Android Bluetooth App Connection Guide

TL;DR

This guide shows you how to connect an Android app to a Bluetooth module (like HC-05 or similar). It covers checking permissions, scanning for devices, pairing, and establishing a connection. We’ll also look at basic data transfer.

Connecting Your Android App to a Bluetooth Module

1. Check Bluetooth Permissions:
   • In your app’s AndroidManifest.xml file, make sure you have the necessary permissions:

     <uses-permission android_name="android.permission.BLUETOOTH"/
     <uses-permission android_name="android.permission.BLUETOOTH_ADMIN"/
     <uses-permission android_name="android.permission.ACCESS_FINE_LOCATION"/
     

   • Important: ACCESS_FINE_LOCATION is required for Bluetooth scanning on newer Android versions, even if you don’t need location data. Explain this to your users in the app description.
2. Enable Bluetooth:
   • Use the BluetoothAdapter class to check if Bluetooth is enabled:

     BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
     if (bluetoothAdapter == null) {
         // Device does not support Bluetooth
     }
     
     if (!bluetoothAdapter.isEnabled()) {
         Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
         startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
     }

   • REQUEST_ENABLE_BT is an integer you define (e.g., 1) to identify the result of this request.
3. Scan for Bluetooth Devices:
   • Start a scan using BluetoothAdapter.startDiscovery():

     bluetoothAdapter.startDiscovery();

   • Register a BroadcastReceiver to listen for discovered devices:

     IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
     registerReceiver(mBroadcastReceiver, filter);

   • In your BroadcastReceiver’s onReceive() method, handle the found device:

     private final BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
         @Override
         public void onReceive(Context context, Intent intent) {
             String action = intent.getAction();
             if (BluetoothDevice.ACTION_FOUND == action) {
                 BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                 // Add the device to your list
             }
         }
     };

   • Stop scanning after a reasonable time using bluetoothAdapter.cancelDiscovery().
4. Pair with the Device:
   • Create a BluetoothDevice object from the discovered device’s address and MAC address.
   • Attempt to pair using device.createBond():

     if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
         // Request permission
     }
     
      device.createBond();

   • Pairing may require user confirmation on both the Android device and the Bluetooth module (e.g., entering a PIN).
5. Connect to the Paired Device:
   • Get a BluetoothSocket from the paired device using UUID:

     UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805f9b34fb"); // Standard Serial Port Profile
     try {
         socket = device.createRfcommSocketToServiceRecord(MY_UUID);
     } catch (IOException e) {
         // Handle exception
     }

   • Connect to the socket:

     socket.connect();

   • Handle connection errors.
6. Data Transfer:
   • Use an InputStream and OutputStream attached to the BluetoothSocket for sending and receiving data:

     InputStream inputStream = socket.getInputStream();
     OutputStream outputStream = socket.getOutputStream();

   • Write data to the outputStream (e.g., using outputStream.write(data)).
   • Read data from the inputStream (e.g., using inputStream.read(buffer)).
7. Clean Up:
   • Close the socket and unregister the receiver when your activity is destroyed to prevent memory leaks:

     socket.close();
     unregisterReceiver(mBroadcastReceiver);