple app that lets us view the raw data that we send to AWS IoT. Creating visualizations for this data is an option, and probably quite easy for someone with some experience in app development. You can find a link to the GitHub repository [4] for this project In RESOURCES at the end of the article. Our android app will act as a MQTT client and receive the data sent to AWS by Soracom Funnel. For now, we will just display the raw message in json format, but you can also use interactive Android tools to visualize this data.

Now let’s move on with the app development. I would like to thank Felipe Ramos Da Silva for assisting me with this development. We will start with an already-developed Android app in my GitHub repository [4]. We will delve into this project explaining each part, and how we can prepare the app for be used. Go to the AndroidPubSubWebSocket folder in
my GitHub repository. Download the necessary files. Be sure that you have an AWS account to settle up all the configurations on cloud side.

Let’s work first in the AWS side and set up our cloud environment. On the AWS side, there are two main steps to be followed. First, we will have to create some roles on IAM (Identity Access Management), that allow you to securely manage access to AWS services and resources. Because we aren’t using any kind of authentication with the app, we have to create a role to specify to AWS that some devices can use services without being authenticated. Even though this article is a theorical and educational project, it’s not recommended that you enable unauthenticated devices to use the services of your AWS account.

In your AWS console, go to Cognito > Manage Identity Pools > Federated Identities > Create New Identity Pools. Here you will be creating a federated identity pool to give access to your unauthenticated devices. Now you can give a name to the pool and select the option: Enable access to unauthenticated identities.

Once you’ve done that, while creating the pool the console will request that you to create two new roles on IAM. Create these roles and go to IAM > Roles and select the roles that you have created. In the role menu that you’ve created, you will have to attach a policy giving some permissions to this role. Furthermore, in the existing roles, search for AWSIoTFullAccess and attach it. The final platform after setup looks as shown in (Figure 7). Now we are good to go to AWS IoT Core. But don’t forget to note the Cognito Pool ID of the federated identity pool that you’ve created. We will use it in the android app to provide the authentication path to the application.

ACCESSING FROM AWS CONSOLE
In order to make your first IoT device in AWS services, you will have to go to IoT Core from the AWS Management Console. We will create a Thing for our project. To do that, go to IoT Core console and on the sidebar go to Manage > Things, and on the right corner click Create. Next, select the option Create a Single Thing. Because we are doing this project only for learning purposes, just give a name to the device and don’t change any other option. And don’t create a certificate at this time. Once the device is created, you can go into the device’s options. Among a lot of options here, there are two that are important for us:

Shadow: A json document used to store and retrieve current state information for a device. Simply put, it’s MQTT topics that you can publish messages in JSON format.
Interact: In this option you will able to see the REST endpoint to communicate with your device, and some default MQTT topics for your shadow.

Take note of the device endpoint and the update shadow topic. Figure 8 shows both these values. Now, we will move onto the Android app development part. The android app will only have the AWS SDK package as a dependency. If you are using Android Studio, it will download automatically for you when you import the project in your IDE. But if you are using Eclipse, you will have to download it manually. You will need to download the AWS SDK for Android [5] and extract and copy these jars into the libs directory for the project.

LAYOUT

Because this is a simple project, it has only a layout xml file and an activity. In the layout file (activity_main.xml) you will not have to change anything—unless you would like to change the actual GUI of the main activity. Summarizing, this layout is only some buttons and edit texts that will handle the subscribed MQTT topic, or publish a message, where each of them has an ID to be bonded with some object in the main activity class. While this project is binding view elements in the common and tiring way, you should take a look at Butter Knife. Butter Knife is a view binding method that makes the binding easier and faster—making your code more readable and cleaner.

See the Layout file by downloading the necessary files from my GitHub repository [4] and opening the android application folder in Android Studio. Now, let’s move on to the Main Activity of the app.

In the main activity, there are some variables to be changed, they are:

CUSTOMER_SPECIFIC_ENDPOINT—This is the endpoint of your AWS IoT Core created Thing.

COGNITO_POOL_ID—This the ID of the Cognito Identity Pool that you have created.

MY_REGION—Your Thing was created in some of the AWS availability zones. Note where you’ve created it.

This Java code is very simple and can be extended for many IoT android projects. In the onCreate method, all the view elements will be bound with the attributes of the activity Java class, and two important classes for our project will be instantiated.

