Hugo Domenech-Juarez discusses about the possibilities that Android provides by using BLE to connect to sensors and actuators around you. He shares some tips and tricks learned from building a SDK for interacting with the WunderBar, a BLE enabled starter kit for the Internet of Things, and his experiences on how to make your connections secure and fast.

1. What’s all that hype
about BLE?
Software Engineer
relayr
Hugo Doménech Juárez
@hudomju
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2. relayrbring things to life
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8. Why are startups shifting
to hardware products?
- Sensors are cheap!
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9. Prototyping tools
-3d Printer
-CNC Machine
-Laser Cutter
-3d Scanner
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13. What do all these
products have in
common?
-The way they communicate!
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14. Bluetooth
Low Energy
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15. Bluetooth
Classic
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16. Relationship between
Bluetooth and Android
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17. Eclair 2.0 (API 5)
BlueZ
Android 1.x
4.3 (API 18)
Bluedroid
JellyBean
Bluetooth Smart 5.0 (API 20)
Lollipop
Full BLE
Older Broadcom stack - Samsung & HTC < 4.0
Motorola Bluetooth Stack
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18. Bluetooth Low Energy
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19. Central Peripheral
Observer Broadcaster
Android 4.3+ Android 5.0+
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21. BLE Scanning example
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22. BLE Scanning
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23. BLE Scanning
<uses-permission android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
<uses-feature android:name="android.hardware.bluetooth_le"
android:required="false"/>
boolean hasBleFeature() {
return getPackageManager().hasSystemFeature(FEATURE_BLUETOOTH_LE));
}
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24. BLE Scanning
mBluetoothAdapter.startLeScan(mLeScanCallback);
mBluetoothAdapter.stopLeScan(mLeScanCallback);
BluetoothManager manager = (BluetoothManager)
getSystemService(BLUETOOTH_SERVICE);
mBluetoothAdapter = bluetoothManager.getAdapter();
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25. BLE Scanning
private BluetoothAdapter.LeScanCallback mLeScanCallback =
new BluetoothAdapter.LeScanCallback() {
@Override
public void onLeScan(BluetoothDevice device, int rssi,
byte[] scanRecord) {
// You are not in the UI thread
// or in the thread you subscribed for what matters!
}
};
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26. BLE Scanning
/**
* Decodes the services uuid from the advertisement packet since
* {@link android.bluetooth.BluetoothDevice#getUuids()} returns null most of
* the times.
*/
public static List<String> decodeServicesUuid(byte[] data);
/**
* Decodes the device name from the Complete Local Name or Shortened
* Local Name field in the
* Advertisement packet. {@link
* android.bluetooth.BluetoothDevice#getName()} does it already,
* although some phones skip it. i.e. Sony Xperia Z1 (C6903) with Android 4.3
* where getName() always returns <code>null</code>.
*/
public static String decodeDeviceName(byte[] data);
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27. BLE Scanning: Lollipop improvements
mBluetoothAdapter.startScan(filters, scanSettings, scanCallback)
name
deviceAddress
uuid
serviceDataUuid
serviceData
manufacturerId
manufacturerData
Low Power
Balanced
Low Latency
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28. interface ScanCallback {
public void onScanResult(int callbackType, ScanResult result);
public void onBatchScanResults(List<ScanResult> results);
public void onScanFailed(int errorCode)
}
BLE Scanning: Lollipop improvements
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29. Advertisement
GATT server
Hardware feature
- chipset needs to support it
- nexus 9 vs nexus 5 & 7
BluetoothAdapter.isMultipleAdvertisementSupported()
Peripheral mode: Lollipop features
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30. Let’s connect to other
BLE devices!
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31. The GATT Protocol
Peripheral Central
Read - Write - Subscribe
Respond - Push
GATT Peripheral
GATT protocol
Service
Service
Characteristic
Characteristic
Value
Indications
Notifications
Descriptor
Descriptor Descriptor
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Server Client
Generic Attribute Profile

