Android Programming for the nRF8002

Scanning for devices

The scanning for device is done for 2.5 seconds and the results are used to update the listview which holds the list of returned devices. The scanning for the various devices is done using the startScan function which in turn uses the startLeScan function provided by the Android bluetooth library. After 2.5 seconds, this function calls the stopScan function via the mStopRunnable. the mStopRunnable calls the stopScan function and updates the listview using the mListPopulateRunnable. The stopScan function in turn calls the stopLeScan function provided by the Android bluetooth library.

 
 
	private void startScan() {
		mBluetoothAdapter.startLeScan(this);
		setProgressBarIndeterminateVisibility(true);

		handler.postDelayed(mStopRunnable, 2500);
	}

	private Runnable mStopRunnable = new Runnable() {
		@Override
		public void run() {
			stopScan();
			updateText("Press Button To Scan");
			handler.post(mListPopulate);
		}
	};

	private Runnable mListPopulate = new Runnable() {
		@Override
		public void run() {
			listItems.clear();
			for (int i = 0; i < mDevices.size(); i++) {
				device = mDevices.valueAt(i);
				listItems.add(device.getName());
			}
			myarrayAdapter.notifyDataSetChanged();
		}
	};

Connecting to a device is done using the connectToDevice function. This function determines the position of the item in the list view and then connects to it using the device.connect function.

	public void connectToDevice(int i) {
		BluetoothDevice device = mDevices.valueAt(i);
		mConnectedGatt = device.connectGatt(this, true, mGattCallback);
		Log.i("BLEMainActivity:ConnectToDevice",
				"Device State " + device.getBondState());
	}

Communicating with the nRF8002 device

Once the device is connected to the phone, further communication is performed using callback functions. The two callback objects implemented are of the BluetoothGattCallback class and BluetoothGattServerCallback class which are used for the client and server role of the Android program respectively. In this Android program the alarm, battery level and server feature are implemented which is explained below.

Alarm

The Alarm feature of the nRF8002 is implemented using the immediate alert service of the Bluetooth low energy specification. The code snippet that implements the alarm feature is given below.In this function, BluetoothGattCharacterisitic object is first created. This is then associated with the immediate alert service with a mild alert level and then written to the BluetoothGatt object.

	public void soundAlarm(View view) {
		BluetoothGattCharacteristic characteristic;
		characteristic = gattOutside.getService(IMMEDIATE_ALERT_SERVICE)
				.getCharacteristic(ALERT_LEVEL_CHAR);
		characteristic.setValue(ALERT_LEVEL_MILD);

		gattOutside.writeCharacteristic(characteristic);
	}

This function triggers the onCharacteristicWrite method of the BluetoothGattCharacterisitic object. This function then updates the user interface to indicate that an alarm has been sounded.

		@Override
		public void onCharacteristicWrite(BluetoothGatt gatt,
				BluetoothGattCharacteristic characteristic, int status) {

			super.onCharacteristicWrite(gatt, characteristic, status);
			Log.i("BLEMainActivity:onCharacteristicWrite", "Status = " + status);
			updateText("Alarm Sounded!");

		}

Battery level

The battery level feature of the nRF802 is implemented using the battery service of the Bluetooth low energy specification. In this function, BluetoothGattCharacterisitic object is first created. This is then associated with the battery service and the battery level characteristic and then written to the BluetoothGatt object.

	public void getBattery(View view) {
		BluetoothGattCharacteristic characteristic = null;

		characteristic = gattOutside.getService(BATTERY_SERVICE)
				.getCharacteristic(BATTERY_LEVEL_CHAR);
		Log.i("BLEMainActivity:GetBattery", "Characteristic = "
				+ characteristic.toString());

		Boolean b = gattOutside.readCharacteristic(characteristic);
		Log.i("BLEMainActivity:GetBattery", "Reads the battery information "
				+ String.valueOf(b));
	}

This feature triggers the onCharacteristicRead method of the BluetoothGattCallback object. When the Battery button is pressed, the phone sends a read request to the device. The device sends the information  back by calling the onCharacteristicRead method. In this method, we filter the data for the BATTERY_LEVEL_CHAR uuid. If the characteristic matches that UUID, then the battery level information is retrieved and the user interface is updated with the data.

