Bluetooth-connection between Android and Lego Mindstorm NXT

Question

Does anybody know, how to build a bluetooth connection between Android and LEGO-Mindstorm-NXT? The connection between two NXTs works fine. But the other Connection-type likes not so easy. I am working with the LeJOS Firmware 0.85 and the Android SDK Tools (2.2 Froyo).

Karachi

Have you succeded to pair the Android and the LEGO-Mindstorm-NXT first? – Belfort

See below in my answer how does it works. By the first run or the first connect to the NXTs, the Smartphone will be automaticly pair to the NXT and ask you to the key from the nxt to pair with it. – Karachi

Answer 1

So i've solved it and will show all how does it works, because i've seen that a lot of people have problems with that.

The class includes 4 functions:

• Bluetooth enable if not enabled before -> enableBT()
  
• Connect to 2 NXTs -> connectToNXTs()
  
• Write Message to one of the NXTs -> writeMessage(byte msg, String nxt)
  
• Read Message from one of the NXTs -> readMessage(String nxt)
  

Here is the code for the android device (BT_comm.java):

package de.joen.android.CubeScan;


import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.UUID;


import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;

import android.util.Log;

public class BT_Comm {

  //Target NXTs for communication
  final String nxt2 = "00:16:53:04:52:3A";
  final String nxt1 = "00:16:53:07:AA:F6";

  BluetoothAdapter localAdapter;
  BluetoothSocket socket_nxt1, socket_nxt2;
  boolean success = false;

  // Enables Bluetooth if not enabled
  public void enableBT(){
    localAdapter = BluetoothAdapter.getDefaultAdapter();
    // If Bluetooth not enable then do it
    if (!localAdapter.isEnabled()) {
      localAdapter.enable();
      while(!(localAdapter.isEnabled()));
    }
  }

  // Connect to both NXTs
  public boolean connectToNXTs() {

    // Get the BluetoothDevice of the NXT
    BluetoothDevice nxt_2 = localAdapter.getRemoteDevice(nxt2);
    BluetoothDevice nxt_1 = localAdapter.getRemoteDevice(nxt1);
    // Try to connect to the nxt
    try {
      socket_nxt2 = nxt_2.createRfcommSocketToServiceRecord(UUID
          .fromString("00001101-0000-1000-8000-00805F9B34FB"));

      socket_nxt1 = nxt_1.createRfcommSocketToServiceRecord(UUID
          .fromString("00001101-0000-1000-8000-00805F9B34FB"));

      socket_nxt2.connect();    
      socket_nxt1.connect();      

      success = true;

    } catch (IOException e) {
      Log.d("Bluetooth","Err: Device not found or cannot connect");
      success=false;
    }
    return success;    
  }


  public void writeMessage(byte msg, String nxt) throws InterruptedException {
    BluetoothSocket connSock;

    // Swith nxt socket
    if (nxt.equals("nxt2")) {
      connSock=socket_nxt2;
    } else if(nxt.equals("nxt1")) {
      connSock = socket_nxt1;
    } else {
      connSock=null;
    }

    if (connSock!=null) {
      try {

        OutputStreamWriter out = new OutputStreamWriter(connSock.getOutputStream());
        out.write(msg);
        out.flush();

        Thread.sleep(1000);

      } catch (IOException e) {
        // TODO: Auto-generated catch block
        e.printStackTrace();
      }
    } else {
      // Error
    }
  }

  public int readMessage(String nxt) {
    BluetoothSocket connSock;
    int n;

    // Swith nxt socket
    if (nxt.equals("nxt2")) {
      connSock=socket_nxt2;
    } else if (nxt.equals("nxt1")) {
      connSock=socket_nxt1;
    } else {
      connSock=null;
    }

    if (connSock!=null) {
      try {

        InputStreamReader in = new InputStreamReader(connSock.getInputStream());
        n = in.read();
        return n;

      } catch (IOException e) {
        // TODO: Auto-generated catch block
        e.printStackTrace();
        return -1;
      }
    } else {
      // Error
      return -1;
    }
  }
}

To get messages from the Android Smartphone you must have a read call on the NXT-side. Here is the code from the NXT-side wich will accept the connection from the Smartphone and read messages from it:

Boolean isrunning = true;

// Main loop   
while (true)
{
  LCD.drawString(waiting,0,0);
  LCD.refresh();

  // Listen for incoming connection

  NXTConnection btc = Bluetooth.waitForConnection();

  btc.setIOMode(NXTConnection.RAW);

  LCD.clear();
  LCD.drawString(connected,0,0);
  LCD.refresh();  


  // The InputStream for read data 
  DataInputStream dis = btc.openDataInputStream();


  // Loop for read data  
  while (isrunning) {
    Byte n = dis.readByte();
    LCD.clear();
    LCD.drawInt(n, 4, 4);
  }

  dis.close();

  // Wait for data to drain
  Thread.sleep(100); 

  LCD.clear();
  LCD.drawString(closing,0,0);
  LCD.refresh();

  btc.close();

  LCD.clear();
}

Hope this will help others...

Karachi

I had issues with createRfcommSocketToServiceRecord on a HTC Desire which you may want to be aware of if you plan to ditribute code. See (stackoverflow.com/questions/2660968 – Nellynelms

someone left a comment that you should use OutputStream vs OutputStreamWriter as outputstream encodes to unicode and will break for vals larger than 127 ... not idea what that means, but deleting that answer – Unclinch

This really helped me out. If I could upvote you more than once, I would! – Shorter

Answer 2

There is a document I found very useful http://wiki.tinyclr.com/images/d/df/LEGO_MINDSTORMS_NXT_Direct_commands.pdf

The MINDdroid package on github is a fine place to start.

Outherod