CognitoCachingCredentialsProvider—This is the class from AWS SDK that will grant access to all your unauthenticated devices. If the Cognito ID was passed correctly, a token will be given to the device.

AWSIotMqttManager—The MQTT manager that will handle all the connections. If the access to AWS services is granted by CognitoCachingCredentialsProvider, the connect method will be called, passing a callback that monitors the status change of the connection. Note that, in this part of the code, the process when the status changes will not block the UI, so it can be running on UI Thread.

In the onCreate method, the buttons for subscribing and publishing a topic will be assigned to a callback to trigger these events:

subscribeClick—When the subscribe button is pressed, a topic will be subscribed and a callback for new arriving messages will be created. Now you can receive messages from other devices!

publishClick—When this button is pressed, the message will be published on the correspondent topic.

disconnectClick—Used to disconnect from your endpoint, and connect in another.

The activity code is part of the app source code that is included in my GibHib repository for this project [4]. Run the code, and if everything goes well, you will now have a simple way to establish communication between your hardware and the android app, which was the aim of this project. The final app screen is shown in Figure 9. This app is just a simple example that demonstrates how can we get our AWS data on Android in real-time. But, unlike the raw message we obtain in this app in json format, we can easily parse this data to get intense visualization tools in android like graphs, charts and so forth.

First, we have to parse the raw json data. That can be done easily by following the tutorial at [6]. Now, for visualization purposes, we can use the AnyChart-Android library or package. The whole package is open source and its GitHub link is at [7]. Using that, you can easily make you app more interactive and user friendly. For my part, I haven’t attempted it because of my lack of proficiency in Android and Java programming.

CONCLUSION AND FUTURE PLANS

In conclusion, let me emphasize that urban areas are at a massive risk with their increasing population and pollution. And I think this system can be very useful in stopping the current scenario, or at the very least, slowing down its effects. This is just the beginning. With the collected data and the real-time data, we can design a number of applications to improve this situation, or at least figure out the worst affected areas and the reasons behind it.

As for future plans, I have some points in mind that I think will improve this project a lot. First, I’d like to develop a low-cost device that can act as a sensor node. To do this, I’d use the Raspberry Pi Zero and the Soracom connectivity discussed in this article. My second idea is to develop a network of such nodes, so that we can get plenty of data points. This will provide sufficient data to visualize on advanced tools like Heat Maps. Finally, one of the areas of improvement is security for this system. This can be easily achieved by a more in-depth study into the features of AWS Security protocols and credentials.

My thanks to Soracom and Hackster for their wonderful contest that was the basis of this project. My thanks to Soracom for providing me with such wonderful hardware and developer support too. Thank you to Hackster for providing a great platform for Soracom to host its contest, allowing us to interact with people from all around the world and share innovative projects. 

RESOURCES
References:
[1] Rapid IoT Prototyping Kit: https://www.nxp.com/design/designs/nxp-rapid-iot-prototyping-kit:IOT-PROTOTYPING
[2] Starter Kit setup: https://developers.soracom.io/en/start/iot-starter-kit/raspberry-pi
[3] AWS IoT Core setup with Soracom Harvest: https://developers.soracom.io/en/start/aws/funnel-iotcore
[4] GitHub Repository link:https://github.com/Dhairya1007/SUQM
[5] AWS SDK for Android http://aws.amazon.com/mobile/sdk
[6] https://abhiandroid.com/programming/json#JSON_Parsing_In_Android
[7] AnyChart-Android library or package. The whole package is opensource and its GitHub link is at https://github.com/AnyChart/AnyChart-Android

NXP Semiconductors | www.nxp.coM
Raspberry Pi Foundation | www.raspberrypi.org
Soracom | www.soracom.io

PUBLISHED IN CIRCUIT CELLAR MAGAZINE • MARCH 2021 #368 – Get a PDF of the issue

Dhairya A. Parikh

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Dhairya Parikh is an Electronics Engineer and an avid project developer. Dhairya makes projects that can bring a positive impact in a person’s life by making it easier. He is currently working as an IoT engineer. His projects are mainly related to IoT and machine learning. Dhairya can be contacted on dhairyaparikh1998@gmail.com

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