After tried two methods not enough reliable, this method is my last chance to find a well way to determinate distance between a tablet and a robot.

This method using the tablet camera and Bluetooth. Principle is pretty simple, we assume that the robot start from position 1 to position 2. When the robot leave position 1, it sends a Bluetooth signal to the tablet saying “I am started” (This signal is only a character). Once the robot is arriving at the position 2 it sends another signal indicating the distance between position 1 and position 2 (in centimeters). So we can ask us several questions about this new way:

Is it possible to communicate with Bluetooth between the robot and an Android device ?

Is the measure will be precise ?

Is one camera enough do measure the distance ?

I began by EV3 robot Bluetooth communication. Bluetooth protocol is pretty simple, there are only some important steps to follow:

1) Connector declaration

NXTCommConnector connector = Bluetooth.getNXTCommConnector();

2) Established connection

NXTConnection connect = connector.waitForConnection(0, NXTConnection.RAW);

3) Stream declaration

 DataInputStream dis = connect.openDataInputStream();
 DataOutputStream dos = connect.openDataOutputStream();

4) Read or write information

 short n = dis.readShort();

About Bluetooth on the Nexus 7 tablet, we will use a very simple program, made with processing. First of all, we declared and established the connection between the EV3 robot and the Nexus 7 tablet

 bt = new KetaiBluetooth(this);

To send a data you will use :

byte[] data = {'t','e','s','t','\r'};

And you will use the event on the buffer to receive the data :

void onBluetoothDataEvent(String who, byte[] data) {
 if (isConfiguring)

 info += new String(data);


Now, we can share information between EV3 robot and the Nexus 7 tablet.

Next step is about picture treatment, I will talk about it in the next post. I used Processing to do picture treatment because it is a more adapted for thus kind of application.