USB. Bluetooth. Display. IO connectors. Sound. Main CPU Atmel ARM7 JTAG. IO Processor Atmel AVR JTAG. Introduction to the Lego NXT

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1 Introduction to the Lego NXT What is Lego Mindstorm? Andreas Sandberg A kit containing: A Lego NXT computer 3 motors Touch sensor Light sensor Sound sensor Ultrasonic range sensor Lots of Lego bricks... and plenty of fun! 2 Introduction to the Lego NXT The NXT Hardware overview The NXT CPUs Display IO connectors Bluetooth Main CPU Atmel ARM7 IO Processor Atmel AVR USB Sound JTAG JTAG 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 333 Hz Controls motors 3 Introduction to the Lego NXT 4 Introduction to the Lego NXT

2 The NXT External communication Motors 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 I 2 C 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. 5 Introduction to the Lego NXT 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 to the motor. Allows detection of rotation direction and amount. 6 Introduction to the Lego NXT Light sensor Touch sensor Simple photo-sensor that detects the strength of the incoming light. Has a LED mounted to provide illumination. Analog sensor Just a button with some Lego extras for mounting. Nothing fancy. Analog sensor 7 Introduction to the Lego NXT 8 Introduction to the Lego NXT

3 Sound sensor Ultrasonic range sensor Measures sound intensity. Can be run in either DB or DBA mode. Analog sensor Smart sensor uses I 2 C for communication. Detects distance to objects using sound pulses. 9 Introduction to the Lego NXT 10 Introduction to the Lego NXT Overview Overview (contd.) 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? 11 Introduction to the Lego NXT 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 Solaris 1 ) Somewhat limited debugging capabilities. 1 Requires patching and a sacrifice to Cthulhu. 12 Introduction to the Lego NXT

4 Remote controlling Overview LEJOS Overview The NXT can be controlled from a computer (or another NXT!). Libraries exist for most common programming languages. Matlab Python Ruby Java... Requires custom firmware with a small Java Virtual Machine Supports standard Java threads Almost the same code can used both on the NXT and on a computer controlling the NXT Supports Bluetooth and for all communication with the NXT 13 Introduction to the Lego NXT 14 Introduction to the Lego NXT LEJOS Bluetooth practical matters Compiling and linking Bluetooth communication requires pairing to prevent unauthorized access to wireless devices Process is OS dependent Requires a PIN code, the default one is 1234 When communicating with the NXT you should normally specify the name of the target device Unless your NXT has a good name, rename it to something unique nxjc 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. n x j RobotTest Packages the class RobotTest and all its dependencies, including the class library. Similar to the jar tool in some ways. nxjupload b r RobotTest. n x j Uploads the packages to the NXT using Bluetooth. 15 Introduction to the Lego NXT 16 Introduction to the Lego NXT

5 Examples Debug console Examples Motors import l e j o s. nxt.comm. RConsole ; import l e j o s. nxt. Motor ; RConsole. openbluetooth ( 0 ) ; RConsole. p r i n t l n ( " Hello World! " ) ; System. s e t E r r (new PrintStream ( RConsole. openoutputstream ( ) ) ) ; System. e r r. p r i n t l n ( " This i s s t d e r r. " ) ; Motor motor = Motor. A ; motor. setspeed ( ) ; motor. forward ( ) ; Thread. sleep ( ) ; motor. stop ( ) ; 17 Introduction to the Lego NXT 18 Introduction to the Lego NXT Examples Light sensors Hardware demonstration import l e j o s. nxt. SensorPort ; import l e j o s. nxt. LightSensor ; LightSensor sensor = new LightSensor ( SensorPort. S1 ) ; i n t value = mylightsensor. readvalue ( ) ; 19 Introduction to the Lego NXT 20 Introduction to the Lego NXT The source code is available on the course homepage.

6 Get started! Checkout the course homepage: styrsystem/vt10/ Checkout a kit Get started! 21 Introduction to the Lego NXT