User Manual - Computer Science & Engineering
Contents
1. Let s get familiar with what each of the buttons are used for From left to right the first button is the compile button which allows the robot to execute the program the second is the download button it allows the user to download the program to the NXT brick via USB cable provided in the kit the download button will not be activated if user has errors in the program the user will be notified about the error at the bottom of the Bricx CC screen the third is the run button it allows the user to run the program and the last button in red is the stop button which stops a running program User must follow those buttons in given order First compile the program then download it to the NXT Brick run the program and end the program when needed The downloaded programs can be found on the NXT brick After turning on the brick go to My Files then go to Software files and the program files will be located under the software files To runa specific program from the NXT brick itself go to Run NOTE In case the user is unable to communicate with the brick go to Tools click on Close Communication and then click on Find Brick in order to start the communication Also 1f the brick hangs take out the battery from the brick This should be done only if other approaches fail Introduction to NXC Not eXactly C NXC is a high level open source programming language invented by John Hansen It is used to program the Lego Mindstorms2. It turns the specified motors off Output Desired output ports It can be a constant or a variable Example Off OUT_B This will turn off the motor connected to port B Random unsigned int n Returns a signed or unsigned 16 bit random number If the optional argument n is not provided the function will return a signed value Otherwise the returned value will range between 0 and n exclusive n Returns a maximum unsigned value Example Random 40 This statement will generate random numbers between 0 and 40 Play Tone frequency duration This function plays a tone at a specified frequency and for allotted amount of time Frequency defined in Hertz Duration defined in 1 1000 of a second Example PlayTone 100 300 this plays a tone at the frequency of 300 for 0 3 seconds Ts 10 Unsigned long CurrentTick This function allows you to keep track of current system count It returns milliseconds in a long integer Example var CurrentTick var will contain the current system count in milliseconds ClearScreen It clears the NXT brick screen NumOut x y number Lets the user specify the coordinates and the number Example NumOut 0O LCD_LINE1 20 this function will print the number 20 on x coordinate and y coordinate 1 LCD_LINE1 is the first line of the LCD screen There are total of 8 lines on the LCD screen TextOut x y string Lets the user specify the coordina
3. So now that you know what s in the kit let s move on to how to use those parts Where to use what Most of the connectors bricks and plates will be used to build the robot If you need to build a specific type of robot the step by step instructions will be given in the lab handout Otherwise you can use those parts as you need to meet your assignment details The part with the number 4558295 is called the intelligent micro computer LEGO Brick also known as the NXT brick acts as the brain of the robot The brick has a USB port which lets the user download the programs from computer to the brick Besides the USB port the brick has four input ports 1 to 4 to connect sensors and multiplexer for sensors multiplexer is used if the robot requires more than four sensors and three ports A to C to power motors The brick can be charged using the charger or the 4 batteries So no matter what the assignment is the NXT brick is the one thing that is necessary The other essential part of building robots is the use of motors Without motors the robot would not be able to move Motors are also useful when you need to rotate certain part of your robot For example if the robot is supposed to collect and hold balls use motors to open and close a gate Now let s learn what each sensor in you kit is helpful for in general manner Following sensors can be connected to any of the four ports on the bottom of the NXT brick to connect a se
4. NXT kit The NXC Application Programming Interface describes the built in functions constants and macros that can be used to program a robot This document will describe the NXC implementation specifically with BricxCC Basic NXC Functions 1 OnFwd byte output char pwr This function sets output to forward and turns motors on with given pwr output Desired output ports It can be a constant or a variable Motors can only be connected in PORT A C on the NXT brick pwr the motor output power It ranges from 0 to 100 Negative numbers can be used to reverse the direction Example OnFwd OUT_A 100 The above function will turn on the motor connected to the output port labeled A on the NXT Brick with 100 power OnRev byte output char pwr This function sets output to reverse and turns the motors on output Desired output ports It can be a constant or a variable pwr Output power 0 to 100 Negative numbers can be used to reverse the direction Example OnRev OUT_AC 75 This will allow the robot to move backwards with power level 75 Wait unsigned long ms It makes a task sleep for specified amount of time ms the number of milliseconds to sleep Example Wait 4000 This statement tells the robot to sleep for 4 seconds Alternate function for wait Wait SEC_sec This also makes a task sleep for specified amount of time Example Wait SEC_1 Allows the robot to sleep for 1 second Off byte outputs
