Data transfer between Android and Arduino via Bluetooth

This article, shows two examples of working with Bluetooth: 1. Send data to Arduino 2. Data transfer between Android and Arduino.

Arduino

Wiring diagram is the same as in the previous article:

I use Arduino Nano V3 and Bluetooth module HC-06. Also, I connected the external LED to pin 12. Our program:

char incomingByte;  // incoming data
int  LED = 12;      // LED pin

void setup() {
  Serial.begin(9600); // initialization
  pinMode(LED, OUTPUT);
  Serial.println("Press 1 to LED ON or 0 to LED OFF...");
}

void loop() {
  if (Serial.available() > 0) {  // if the data came
    incomingByte = Serial.read(); // read byte
    if(incomingByte == '0') {
       digitalWrite(LED, LOW);  // if 1, switch LED Off
       Serial.println("LED OFF. Press 1 to LED ON!");  // print message
    }
    if(incomingByte == '1') {
       digitalWrite(LED, HIGH); // if 0, switch LED on
       Serial.println("LED ON. Press 0 to LED OFF!");
    }
  }
}

Android

We will use the Java code with an explicit MAC-address of the device. Find MAC-address can be in the program for Android: Bluetooth Terminal:

Our device is "BOLUTEK" with MAC-address 00:15:FF:F2:19:4C.

The first program is very simple, the main activity will contain two buttons: turn on LED and turn off LED. Data transfer in the program will be implemented only on Android devices to Arduino

And our Java code of main activity:

package com.example.bluetooth1;

import java.io.IOException;
import java.io.OutputStream;
import java.lang.reflect.Method;
import java.util.UUID;
 
import com.example.bluetooth1.R;
 
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;
 
public class MainActivity extends Activity {
  private static final String TAG = "bluetooth1";
   
  Button btnOn, btnOff;
   
  private BluetoothAdapter btAdapter = null;
  private BluetoothSocket btSocket = null;
  private OutputStream outStream = null;
   
  // SPP UUID service 
  private static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
 
  // MAC-address of Bluetooth module (you must edit this line)
  private static String address = "00:15:FF:F2:19:5F";
   
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
 
    setContentView(R.layout.activity_main);
 
    btnOn = (Button) findViewById(R.id.btnOn);
    btnOff = (Button) findViewById(R.id.btnOff);
     
    btAdapter = BluetoothAdapter.getDefaultAdapter();
    checkBTState();
 
    btnOn.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {
        sendData("1");
        Toast.makeText(getBaseContext(), "Turn on LED", Toast.LENGTH_SHORT).show();
      }
    });
 
    btnOff.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {
        sendData("0");
        Toast.makeText(getBaseContext(), "Turn off LED", Toast.LENGTH_SHORT).show();
      }
    });
  }
  
  private BluetoothSocket createBluetoothSocket(BluetoothDevice device) throws IOException {
      if(Build.VERSION.SDK_INT >= 10){
          try {
              final Method  m = device.getClass().getMethod("createInsecureRfcommSocketToServiceRecord", new Class[] { UUID.class });
              return (BluetoothSocket) m.invoke(device, MY_UUID);
          } catch (Exception e) {
              Log.e(TAG, "Could not create Insecure RFComm Connection",e);
          }
      }
      return  device.createRfcommSocketToServiceRecord(MY_UUID);
  }
   
  @Override
  public void onResume() {
    super.onResume();
 
    Log.d(TAG, "...onResume - try connect...");
   
    // Set up a pointer to the remote node using it's address.
    BluetoothDevice device = btAdapter.getRemoteDevice(address);
   
    // Two things are needed to make a connection:
    //   A MAC address, which we got above.
    //   A Service ID or UUID.  In this case we are using the
    //     UUID for SPP.
   
	try {
		btSocket = createBluetoothSocket(device);
	} catch (IOException e1) {
		errorExit("Fatal Error", "In onResume() and socket create failed: " + e1.getMessage() + ".");
	}
       
    // Discovery is resource intensive.  Make sure it isn't going on
    // when you attempt to connect and pass your message.
    btAdapter.cancelDiscovery();
   
    // Establish the connection.  This will block until it connects.
    Log.d(TAG, "...Connecting...");
    try {
      btSocket.connect();
      Log.d(TAG, "...Connection ok...");
    } catch (IOException e) {
      try {
        btSocket.close();
      } catch (IOException e2) {
        errorExit("Fatal Error", "In onResume() and unable to close socket during connection failure" + e2.getMessage() + ".");
      }
    }
     
    // Create a data stream so we can talk to server.
    Log.d(TAG, "...Create Socket...");
 
    try {
      outStream = btSocket.getOutputStream();
    } catch (IOException e) {
      errorExit("Fatal Error", "In onResume() and output stream creation failed:" + e.getMessage() + ".");
    }
  }
 
