MATLAB NXT Bluetooth Router

The system relies on the RWTH – MINDSTORMS NXT Toolbox, the NXT Fantom Library, and John Hansen’s enhanced firmware.  The brick software is written in Not eXactly C (NXC), which requires Brick CC 3.3.

Daniele Benedettelli also has a book published titled Creating Cool MINDSTORMS NXT Robots (Technology in Action)

• LDraw
• MLCad
• L3P
• POV-Ray v3.6

which can be downloaded with the LDraw All In One Installer

In this tutorial, we will be aiming for a nice simple still image of three bricks.  In later tutorials, we will animate them.  That will require extra software to put a series of inages together to form a video or an animated gif.  I use Adobe ImageReady to make animated gifs, but there are cheaper solutions.

You can also download all the files we will create here
BE_render_tutorial_1.zip
and follow along.

STEP 1: Create an MLCad file of the scene to be rendered

Open MLCad and prepare to place a few LEGO pieces in the scene.

Step 1.1: Set up a 1×1 brick
On the upper left-hand side, click on Brick.
Drag the 1×1 brick into one of the three viewing panels.
With the brick selected click the RED color button to color it red.
Right-click on the brick and select Enter Pos. + Rot…
Use Position Values should be checked
Set the X and Z values all to zero and Y to -100 (negative 100)

Step 1.2: Add a 2×4 brick
Following the steps above, find the 2×4 brick in the Brick list (+ will expand the list) and add it to the scene.  Set its color to YELLOW and its position to X=100, Y=-100,  Z=50.

Step 1.3: Add a 2×6 plate
Following the steps above, find the 2×6 plate in the Plate list (you will have to scroll down to the Plate tab) and add it to the scene.  Set its color to BLUE and its position to X=100, Y=-100,  Z=-100.

Be sure that these pieces are all at Y=-100.  The -y direction points upward and this will place them above the Y=0 plane.

Step 1.4: Save your work as part-zoo-1.ldr

The screenshot below shows what you should see at this point on your MLCad screen.

MLCad Screenshot

STEP 2: Create a POVRay file using L3PAO

Open LP3AO (L3P-Add-on) keeping in mind where you stored your MLCad files.  This figure shows you the basic L3PAO window.

L3PAO Screenshot

Step 2.1: In the L3P-Add-on window set the Model File to point to your MLCad file.  To browse, you may need to click on the button labeled …

Step 2.2: In the L3P-Add-on window set the POV-Ray Output File to point to the folder where you want your POV-Ray file to go.  To browse, you may need to click on the button labeled …

Step 2.3: In the middle of the right-hand column is the Quality Level setting.  Set this to 2.  IF you select 3 it prints the LEGO logo on every stud.  If you want this, you may leave it.  But I prefer to remove them.

Step 2.4: At the bottom of the middle column is the Render upon Completion option.  This will launch POV-Ray automatically.  However, if you have problems with the automatic launch, turn this option off and load it manually.  In later tutorials, we will edit the POV-Ray file manually anyway.

Step: 2.5: To start L3PAdd-on click on the Run L3P button in the lower right.  This will create the POV-Ray part-zoo-1.pov file in the directory you specified, and possibly launch POV-Ray depending on the settings you used in Step 2.4 above.

STEP 3: Render the Image with POV-Ray

If you launched POV-Ray automatically, you will already have your image.  Here we assume that you will render it manually.

POV-Ray Screenshot

Step 3.1: Open POV-Ray and in the File Menu, use Open File to open the .pov file that was created by L3pAO.

Step 3.2: Once the file is open, you can simply press the Run button on the upper bar.  This will create a default image, which is a 640×480 .bmp bitmap image.  This is saved automatically in the same folder as your .pov file.  Here it is:

Part-Zoo-1 Default image

Note that the LEGO pieces are lifted up above the floor.  This is because we set their y-coordinates to be -100, which is above the floor at zero.  Remember that negative y is up.  We now look to change a few features of our render.

Step 3.3: If you click on the Ini button (to the left of Run above), you will go to a screen that enables you to change the size of the output image.  The Section field on the right has many options that include the resolution of the final image as well as whether Anti-Aliasing (AA) is used.  Try changing the resolution and look at the differences between anti-aliased images and non-anti-aliased images.

Note however, that the output images will always be saved in either .bmp or .png format.  You will have to use another program to convert them to other formats if you are interested.

