1. 1 Working with the Bluetooth radio Nilanjan Banerjee Mobile Systems Programming University of Arkansas Fayetteville, AR nilanjan.banerjee@gmail.com

2. How does the Bluetooth protocol work? discovery pairing RFComm Scanning for other BT Devices --- inquiry scan Followed by page scan. Take about 15-20 seconds Authentication process where two devices exchange a pin. Once paired the info is maintained in service discovery db Service Discovery Every server device publishes a set of service that client connect to After pairing the devices communicate amongst each other over a RF communication channel

3. Android implementation overview? BluetoothAdapte r BluetoothDevice BluetoothServerSocket BluetoothSocket Access to the local Bluetooth device and its properties Access to any Bluetooth device (usually remote) Socket interface for the server-end Socket interface for the client-end

4. Bluetooth Permissions Permission BLUETOOTH is used ONLY for communication –Requesting a connection, accepting a connection, and transferring data Permission BLUETOOTH_ADMIN is used for controlling the device –Device discovery, changing the settings of the Bluetooth device etc.

5. Setting up the Bluetooth Adapter –Use BluetoothAdapter to get a reference to the Bluetooth device If Bluetooth device is not supported the adapter returns a NULL –Enable Bluetooth device using an Intent and starting a new Activity with the Bluetooth device It does ask the user whether he wants to enable the device How do you know that the Bluetooth device is enabled? --- the resultcode in onActivityResult() callback will be RESULT_OK. Bluetooth adapter = BluetoothAdapter.getDefaultAdapter(); if(adapter == null) { //Device does not support Bluetooth. } if(!adapter.isEnabled()) { Intent enableBT = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); startActivityForResult(enableBT, REQUEST_ENABLE_BT); }

6. Discovering devices Set pairedDevices = adapter.getBondedDevices(); if (pairedDevices.size() > 0) { for(BluetoothDevice device: pairedDevices) { //get access to the devices name through device.getName(); //get access to the devices MAC address through device.getAddress(); } //discovering devices adapter.startDiscover(); private final BroadcastReceiver mReceiver = new BroadcastReceiver() { public void onReceive(Context context, Intent intent) { String action = intent.getAction(); if(BluetoothDevice.ACTION_FOUND.equals(action)) { BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE); //get the name of the device through device.getName(); //get the MAC address of the device through device.getAddress(); } IntentFilter filter = new IntentFilter(Bluetooth.ACTION_FOUND); registerReceiver(mReceiver, filte); //register for broadcast receiver when a BT device is found. –First step is to find devices that you have already paired with: these are devices you do not need to pair to get connected –Use a broadcast receiver discover new Bluetooth devices

7. Enabling Discovery Intent discoverable = new Intent(BluetoothAdapter.BLUETOOTH_ACTION_DISCOVERABLE); Discoverable.putExtras(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300); startActivity(discoverable); –Why do you need to set a devices Bluetooth to Discoverable If you are a server and you want client devices to connect to you If you want other devices to see you in order to pair with you –You set it up using an Intent A parameter that you can set up is the time that you want the device to be discoverable Default = 120 seconds, 0 forever, max = 3600, 3600 – default is taken.

8. Connecting to a device (server-side) –Just like a TCP socket called BluetoothServerSocket –You wait on an accept() (blocking call) till you receive an incoming connection request –accept() is blocking so it should happen in a separate thread from the UI thread public class AcceptConnection extends Thread{ private final BluetoothServerSocket soc; public AcceptConnection() { try { soc = adapter.listenUsingRfcommWithServiceRecord(NAME, UDID); } catch(IOException e){} } public void run() { BluetoothSocket socket = null; while(true) { try { soc.accept(); } catch(IOException e) { break; } if(soc != null) { //spawn another thread to manage the connection } } Name of the service Unique ID for the service

9. Connecting to a device (client-end) –Connect() is a blocking call so needs to happen in a thread separate from the UI thread –From the remote device, create a Rfcomm channel for data transfer. public class ClientThread extends Thread { BluetoothSocket temp = null; public ClientThread(Bluetooth device) { try { temp = device.createRfcommSocketToServiceRecord(UDID); }catch(Exception e) { } } public void run() { adapter.cancelDiscover(); try { temp.connect(); } catch(Exception e) { } //manage the connection }

10. Data transfer using the server/client socket –Attach an InputStream and an OutputStream to the the socket –Use read(byte[]) and write(byte[]) to read and write --- both are blocking calls public class ClientThread extends Thread { BluetoothSocket temp = null; public ClientThread(Bluetooth device) { try { temp = device.createRfcommSocketToServiceRecord(UDID); }catch(Exception e) { } } public void run() { byte[] buffer = new byte[1024]; int numbytes; adapter.cancelDiscover(); try { numbytes = temp.read(buffer); //do whatever you want with the bytes } catch(Exception e) { } //manage the connection }