Connect multiple devices to one device via Bluetooth

Question

I would like to create a game  where you must connect multiple devices  4   to a main device  ex  a tablet  via Bluetooth  There would be two apps  a main one to which all data would be send from the phones  and to the phones  Is that even possible

User · Answer

Yes you can do so and I have created a library for the same.
This allows you to connect up-to four devices to the main server device creating different channels for each client and running interactions on different threads.
To use this library simple add compile com.mdg.androble:library:0.1.2 in dependency section of your build.gradle .

User · Answer

This is the class where the connection is established and messages are recieved  Make sure to pair the devices before you run the application  If you want to have a slave master connection  where each slave can only send messages to the master   and the master can broadcast messages to all slaves  You should only pair the master with each slave   but you shouldn t pair the slaves together         package com example gaby coordinatorv1      import java io DataInputStream      import java io IOException      import java io InputStream      import java io OutputStream      import java util ArrayList      import java util HashMap      import java util Set      import java util UUID      import android bluetooth BluetoothAdapter      import android bluetooth BluetoothDevice      import android bluetooth BluetoothServerSocket      import android bluetooth BluetoothSocket      import android content Context      import android os Bundle      import android os Handler      import android os Message      import android util Log      import android widget Toast       public class Piconet             private final static String TAG   Piconet class getSimpleName                Name for the SDP record when creating server socket         private static final String PICONET    ANDROID PICONET BLUETOOTH            private final BluetoothAdapter mBluetoothAdapter              String  device address            BluetoothSocket  socket that represent a bluetooth connection         private HashMap lt String  BluetoothSocket gt  mBtSockets              String  device address            Thread  thread for connection         private HashMap lt String  Thread gt  mBtConnectionThreads           private ArrayList lt UUID gt  mUuidList           private ArrayList lt String gt  mBtDeviceAddresses           private Context context            private Handler handler   new Handler                 public void handleMessage Message msg                    switch  msg what                        case 1                          Toast makeText context  msg getData   getString  msg    Toast LENGTH SHORT  show                            break                      default                          break                                                       public Piconet Context context                this context   context               mBluetoothAdapter   BluetoothAdapter getDefaultAdapter                 mBtSockets   new HashMap lt String  BluetoothSocket gt                 mBtConnectionThreads   new HashMap lt String  Thread gt                 mUuidList   new ArrayList lt UUID gt                 mBtDeviceAddresses   new ArrayList lt String gt                     Allow up to 7 devices to connect to the server             mUuidList add UUID fromString  a60f35f0-b93a-11de-8a39-08002009c666                 mUuidList add UUID fromString  54d1cc90-1169-11e2-892e-0800200c9a66                 mUuidList add UUID fromString  6acffcb0-1169-11e2-892e-0800200c9a66                 mUuidList add UUID fromString  7b977d20-1169-11e2-892e-0800200c9a66                 mUuidList add UUID fromString  815473d0-1169-11e2-892e-0800200c9a66                 mUuidList add UUID fromString  503c7434-bc23-11de-8a39-0800200c9a66                 mUuidList add UUID fromString  503c7435-bc23-11de-8a39-0800200c9a66                  Thread connectionProvider   new Thread new ConnectionProvider                 connectionProvider start                          public void startPiconet                 Log d TAG    -- Looking devices --                    The devices must be already paired             Set lt BluetoothDevice gt  pairedDevices   mBluetoothAdapter                      getBondedDevices                if  pairedDevices size    gt  0                    for  BluetoothDevice device   pairedDevices                           X   Y and Z are the Bluetooth name  ID  for each device you want to connect to                     if  device    null  amp  amp   device getName   equalsIgnoreCase  X      device getName   equalsIgnoreCase  Y                                  device getName   equalsIgnoreCase  Z      device getName   equalsIgnoreCase  M                               Log d TAG    -- Device     device getName       found --                            BluetoothDevice remoteDevice   mBluetoothAdapter                                  getRemoteDevice device getAddress                             connect remoteDevice                                                         else                   Toast makeText context   No paired devices   Toast LENGTH SHORT  show                                     private class ConnectionProvider implements Runnable                Override             public void run                     try                       for  int i 0  i lt mUuidList size    i                              BluetoothServerSocket myServerSocket   mBluetoothAdapter                                  listenUsingRfcommWithServiceRecord PICONET  mUuidList get i                            Log d TAG       Opened connection for uuid     i                                        This is a blocking call and will only return on a                            successful connection or an exception                         Log d TAG       Waiting connection for socket     i                                    BluetoothSocket myBTsocket   myServerSocket accept                            Log d TAG       Socket accept for uuid     i                                    try                                  Close the socket now that the                                connection has been made                              myServerSocket close                              catch  IOException e                                Log e TAG       IOException when trying to close serverSocket                                                           if  myBTsocket    null                                String address   myBTsocket getRemoteDevice   getAddress                                 mBtSockets put address  myBTsocket                               mBtDeviceAddresses add address                                Thread mBtConnectionThread   new Thread new BluetoohConnection myBTsocket                                mBtConnectionThread start                                 Log i TAG      Adding     address     in mBtDeviceAddresses                                    mBtConnectionThreads put address  mBtConnectionThread                             else                               Log e TAG       Can t establish connection                                                                          catch  IOException e                        Log e TAG       IOException in ConnectionService ConnectionProvider       e                                                      private class BluetoohConnection implements Runnable               private String address               private final InputStream mmInStream               