Loïc Cuvillon, Bernard Bayle -...

Introduction to MechatronicsDiscover robots with the Lego Mindstorms

Loïc Cuvillon, Bernard Bayle

Télécom Physique StrasbourgStrasbourg University

Introduction to Mechatronics 1 / 98

Mobile robots Wheeled Mobile Robots Technology Navigation

Part I

Introduction to Mobile Robotics



Outline

1 Mobile robotsClassification and applicationsIssues

2 Wheeled Mobile Robots TechnologyMechanical architectureEmbedded systemActuatorsSensors

3 NavigationLocalizationMappingPlanningControl



Outline






Classification and applications

Outline







Mobile robots classification

Mobile robotsRobots with a moving base, by opposition with robotic manipulators.Classification based on the locomotion type.

Wheeled robots





Mobile robotsRobots with a moving base, by opposition with robotic manipulators.Classification based on the locomotion type.

Legged robots





Wheeled robots, legged robots+

flying robots, undersea robots.




Wheeled mobile robots applications

A few industrial applications

Automatic Guided Vehicles (AGV)FMC Technologieshttp://www.fmcsgvs.com





More and more general public applications

ToysTribot, WowWee

http://www.wowwee.com

Automatic vacuum cleanersDirtyDog, iRobot

http://www.irobot.com





Education and research

Khepera II , K-teamhttp://www.k-team.com

1 h autonomy, 1 m/s max7x3 cm, 80g (payload<250g) Multi-robot navigation

SRIhttp://www.ai.sri.com/centibots/index.html





A few High-Tech applications

Spatial exploration robotsSojourner mission to Mars

http://mars.jpl.nasa.gov/MPF/rover/sojourner.html





A few High-Tech applications

Inspectionhttp://crasar.csee.usf.edu



Issues

Outline






Issues

Issues

TechnologyIssues:

mechanical architectureembedded systemactuatorssensors

NavigationIssues:

localizationmappingplanningcontrol



Outline






Mechanical architecture

Outline







Mobile robots mechanical architecture

A large amount of systemsseveral types of wheelsarticulated platformscaution: all the architectures arenot kinematically consistent

Lego Tribot: a simple differential drivemobile robot

simple to build: 2 fixed wheels,with 2 independent actuatorsdifferential drive locomotionnonholonomic, nonlinear. . . not sosimple




Lego TriBot modelling

O

y

xx

y

CIR

O′

L

ρ

ω

θ

v

ϕr

ϕl

vr

vl

Wheels velocities (!anglesconvention) :

vr = −r ϕr = (ρ+ L)ωvl = r ϕl = (ρ− L)ω

and then:

v =vr + vl2

ω =−r(ϕr + ϕl)

2LDifferential kinematics:

x = v cos θy = v sin θθ = ω



Embedded system

Outline






Embedded system

Lego TriBot embedded system

NXT BlockThe core of the robot, which enables to get measurements and to control theactuators.

Refer to the first part of the talk for more details. . .

NXT InputsNXT Outputs

Sound Sensor

Touch Sensor

Light Sensor

Servo Motors

Ultrasonic Sensor

with position encoders

(contact switch)

(pressure in dB) (distance in cm)

(light intensity in %)

Buttons

LCD screen

Speaker

with BluetoothNXT processor



Actuators

Outline






Actuators

LEGO Mindstorms Servo-motor

Encoder wheel andwith optical sensor

Gear train (1:48)

Running_modesON: power control

open loop controlreference: % of the max power

ON & REGULATED:speed regulationuse of position sensor signalsclosed loop with PID controller

ON & BRAKE: electronic brakingOFF: coasting (free motion)



Sensors

Outline






Sensors

Ultrasonic Telemeters

http://www.pages.drexel.edu/ kws23/tutorials/ultrasonic/ultrasonic.html

Properties:alternate emission/receptionsounds not heard by humanear (ultrasound=20kHz to200kHz)minimal measurementdistance and variablemaximal frequency=f(maximaldistance)different drawbacks(directivity, reflectivity,ambient conditions sensitivity)



Sensors

Lego TriBot Ultrasonic Telemeter



Outline






Localization

Outline






Localization

Dead reckoning

OdometryComputation of the configuration by velocities integration:

x(t) =! t

0x(τ )dτ, y(t) =

! t

0y(τ )dτ, θ(t) =

! t

0θ(τ )dτ.

