Download - Introduction to the Lego NXT - Uppsala University · Lego Hardware Developing for the NXT Remote controlling Overview The NXT can be controlled from a computer (or another NXT!).

Introduction to the Lego NXT

Andreas Sandberg <[email protected]>

Lego Hardware Developing for the NXT

What is Lego Mindstorm?

A kit containing:A Lego NXT computer3 motorsTouch sensorLight sensorSound sensorUltrasonic range sensorLots of Lego bricks. . . and plenty of fun!

2 | Introduction to the Lego NXT


The NXTHardware overview

Main CPUAtmel ARM7

Sound

IO ProcessorAtmel AVR

Display Bluetooth

JTAG

JTAG

USB

IO c

onne

ctor

s



The NXTCPUs

The main CPU (AT91SAM7S256) is an ARM7TDMI based�controller from Atmel.

� 32-bit RISC� Running at 48 MHz� 256 KiB Flash� 64 KiB RAM

IO coprocessor (Atmel ATmega 48)� Running at 8 MHz� 8-bit RISC (AVR)� 4 KiB Flash� 512 B RAM� Samples analog sensors with @ 333 Hz� Controls motors



The NXTExternal communication

Bluetooth� Only supports the serial profile (� 200 kb/s).� Requires that devices have been paired.� Useful for wireless debugging or robot cooperation.� May sometimes be used to upload software to the NXT.

USB� Normally used for software upload� Can be used for debugging� Firmware uploading

I2C� Used for low-speed (9600 b/s) serial communication with

sensors.RS485

� High-speed (� 1 Mb/s) serial communication.� Can be used for wired communication between robots.� Not used in default firmware.



Motors

Included motors linear and not step motors.� Speed is controlled using Pulse Width Modulation.� The AVR �controller handles PWM generation.

Feedback is provided by a quadrature encoder attached tothe motor.

� Allows detection of rotation direction and amount.



SensorsLight sensor

Simple photo-sensor that detects the strength of theincoming light.Has a LED mounted to provide illumination.Analog sensor



SensorsTouch sensor

Just a button with some Lego extras for mounting. Nothingfancy.Analog sensor



SensorsSound sensor

Measures sound intensity.Can be run in either DB or DBA mode.Analog sensor



SensorsUltrasonic range sensor

“Smart” sensor – uses I2C for communication.Detects distance to objects using sound pulses.



Developing for the NXTOverview

NXT-G� Bundled with the NXT.� Graphical drag and drop flowchart programming.� Doesn’t work for large applications, unstable.� Requires Windows.

RobotC� Commercial, but the department has licenses.� C-based language, but not “vanilla” C.� Has an integrated development environment with

debugging.� Requires Windows.

Not eXactly C� Has an IDE (Bricx Command Center)� Debugger support� Supports at least Windows and OSX� No releases in a long time – development has stagnated?



Developing for the NXTOverview (contd.)

nxtOSEK� GCC development environment (real C!)� Uses some Japanese embedded OS used in the

automotive industry.� C/C++ library for accessing IO devices.

LEJOS� Mini-Java implementation.� Uses the standard Java compiler, but a limited class library.� Has a plugin for Eclipse.� Works on most operating systems (even Solaris1)� Somewhat limited debugging capabilities.

1Requires patching and a sacrifice to Cthulhu.12 | Introduction to the Lego NXT


Remote controllingOverview

The NXT can be controlled from a computer (or anotherNXT!).Libraries exist for most common programming languages.

� Matlab� Python� Ruby� Java� . . .



LEJOSOverview

Requires custom firmware with a small Java VirtualMachineSupports standard Java threadsAlmost the same code can used both on the NXT and on acomputer controlling the NXTSupports Bluetooth and for all communication with the NXT



LEJOSBluetooth – practical matters

Bluetooth communication requires pairing to preventunauthorized access to wireless devices

� Process is OS dependent� Requires a PIN code, the default one is ’1234’

When communicating with the NXT you should normallyspecify the name of the target deviceUnless your NXT has a ’good’ name, rename it tosomething unique



Compiling and linking

nx jc RobotTest . java

Compiles the RobotTest.java class and all its dependencies,similar to the javac command.

n x j l i n k �o RobotTest . nx j RobotTest

Packages the class RobotTest and all its dependencies,including the class library. Similar to the jar tool in some ways.

nx jup load �b �r RobotTest . nx j

Uploads the packages to the NXT using Bluetooth.



ExamplesDebug console

import l e j o s . nx t .comm. RConsole ;

RConsole . openBluetooth ( 0 ) ;RConsole . p r i n t l n ( " He l lo World ! " ) ;

System . se tE r r (new Pr intSt ream (RConsole . openOutputStream ( ) ) ) ;

System . e r r . p r i n t l n ( " This i s s t d e r r . " ) ;



ExamplesMotors

import l e j o s . nx t . Motor ;

Motor motor = Motor .A ;motor . setSpeed ( 3 6 0 ) ;motor . forward ( ) ;Thread . s leep (1000) ;motor . stop ( ) ;



ExamplesLight sensors

import l e j o s . nx t . SensorPort ;import l e j o s . nx t . L ightSensor ;

L ightSensor sensor = new LightSensor (SensorPort . S1 ) ;

i n t value = myLightSensor . readValue ( ) ;



Hardware demonstration

The source code is available on the course homepage.



Get started!

Checkout the course homepage:http://www.it.uu.se/edu/course/homepage/

styrsystem/vt10/

Checkout a kitGet started!


http://www.it.uu.se/edu/course/homepage/styrsystem/vt10/

http://www.it.uu.se/edu/course/homepage/styrsystem/vt10/