5. analog sensors Most of the sensors mentioned above can be used in any combination with the sensor multiplexer Some of the exceptional sensors are sound sensor and Hi Technic magnetic sensor As mentioned above these are the main parts which are not included in the kit and are ordered separately Also these are the parts that will be used on regular basis in lab The limits and orientations of these parts should be kept in mind while building a robot and writing the program for it These parts are sensitive so be careful to not get the sensors scratched otherwise the results might not be as precise Building a robot Refer to the instruction manual in the CD provided in the kit to build your first robot After that use the lab guidelines to build the robot that would meet all the requirements For further help use http cache lego com downloads education 9797 LME UserGuide US low pdf Introduction to ROS ROS is an open source operating system for robots It provides the basic operating system services such as hardware abstraction low level device control implementation of commonly used functionality message passing between processes and package management It runs on Unix based platform It is implemented in C Python and Lisp More information about ROS can be found here http www ros org wiki ROS Using ROS with NXT ROS provides a NXT software stack that is essential to interface NXT robots with ROS NXT ROS suppor
6. 8 22 2011 Introduction to Lego Kit NXC and ROS Index INTRODUCTION TO THE LEGO MINDSTORMS EDUCATION KIT a What s in the kit b Where to use what c Details of Sensors and Multiplexer BUILDIG A ROBOT INTRODUCTION TO ROS a Using ROS with NXT b Issues for using NXT with ROS INTRODUCTION TO BRICXCC a Starting with Bricx CC INTRODUCTION OF NXC a Basic NXC Functions b Macros c Sensor Functions d Multiplexer e Multi tasking with NXC USEFUL LINKS Page 01 Ol 01 02 06 07 07 07 09 09 11 11 14 14 17 17 19 INTRODUCTION TO THE LEGO MINDSTROMS EDUCATION KIT What s in the kit The kit contains two pamphlets which provide the details of the parts in the kit The pamphlet with the number 4581599 at the top of the pamphlet provides a picture of each part its part number and quantity of the part in the kit For example Here the picture represents the part called 1 2 yellow Bush 10x means there are total of 10 1 2 yellow Bush in the kit and the number after x is the part 10x 4939601 number The other side of this pamphlet and the other pamphlet represents the same details as the side that we just saw but without the part numbers You will be given other sensors detail of which is not included in these pamphlets because those are ordered separately Details of those parts are given briefly in the next section and will be discussed throughout the paper
7. XC driver The driver provides all the definitions functions and variables that are required for the SMUX to work with different sensors It can be found here http www hitechnic com file php f 970 smux driver nxc 0 4 zip Multitasking with NXC NXT and NXC both supports multi threading which is an ability of an operating system to execute different parts of a program simultaneously A task can be defined using the keyword task in the following manner task name code for the task goes here j To schedule the listed tasks to execute once the current task has completed executing the following function would be useful Precedes task task1 task task2 task task3 task taskN All the tasks will execute simultaneously unless other dependencies prevent them from doing so Any number of tasks may be listed in the Precedes statement Tasks can be stopped as follows stop functionName In order to stop all the running tasks concurrently use the following statement StopAllTasks Bricx CC and NXC are the best options because they have all the features that are essential to program a robot Since ROS doesn t support many of the sensors NXC is an appropriate choice for the class due to its compatibility with all the equipment provided in the NXT kit NXC is similar to C so it makes it easy for the students to learn and use it for the class because they will already be familiar with C NXC and
