Today, we’re almost constantly connected by miniaturised powerful computers and sensors. The network of these smart devices is making up a new field of computer engineering called the Internet of Things. In this talk, after a short overview of Internet of Things we will show you how to connect your Android device to this type of network using Bluetooth Low Energy.

1. A brief overview
of BLE on Android
Luka Bašek, Android engineer @ Ars Futura

2. Scope
1. Internet of Things
2. Bluetooth Low Energy
3. BLE on Android
4. Showcase
5. Tips
6. Resources

3. 1. Internet of Things
System of devices embedded with sensors, software,
electronics and connectivity to allow it to perform exchanging
information with other connected devices or networks.

4. IoT Features
• Connectivity
• Data
• Communication Protocols
• Analyzing
• Intelligence
• Action

5. Communication protocols
Source: industrytoday.com

6. 2. Bluetooth Low Energy
• WPAN
• 100m range
• Low power and long life span devices
• Easy connection - communication
• Small amount of data

7. Device Roles
• Peripheral (Server)
• Data provider
• Responds to commands
• BLE device (e.g. Smartwatch)
• Central (Client)
• Data consumer
• Send commands
• Mobile device
Peripheral
(GATT Server)
Profile
Services
Characteristics
Central
Connect peripheral to
Read/Write
attributes

8. Generic Attribute Profile (GATT)
• Define how to exchange data using
predefined attributes
• Peripheral side
• Service - a group of one or more
Characteristics
• Characteristics - represents a
piece of information/data that a
server wants to expose to a client
• Operation: Read, Write and Subscribe
• Descriptor - metadata
• Each property has its own UUID
Profile
Service Service
Characteristics
Characteristics
Characteristics
Characteristics
Value
Descriptor
Descriptor
Value
Descriptor
Descriptor
Value
Descriptor
Descriptor
Value
Descriptor
Descriptor

9. Weather station GATT- Example
Weather Station Profile
SERVICE_SENSOR
UUID: ("4fafc201-1fb5-459e-8fcc-c5c9c331914b”)
CHARACTERISTIC_TEMPERATURE
UUID: ("97ac5581-dc51-4408-869b-f672b46025b4”)
PROPERTY_READ + PROPERTY_NOTIFY
CHARACTERISTIC_HUMIDITY
UUID: ("186457ad-2bea-408e-8616-f978a2b0c2ef”)
PROPERTY_READ + PROPERTY_NOTIFY

10. 3. BLE on Android

11. Preconditions
• Minimum API level: 18 (Android 4.3)
• Permissions - AndroidManifest.xml
• System feature – BLE

12. AndroidManifest.xml
<!--Permissions-->
<uses-permission android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
<!--Play Store feature-based filtering-->
<!--Optional-->
<uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>

13. System Feature - BLE
// Check if Bluetooth adapter enabled
fun isBluetoothEnabled(): Boolean =
(getSystemService(Context.BLUETOOTH_SERVICE) as BluetoothManager).adapter.isEnabled
// Check if Bluetooth Low Energy feature available
fun isBleSupported(): Boolean =
(getSystemService(Context.BLUETOOTH_SERVICE) as BluetoothManager).adapter != null &&
packageManager.hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)

14. Scanning
// Start BLE Scanner
bluetoothAdapter.bluetoothLeScanner.startScan(
listOf(scanFilter), // Criteria for filtering results from Bluetooth LE scans
scanSettings, // Bluetooth LE scan settings
object : ScanCallback() { // Processing scan results or errors
override fun onScanResult(callbackType: Int, result: ScanResult) {}
override fun onBatchScanResults(results: MutableList<ScanResult>) {}
override fun onScanFailed(errorCode: Int) {}
})

15. Scanning
2019-10-09 15:26:14.777 27927-27941/co.arsfutura.ble.test W/Binder: Caught a RuntimeException
from the binder stub implementation.
java.lang.SecurityException: Need ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION
permission to get scan results
😧 Location permission? 😧
<!--Optional-->
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-feature android:name="android.hardware.location" android:required="true"/>

16. Scanning
• Be aware about:
• Bluetooth Adapter must be ON
• Location Permission must be granted
• Location Service must be ON
• Scanning must be stopped manually
• bluetoothAdapter.bluetoothLeScanner.stopScan(callback)