  @Override
  public void onPause() {
    super.onPause();
 
    Log.d(TAG, "...In onPause()...");
 
    if (outStream != null) {
      try {
        outStream.flush();
      } catch (IOException e) {
        errorExit("Fatal Error", "In onPause() and failed to flush output stream: " + e.getMessage() + ".");
      }
    }
 
    try     {
      btSocket.close();
    } catch (IOException e2) {
      errorExit("Fatal Error", "In onPause() and failed to close socket." + e2.getMessage() + ".");
    }
  }
   
  private void checkBTState() {
    // Check for Bluetooth support and then check to make sure it is turned on
    // Emulator doesn't support Bluetooth and will return null
    if(btAdapter==null) { 
      errorExit("Fatal Error", "Bluetooth not support");
    } else {
      if (btAdapter.isEnabled()) {
        Log.d(TAG, "...Bluetooth ON...");
      } else {
        //Prompt user to turn on Bluetooth
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, 1);
      }
    }
  }
 
  private void errorExit(String title, String message){
    Toast.makeText(getBaseContext(), title + " - " + message, Toast.LENGTH_LONG).show();
    finish();
  }
 
  private void sendData(String message) {
    byte[] msgBuffer = message.getBytes();
 
    Log.d(TAG, "...Send data: " + message + "...");
 
    try {
      outStream.write(msgBuffer);
    } catch (IOException e) {
      String msg = "In onResume() and an exception occurred during write: " + e.getMessage();
      if (address.equals("00:00:00:00:00:00")) 
        msg = msg + ".\n\nUpdate your server address from 00:00:00:00:00:00 to the correct address on line 35 in the java code";
      	msg = msg +  ".\n\nCheck that the SPP UUID: " + MY_UUID.toString() + " exists on server.\n\n";
       
      	errorExit("Fatal Error", msg);       
    }
  }
}

Android - transmit and receive data to the Arduino

To receive data from Arduino, in Android application we need to use threads. On the main window activity we add a new element TextView, which will be used to display the received data from the Arduino

package com.example.bluetooth2;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Method;
import java.util.UUID;
 
import com.example.bluetooth2.R;
 
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
 
public class MainActivity extends Activity {
  private static final String TAG = "bluetooth2";
   
  Button btnOn, btnOff;
  TextView txtArduino;
  Handler h;
   
  final int RECIEVE_MESSAGE = 1;		// Status  for Handler
  private BluetoothAdapter btAdapter = null;
  private BluetoothSocket btSocket = null;
  private StringBuilder sb = new StringBuilder();
  
  private ConnectedThread mConnectedThread;
   
  // SPP UUID service
  private static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
 
  // MAC-address of Bluetooth module (you must edit this line)
  private static String address = "00:15:FF:F2:19:5F";
   
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
 
    setContentView(R.layout.activity_main);
 
    btnOn = (Button) findViewById(R.id.btnOn);					// button LED ON
    btnOff = (Button) findViewById(R.id.btnOff);				// button LED OFF
    txtArduino = (TextView) findViewById(R.id.txtArduino);		// for display the received data from the Arduino
    
    h = new Handler() {
    	public void handleMessage(android.os.Message msg) {
    		switch (msg.what) {
            case RECIEVE_MESSAGE:													// if receive massage
            	byte[] readBuf = (byte[]) msg.obj;
            	String strIncom = new String(readBuf, 0, msg.arg1);					// create string from bytes array
            	sb.append(strIncom);												// append string
            	int endOfLineIndex = sb.indexOf("\r\n");							// determine the end-of-line
            	if (endOfLineIndex > 0) { 											// if end-of-line,
            		String sbprint = sb.substring(0, endOfLineIndex);				// extract string
                    sb.delete(0, sb.length());										// and clear
                	txtArduino.setText("Data from Arduino: " + sbprint); 	        // update TextView
                	btnOff.setEnabled(true);
                	btnOn.setEnabled(true); 
                }
            	//Log.d(TAG, "...String:"+ sb.toString() +  "Byte:" + msg.arg1 + "...");
            	break;
    		}
        };
	};
     
    btAdapter = BluetoothAdapter.getDefaultAdapter();		// get Bluetooth adapter
    checkBTState();
 
    btnOn.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {
    	btnOn.setEnabled(false);
    	mConnectedThread.write("1");	// Send "1" via Bluetooth
        //Toast.makeText(getBaseContext(), "Turn on LED", Toast.LENGTH_SHORT).show();
      }
    });
 
    btnOff.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {
    	btnOff.setEnabled(false);  
    	mConnectedThread.write("0");	// Send "0" via Bluetooth
        //Toast.makeText(getBaseContext(), "Turn off LED", Toast.LENGTH_SHORT).show();
      }
    });
  }
  
  private BluetoothSocket createBluetoothSocket(BluetoothDevice device) throws IOException {
      if(Build.VERSION.SDK_INT >= 10){
          try {
              final Method  m = device.getClass().getMethod("createInsecureRfcommSocketToServiceRecord", new Class[] { UUID.class });
              return (BluetoothSocket) m.invoke(device, MY_UUID);
          } catch (Exception e) {
              Log.e(TAG, "Could not create Insecure RFComm Connection",e);
          }
      }
      return  device.createRfcommSocketToServiceRecord(MY_UUID);
  }
   