8. above the target surface and not at an angle to the target surface oo nt oat WN a oO Sound Sensor This sensor is not very useful in noisy area since the sensor is able to measure noise level frequencies around 3 6 kHz where the human ear is most sensitive The sound sensor can measure sound level in dB and dBA To trigger the sensor user can clap hands whistle or snap fingers to create the sound Our lab environment is not the best environment for using the sound sensor but if noise level is kept to minimum it would work as designed Light Sensor This sensor is used to detect the light intensity This sensor enables the robot to distinguish between light and dark as well as determine the light intensity in a room or the light intensity of different colors You will learn about Photophilic attracted to light and Photophobic afraid of light robots So based on the lab requirements your robot will use light sensor to follow or move away from the light Ultrasonic Sensor Just like color and light sensor Ultrasonic sensor is used as a robot s eyes The sensor can detect the objects and measure its closeness in inches or centimeters The maximum distance this sensor can measure is 233 cm with a precision of 3 centimeters How it works is that it sends out ultrasonic sound waves that bounce off an object ahead of it and then back at it Then it senses the time it took for that to happen B
9. ased on those two tasks the sensor returns the signal to the program Hi Technic Compass Sensor The Hi Technic compass sensor is designed to calculate the angle it s facing The compass sensor has a digital magnetic compass that measures the earth s magnetic field to calculate the angle The calculated value of the angle is returned as a number from O to 359 Based on our testing we found that the sensor 1S very sensitive and getting precise results requires the robot stay horizontal should be mounted at least 6 inches away from the motors and at least 4 inches away from the NXT brick So when required to use this sensor the user must be very careful not to ignore the given details Hi Technic Magnetic Sensor The magnetic sensor is used to detect the magnetic fields that are present i i Wh Fa around the front of the sensor in a vertical orientation The picture on right side shows how the magnet should be placed for the sensor to iy ee A Dee reir detect the magnetic fields correctly When the magnetic field has north uppermost the reading will increase Hi Technic IR Seeker Sensor IR seeker is a multi element infrared detector and is used to detect infrared signals One of the sources of infrared signal is the Hi technic IR Electric Ball The curved end cap of the sensor is designed to increase directional performance by minimizing distortion of light signals entering the sensor The IR seeke
10. e number of the port it is connected to Infrared Seeker Sensor To read HiTechnic IRSeeker2 AC values use the following function bool ReadSensorHTIRSeeker2AC const byte port byte amp dir byte amp s1 byte amp s3 byte amp s5 byte amp s7 byte amp 9 Port The sensor port dir the direction 1 The signal strength from sensor 1 3 The signal strength from sensor 3 5 The signal strength from sensor 5 7 The signal strength from sensor 7 9 The signal strength from sensor 9 Example byte s1 s3 s5 s7 s9 Bool result ReadSensorHTIRSeeker2AC IN_1 dir s1 s3 s5 s7 s9 It read direction and five signal strength values from the HiTechnic IRSeeker2 sensor in AC mode Returns a boolean value indicating whether or not the operation completed successfully The port must be configured as a Lowspeed port before using this function Multiplexer The HiTechnic Sensor Multiplexer SMUX allows the user to connect four NXT sensors to a single NXT port The NXT sensors can be connected to the SMUX using the NXT wire provided in the NXT kit SMUX uses the digital I2C communications protocol and uses a 9v battery Sensors supported by SMUX from our kit are 1 HiTechnic Color Sensor 4 Touch Sensor 2 HiTechnic Compass Sensor 5 Light Sensor 3 HiTechnic IRSeeker 6 Ultrasonic Sensor Note The SMUX does not support the sound and the magnet sensor To use SMUX with NXC the user needs to download the N
11. em to the robot start and stop the programs browse the NXT flash memory and much more Several programming languages can be used to program the robots in the Lego kit such as Next Byte Codes NBC Not Quite C NQC and Not eXactly C NXC This tutorial will use BricxCC as the programming environment and NXC as the programming language to program the robots BricxCC can be downloaded from here http bricxcc sourceforge net Starting with Bricx CC After starting the Bricx CC program the following window appears Select USB as a port and NXT as a brick type and click on OK Find Brick Searching for the brick Brick Type NXT Firmware Standard brickOS pF orth leAJOS Other Cancel Help E There is an alternate way to search for the NXT brick After starting the Bricx CC go to Tools from top bar menu and click on Find Brick The following is the screenshot of the user interface window pai a ere Var Sees eae E IEX LommMand enter File Edit Search View Compile Tools Window Help DenRS Aelad BG F Pom OB O no port The user interface window looks like and acts like a text editor It allows one to create a new file open a file save compile download programs and etc To create a new file click on File and choose New This will open a new window to start writing the program Here is a program toolbar which will be constantly used to compile download run and end programs
