Lego Mindstorms and NXT-G

Magnus Eriksson, Mid Sweden University 2012Based on a presentations by National Instruments and Pavel Petrovič

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Lego Mindstorms can be used for rapid prototyping of intelligent and

sensor-based systems

Rubik’s cubesolver

Pen-Drawer Robot

The NXT2.0 unit

(Motor ports)

(Sensor ports)

Motors and Sensors

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• Built-in rotation sensors (“servo”)

NXT Motors

The NXT2.0 Unit – an embedded system

• 64K RAM, 256K Flash• 32-bit ARM7 microcontroller• 100 x 64 pixel LCD graphical

display• Sound channel with 8-bit

resolution• Bluetooth wireless

communications • Stores multiple programs

– Programs selectable using buttons

LEGO Mindstorms for NXT

(NXT-G)

NXT-G graphical programming language

Based on the LabVIEW programming language GProgram by drawing a flow chart

NXT-G PC program interface

Toolbar

Workspace

Configuration Panel

Help & Navigation

ControllerPalettes

Tutorials

Web Portal

Sequence Beam

NXT-G tools

• Pointer tool: move blocks, select blocks• Pan tool: move within workspace• Comment tool: add notes to your code

Intro to NXT-G: Palettes

Common: Complete: Custom:Most All blocks Downloa Own blockscommonlyused blocks

Writing a Basic Program• Drag and drop block(s) on sequence beam

• Manipulate Configuration Panel & Download

Intro to NXT-G: Controller

Download & Run Selection

Download & Run

NXT Window

Download Stop

NXT Rotation Sensor

• Built in to motors• Measure degrees

or rotations• Reads + and -• Degrees: accuracy

+/- 1• 1 rotation =

360 degrees

Viewing Sensors

• Connect sensor• Turn on NXT• Choose “View”• Select sensor type• Select port

NXT Sound Sensor• Sound sensor can measure in dB and dBA

– dB: in detecting standard [unadjusted] decibels, all sounds are measured with equal sensitivity. Thus, these sounds may include some that are too high or too low for the human ear to hear.

– dBA: in detecting adjusted decibels, the sensitivity of the sensor is adapted to the sensitivity of the human ear. In other words, these are the sounds that your ears are able to hear.

• Sound Sensor readings on the NXT are displayed in percent [%]. The lower the percent the quieter the sound.

http://mindstorms.lego.com/Overview/Sound_Sensor.aspx

Challenge: Stop with sound

• Program your NXT car to drive until you yell “Stop”

Example Program: Stop with Sound

NXT Ultrasonic/Distance Sensor

• Measures distance/proximity

• Range: 0-255 cm• Precision: +/- 3cm• Can report in

centimeters or inches

http://mindstorms.lego.com/Overview/Ultrasonic_Sensor.aspx

Challenge: Parking NXT

• Program your NXT car to drive forward until you “find a parking spot” (hit a touch sensor)

• The car should then turn into the spot, and stop when it gets close enough to wall.

Example Program: Parking NXT

A note about NXT memory• Memory space is limited!• To clear space, use NXT window• Show and delete system files for more space

NXT Structure: Loops

Challenge: Stay on Table

• Program your NXT to stay on the table

Example Program: Stay on Table

NXT Structure: Switch

Challenge: Remote Control

• Program car to drive while the touch sensor is pushed and stop while the touch sensor is released

Example Program: Remote Control

NXT Sound• NXT can play sound files or notes• Sounds take up more memory space

NXT Display• Display images, text, or drawings• Choose location on display screen• 100 x 64 pixels (up to 7 lines of text)• Graphics take up memory space

Challenge: Say Hello

• Have the NXT say hello using sound and the display screen

• Don’t forget – the program ends after the last block. You may need a wait for to see the display.

• Caution: one of the options in the configuration panel is Clear – use it to clear screen. Otherwise, uncheck the box!

Example Program: Say Hello

My Blocks• Create custom blocks• Saved in custom palette• Download blocks from the web

Creating My Blocks

• Write the code for the My Block

Creating My Blocks

• Select all the blocks to be used for My Block

Creating My Blocks• Choose “Create My Block” on toolbar• Or, go to the Edit menu and select “Make a

new My Block”

Creating My Blocks• Name My

Block

• Add a description

Creating My Blocks• Create a

custom icon

Creating My Blocks

• My Block appears in Custom Palette

Signal flows and variables

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An advanced program

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Multi-treading

LEGO Mindstorms 3.0 EV3

Getting started with mindstorms EV3

https://www.youtube.com/watch?v=vv5X3zzkBk4

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• Master-slave: only master initiates communication• Master can connect up to 3 slaves• Optional acknowledgement, request reply• Mailboxes #1-10• Sending:

– Master: NXTCommBTWrite(slave, mailbox)– Slave: NXTMessageWrite(mailbox)

• Receiving: both sides NXTMessageRead()• Unreliable & Quite complex, but does not block

NXT BlueTooth Protocol

Silvian Toledo: http://www.tau.ac.il/~stoledo/lego/btperformance.html

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LEGO Digital Designer ldd.lego.com

CAD-verktyg – Eventuellt för Civing Teknisk design

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Pneumatics

För Civing Teknisk design

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NXT Non-standard sensors: HiTechnic.com

• Compass• Gyroscope• Accellerometer/tilt sensor, • Color sensor• IRSeeker• Prototype board with A/D converter

for the I2C bus För Elektroniksystemstudenter

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Issues of the standard firmware

För datateknikstudenter

Only one data type Unreliable bluetooth communication Limited multi-tasking Complex motor control Simplistic memory management Not suitable for large programs Not suitable for development of own tools or blocks

Other programming languages and environments

– Java leJOS– Microsoft Robotics Studio– RobotC – NXC - Not eXactly C– NXT Logo– Lego NXT Open source firmware and software

development kit

För datateknikstudenter

leJOS

• A Java Virtual Machine for NXT• Freely available

– http://lejos.sourceforge.net/• Replaces the NXT-G firmware• LeJOS plug-in is available for the Eclipse free

development environment• Faster than NXT-G

För datateknikstudenter

Example leJOS Programsonar = new UltrasonicSensor(SensorPort.S4);Motor.A.forward();Motor.B.forward();while (true) { if (sonar.getDistance() < 25) { Motor.A.forward(); Motor.B.backward(); } else { Motor.A.forward(); Motor.B.forward(); } }

För datateknikstudenter

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NXT Logo example: line-following to "follow []

[

setsensor 3 5 128

motor 0 "onrev 40

while ["true]

[

while [ge? sensor 3 59] []

motor 0 "float 0

motor 2 "onrev 40

wait 50

while [lt? sensor 3 60] []

motor 2 "float 0

motor 0 "onrev 40

]

]

För datateknikstudenter

Gruppindelning