AirLink App

The AirLink Mobile app is a communication app skeleton enabling gateway functionality i.e. end to end communication between AirLink Bluetooth® devices and an AirLink server. The app is intended to act as a base that takes care of device interactions, on which different customer experiences can be built by the businesses adopting AirLink.

Once the App Instance is authenticated to the tenant or customer by the application server transferring the provisioning codes, it can provision the phone as an AirLink gateway using the phone’s IMEI. This allows flexibility in lost phones by tying functionality and device ownership to an authenticated user rather than a particular phone. The app provides a UI for entering these codes until the application server is enabled.

The app can be used for the following purposes:

1. Scanning and connecting to AirLink devices automatically

2. Registering AirLink devices to the server securely

3. Updating Pay-as-you-go status of the device securely

4. Posting data from the device to the server with authentication

5. Finding AirLink devices even when the app is not running, and posting their locations to the server

Architecture

Platform : Xamarin

App Development Framework

Xamarin multi-platform mobile app development framework

Xamarin uses a MVVM Architecture

Material Design:

This app uses Material Design for it’s pages:

Xamarin.Forms 101: Using Material Design in Xamarin Forms

Let's take a step back in a new mini-series that I like to call Xamarin.Forms 101. In each episode we will walk through a basic building block of Xamarin.Forms to help you build awesome cross-platform

https://channel9.msdn.com/Shows/XamarinShow/XamarinForms-101-Using-Material-Design-in-Xamarin-Forms

Secure Storage:

This app uses secure storage to save all authentication secrets

Xamarin.Essentials: Secure Storage - Xamarin

The SecureStorage class helps securely store simple key/value pairs. To start using this API, read the getting started guide for Xamarin.Essentials to ensure the library is properly installed and set up in your projects.

https://docs.microsoft.com/en-us/xamarin/essentials/secure-storage?tabs=android

Preparing for Release:

Preparing an Application for Release - Xamarin

After an application has been coded and tested, it is necessary to prepare a package for distribution. The first task in preparing this package is to build the application for release, which mainly entails setting some application attributes. Use the following steps to build the app for release: Each of these steps is described below in more detail.

https://docs.microsoft.com/en-us/xamarin/android/deploy-test/release-prep/?tabs=windows#AOT_Compilation

Next:

NuGet packages

• Acr.UserDialogs (7.2.0.562)

• ble.net(1.2.1)

• NetStandard.Library (2.0.3)

• Newtonsoft.Json (13.0.1)

• PeterO.Cbor(4.5.0)

• Plugin.BLE (2.1.2)

• Rg.plugins.Popup (2.0.0.12)

• sqlite-net (1.6.292)

• sqlite-net-pcl (1.8.116)

• Xamarin.CommunityToolkit (1.3.2)

• Xamarin.Essentials (1.7.0)

• Xamarin.Forms (5.0.0.2291)

• Xamarin.Forms.PancakeView (2.3.0.763-beta)

• Xamarin.Forms.Visual.Material (5.0.0.2291)

• ZXing.Net.Mobile (3.1.0-beta2)

Software

Visual Studio 2019, available for Mac/Windows

https://visualstudio.microsoft.com/vs/

Visual Studio setup and to Git library instructions (Mac)

Dev hardware

Computer recommendation: 8GB RAM, 128GB SSD, 2.0+ GHz processor

Test AirLink Device: BLE Development Kit or any device with BLE.

Test Airlink Gateway Device: Android mobile phone.

Set Up Device for Development - Xamarin

This article explains how to setup an Android device and connect it to a computer so that the device may be used to run and debug Xamarin.Android applications. After testing on an Android emulator, you will want to see and test your apps running on an Android device.

https://docs.microsoft.com/en-us/xamarin/android/get-started/installation/set-up-device-for-development

Platform : Flutter

App Development Framework

Flutter multi-platform mobile app development framework

Flutter uses a layered Architecture

Flutter architectural overview

A high-level overview of the architecture of Flutter, including the core principles and concepts that form its design.

https://docs.flutter.dev/resources/architectural-overview

UI Design:

Flutter packages

To realize the Bluetooth requirements and other core functionality of AirLink, the AirLink app (gateway) uses the following packages:

• line_icons: ^2.0.1

• flutter_blue: ^0.8.0

• cbor: ^5.0.1

• convert: ^3.0.1

• hex: ^0.2.0

• flutter_secure_storage: ^5.0.2

• flutter_dotenv: ^5.0.2

• http: ^0.13.4

• device_info_plus: ^3.2.2

• flutter_barcode_scanner: ^2.0.0

• location: ^4.3.0

• sqflite: ^2.0.2

• provider: ^6.0.3

• app_settings: ^4.1.8

• workmanager: ^0.5.0

• permission_handler: ^10.2.0

• timezone: ^0.9.0

Gateway Sync

The primary role of the AirLink gateway is to keep AirLink devices and the AirLink server in sync with respect to the state and operation of the device. There are three types of data sync:

1. Server updates Device: Pay as you go credits after payment are the primary server update, along with client and configuration data

   

2. Device posts time-series telemetry via primary gateway: Device posts various IoT data described in Nexus Resource Models relating to energy generation, consumption, battery use as well as productive output. In this case, the app actually masquerades as the device and posts data directly into the device's telemetry endpoint. This is enabled for the app via user input of device access token or in a production app, from the server pairing the gateway with devices via sharing of the access token automatically upon sale. Location is added by the gateway.

3. Neighborhood watch gateway posts device advertisement: If the app finds an AirLink device that is not registered as managed by that app, it will post it to the server as a 'piggy-back' onto it's own telemetry, which the server then snips out and decides to post to the original device or forward on to the lost devices database

   

To convert between server-friendly JSON and Bluetooth-service friendly CBOR/.NET objects, the Json.NET and PeterO.CBOR libraries are used. Since the list of properties can vary, we use collections and read the property types = device resource models such as “/batt” and “/temp” from the Bluetooth Descriptors.

Serializing Collections

Product p1 = new Product { Name = "Product 1", Price = 99.95m, ExpiryDate = new DateTime(2000, 12, 29, 0, 0, 0, DateTimeKind.Utc), }; Product p2 = new Product { Name = "Product 2", Price = 12.50m, ExpiryDate = new DateTime(2009, 7, 31, 0, 0, 0, DateTimeKind.Utc), }; List products = new List (); products.Add(p1); products.Add(p2); string json = JsonConvert.SerializeObject(products, Formatting.Indented);

https://www.newtonsoft.com/json/help/html/SerializingCollections.htm

App UX Interactions

App Components

GitHub - EnAccess/Airlink-App

Contribute to EnAccess/Airlink-App development by creating an account on GitHub.

https://github.com/EnAccess/Airlink-App

App Screenshots

Configuring to connect to server

First Step: Enter the information from AirLink Server and Provision the phone as a gateway on the server.

If you enter the data correctly including the tenant administrator, the gateway will provision.

Connecting to AirLink devices

Second Step: Your phone is ready to sync devices. Discover AirLink devices in the vicinity!

Once you find a device, tapping on it simply brings up a list of Nexus resources available on the device

Authorizing the gateway to the device with the Access Token

Always, when connecting to a device, we recommend that the device lock it’s properties until the (default or server) access token is supplied. Authorizing the device supplies it with the default access token.

To authorize the device, simply tap the “Authorize” button. The default access token is already saved on both the App and the device. The device will then compare its access token with this default one. Once they match, the device will be successfully authorized.

Once authorized, you can now read data from the device. The App receives CBOR encoded data from the device, and decodes it into a JSON that is more amenable to posting to the server, and displays this for each property when tapped.

Serializing and provisioning a new device and preparing it for accepting tokens

If a device has just been manufactured, it may not yet be serialized, and be locked with a default access token. Enter this token, then press “Provision” to provision the device. The app will prompt for serial number entry.

Scan or enter by hand this serial number. This is a one-time activity after which the device will forever remember it’s serial number. However if the serial number exists on the server, the provisioning will fail.

As long as a unique serial number is supplied, the server accepts the device and returns a device-specific access token, which the app saves automatically to secure storage as well as displays in the access token field

Entering Tokens

Some properties are writeable, especially true for the PAYG token property, found in the “PC” resource. Tapping this will open a prompt to enter a token. During the Provisioning stage, the token generator on the server is initialized and matched to each device’s secret. Hence, the token can be obtained from the server automatically by syncing the phone, or by manually copying the PC_tkn property value and inputting by hand while the phone is offline.

PAYG tokens are single-use and must match the individual device. If these criteria are met, the device accepts the token.

Synchronizing data with the server over the lifetime of the device

All AirLink properties can be kept in sync between the server and the individual device simply by tapping the Sync button, or using the underlying function in an automated flow in your custom version of the app

The ability of the gateway to post device data to the server (”Client Scope”) as well as pull server data into the device (”Shared Scope”) generates a success message. All failure messages can be effectively debugged using the USB-connected debug mode of Visual Studio.

Copyright 2021 Simusolar Inc