The TriBot example, with a Te sampling period:

x(k + 1) = x(k) + v(k)Te cos θ(k)y(k + 1) = y(k) + v(k)Te sin θ(k)θ(k + 1) = θ(k) + ω(k)Te

RemarkOdometry: current configuration relative to the initial configuration.



Mapping

Outline






Mapping

Environment mapping

Occupancy grid: discrete map of the environmentCell decomposition, with probability of collision from sensors measurements.The simplest case: binary grid, without filtering, trusting the odometrylocalization.



Planning

Outline






Planning

Configuration space

DefinitionConfiguration space = set of all the accessible configurations of the robot:

robot represented as a point: obstacles augmentationrobot with complex shapes and kinematics: more difficult problem. Overpessimistic obstacle augmentation can close doors !



Planning

Roadmaps

Visibility roadmapGraph capturing the environment topology from the polygonal obstaclesvertices.

link initial point and goal to visible vertices



Planning

Roadmaps


apply the same to the new vertices



Planning

Roadmaps


search for a path in the graph



Control

Outline






Control

Path following problem

ProblemFind ω such that d(P, C) decreases to zero, with v imposed.

x′

y ′

Ox

O′

C

θr

Or

xr

yry

Pd

a

θeIt can be showna that:

s =v cos θe − aω sin θe

1− dc(s) ,

d = v sin θe + aω cos θe,θe = ω − sc(s).

a|d c(s)|<1 under some adequate initial conditions of the



Control

Path following control law

Distance equation:d = v sin θe + aω cos θe

It comes that:ω = −

v sin θea cos θe

−v

cos θek(d , θe)d ,

with k(d , θe) ! 0 such that k(d , ±π

2 ) = 0 gives:

d = −vak(d , θe)d .

ConsequenceIf a, v et k(d , θe) > 0: |d | decreases along any path.

RestrictionsNo control of the orientation.

Can be solved at the planning step.


Lego Mindstorms Hardware NXT Programming with NBC/NXC Bluetooth communication

Part II

Hardware and Programming under Linux



Outline

4 Lego Mindstorms HardwareOverviewNXT Brick Hard/Firm-ware

5 NXT Programming with NBC/NXCCompilation and download to the NXTNXC syntax and multi-taskingNXC I/O API

6 Bluetooth communicationBluetooth ProtocolBluetooth communication with PCBluetooth communication between NXT



Outline






References

NXC Programming

[NXC07] J.C. Hansen, NXT Power Programming, Variant Press, 2007

[NXC] J.C Hansen, Not eXactly C Programmer’s Guide,http://bricxcc.sourceforge.net/nbc/

[NXCT] D. Benedettelli. , Programming LEGO NXT Robots using NXC,http://bricxcc.sourceforge.net/nbc/nxcdoc/NXC_tutorial.pdf

NXT Bluetooth and USB communication

[BLUE] J. Schultz, Lego, Bluetooth and Linux, http://www.cs.uleth.ca/benkoczi/3720/data/NXT_Bluetooth_handout-jeremy.pdf

[NXTLIBC] Lego Mindstorms NXT Bluetooth library in C,http://www.quietearth.us/nxtlibc.htm



Overview

Outline






Overview

Why the Lego Mindstorms?

fun (look back on childhood)cheap (for the content)and not the least: highly valuable for education

computer sciencescontrol systems theoryrobotics



Overview

Lego Mindstorms Overview

NXT InputsNXT Outputs

Sound Sensor

Touch Sensor

Light Sensor

Servo Motors

Ultrasonic Sensor

with position encoders

(contact switch)

(pressure in dB) (distance in cm)

(light intensity in %)

Buttons

LCD screen

Speaker

with BluetoothNXT processor



Overview

NXT brick

Battery levelNXT brick name(configurable)

