// Legacy Bluetooth API ( < 21)
	private BluetoothAdapter mBluetoothAdapter;
	private BluetoothAdapter.LeScanCallback mLeScanCallback;
	// Modern Bluetooth API (>= 21)
	private ScanCallback mScanCallback;
	private BluetoothLeScanner mLEScanner;

  @TargetApi(21)
	private void initBluetooth(Activity activity) {
		mActivity = new WeakReference<Activity>(activity);

		final BluetoothManager bluetoothManager =
				(BluetoothManager) mActivity.get().getSystemService(Context.BLUETOOTH_SERVICE);
		mBluetoothAdapter = bluetoothManager.getAdapter();

		if (Build.VERSION.SDK_INT < 21) {
			mLeScanCallback = new BluetoothAdapter.LeScanCallback() {
				@Override
				public void onLeScan(final BluetoothDevice device, int rssi,
									 byte[] scanRecord) {
					mActivity.get().runOnUiThread(new Runnable() {
						@Override
						public void run() {
							Log.i("onLeScan", device.toString());
							connectToDevice(device);
						}
					});
				}
			};
		} else {
			mScanCallback = new ScanCallback() {
				@Override
				public void onScanResult(int callbackType, ScanResult result) {
					Log.d("result", result.toString());
					BluetoothDevice btDevice = result.getDevice();
					connectToDevice(btDevice);
				}

				@Override
				public void onBatchScanResults(List<ScanResult> results) {
					for (ScanResult sr : results) {
						Log.d("ScanResult - Results", sr.toString());
					}
				}

				@Override
				public void onScanFailed(int errorCode) {
					Log.e("Scan Failed", "Error Code: " + errorCode);
				}
			};
		}
	}

	/**
	 * start and stop Bluetooth LE scanning
	 * This will use the legacy API before Lollipop (21)
	 * @param enable scanning active or not
	 */
	private void scanLeDevice(final boolean enable) {
		Log.d("scanLeDevice", "enable="+enable);
		if (enable) {
			mHandler.postDelayed(new Runnable() {
				@Override
				public void run() {
					if (Build.VERSION.SDK_INT < 21) {
						mBluetoothAdapter.stopLeScan(mLeScanCallback);
					} else {
						mLEScanner.stopScan(mScanCallback);

					}
				}
			}, SCAN_PERIOD);
			if (Build.VERSION.SDK_INT < 21) {
				mBluetoothAdapter.startLeScan(mLeScanCallback);
			} else {
				mLEScanner.startScan(filters, settings, mScanCallback);
			}
		} else {
			if (Build.VERSION.SDK_INT < 21) {
				mBluetoothAdapter.stopLeScan(mLeScanCallback);
			} else {
				mLEScanner.stopScan(mScanCallback);
			}
		}
	}