heeyato21c/bleclientblessedpart2

The sample app is working with the library BLESSED-ANDROID

Bluetooth Low Energy Client with BLESSED-ANDROID library (part 2)

This is the part 2 BLE Client example using the library in https://github.com/weliem/blessed-android.

The code is changed to get a better user experience. The changes took place in the BluetoothHandler.java file to connect to the sample server app (BleServerBlessedOriginal).

The library in use (BLESSED-ANDROID) is available here: https://github.com/weliem/blessed-android provided by Martijn van Welie.

For a general overview on Bluetooth Low Energy (BLE) see this perfect article "The Ultimate Guide to Android Bluetooth Low Energy", available as PDF in the docs folder as well: https://punchthrough.com/android-ble-guide/.

Screenshot of the running app after connection to the server.

To check that the server is up and running I recommend to additionally install another app on the second device that allows to connect to the "Server", I'm using nRF Connect for Mobile and it is available on the Google's PlayStore: https://play.google.com/store/apps/details?id=no.nordicsemi.android.mcp&hl=de&gl=US. I provide a simple manual on how to work with the nRF Connect-app here: nRFConnect_manual or see my article on Medium: https://medium.com/@androidcrypto/connect-the-android-nrf-connect-mobile-app-with-a-bluetooth-low-energy-device-8ba900d70286

To get the Client app to build you need 2 additional dependencies, add them in build.gradle(app):

    implementation 'com.jakewharton.timber:timber:5.0.1'
    implementation 'com.github.weliem:blessed-android:2.3.4'

Additionally a new line is necessary in the settings.gradle file (project settings):

add the line maven { url 'https://jitpack.io' }:

dependencyResolutionManagement {
    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
    repositories {
        google()
        mavenCentral()
        maven { url 'https://jitpack.io' }
    }
}

You may notice that the AndroidManifest.xml does not contain any Bluetooth related permissions - they are all set within the library but you are asked to grant some runtime permissions during startup (depending on the Android
SDK version running on your Smartphone the server is running on).

Notice regarding a bug in the blessed-library's log system: in BluetoothServer.java you will notice an "error" on line 185 ("Cannot resolve method 'plant(timber.log.Timber.DebugTree)'"):

Timber.plant(new Timber.DebugTree());

This error is filed as a Timber issue and may get corrected in a newer version. The good news is - you can build your app regardless of this error and you still see the logged messages in your LogCat.

Important notice when working with an emulated device running on a Smartphone (e.g. the BleServerBlessedOriginal):
For security reasons the address the server can get connected is changing very often so when using a client app like the nRF Connect-app it is often necessary to (re)run a scan AND choose the newest entry (mostly the most bottom down one).

This example app is providing just a minimal UI but it is worth to see the LogCat output where you can see e.g. that the example Server app is providing the (server's) time every second. In an enhanced version this data will get shown on the UI...

sample LogFile:

...
BluetoothLeScanner       D  Start Scan with callback
BluetoothLeScanner       D  onScannerRegistered() - status=0 scannerId=9 mScannerId=0
BluetoothCentralManager  I  scan started
BluetoothHandler         I  Found peripheral 'SM-A515F'
BluetoothLeScanner       D  Stop Scan with callback
BluetoothPeripheral      I  connect to 'SM-A515F' (68:D0:C8:D5:4A:AA) using transport LE
BluetoothGatt            D  connect() - device: 68:D0:C8:D5:4A:AA, auto: false
BluetoothGatt            D  registerApp() - UUID=d2d69178-2364-4f70-a731-2cc400eb3d07
BluetoothPeripheral      I  peripheral '68:D0:C8:D5:4A:AA' is connecting
BluetoothPeripheral      D  discovering services of 'SM-A515F' with delay of 0 ms
BluetoothPeripheral      I  discovered 5 services for 'SM-A515F'
BluetoothPeripheral      D  reading characteristic <00002a29-0000-1000-8000-00805f9b34fb>
BluetoothHandler         I  Received manufacturer: samsung
BluetoothPeripheral      D  reading characteristic <00002a24-0000-1000-8000-00805f9b34fb>
BluetoothHandler         I  Received modelnumber: SM-A515F
BluetoothGatt            D  setCharacteristicNotification() - uuid: 00002a2b-0000-1000-8000-00805f9b34fb enable: true
BluetoothHandler         I  SUCCESS: Notify set to 'true' for 00002a2b-0000-1000-8000-00805f9b34fb
BluetoothPeripheral      D  writing <e6070a170d2623073a01> to characteristic <00002a2b-0000-1000-8000-00805f9b34fb>
BluetoothHandler         I  Received device time: Sun Oct 23 13:38:37 GMT+02:00 2022
BluetoothHandler         I  SUCCESS: Writing <e6070a170d2623073a01> to <00002a2b-0000-1000-8000-00805f9b34fb>
BluetoothGatt            D  setCharacteristicNotification() - uuid: 00002a37-0000-1000-8000-00805f9b34fb enable: true
BluetoothHandler         I  SUCCESS: Notify set to 'true' for 00002a37-0000-1000-8000-00805f9b34fb
BluetoothHandler         D  79
BluetoothHandler         I  Received device time: Sun Oct 23 13:38:35 GMT+02:00 2022
BluetoothHandler         D  77
...

Some technical details on this app:

minimum SDK is 21
compiled/target SDK is 33
Gradle version is 7.4

The library blessed-android is MIT-licensed.