USB 2.0 connector

B : ON, invisible B< : ON, visibleB<> : ON, connected

usb : connected, working]−[ : connected, not working

On/Enter button

Clear/Go back buttonNavigation buttons

S4S1 S2 S3Sensor port

OUT_A OUT_B OUT_CServo outputs

Loudspeaker

USB indicator

Bluetooth indicator



Overview

NXT brick Menus

On/off

Connections

Visability

Searchto bluetooth device)(search and connect

Motor rotation

Sound dBA

Ultrasonic cm

Sound files

Software File(bytecode executableupload from computer)

(LCD display distance from sensor)

Delete Files

Volume

NXT version(firmware version)

NXT ProgramSettingsBluetoothMy files View (testing)

NXT Program Example :

= "Forward until an object detection, then turn left. Repeat"

NXT files

savedin



Overview

NXT-G (LabView)

advance graphical interface for programming NXTfunctional block and control flow



Overview

Some fun NXT Projects

Rubik’s Cube Solverby Daniele Benedettelli

NXTway-GS ENSPS (model by Y.Yamamoto)



NXT Brick Hard/Firm-ware

Outline







Hardware specification

S1 S2 S3 S4

−single and double H−bridge(OUT_A and OUT_BC)

−48MHz, 64KB RAM−256KB FLASH−I2C interface with AVR proc.and digital sensor (ultrasonic)

−class 2−10 meters range

−high speed communication lineon Port S4 (for future use)

−A/D converter for analogic sensor(light,sound,touch )

−PWM signal generator

LB1930 & LB1836

AT91SAM7S256Amtel 32 bit ARM Processor

Bluetooth Chip

USB 2.0 connector

8bit AVR Co−Processor

RS485 UART




LEGO Mindstorms Servo-motor

Encoder wheel andwith optical sensor

Gear train (1:48)

Running_modesON: power control

open loop controlreference: % of the max power

ON & REGULATED:speed regulationuse of position sensor signalsclosed loop with PID controller

BRAKE: electronic brakingOFF: coasting (free motion)




LEGO Mindstorms Servo-motor driving

O V

9 V

90% duty cycle

O V

9 V10% duty cycle

Power controlPWM (Pulse Width Modulation) ofa 8 kHz signal

90% duty cycle ≈ 8.1 V20% duty cycle ≈ 1.8 V

+Vcc

0V

In2

In2In1

M

In1

+−

In1=High, In2=Low In1=Low, In2=High

+Vcc

0V

In1 In2

In2In1

M +−

Direction and brakingH-bridge with DC motorsIN1 IN2 ActionH L ForwardL H ReverseL L Brake




Electronic braking

e

i

U

R

Lτ = Ki

ω = Ke

e : back e.m.fτ : motor torqueω : motor angular speed

Braking1 motor motion: e = 02 short circuit current i ≃ − e

R

→ torque τ in opposition to themotion




Hardware specification

I2C: Inter-IntegratedCommunicationuse 3 lines (data,clock,ground)UART: Universal AsynchronousReceiver Transmitter(serial line/port)

Note:each sensor port (S1-4) can beused with digital or analog sensor.6 wires by port: 3 for I2C + 3 foranalog signals




NXT Firmware

Processor

Boot loader/boot code

LEGO firmwarewith CodeByte interpreter

Executables (.rxe)

HARD

SOFT

Boot code/loaderinitialization of the hardwareload the firmware

Firmware : a basic operating systemmulti-thread (thread: light task)provides an API for I/O(displays the menus)interprets ByteCode executables(.rxe)

firmware and files stored inFLASH memory



Outline






Compilation and download to the NXT

Outline







NBC/NXC

NBC: Next Byte Codesname of an assembly languagename of an open source assembler available under MPL licenseproduces executable bytecode for the native LEGO firmware

NXC: Not eXactly Chigh level programming language: C-like syntaxcompiler built upon nbc.nxc (source)→ .rxe (ByteCode executable)




Compilation and Execution

Compilation under linuxnbc compiler available from [NXC]compilation of a source file *.nxc and upload to the brick:nbc -EF -d toto.nxc

Execution after upload.rxe listed in the brick Menu : Software Filesstart/stop the progam with the NXT buttons