Step 3.4: You can try playing with the commands in the .pov file.  POV-Ray acts like an editor and you can manually edit your files.  For example, there is a section near the bottom that reads:

// Floor:
object {
plane { y, 24 hollow }
texture {
pigment { color rgb <0.8,0.8,0.8> }
finish { ambient 0.4 diffuse 0.4 }
}
}

This code controls the floor of the image.  If you delete it completely, the floor will disappear as you can see here in this image:

Part-Zoo-1 with No Floor

Step 3.4: IF you don’t like the black background, look in the .pov file for the Background section:

// Background:
background { color rgb <0,0,0>}

Changing the rgb (red, green, and blue) colors to <0.7, 0.7, 1.0>:

// Background:
background { color rgb <0.7, 0.7, 1.0>}

Will give you an image with no floor and a light blue background:

Part-Zoo-1 with a blue blackground

We have explored making simple cad images in MLCad, generating a .pov file using L3PAO, and rendering a high-quality bitmap image using POV-Ray.   You should read through the .pov file and try to figure out what the different parts do.  You can change their values and re-render the image to see what impact your changes have.  Just remember that POV-Ray saves the changes on top of the original file,  so you may want to make a backup first.

Happy Rendering!

Here are the MATLAB packages that I know of.  The first two are specifically geared toward the NXT; whereas the last is a general robotics package.

• LEGO MINDSTORMS NXT Toolkit for MATLAB and Simulink
  http://www.mathworks.com/programs/mindstorms/
• Robotics Toolbox for MATLAB (Release 7.1) (P.I. Corke)
  http://petercorke.com/Robotics%20Toolbox.html
• RWTH Mindstorms NXT Toolbox for Matlab
  http://www.mindstorms.rwth-aachen.de/

So for those interested in some LEGO electronics hacking, here is a list of supplies that will get you up and running fast for about $275… just a but more than the cost of a single Mindstorms kit.  Plus you’ll now get to learn electronics!

First, check out the book:
Making Things Talk: Practical Methods for Connecting Physical Objects

This book explains how to wire, program and interconnect various microcontrollers, some of which are very closely related to those used by the NXT Brick.

Supply List

Item Number	Description	Quantity	Unit Price	Total
Amazon.com
	Making Things Talk	1	$19.79	$19.79
Jameco.com
19166	Desoldering Pump	1	$4.95	$4.95
159291	Wire Stripper	1	$10.15	$10.15
161411	Diagonal Cutter	1	$7.49	$7.49
35474	Needlenose Pliers	1	$5.49	$5.49
127271	Mini Screwdriver	1	$1.89	$1.89
681002	Helping Hands	1	$8.75	$8.75
159611	Power Connector	2	$1.79	$3.58
10444	Alligator Test Clip Leads	2	$4.39	$8.78
103377	Header Pins	10	$0.16	$1.60
119011	Push Button (PCB Type)	10	$0.27	$2.70
29082	Potentiometer	2	$1.05	$2.10
242115	LM1117T-3.3 Voltage Regulator	3	$1.39	$4.17
51262	7805T 5v Voltage regulator	3	$0.32	$0.96
38236	2N2222A Transistor NPN	5	$0.41	$2.05
32993	TIP120 Power Transistor	5	$0.45	$2.25
643488	3.3V Zener Diode	5	$0.03	$0.16
35991	1N4004 Diode	5	$0.04	$0.20
152792	LED Yellow	10	$0.17	$1.70
152805	LED Red	10	$0.21	$2.10
153139	LED Orange	10	$0.35	$3.50
156962	LED Green (567 nm)	10	$0.20	$2.00
334529	LED Bargraph Red	1	$1.31	$1.31
334537	LED Bargraph Yellow	1	$1.23	$1.23
334511	LED Bargraph Green	1	$1.28	$1.28
17187	7-segment LED Display	3	$0.88	$2.64
38818	4-switch DIP	4	$0.48	$1.92
38842	8-switch DIP	2	$0.89	$1.78
103166	Resistor Refill	1	$12.95	$12.95
15270	0.1 uF	10	$0.15	$1.53
94161	1 uF	10	$0.12	$1.20
29891	10 uF	10	$0.06	$0.60
158394	100 uF	10	$0.11	$1.08
MPJA
4443 TE	Solderless Breadboard	1	$4.95	$4.95
4447 TE	Large Solderless Breadboard	1	$22.95	$22.95
7027 TE	Jumpers	2	$3.95	$7.90
14213 TE	Digital Multimeter	1	$14.95	$14.95
15860 TL	Mini Soldering Station	1	$14.95	$14.95
Sparkfun
Wiring Platform	DEV-00744	1	$84.95	$84.95
Radio Shack
64-025	Lead Free Solder	1	$3.89	$3.89

Note that the light gray items are optional, and not necessary.

Also, this list does not include some sort of power supply. Pulling one out of an old computer is an easy option. Or rechargeable batteries work well too (in which case you will need battery holders).

Last, there are special items in the book Making Things Talk that you may decide to purchase separately, such as flex sensors, or bluetooth boards, etc.

You can store your electronics in much the same way you store your small LEGO parts. Check out the article on Storage.

Enjoy Hacking!