Using Matlab, RealTerm and Bluetooth to control Lego Mindstorm NXT

Developed by Gregory Gutt,  greg@mymailbox.org
For the George Mason University Neural Engineering Laboratory 

Background:  My wife (Nathalia Peixoto) is a professor at George Mason University in the ECE Department.  She wants to control a Lego Mindstorm NXT Robot using increasingly sophisticated biosensors and voice recognition.  Matlab was the ideal platform to create the tools and interfaces because of its relatively easy development environment and sophisticated digital signal processing tools.  I developed this code for her Laboratory.

Important references:

1)See Mindstorm NXT Bluetooth Development documentation to understand the
structure of Byte Strings.  Appendix 2-LEGO MINDSTORMS NXT Direct commands.pdf.  http://mindstorms.lego.com/Overview/NXTreme.aspx

2) RealTerm and Matlab: http://realterm.sourceforge.net/realterm_from_matlab.html

3) Example of Bluetooth Remote for NXT written in C: www.norgesgade14.dk/legoSider/mindstorm_en.html


Start Up Procedure:

I. Make sure your Bluetooth hardware and software support Virtual Serial Port Mapping.  Basically this allows standard serial port software to send commands through Bluetooth.  I had some problems using the default Windows XP drivers with a Zoom USB Bluetooth interface.  However, when I installed the software that came with the device all went well.  For illustration purposes I will assume the following configuration:  Com Port 5, 9600 Baud, 8 bits, 1 stop pit, No Parity, No Flow Control.  

II. The first step is to download and install RealTerm (http://realterm.sourceforge.net/).  RealTerm is an outstanding terminal program and offered free of charge (see the site for license terms).  This tool allows for ROBUST RS-232 communications within Matlab.  It also provides a good way to observe communication traffic, which is critical when developing and debugging new code.  In principle you can also use the embedded Matlab RS-232 communications.  However, some versions of Matlab have known serial port issues.

III. Test the interface.  Turn on the Mindstorm and establish a Bluetooth connection with your PC.  Assuming this is done correctly you should now have Com Port 5 (or another port) ready for communication.  Run RealTerm and set the following configuration.

Display Tab:  Click these options -  Hex[space], Half Duplex
Port Tab:  Baud-9600, Port 5 (or per your configuration), Click Open, (Other defaults: Parity-None, 8 bits, Stop Bits - 1, Hardware Flow Control - None, etc.).

Go to the send tab and copy and paste the following byte stream into one of the "Send Numbers" fields:  0x06 0x00 0x80 0x03 0xB8 0x01 0x28 0x00
Hit the "Send Numbers" button to the right of the copied text.  If all goes well you should here a brief "beep".  If you  here the "beep", great! You are half way there.  If not, debug to this point before proceeding.


IV. Try the Matlab program.  Close down real term.  Open matlab and run the m-file: mindstorm.m  The file is documented with useful comments.  If all goes well you should hear "Ode to Joy" and see motor 0 move back and forth.  I developed this m-file in Matlab 6.5 Release 13.