Compilation and Execution

Cross−compilation process

1−Source editing

2−Compilation (nbc)

USB cable

3−Upload of .rxe file4−Execution on the NXT(menu Program Files)

nbc −EF −d toto.nxc

toto.nxc




communication tool : NeXTTool

NeXTToolrunning on PC to communicate with the NXT brickvia USB or BT (BlueTooth if configured)list of functions: NexTTool -h

Examplesto download a file via USB cable :NeXTTool /COM=usb -download=toto.rxe

to obtain info on the brick (free memory, BT address):NeXTTool /COM=usb -deviceinfo

to play a musical tone of 500Hz:NeXTTool /COM=usb -playtone=500



NXC syntax and multi-tasking

Outline







Not Exactly C

C like syntax butNo pointers !

new types: Arrays and stringno parameter passed by address

Multi-tasking : more than one program (task) on executiontime-sharing operating system




Types

bool, byte, unsigned char, char 8 bitunsigned int, short, int 16 bitunsigned long, long 32bit

float 32 bits (in recent version of NXC)string Array of charactersstruct User defineArrays Array of any type

Type conversionsno explicit conversion - no cast operator (type).please remind that an operation on integers give an integers :float y;y=3/10; differs from y=3.0/10// -> y = 0.0 // -> y=0.3

be also careful with order of calculus for int:int y; int x=7;y=x*3/10 differs from y=x/10*3// -> y=2 // -> y=0




Arraysno pointers→ no dynamic allocation with malloc

byte myvector[2]; //2 byte array

int myarray[]; // int array (no dimension)

ArrayInit(myarray,0,10);// allocation of 10 null entries (equiv. to malloc)

myarray[0]= 15;




String type

Stringarray of bytesdeclaration:

string msg1, test=’’toto’’;msg1="yes";

manipulation functions:msg=NumToStr(i);

//convert number in stringmsg=StrCat(str1,str2);

//concatenationn=StrToNum(str);

//convert string to numbery=StrLen(str);

//return length of the string




Program structure: Functions

parameter passed by valuereturn for non-void function

int foo (int x){ x++;

return x;}

task main{

int x,y=1;x=foo(y);

//y still equal to 1}

parameter passed by reference

void foo (int &x) // !!{x++;}

task main{int y=1;foo(y);

//y now equal to 2foo(2);

//ERROR (not a variable)}




Control structures

Test Expression

= equal!= not equaltrue Truefalse False

Expr True if Expr!=0&& logical AND between conditions|| logical OR between conditions

if, if . . . elseif (x==1){x=2; z=3;}

elsey=4;

forfor (i=1; i<10; i++)

{;}

whilewhile (x<10){x++ ; // something needed !!}

do.. whiledo

{ x++ ;}while (x<10)




Control structures

switchswitch (x){

case 1 :z=3;break;

case 2 :// some codebreak;

default:// some codebreak;

}

repeat and until control structure available but not C standard




Program structure: Main Task

source.nxc :

long time; //global var.

task main (){

int x;...

}

Task main ()entry point of the programequivalent to the C function main()no parameter, no return value




Program structure: Periodic Task

source.nxc :

long time; //global var.

task main (){

while(1){

...Wait(500);//wait, sleep 500 ms

}}

Periodic Taskan infinite Taska timing function to set a period




Program structure: Tasks and Multi-tasking

task odometrie(){ while(true)

{...Wait(500);

}}

task main (){

start odometrie;

while(true){ OnFwd(OUT_A,50);

if (x==1)stop odometrie;

...Wait(1000);

}}

multithreading in NXT=concurrent execution of tasksin time sharingat least one entry task called”main”

APIstart task1 or StartTask(task1) ;stop task2; and StopAllTasks();precedes(task1,task2,..);launch the task after end of main




Program structure: Tasks and Multi-threading

Time sharing of the processor for periodic tasks (with sleep)

t

t

t

0 50 100 150

+

Task main

Task odometrie

=global cpu usage

(Equitable) Time sharing for non-periodic tasks

0 50 100 150

t




Preprocessor

Preprocessor directiveinclude files#include ’’foo.h’’#include <foo.h> //error no libray path

macro and define (recommended!)#define TIMEOUT 200 //0.2 ms timeout#define NORMAL_SPEED 50