32. The GATT Protocol
class BluetoothAdapterLeScanCallback {
void onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord) {
device.connectGatt(context, false, mBluetoothGattReceiver);
}
}
class BluetoothGattReceiver {
@Override
public void onConnectionStateChange(BluetoothGatt gatt, int status,
int newState) {}
}
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33. The BluetoothGatt
discoverServices
writeCharacteristic
readCharacteristic
writeDescriptor
setCharacteristicNotification
readDescriptor
readRemoteRssi
beginReliableWrite
executeReliableWrite
abortReliableWrite
readMtu
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34. The BluetoothGattCallback
onServicesDiscovered
onCharacteristicWrite
onCharacteristicRead
onDescriptorWrite
onCharacteristicChanged
onDescriptorRead
onRemoteRssiRead
onReliableWriteCompleted
onMtuChanged
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35. Why would you write
characteristics?
A practical example
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39. Data subscriptions: Indication / Notification
gatt.setCharacteristicNotification(characteristic, enable);
descriptor.setValue(ENABLE_NOTIFICATION_VALUE);
gatt.writeDescriptor(descriptor);
gatt.setCharacteristicNotification(characteristic, enable);
descriptor.setValue(ENABLE_INDICATION_VALUE);
gatt.writeDescriptor(descriptor);
gatt.setCharacteristicNotification(characteristic, enable);
descriptor.setValue(DISABLE_NOTIFICATION_VALUE);
gatt.writeDescriptor(descriptor);
@Override
public void onCharacteristicChanged(
BluetoothGatt gatt,
BluetoothGattCharacteristic characteristic) {
}
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40. Reliable Write ?= Long Write
gatt.beginReliableWrite();
characteristic.setValue(data);
gatt.reliableWriteCharacteristic(mBluetoothGatt, characteristic, subscriber);
gatt.executeReliableWrite();
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18 byte: 16 bytes content + 1 offset + 1 length package
Regular Write supports 18 bytes

41. Disconnecting GATT vs Closing GATT
gatt.disconnect();
@Override
public void onConnectionStateChange(BluetoothGatt gatt, int status,
int newState) {
if (newState == STATE_DISCONNECTED &&
noLongerInterestedInTheDevice) {
gatt.close();
}
}
gatt.close();
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42. Stack metrics: why you should close your GATT
- Constants defined in BlueDroid
- Max concurrent active notifications
- BTA_GATTC_NOTIF_REG_MAX
- (4) Android 4.3
- (7) Android 4.4
- (15) Android 5.0+
- Max concurrent GATT connections
- BTA_GATTC_CON_MAX
- (4) Android 4.3
- (7) Android 4.4+
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43. … and one last thing
Security
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44. Security
Pairing
Bonding
Encryption Re-establishment
- Just Works
- Passkey Entry
- Out Of Band
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45. Security: Instability
static class UndocumentedBleStuff {
static boolean isUndocumentedErrorStatus(int status) {
return status == 133 || status == 137;
}
static void fixUndocumentedBleStatusProblem(BluetoothGatt gatt,
BluetoothGattReceiver receiver) {
DeviceCompatibilityUtils.refresh(gatt);
gatt.getDevice().connectGatt(RelayrApp.get(), false, receiver);
}
}
GATT_INSUFFICIENT_AUTHENTICATION
GATT_INSUFFICIENT_ENCRYPTION
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46. Security: Instability
boolean refresh(BluetoothGatt gatt) {
try {
Method localMethod = gatt.getClass().getMethod("refresh", new Class[0]);
if (localMethod != null) {
return (Boolean) localMethod.invoke(gatt);
}
} catch (Exception localException) {
Log.e(TAG, "An exception occurred while performing: refresh”,
localException.getCause());
}
return false;
}
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47. Security: Instability
class DeviceCompatibilityUtils {
boolean createBond(BluetoothDevice device) {
if (isSdk19())
return doCreateBond(device);
return callMethod(device, "createBond");
}
@TargetApi(Build.VERSION_CODES.KITKAT)
boolean doCreateBond(BluetoothDevice device) {
return device.createBond();
}
boolean removeBond(BluetoothDevice device) {
return callMethod(device, "removeBond");
}
}
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48. So we can develop now for Android
Wearables right?
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49. Bluetooth SIG (Special Interest Group)
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51. Questions?
Hugo Doménech
@hudomju
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