  @Override
  public void onResume() {
    super.onResume();
 
    Log.d(TAG, "...onResume - try connect...");
   
    // Set up a pointer to the remote node using it's address.
    BluetoothDevice device = btAdapter.getRemoteDevice(address);
   
    // Two things are needed to make a connection:
    //   A MAC address, which we got above.
    //   A Service ID or UUID.  In this case we are using the
    //     UUID for SPP.
    
	try {
		btSocket = createBluetoothSocket(device);
	} catch (IOException e) {
		errorExit("Fatal Error", "In onResume() and socket create failed: " + e.getMessage() + ".");
	}
   
    // Discovery is resource intensive.  Make sure it isn't going on
    // when you attempt to connect and pass your message.
    btAdapter.cancelDiscovery();
   
    // Establish the connection.  This will block until it connects.
    Log.d(TAG, "...Connecting...");
    try {
      btSocket.connect();
      Log.d(TAG, "....Connection ok...");
    } catch (IOException e) {
      try {
        btSocket.close();
      } catch (IOException e2) {
        errorExit("Fatal Error", "In onResume() and unable to close socket during connection failure" + e2.getMessage() + ".");
      }
    }
     
    // Create a data stream so we can talk to server.
    Log.d(TAG, "...Create Socket...");
   
    mConnectedThread = new ConnectedThread(btSocket);
    mConnectedThread.start();
  }
 
  @Override
  public void onPause() {
    super.onPause();
 
    Log.d(TAG, "...In onPause()...");
  
    try     {
      btSocket.close();
    } catch (IOException e2) {
      errorExit("Fatal Error", "In onPause() and failed to close socket." + e2.getMessage() + ".");
    }
  }
   
  private void checkBTState() {
    // Check for Bluetooth support and then check to make sure it is turned on
    // Emulator doesn't support Bluetooth and will return null
    if(btAdapter==null) { 
      errorExit("Fatal Error", "Bluetooth not support");
    } else {
      if (btAdapter.isEnabled()) {
        Log.d(TAG, "...Bluetooth ON...");
      } else {
        //Prompt user to turn on Bluetooth
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, 1);
      }
    }
  }
 
  private void errorExit(String title, String message){
    Toast.makeText(getBaseContext(), title + " - " + message, Toast.LENGTH_LONG).show();
    finish();
  }
 
  private class ConnectedThread extends Thread {
	    private final InputStream mmInStream;
	    private final OutputStream mmOutStream;
	 
	    public ConnectedThread(BluetoothSocket socket) {
	        InputStream tmpIn = null;
	        OutputStream tmpOut = null;
	 
	        // Get the input and output streams, using temp objects because
	        // member streams are final
	        try {
	            tmpIn = socket.getInputStream();
	            tmpOut = socket.getOutputStream();
	        } catch (IOException e) { }
	 
	        mmInStream = tmpIn;
	        mmOutStream = tmpOut;
	    }
	 
	    public void run() {
	        byte[] buffer = new byte[256];  // buffer store for the stream
	        int bytes; // bytes returned from read()

	        // Keep listening to the InputStream until an exception occurs
	        while (true) {
	        	try {
	                // Read from the InputStream
	                bytes = mmInStream.read(buffer);		// Get number of bytes and message in "buffer"
                    h.obtainMessage(RECIEVE_MESSAGE, bytes, -1, buffer).sendToTarget();		// Send to message queue Handler
	            } catch (IOException e) {
	                break;
	            }
	        }
	    }
	 
	    /* Call this from the main activity to send data to the remote device */
	    public void write(String message) {
	    	Log.d(TAG, "...Data to send: " + message + "...");
	    	byte[] msgBuffer = message.getBytes();
	    	try {
	            mmOutStream.write(msgBuffer);
	        } catch (IOException e) {
	            Log.d(TAG, "...Error data send: " + e.getMessage() + "...");     
	          }
	    }
	}
}

Video:

Code updated: 28.01.2013

Download APK-files for Android: bluetooth1.apk and bluetooth2.apk

Download source code for Arduino and Android

Author: Koltykov A.V.