Aus JSUG

written by Christoph P; created Sunday, January 4, 2009

[Bearbeiten] introduction

[Bearbeiten] lego mindstorm

• using common lego technic parts
• intelligent brick (brain)
• two connection types: usb, bluetooth
• runs with 6 AA batteries
• tech specs
  • ram
  • input sensors: light, audio, ultrasonic, touch
  • output: up to three motors
  • third party parts available too

[Bearbeiten] lejos

environment for running a java vm and custom java code on the lego mindstorm nxt (and rcx).

features offered:

• java 5 (preemptive threads, synchronization, exceptions, ...)
• file system
• full access to hardware (sensors, motors)
• event listeners
• playing wav files (11025khz, 8bit, 1 channel, pcm)
• and much more!

remember: there is no common JDK (JRE) available on the nxt, you only are able to use a much slimmer reimplementation of the standard library (API documentation).

[Bearbeiten] setup

first of all before going on reading this chapter, please have a look at the official readme file provided with each lejos distribution.

for troubleshooting or if you experience problems or just have any question about the setup, consult the official forum:
http://lejos.sourceforge.net/forum/viewforum.php?f=7 (i am sure andy will respond promptly with a very nice and useful answer).

[Bearbeiten] requirements

• java 5 or later
• ant
• lego mindstorm nxt software installed
• libusb (http://libusb.sourceforge.net/)
• jfantom
• NXJ_HOME environment variable set
• add NXJ_HOME/bin to PATH

[Bearbeiten] build distribution

# cd $NXJ_HOME/build
# ant

[Bearbeiten] flash the firmware

• boot nxt in firmware upload mode via pressing the hidden button (at the back of the nxt, upper left corner below the usb port) for at least 5 seconds until you hear the bricket ticking.
• connect computer and nxt via usb
• invoke nxjflash; done (hopefully)

[Bearbeiten] usage

[Bearbeiten] nxj tools overview

• nxj ...
• nxjbrowse ...
• nxjc ...
• nxjconsole ...
• nxjconsoleviewer ...
• nxjdataviewer ...
• nxjflash ...
• nxjflashg ...
• nxjlink ...
• nxjmonitor ...
• nxjpccomm ...
• nxjsocketproxy ...
• nxjupload ...

[Bearbeiten] hello world

• invoke nxjc
• either nxj and finished, or link and upload separately

[Bearbeiten] eclipse plugin

[Bearbeiten] codesamples

[Bearbeiten] play a soundfile

import java.io.File;
 
import lejos.nxt.Button;
import lejos.nxt.LCD;
import lejos.nxt.Sound;
 
public class PlaySound {
	public static void main(String[] args) {
		final File soundFile = new File("r2d2.wav");
		LCD.drawString("Play: " + soundFile.getName(), 0, 1);
		Sound.playSample(soundFile, 100); // 100 ... volume
 
		try {
			LCD.drawString("Enter to Exit", 0, 2);
			Button.ENTER.waitForPressAndRelease();
		} catch (InterruptedException e) { }
 
	}
}

[Bearbeiten] appendix

[Bearbeiten] icommand

[Bearbeiten] links

• http://lejos.sourceforge.net/ ... official lejos website