Project from Real-Time Systems –
Lego Mindstorms NXT
April 16, 2014
Lego Mindstorms NXT
Lego Mindstorms
• manufactured by LEGO, http://mindstorms.lego.com
• history:
• RCX, 1998
• NXT, 2006; NXT 2.0, 2009
• EV3, 2003
• use in education:
• out-of-the-box, easy to use
• widely adopted,
• faithfully illustrates the features of embedded real-time
systems and their programming.
Lego Mindstorms NXT
NXT Brick
• 32-bit ARM7 microcontroller, 256 KB FLASH memory, 64 KB
RAM
• timer doing 1000 ticks per second
• 4 input ports, 3 output ports, peripherals connected via
modified RJ12 cables
• USB port, Bluetooth interface
• loudspeaker (conversion tools from MIDI, WAW, etc.
available)
• buttons, display
• power source: 6 AA batteries
Lego Mindstorms NXT
Motors & Sensors
Motors
• 3 electric motors, built-in gear
• synchronization, built-in rotation sensor (accuracy +- 1 deg)
• typical use:
• set power (0-100), direction (fwd, rev), set on/off, or
• turn the shaft by a given angle at a given power.
Sensors
• touch sensor (binary: pressed/not pressed)
• sound sensor - measures acoustic pressure, up to 90 dB, works
with a percentage of max value.
• light sensor - measures intensity of ambient/reflected light
• ultrasound sensor - measures distance to objects (0 – 255 cm,
+- 3cm), accuracy depends on size, shape and composition of
objects
Lego Mindstorms NXT
Programming Environments
Visual:
• NXT-G (bundled)
• Robolab
“Code-based”:
• NXC (Not eXactly C)
• C-like syntax, IDE for Win (BricxCC), compiler (NBC) source
available for Mac and Linux
• leJOS NXJ
• firmware replacement allowing to run Java on NXT Brick
• comes with rich Java API
• plug-ins for Eclipse
• ... and many others (see, e.g., Wikipedia, or http:
//www.teamhassenplug.org/NXT/NXTSoftware.html).
All reasonable languages support multitasking.
Lego Mindstorms NXT
Project: Organization
• work in teams
• each team chooses a leader
• submit short project abstract (up to 1/2 page) by April 8
• work :)
• submit a project report (up to 5 pages) and program source
by May 11
• presentation of results (probably) during a lecture on May 14
Contact: xnovot18@fi.muni.cz
Lego Mindstorms NXT
Project: Requirements
• the robot performs a non-trivial, meaningful and a
well-defined task.
• the robot uses at least 2 motors and 2 sensors
• the robot uses display or speaker
• the implementation uses concurrency in a meaningful way (at
least 2 threads running in parallel)
• the resulting system is a hard real-time system (i.e., a
successful completion of the defined task depends on a correct
timing)
• implementation in NXC or leJOS is preferred, choice of a
different language should be consulted in advance
Lego Mindstorms NXT
Project: Evaluation
Project report:
• up to 5 pages
• describes the task performed by the robot and the
implementation, substantiates changes from the project
abstract, describes difficulties encountered during
implementation, points out the use of concurrency
• specify the contribution of individual members (does not have
to be equal, but team members may “kick out” work-avoiding
colleagues)
Source code:
• non-visual language
• well-documented source code
Presentation:
• with slides and demo, not necessarily by the team leader
Lego Mindstorms NXT
Project: Topic
• it is a part of the project to choose an interesting yet doable
goal
• search the internet for inspiration (e.g., YouTube: Lego
Mindstorms)
• all-time classics: finding, picking up and transporting a ball;
following a black line; navigation through a maze
Lego Mindstorms NXT
Quick Start Guide
• if possible, install Lego Mindstorms, BricxCC, or leJOS
• play around for a while, test the sensors etc.
• read manuals and tutorials on the web
• build a simple robot and try to compile a simple program
• discuss the project
Lego Mindstorms NXT