NXC I/O API

Outline






NXC I/O API

API functions

TimeWait(2000);// sleep for 2s

x=CurrentTick();// system time in ms (since the power on)

Math and Trigonometry Functions-abs(), sqrt()-cos(), sin(), acos() in radiansand return a float

x=cos(3.14159); //returns -1

SoundPlayTone (440,500);

// frequency=440 Hz, duration 500 ms



NXC I/O API

LCD Screen API

Screen Resolution100x64 pixels8 lines : LCD_LINE1,...LCD_LINE8char size : 6x8 pixeldefault mode : overwriting without clearing of thescreen

Screen functions:with X and Y, the column in pixel and Y the line(LCD_LINEx)

Display a string variable:TextOut(X,Y,string);

display a numeric variable:NumOut(X,Y,var);

clear the screen:ClearScreen();



NXC I/O API

LCD Screen API

task main (){int i=1;TextOut(0,LCD_LINE1,"toto:");

// display toto on line 1NumOut(20,LCD_LINE1,i);

//display i on line 1 and column 20Wait(3000);ClearScreen();LineOut(40,40,60,60);

//plot a line from (40,40) to (60,50) coordinatesWait(3000);

}



NXC I/O API

Output Control API : Servo-motor

Parameterspower in percent: [-100,+100] (negative = reverse)port name to select motor: OUT_A, OUT_B, OUT_Cor multiple selection : OUT_AB, OUT_AC, OUT_BC,OUT_ABC

Motor functions:power control: OnFwd(port,power);

speedcontrol: OnFwdReg(port,power,mode);

2 synchronized motor control:OnFwdSync(OUT_AC,power,sterring)

rotation control:RotateMotor(port,power,angle);

brake: Off(port)

stop without braking: Float(port)



NXC I/O API


OnFwd : Unregulated power controlno regulation (speed can vary according to the load)reference = power in % , output selection= OUT_A, OUT_BC, OUT_ABC. . .

task main(){OnFwd(OUT_AC,85); //motor AC fwd at 85% of powerWait(1500); // run for 1.5 sOnRev(OUT_A,90); //motor A reverse at 90%,

//C still going fwd at 85%Float(OUT_C); //motot C power off, free decelerationWait(1500);Off(OUT_ABC); //motor ABC power off with braking

}



NXC I/O API


OnFwdReg : Speed Regulated modePID regulation of the motor speed (power will increase if load increases)reference = speed in % of maximal speed

task motor_status(){while(1)NUMOUT(0,LCD_LINE1,MotorActualSpeed(OUT_A));

//diplay not speed but power!!}

task main() {start motor_status;

OnFwdReg(OUT_A, 40, OUT_REGMODE_IDLE);//same as OnFwd, no regulation

Wait(5000);OnFwdReg(OUT_A,40,OUT_REGMODE_SPEED); //speed regulationWait(5000);Off(OUT_A);StopAllTasks();

}Introduction to Mechatronics 76 / 98


NXC I/O API


OnFwdSync: Synchronized modeonly for a pair of motors (OUT_xy)synchronized the rotation (useful to go in straight line for mobile robot)if one motor slow down, the other adaptslast parameter: steering or turn percentage

task main() {OnFwdSync(OUT_AC, 50, 0); //Motors A and C same speedWait(2000);OnFwdSync(OUT_AC, 40 , 50); //motor A stopWait(2000);OnFwdSync(OUT_AC, 40 , 100);

//motor A speed opposite of CWait(2000);Off(OUT_AC);

}



NXC I/O API


RotateMotor: Position-based moderegulation of rotation position in degree

#define degree 180

task main() {RotateMotor(OUT_AC,56, degree);

//rotation of 180 degree at 56% of power}



NXC I/O API

Input API : Sensors

Configuration of the sensors (input ports)1 a port name: S1, S2, S3 or S4;2 a TYPE (TOUCH,SOUND. . . ) with SetSensorType(port,TYPE)3 a MODE (RAW, BOOL. . . ) with SetSensorMode(port,MODE)