12. nsor to the brick use the standard NXT wire provided in the kit Details of Sensors and Multiplexer Touch Sensors Touch sensor helps robot avoid obstacles in its way Furthermore it helps detect which way the robot should go whether the robot is stuck somewhere or not The use of two touch sensors would make it easy for the robot to avoid obstacles since it would help detect where the obstacles are and what the robot needs to do in order to avoid them To connect touch sensor to the NXT brick use the cables provided in the kit Hi Technic Color Sensors These sensors are used for the projects that are related to colors Some of the possible usages are search for a certain color item follow a given colored line avoid a certain colored object or read the color value and based on that make a specific decision There are many other ways one can use color sensor but for lab purposes the usage will be limited to the things mentioned above The color sensor can detect a wide range of colors Following is the chart of colors that a color sensor can detect and the values corresponding to those colors mm 0 11 The color sensor operates by using a single white LED to illuminate 17 the target and analyses the color components of the light reflected 13 14 by the target s surface and calculates a color value which is returned 45 tothe program Since it uses a single LED for best results it should 16 be positioned straight
13. onfigure the port as lowspeed Void SetSensorLowspeed const byt amp port bool bIsPowered true port the port to configure blIsPowered A boolean flag indicating whether to configure the port for powered or unpowered I2C devices The default value for this optional parameter is true Compass Sensor Read the compass heading value of the HiTechnic Compass sensor on the specified port Use the following function int SensorHTCompass const byte amp port port The port to configure The port must be configured as a Lowspeed port before using this function Example SensorHTCompass IN_2 Indicates the type of the sensor and the number of the port to which the sensor is connected to Color Sensor Read the compass heading value of the HiTechnic Color sensor on the specified port Use the following function int SensorHTColorNum const byte amp port port The port to configure The port must be configured as a Lowspeed port before using this function Example SensorHTColorNum IN_3 Indicates the type of the sensor and the number of the port to which the sensor is connected to Magnetic Sensor To configure the sensor on the specified port as a HiTechnic Magnet sensor use the following function Void SetSensorHTMagnet const byte amp port Port The sensor port Input port constants are used when calling NXC sensor control API functions Example SetSensorHTMagnet IN_1 indicates the type of the sensor and th
14. ort website http www ros org wiki Support says If you didn t get a response then likely nobody has had time to answer you Alternatively it could be that nobody knows the answer So with this way of support one might get response as soon as in a few seconds or never ROS has a large community of users and a lot of questions are asked on regular basis so getting response is not a big problem but sometimes there are questions which no one has answer to and that is when one is left on its own to figure things out Those were the main problems with using ROS and that is why we chose to work with NXC Not Exactly C NXC works well with all the mentioned sensors and other NXT sensors and parts NXC has a great web support this website http bricxcc sourceforge net nbc nxcdoc nxcapi main html has the guide to NXC function list examples library files and other related information to get user started with NXC and is great for reference use Also with Google some of the solutions to NXC related issues can be found So until the ROS becomes compatible with NXT sensors and parts NXC is the best option For more information about NXT ROS visit http www ros org wiki Robots NXT Introduction to BricxCC Bricx Command Center also known as BricxCC is an Integrated Development Environment IDE used to program the Lego Mindstorms series It runs on Windows PCs XP Vista and Windows 7 BricxCC allows one to write programs download th