17. GATT Workflow
1. Connect to GATT
2. Discover Services
3. Enable Characteristics notifications
4. Start Communicating
• Read/Write Characteristics values
• Read/Write Descriptor values
• Subscribe on Characteristics changes

18. Connecting
fun connectToDevice(context: Context, bluetoothDevice: BluetoothDevice){
// Do not use autoConnect = true
bluetoothDevice.connectGatt(context, false, bluetoothGattCallback)
}

19. Bluetooth GATT Callback
val bluetoothGattCallback : BluetoothGattCallback = object: BluetoothGattCallback() {
override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {}
override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {}
override fun onCharacteristicRead(gatt: BluetoothGatt, char: BluetoothGattCharacteristic, status: Int) {}
override fun onCharacteristicWrite(gatt: BluetoothGatt, char : BluetoothGattCharacteristic, status: Int){}
override fun onCharacteristicChanged(gatt: BluetoothGatt, char : BluetoothGattCharacteristic) {}
override fun onDescriptorWrite(gatt: BluetoothGatt, desc: BluetoothGattDescriptor, status: Int) {}
override fun onDescriptorRead(gatt: BluetoothGatt, desc: BluetoothGattDescriptor, status: Int) {}
}

20. Discover Services
• Call on newState == BluetoothProfile.STATE_CONNECTED
when(newState){
BluetoothProfile.STATE_CONNECTING -> {}
BluetoothProfile.STATE_CONNECTED -> {
gatt.discoverServices()
}
BluetoothProfile.STATE_DISCONNECTING -> {}
BluetoothProfile.STATE_DISCONNECTED -> {}
}

21. Enable Characteristics notifications
// Check if Characteristic notifiable
fun isCharacteristicNotifiable(characteristic: BluetoothGattCharacteristic): Boolean {
return characteristic.properties and BluetoothGattCharacteristic.PROPERTY_NOTIFY != 0
}
// Subscribe on Characteristic change
fun enableNotification(characteristic: BluetoothGattCharacteristic?) {
characteristic?.getDescriptor(SENSOR_DESCRIPTOR_UUID)?.run {
value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE
gatt?.writeDescriptor(this)
gatt?.setCharacteristicNotification(characteristic, true)
}
}
😨

22. Enable Characteristics notifications
override fun onDescriptorWrite(
gatt: BluetoothGatt,
descriptor: BluetoothGattDescriptor,
status: Int ) {
val characteristic = gatt.getService(SERVICE_UUID).getCharacteristic(CHARACTERISTIC_UUID)
characteristic.value = byteArrayOf(1, 1)
gatt.writeCharacteristic(characteristic)
}
🤯

23. Read/Write Characteristics
fun readDataFromCharacteristic(
gatt: BluetoothGatt,
characteristic: BluetoothGattCharacteristic ){
gatt.readCharacteristic(characteristic)
}
fun writeDataToCharacteristic(
gatt: BluetoothGatt,
char: BluetoothGattCharacteristic,
data: ByteArray ) {
char.value = data
gatt.writeCharacteristic(char)
}

24. Limitations
• Central can be connected to 7 peripherals at a time
• Max 15 characteristics can be observed per peripheral
• Transfer data packet can contain maximum of 20 bytes
(MTU!)

25. 4. Showcase
• ESP32 + BME280
• Temperature + Humidity
• github.com/lbasek/ble-weather-station

26. 5. Tips
• Use a blocking screen if the application requires some of
permissions or location service
• Do every GATT operation serially - Command Queue
• Retry Mechanism - Unstable connection $
• GATT_ERROR : 133 🤬

27. Libraries
• RxAndroidBle - github.com/Polidea/RxAndroidBle
• BleGattCoroutines - github.com/Beepiz/BleGattCoroutines
• Sweetblue - sweetblue.io
• Android-BLE-Library - github.com/NordicSemiconductor/Android-
BLE-Library

28. Tools
• nRF Connect for Mobile
• play.google.com

29. 6. Resources
• Bluetooth low energy overview - Official Android Documentation
• Bluetooth Low Energy on Android – Top Tips for the Tricky Bits, Stuart Kent
• Android BLE, Andrew Lunsford
• Practical Bluetooth Low Energy on Android, Erik Hellman
• Getting Started with Bluetooth Low Energy, Kevin Townsend, Carles
Cufí, Akiba, Robert Davidson, O'Reilly Media