The infrared communication system is used to download firmware and programs to the RCX brick from the USB IR tower. The advantages of wireless communication are obvious, but the sometimes baffling (mis)behaviors - failed downloads yielding a plethora of errors - can be frustrating. The following tips and tricks have been found to give the highest rate of successful downloads with our setup.
Plug an AC adapter into your RCX brick. You'll find a few of them scattered around the lab.
Find a computer nearby, and log in. Plug your USB tower into one of the USB ports on the front of the computer. You can find the USB ports by flipping up the front panel. Of the two ports that are there, you'll find that it's easier to get the plug into the port that's in back of the other. The USB plug should be oriented so that you see the word LEGO facing you, and the plug goes in at something of an angle.
The RCX will successfully program when 2 to 6 inches away from the IR tower. If the RCX is close to the IR tower (2-4 inches away), the RCX must be directly aimed at the tower, or else communication may fail. Five inches is the optimum distance to have between the RCX and the tower. The end of the brick with the dark window should be pointed directly at the front (dark side) of the USB IR tower. Elevate the bottom of the brick approximately 1 inch off the table relative to the bottom of the IR tower for best chance of success. (Put in on a book.) Do not obstruct the area between the RCX and the tower. Do not move either the tower or the RCX brick while downloading. Take a piece of paper, cardboard, or a thin book and place it over the tower and the brick, which helps block out the flourescent lights which interfere with the infrared transmissions. It helps if you can place the tent such that you can still see the LCD display on the brick.
We're going to download the leJOS firmware from the computer to the brick. This is something that you only need to do once for your brick, unless it sits without power (no batteries or anything) for a few minutes. But as long as your brick has batteries in it with some amount of power, or you change your batteries reasonably quickly, you won't need to download firmware more than once. That's good, because it takes a while.
Go to the "Start" menu and select "Run..." In the "Open:" text field enter "cmd" (sans quotation marks) and click OK. A command prompt will open. Make sure the brick is positioned and powered up (use the red On-Off button). At the command prompt type "firmdl" and press enter. Hopefully, the brick will beep and the firmware will begin downloading. Note: Do not multitask while downloading - we've found that using opening programs or browsing the web can cause the download to fail. If you do get an error message, reposition and power-cycle the RCX brick, and attempt "firmdl" once again. If you continue having trouble, try different distances and heights within the constraints suggested above. Ask for help: it can take a little practice to get this to work. You will be notified onscreen and the brick will beep when the download is complete. Notice that when the leJOS firmware is on the brick, the LCD displays the battery voltage. When the official MindStorm firmware is on the brick (i.e. just after you replace the batteries), just the little person and the number 1 is displayed.
Next we'll build Tippy, a simple robot whose design is in Bagnall's book. Grab a fresh set of rechargeable batteries from CMC 307 (the student lounge), put them in your brick (just pop off the gray bottom), and then follow the instructions from pages 20-25 to build Tippy. Remember to keep an AC adapter plugged into your brick whenever you can to preserve battery power. The AC adapter will not charge your batteries, unfortunately.
We have installed Crimson Editor on all Windows machines that you will be using. Crimson Editor is a free text editor with tabs and other features that is available for download at http://www.crimsoneditor.com. Feel free to install Notepad or Wordpad instead if you wish, but you will probably find that Crimson Editor has better features.
Open up Crimson Editor, enter the following program, and save it
somewhere to your home folder. Call it HelloWorld.java
import josx.platform.rcx.*;
public class HelloWorld
{
public static void main(String[] args) throws Exception
{
LCD.clear();
TextLCD.print ("hello");
Thread.sleep(2000);
TextLCD.print ("world");
Thread.sleep(2000);
}
}
You now need to navigate from within the DOS prompt that you opened
up to the directory where you saved your HelloWorld.java
file. If you are unfamiliar with DOS, click on
and work through this quick help file.
To compile your code, you use the 'lejosc' command. So compile your program by typing
lejosc -source 1.2 HelloWorld.java
The -source 1.2 is necessary in order to convince
leJOS to play nicely with Java 1.5. Once your code has successfully
compiled, download your program to the RCX brick: make sure that your
brick is positioned properly and on, and your tent is set up. Then
type
lejos HelloWorld
This will download your compiled code to the brick. When the code has completed downloading, push the Run button, and you should see "hello world" display on the LCD screen.
If you have time remaining... start on the next assignment!