public BluetoohConnection BluetoothSocket btSocket                     InputStream tmpIn   null                   try                       tmpIn   new DataInputStream btSocket getInputStream                       catch  IOException e                        Log e TAG       IOException on create InputStream object       e                                     mmInStream   tmpIn                             Override             public void run                     byte   buffer   new byte 1                   String message                       while  true                         try                           int readByte   mmInStream read                            if  readByte    -1                                Log e TAG   Discarting message      message                               message                                   continue                                                    buffer 0     byte  readByte                           if  readByte    0       see terminateFlag on write method                             onReceive message                               message                                 else      a message has been recieved                             message    new String buffer  0  1                                                   catch  IOException e                            Log e TAG       disconnected       e                                              mBtDeviceAddresses remove address                       mBtSockets remove address                       mBtConnectionThreads remove address                                                                      param receiveMessage                     private void onReceive String receiveMessage                if  receiveMessage    null  amp  amp  receiveMessage length    gt  0                    Log i TAG             receiveMessage                              Bundle bundle   new Bundle                    bundle putString  msg   receiveMessage                   Message message   new Message                    message what   1                  message setData bundle                   handler sendMessage message                                                    param device             param uuidToTry             return                     private BluetoothSocket getConnectedSocket BluetoothDevice device  UUID uuidToTry                BluetoothSocket myBtSocket              try                   myBtSocket   device createRfcommSocketToServiceRecord uuidToTry                   myBtSocket connect                    return myBtSocket                catch  IOException e                    Log e TAG   IOException in getConnectedSocket   e                             return null                     private void connect BluetoothDevice device                BluetoothSocket myBtSocket   null              String address   device getAddress                BluetoothDevice remoteDevice   mBluetoothAdapter getRemoteDevice address                  Try to get connection through all uuids available             for  int i   0  i  lt  mUuidList size    amp  amp  myBtSocket    null  i                         Try to get the socket 2 times for each uuid of the list                 for  int j   0  j  lt  2  amp  amp  myBtSocket    null  j                          Log d TAG       Trying connection       j     with     device getName        uuid     i                                  myBtSocket   getConnectedSocket remoteDevice  mUuidList get i                        if  myBtSocket    null                            try                               Thread sleep 200                             catch  InterruptedException e                                Log e TAG   InterruptedException in connect   e                                                                                               if  myBtSocket    null                    Log e TAG       Could not connect                        return                            Log d TAG       Connection established with     device getName                          mBtSockets put address  myBtSocket               mBtDeviceAddresses add address               Thread mBluetoohConnectionThread   new Thread new BluetoohConnection myBtSocket                mBluetoohConnectionThread start                mBtConnectionThreads put address  mBluetoohConnectionThread                       public void bluetoothBroadcastMessage String message                  send message to all except Id             for  int i   0  i  lt  mBtDeviceAddresses size    i                      sendMessage mBtDeviceAddresses get i   message                                    private void sendMessage String destination  String message                BluetoothSocket myBsock   mBtSockets get destination               if  myBsock    null                    try                       OutputStream outStream   myBsock getOutputStream                        final int pieceSize   16                      for  int i   0  i  lt  message length    i    pieceSize                            byte   send   message substring i                                  Math min message length    i   pieceSize   getBytes                            outStream write send                                                we put at the end of message a character to sinalize that message                        was finished                     byte   terminateFlag   new byte 1                       terminateFlag 0    0     ascii table value NULL  code 0                      outStream write new byte 1                      catch  IOException e                        Log d TAG   line 278   e                                                      Your main activity should be as follow     package com example gaby coordinatorv1   import android app Activity  import android os Bundle  import android view View  import android widget Button   public class MainActivity extends Activity        private Button discoveryButton      private Button messageButton       private Piconet piconet        Override     public void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           setContentView R layout activity main            piconet   new Piconet getApplicationContext              messageButton    Button  findViewById R id messageButton           messageButton setOnClickListener new View OnClickListener                  Override             public void onClick View v                    piconet bluetoothBroadcastMessage  Hello World--- Gaby Bou Tayeh                                        discoveryButton    Button  findViewById R id discoveryButton           discoveryButton setOnClickListener new View OnClickListener                  Override             public void onClick View v                    piconet startPiconet                                          And here s the XML Layout      lt LinearLayout xmlns android  http   schemas android com apk res android  xmlns tools  http   schemas android com tools  android layout width  match parent  android layout height  match parent  tools context   MainActivity   gt    lt Button     android id    id discoveryButton      android layout width  wrap content      android layout height  wrap content      android text  Discover        gt    lt Button     android id    id messageButton      android layout width  wrap content      android layout height  wrap content      android text  Send message        gt      Do not forget to add the following permissions to your Manifest File         lt uses-permission android name  android permission BLUETOOTH    gt   lt uses-permission android name  android permission BLUETOOTH ADMIN    gt