TYPE DescriptionSENSOR_TYPE_TOUCH touch sensor

SENSOR_TYPE_LIGHT_ACTIVE light sensor with LED onSENSOR_TYPE_LIGHT_INACTIVE light sensor with LED offSENSOR_TYPE_SOUND_DB sound pressure in dBSENSOR_TYPE_LOWSPEED I2C sensor (Ultrasonic)

MODE DescriptionSENSOR_MODE_RAW value between 0 < x < 1024SENSOR_TYPE_BOOL 0 if x<512, else 1

SENSOR_TYPE_PERCENT value between 0 < x < 100SENSOR_TYPE_EDGE count number of transitionSENSOR_TYPE_TOUCH count number of level change



NXC I/O API

Input API : Analog Sensors

Fast initialisation of Analog Sensorsport where sensor is connected : S1, S2, S3, S4.touch sensor (mode bool):

SetSensorTouch(port);

light sensor (mode percent):SetSensorLight(port);

sound sensor (mode percent):SetSensorSound(port);

Read analog sensors:function SensorValue(port)

var1=SensorValue(S1);

or the macros SENSOR_1, SENSOR_2, SENSOR_3and SENSOR_4:

var1=SENSOR_1;



NXC I/O API

Input API : Numeric Sensors

Initialisation of Numeric Sensorsfor the sonar sensorset numeric communication (i2c) on the port:

SetSensorLowspeed(port);

Read numeric sensors:specific function for each sensorsonar sensor (value in centimeters):

dist=SensorUS(port);

Rotation count of motors:motor selected by port: OUT_A, OUT_B, OUT_Cread the motor position in degree:long position=MotorRotationCount(port);

reset the motor position (and stop motor):ResetRotationCount(port);



NXC I/O API

Input API : Sensors and rotation

task main(){

bool cont; int dist;

SetSensorTouch(S1);SetSensorLowspeed(S2);ResetRotationCount(OUT_A);

while(1){

cont=SENSOR_1; // or cont=SensorValue(S1);dist=SensorUS(S2);if (cont==1){ TextOut(0,LCD_LINE1,"Pressed"); PlayTone(440,500); }

else TextOut(0,LCD_LINE1,"Released");

if (MotorRotationCount(OUT_A) > 180)TextOut(0,LCD_LINE2,"Half-rotation!"); }

}



NXC I/O API

One example : "Move forward but avoid obstacles"

Moteur A et B en avant, 80% de la vitesse

{OnFwd(OUT_AB, 80);

{ Off(OUT_AB); RotateMotor(OUT_A, 80, 360); }}

Si distance (par ultrason) < 15 cm

Rotation Moteur A, vitesse 80%, 360

Arrêt moteur A et B

Un pied

if ( SensorUS(4) < 15 )

while (true)



NXC I/O API

One example : "Move forward but avoid obstacles"

Implementation 1

#define NEAR 15 //cm

task main(){SetSensorLowspeed(S4);

while(true){OnFwd(OUT_AC,50);

while(SensorUS(S4)>NEAR);//do nothing: waitOff(OUT_AC);OnRev(OUT_C,40); //turn

//angle linked to wait timeWait(800);}

}

Implementation 2


task main(){SetSensorLowspeed(S4);

while(true){

OnFwd(OUT_AC,50);

if (SensorUS(S4)<NEAR){ Off(OUT_AC);

OnRev(OUT_C,40);Wait(800); }

}}



NXC I/O API

One example : third implementation


mutex motor_mutex;

task obstacle_test(){ while(1)

{if (SensorUS(S4)<NEAR){Acquire(motor_mutex);Off(OUT_AC);OnRev(OUT_C,40);Wait(800);Release(motor_mutex);}

}}

task move(){

while(true){ Acquire(motor_mutex);OnFwd(OUT_AC,50);Release(motor_mutex); }}

task main(){SetSensorLowspeed(S4);start obstacle_test; start move; }

Implementation 3: Multiple tasksrunning in concurrency (problem)mutex: mutual exclusion =prevent the 2 tasks to controlmotors simultaneouslya task block on Acquire(), ifanother has already Acquire themutex→ must wait for theRelease



