How to interact between an Android and a running NXT program using Bluetooth

Question

I have modified the Minddroid github Android program to read sensors on a LEGO NXT (wonderful device!). Now I would like to read and write Bluetooth messages to a Mindstorms program running in the NXT. So that I can run a NXT program and send the results / readings to the Android when the Android asks for them.

Answer 1

I've created a project where the NXT sends data back to my Android device. Here's some code that should work:

This is all the Android side code:

This is a class that I wrote, that will take care of connecting and communicating via bluetooth.

public class Connector {

    public static final String TAG = "Connector";

    public static final boolean BT_ON = true;
    public static final boolean BT_OFF = false;

    public BluetoothAdapter bluetoothAdapter;
    public BluetoothSocket bluetoothSocket;
    public String address;

    public Connector(String address) {
        this.address = address;
        this.bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

    }

    public void setBluetooth(boolean state) {
        if(state == Connector.BT_ON) {
            // Check if bluetooth is off
            if(this.bluetoothAdapter.isEnabled() == false)
            {
                this.bluetoothAdapter.enable();
                while(this.bluetoothAdapter.isEnabled() == false) {

                }
                Log.d(Connector.TAG, "Bluetooth turned on");

            }

        }
        // Check if bluetooth is enabled
        else if(state == Connector.BT_OFF) {
            // Check if bluetooth is enabled
            if(this.bluetoothAdapter.isEnabled() == true)
            {
                this.bluetoothAdapter.disable();
                while(this.bluetoothAdapter.isEnabled() == true) {

                }
                Log.d(Connector.TAG, "Bluetooth turned off");

            }

        }

    }

    public boolean connect() {

        boolean connected = false;
        BluetoothDevice nxt = this.bluetoothAdapter.getRemoteDevice(this.address);

        try {
            this.bluetoothSocket = nxt.createRfcommSocketToServiceRecord(UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"));
            this.bluetoothSocket.connect();
            connected = true;

        } 
        catch (IOException e) {
            connected = false;

        }

        return connected;

    }

     public Integer readMessage() {
         Integer message;

         if(this.bluetoothSocket!= null) {
             try {
                 InputStreamReader input = new InputStreamReader(this.bluetoothSocket.getInputStream());
                 message = input.read();
                 Log.d(Connector.TAG, "Successfully read message");

             } 
             catch (IOException e) {
                 message = null;
                 Log.d(Connector.TAG, "Couldn't read message");

             }  
         }
         else {
             message = null;
             Log.d(Connector.TAG, "Couldn't read message");

         }

         return message;

     }


}

In your activity class, you can create a Connector object. In the onCreate() method, you'll have to connect to establish a connection to the NXT like so:

// Establish a bluetooth connection to the NXT
this.connector = new Connector("00:16:53:12:B6:78");
this.connector.setBluetooth(Connector.BT_ON);
this.connector.connect();

Now to read a message from the NXT (an Integer object) you can do it like this:

this.connector.readMessage();

To close the connection:

this.connector.setBluetooth(Connector.BT_OFF);

This is all the NXT side code:

NOTE: Download leJOS for all the code to work (leJOS will allow you to code your NXT in java).

Define these two objects in your main class:

public static DataOutputStream dataOutputStream;
public static NXTConnection bluetoothConnection;

To connect to you phone:

bluetoothConnection = Bluetooth.waitForConnection();
bluetoothConnection.setIOMode(NXTConnection.RAW);
dataOutputStream = bluetoothConnection.openDataOutputStream();

To send data to the phone in form of an Integer object:

dataOutputStream.write(100);
dataOutputStream.flush();

To disconnect run this:

dataOutputStream.close();
bluetoothConnection.close();

I hope this helps.

Answer 2

I was getting slightly confused with the bluetooth commands, but now I see that you need to download leJOS!

I usually try to avoid messing with the firmware on the NXT, but java is a lot easier to deal with!

For anyone that is interested, you can send commands down to the NXT from your android in its native format, although its not as pretty as listed above. There is a great tutorial here: http://www.robotappstore.com/Knowledge-Base/Programming-LEGO-NXT-Mindstorms/92.html

But if you want to download an app for free, here is one: http://www.robotappstore.com/Apps/Lego-NXT-Mindstorms-Driver---Android-app.html?x=693A00AA-7F15-46E7-9616-8101068DB58D

There are a bunch more, if you just search around on there too

Hope this helps!