This version of the tutorial is for the 0.85 release of leJOS NXJ.

Prerequisites

USB Driver

To run leJOS NXJ on Microsoft Windows you will need a suitable USB driver on your PC. If you have installed the standard LEGO Mindstorms software, a suitable driver will already be installed. If you do not wish to install the LEGO software on your PC you can get a driver from The RobotC site.

Java Development Kit

You will also need a Java Development Kit (JDK) on your PC. Note that a Java Runtime Environment (JRE) is not sufficient as it does not allow you to compile Java programs. You can download the latest JDK from http://java.sun.com/. Follow the instructions for installing it. leJOS NXJ works has been tested with JDK versions 1.5 and 1.6, but will not work with earlier versions. JDK 1.6 is recommended, and some PC sample programs will not wiork with JDK 1.5.

You will need to add the JDK bin directory to your system or user PATH, so that commands such as javac and java can be called from a command prompt. If you do not know how to do this, see the "Setting up environment variables" section below.

It is also a good idea to set the environment variable JAVA_HOME to the folder where you installed the JDK. This is necessary if you use the ant build system.

Bluetooth Stack

If you want to communicate with the NXT over Bluetooth, you will need a Bluetooth dongle or built-in support on your PC, and a Bluetooth software stack. leJOS NXJ has been tested with the Microsoft and Widcomm stacks, but should work with others.

You can use leJOS NXJ without Bluetooth.

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Downloading the software

You can download the leJOS NXJ software from The leJOS NXJ download page.

It is recommended that you use the Windows installer, but there is a ZIP file release that you can use if you prefer to do a manual installation.

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Running the GUI installer

Run leJOS_NXJ_0.8.5-Setup.exe and you will see the following screen:

Select "Yes" and you will see:

Note that Installjammer is the open source software we have used to produce the installer.

Click "Next and you will see:

You can change the destination if you need to. Click on the "Browse" button to change the destination.

The JDK version that we have detected is displayed on this screen

Once you have selected the destination, click "Next" and you will see:

Again you can change the destination for the leJOS projects. It defaults to leJOSNXJProjects in the users home directory. On Windows Vista this is C:\Users\user and on XP it is C:\Documents and Settings\user.

All the Java source in leJOS NXJ is issued as projects that can be opened in Eclipse and Netbeans.

Once you have selected the projects destination, the installation will start. If you already have leJOS NXJ installed in the selected destination, you will see:

Click next and the previous version will be uninstalled:

Once you have confirmed that you want the old version uninstalled, you will see:

and then:

After any previous version has been uninstalled, the installation of the new version starts and you see:

Check that the destination directories are correct and click "Next". You will see:

When the software installation is complete, you see:

When you click "Finish" the GUI version of the NXJ firmware flash utility will start bto allow you to update the firmware on one of more NXTs.

You will see:

Click "Start Program" and you will be asked:

Click OK and you will be asked:

If you select "Yes" all current files on the NXT are erased. It is a good idea to select this as old .nxj files may not work with the new firmware.

You will then see:

Make sure that your NXT is connected to the PC by the USB cable and witched on. Then press "OK" and you should see some progess messages, such as:

When your NXT has been updated, you will be asked:

If you have more NXTs to update, click "Yes". When you have finished click "No" and the flash utility will terminate and then the installer will terminate, and you are done.

Skip to the section below on testing your installation.

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Manual installation

Skip this section and go to "Testing the Installation" if you are using the GUI installer.

Unzipping the release

Unzip the release to a folder such as c:\lejosbeta85. The zip file includes a directory called lejos_nxt, so your NXJ_HOME folder will be c:\lejosbeta85\lejos_nxt.

Setting up environment variables

You need to set:

Setting JAVA_HOME is not always necessary, but is good practice. The bin directory for the JDK may already be on your PATH.

You can set these environment variables by going to Control Panel > System > Advanced > Environment Variables and creating them or editing existing values. You can set them either as user or system variables depending on whether you want leJOS NXJ to be available to all users or just the current user.

Using a Command Window

You will need to run command-line commands to test your installation and optionally to flash the firmware. If you plan to use IDE such as Eclipse or Netbeans, once you have installed your IDE, you should not need to use the command window any more.

You can start a command window on Windows XP by Start > Run and typing cmd. On Vista, type "Command Prompt".

Type set to list environment variables and check they are all set up correctly.

Flashing the Firmware

As leJOS NXJ is a firmware replacement, you will need to flash the firmware to your NXT. Note that this will overwrite any existing firmware. If you have the standard LEGO firmware or other third-party firmware on your NXT, existing files will be lost.

The 0.85 release increases the amount of flash memory used by the firmware and the startup menu, so the first time you flash this version of the firmware, existing leJOS NXJ files will be deleted.

Make sure your NXT is attached to the PC by its USB cable, and switch it on by pressing the orange button.

You can either use the command line nxjflash command or the nxjflashg GUI program.

Using the command line:

Type nxjflash to flash the leJOS NXJ firmware. If your NXT is in firmware update mode, the firmware will be updated. You will see some messages on your command window, and the NXT should show the leJOS splash screen and then the leJOS NXJ menu. If your NXT has a previous version of the leJOS or LEGO firmware on it, a list of the NXTs connected to the USB will be shown, and you will be asked to input the number in the list of the NXT you want updated - this will be 1 if a single NXT is connected to your PC. If your NXT has other firmware on it, or if nxjflash fails, you must put your NXT into firmware update mode. Press the reset button (at the back of the NXT , upper left corner) for more than 4 seconds. A straightened paper clip could be useful for this. Your NXT will audibly tick when it is firmware update mode. Then try nxjflash again.

Using the GUI version:

The GUI version of nxjflash is NXJFlashG. You start it by running the file nxjflashg.bat from the leJOS NXJ bin folder. When the program window opens, click on Start Program and follow the instructions. A more complete explanation is in the tutorial "PC GUI Tools".

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Testing your Installation

You can check that you have successfully installed leJOS NXJ on your PC and your NXT by compiling and running your first program.

Compiling and running your first program

Java programs need to be compiled to class files before they can be run. For leJOS NXJ, all the class files that are to be run on the NXT needed to be linked to produce a binary file (with the extension .nxj) and this must then be uploaded to the NXT.

To run a sample program, such as the View.java sample, follow these steps:

Start a command window, and change directory to the View sample folder:

 cd leJOSNXJProjects\samples\View 

Compile the program with the nxjc command:

 nxjc View.java 

Then link, upload and run it with the nxj command:

 nxj -r View 

You should see the menu of the View sample on your NXT.

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