Outline






Bluetooth Protocol

Outline






Bluetooth Protocol

Bluetooth

wireless protocolfor electronics (phone headset), computer peripherals (WiiMote,keyboard)2.4 GHz short-range radio frequency bandwidth : unlicensed frequency

Classclass 1: 100 mW ≈ 100metersclass 2: 2.5 mW ≈ 10 meters (LEGO NXT)

Search and Pairingsearch service available to find new Bluetooth devicepairing: trust communication by learning of a common passkey-input of the passkey on both device-key used to encrypt communication



Bluetooth communication with PC

Outline







Pairing between PC and NXT -1

Get NXT Bluetooth addresseach Bluetooth as an unique address on 6 bytes (MAC address)

1 command hcitool : give name and Bluetooth address of available device>hcitool scanScanning ...

00:16:53:04:B3:46 NXT2 NeXTTool, while NXT connected by USB>NeXTTool /COM=usb -deviceinfoBrick name = NXT12Bluetooth Address = 00:16:53:0B:2E:D4Bluetooth signal strength = 0,0,0,0Free memory = 31716




Pairing between PC and NXT -2

Pairing under ubuntu Linux 9.101 On Linux: right click on the Bluetooth-applet > set up new device2 select NXT and in PIN option select custom PIN ’1234’(but a new one can be set)

3 click Forward, Linux will initiate a connection to the NXT4 On NXT: a pop-up ask for the passkey, validate the default ’1234’ (orgive the new one)

5 it is a one time operation, NXT now appears in Bluetooth-applet >preferences > known devices




NXTlibC

A simple library to perform Direct CommandRun on the PC to interact with the NXT brick via Bluetoothcompilation:gcc -lm -lbluetooth -lnxtlibc test.c -o test

API of NXTlibC : samplesnxt_bluetooth_initialize() , nxt_bluetooth_done()get_battery_level()play_tone()...message_write() and message_read() (see next section)




play_tone.c with NXTlibC

#include <stdio.h>#include <nxtlibc.h>

#define MAC "00:16:53:02:f3:31"

int main (void){int ret;// * * * * * Connection Ãa la brique * * * * * //nxt_bluetooth_initialize(MAC);

play_tone(500, 2000);

// * * * * * Verification de la batterie * * * * * //ret = get_battery_level();

nxt_bluetooth_done();

return 0; }




NXTlibC

Message ExchangePC = masterNXT = slave20 mailboxes available on the NXT

mailboxes 0-9 reserved for Master inputmailboxes 10-19 reserved for NXT output

one mailbox can store up to 5 messages of 64 bytes each? behaviour if mailbox full




NXTlibC

Message Exchange1 PC writes its message in mailbox A (with nxtlibc functions)2 NXT check the mailbox A (with nxc functions)3 If needed, NXT writes its response in mailbox B4 PC checks the answer in mailbox B

message_write(3,size,message)PC −NxtLibC

1−

4−

2−3−

O

10

13

19

3

9

mailboxesNXT−NXC

string buf, res;ReceiveMessage(3,true,buf)

SendMessage(10+3,res)

message_read(10+3,0,....,reponse)




message.c with NXTlibC

#include <stdio.h>#include <nxtlibc.h>#define MAC "00:16:53:02:f3:31"

int main (void){unsigned char return_inbox[1], return_size[1];unsigned char message[]="home";unsigned char *data;

// * * * * * Connection Ãa la brique * * * * * //nxt_bluetooth_initialize(MAC);

message_write(3,5, message);getchar(); //or sleep to let NXT some time to answermessage_read(13, 0, 1, return_inbox, return_size,

(unsigned char**)&data);

printf("++message: %s\n",data);

nxt_bluetooth_done();

return 0; }




message.nxc

task main() {

string buffer, message="none";char result;

while(1) {// read mailbox 3result = ReceiveMessage(3, true, buffer);if (result == 0) //if something is read{ message = "sweet";// send message back to master in mailbox 13SendMessage(3+10, message);}

Wait(500);}

}



Bluetooth communication between NXT

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Loïc Cuvillon, Bernard Bayle -...

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