		@Override
		public void onCharacteristicRead(BluetoothGatt gatt,
				BluetoothGattCharacteristic characteristic, int status) {
			super.onCharacteristicRead(gatt, characteristic, status);
			if (DEVICE_NAME_CHAR.equals(characteristic.getUuid())) {
				String DevName = characteristic.getStringValue(0);
				Log.i("BLEMainActivity:onCharacteristicRead", "Device Name is "
						+ DevName + " Status = " + status);
				updateText("Device Name is " + DevName);
			}

			if (BATTERY_LEVEL_CHAR.equals(characteristic.getUuid())) {
				int BattLevel = characteristic.getIntValue(
						BluetoothGattCharacteristic.FORMAT_UINT8, 0);
				Log.i("BLEMainActivity:onCharacteristicRead",
						"Battery Level is " + BattLevel);
				updateText("Battery Level = " + BattLevel);
			}

			
		}

Server

The server feature of the android program enables the nRF8002 device to send information to the phone. The gattServer object is created with mBluetoothGattServerCallback object as one of the parameters. Then a service is created with the IMMEDIATE_ALERT_SERVICE and a characteristic with PROPERTY_WRITE_NO_RESPONSE. This is the characteristic needed for the button press to be sent from the device to the phone. The values needed for characteristic such as set using the setValue method. Finally, the service is then added to the server using the addService method.

 
	public void setupGattServer(View view) {

		final BluetoothManager bluetoothManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
		BluetoothGattServerCallback mBluetoothGattServerCallback = new BluetoothGattServerCallback() {
			@Override
			public void onConnectionStateChange(BluetoothDevice device,
					int status, int newState) {
				Log.i("BLEMainActivity:BluetoothGattServerCallback:onConnectionStateChange",
						"device : " + device + " status : " + status
								+ " new state : " + newState);
			}

			@Override
			public void onServiceAdded(int status, BluetoothGattService service) {
				Log.i("BLEMainActivity:BluetoothGattServerCallback:onServiceAdded",
						"service : " + service.getUuid() + " status = "
								+ status);
			}

			@Override
			public void onCharacteristicReadRequest(BluetoothDevice device,
					int requestId, int offset,
					BluetoothGattCharacteristic characteristic) {
				Log.i("BLEMainActivity:BluetoothGattServerCallback:onCharacteristicReadRequest",
						"device : " + device.getAddress() + " request = "
								+ requestId + " offset = " + offset
								+ " characteristic = "
								+ characteristic.getUuid());
		
			}

			@Override
			public void onCharacteristicWriteRequest(BluetoothDevice device,
					int requestId, BluetoothGattCharacteristic characteristic,
					boolean preparedWrite, boolean responseNeeded, int offset,
					byte[] value) {
				super.onCharacteristicWriteRequest(device, requestId,
						characteristic, preparedWrite, responseNeeded, offset,
						value);
				Log.i("BLEMainActivity:BluetoothGattServerCallback:onCharacteristicWriteRequest",
						"device : " + device.getAddress()
								+ " characteristic : "
								+ characteristic.getUuid() + "Value = "
								+ value.toString());
				updateText("Received button press event");

			}

			@Override
			public void onDescriptorReadRequest(BluetoothDevice device,
					int requestId, int offset,
					BluetoothGattDescriptor descriptor) {
				Log.i("BLEMainActivity:BluetoothGattServerCallback:onDescriptorReadRequest",
						"device : " + device.getAddress() + " request = "
								+ requestId + " offset = " + offset
								+ " descriptor = " + descriptor.getUuid());
			}

			@Override
			public void onDescriptorWriteRequest(BluetoothDevice device,
					int requestId, BluetoothGattDescriptor descriptor,
					boolean preparedWrite, boolean responseNeeded, int offset,
					byte[] value) {
				Log.i("BLEMainActivity:BluetoothGattServerCallback:onDescriptorWriteRequest",
						"device : " + device.getAddress() + " \n descriptor : "
								+ descriptor.getUuid());
			}

			@Override
			public void onExecuteWrite(BluetoothDevice device, int requestId,
					boolean execute) {
				Log.i("BLEMainActivity:BluetoothGattServerCallback:onExecuteWrite",
						"device : " + device.getAddress() + " request = "
								+ requestId + " execute = " + true);
			}
		};
		BluetoothGattServer gattServer = bluetoothManager.openGattServer(
				getApplicationContext(), mBluetoothGattServerCallback);
		BluetoothGattService service = new BluetoothGattService(
				IMMEDIATE_ALERT_SERVICE,
				BluetoothGattService.SERVICE_TYPE_PRIMARY);
		BluetoothGattCharacteristic characteristic = new BluetoothGattCharacteristic(
				ALERT_LEVEL_CHAR,
				BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE,
				BluetoothGattCharacteristic.PERMISSION_WRITE);
		characteristic.setValue(ALERT_LEVEL_CHARACTERISTIC_VALUE,
				ALERT_LEVEL_CHARACTERISTIC_FORMATTYPE,
				ALERT_LEVEL_CHARACTERISTIC_OFFSET);
		service.addCharacteristic(characteristic);
		gattServer.addService(service);
		Log.i("BLEMainActivity:setupGattServer",
				"Gatt server setup complete : " + gattServer.toString());

	}