User · Answer

That is partly possible  for max 2 devices   because device can be connected only to one other device same time  Better solution in your case will be create an TCP server which sends informations to other devices - but that  of course  requires internet connection  Read also about Samsung Chord API - it provides functions which you need  but then every devices have to be connected to one and the same Wi-Fi network

User · Answer

Bluetooth 4 0 Allows you in a Bluetooth piconet one master can communicate up to 7 active slaves  there can be some other devices up to 248 devices which sleeping   Also you can use some slaves as bridge to participate with more devices

User · Answer

I don t think it s possible with bluetooth  but you could try looking into WiFi Peer-to-Peer  which allows one-to-many connections

User · Answer

Yes  that is possible   At its lowest level Bluetooth allows you to connect up to 7 devices to one master device    I have done this and it has worked well for me  but only on other platforms  linux  where I had lots of manual control - I ve never tried that on Android and there are some possible complications so you will need to do some testing to be certain   One of the issues is that you need the tablet to the master and Android doesn t give you any explicit control of this   It is likely that this won t be a problem because   the tablet will automatically become the master when you try to connect a second device to it  or   you will be able to control the master slave roles by how you setup your socket connection  I will caution though that most apps using Bluetooth on mobile are not attempting many simultaneous connections and Bluetooth can be a bit fragile  e g  what if two devices already have a Bluetooth connection for some other app - how might that affect the roles

User · Answer

I think its possible provided if it is a serial data in broadcasting method  but you will not be able to transfer any voice audio data to the other slave device  As per Bluetooth 4 0  the protocol does not support this  However there is a improvement going on to broadcast the audio voice data

[android] Connect multiple devices to one device via Bluetooth

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