15. r can receive signals from 9 different angles Following picture shows those 9 directions and its values 4 5 es a For example if the value returned from the signal is 5 then the object a ee XB Fi 7 is right ahead of the sensor And if it s 1 or 9 then the object is behind 2 Bs 5 a andon left or right respectively 3 f ns N When no signal is detected the sensor returns 0 Hi Technic Infrared Electronic Ball The electric ball is designed to work with IR seeker sensor The ball has 20 infrared LEDs which helps IR seeker detect where the ball is To turn the ball on user needs 4 AAA batteries to power it Since the ball has plastic shell which can be broken easily users needs to be careful in using it With the ball and the IR seeker a robot can be designed to play soccer Also if there is more than one robot designed for the same task they can compete with each other and that would definitely be an exciting lab environment Hi Technic Sesnor Multiplexer This is very helpful equipment when a user has to use more than four sensors With the sensor multiplexer 4 sensors can be connected to one Hi Tosh Nic SGAO NXT sensor port And if needed more than one Multiplexer multiplexer can be used as well Most of the sensors mentioned above can be used with it but there are a few exceptions Multiplexer requires standard 9 volt battery to power each of the attached sensors It supports wide range of digital and
16. tSensorTouch const byte amp port port The port to configure Example SetSensorTouch IN_1 Indicate the type of the sensor and the number of the port to which the sensor is connected to Light Sensor To configure the light sensor use the following function Void SetSensorLight const byte amp port port The port to configure Example SetSensorLight IN_2 Indicates the type of the sensor and the number of the port to which the sensor is connected to To read ambient light intensity with led off configure sensor as follows SetSensorType IN_2 IN_TYPE_LIGHT_INACTIVE SetSensorMode IN_2 IN MODE PCTFULLSCALE ResetSensor IN_2 Sound Sensor To configure the sound sensor use the following function Void SetSensorTouch const byte amp port port The port to configure Example SetSensorSound IN_3 Indicate the type of the sensor and the number of the port to which the sensor is connected to Ultrasonic Sensor To configure the ultrasonic sensor use the following function byte SensorUS const byte amp port port The port to configure Example SensorUS IN_1 Indicate the type of the sensor and the number of the port to which the sensor is connected to It returns a value between 0 and 255 Since an ultrasonic sensor is an 2C digital sensor its value cannot be read using the standard Sensor n value The port must be configured as a Lowspeed port before using this function Use the following function to c
17. tes and the string Example TextOut 1 LCD LINE6 H1 this will print the string H1 on specified coordinates Here is a sample program using the above functions Note More functions can be found in the NXC_tutorial pdf E Testne o task main i OnFwd OUT BC 75 move motors connected to port B amp C forward with 75 power Wait 3000 keep moving for 3 seconds PlayTone 100 play tone with given frequency OnRev OUT BC reverse motors with 50 porer Wait 2000 keep reversing for 2 seconds PlayTone 100 beep Ort OUT BC fturn off both motors Wait 2000 keep them off for 2 seconds OnFwd OUT BC turn on a move forvard vith full speed Wait 3000 keep moving for 3 seconds PlayTone 100 beep with 600 Hz frequency for 3 seconds Ort OUI BC fturn both motors off Macros NXC allows defining macros Macros are a list of commands or actions that you use frequently For instance if you want your robot to move forward for random seconds and beep with the frequency of 100 for 0 1 seconds you can do the following define move_forward OnFwd OUT_BC 75 PlayTone 100 100 define random_time int time time Random 5 Wait time JERE Main Program 27 int time task main move_forward random_time move_forward random_time Sensor Functions l Touch Sensor To configure the touch sensor use the following function Void Se
18. the Bricx CC IDE will definitely help the students gain knowledge about how to program robots to do specific tasks Useful Links NXC Tutorial 1 http www engineering uiowa edu cie Labs NXC_tutorial pdf NXC Tutorial 2 http bricxcc sourceforge net nbc NXC Data Structures http bricxcc sourceforge net nbc nxcdoc nxcapi annotated html NXC Data Fields a E http bricxcc sourceforge net nbc nxcdoc nxcapi elobals 0x72 html index r NXT Robot Examples http www legomylegobot com NXT Sensors http www hitechnic com products Multiplexer Driver http www hitechnic com file php f 970 smux driver nxc 0 4 zip ROS http www ros org wiki ROS NXT ROS http www ros org wiki Robots NXT 10 More help needed Contact us Navneet at saggunavi gmail com and Nirali at eS es b niralie gmail com
19. ts NXT touch RGB color ultrasonic accelerometer gyro and range sensors There are some issues with using NXT ROS which are explained in the following section Issues for using NXT with ROS Most of the sensors we are using are Hi Technic the reason is that they provide better results compared to regular sensors For example regular color sensor detects only red green and blue while Hi Technic color sensor has wider range and can detect colors all the colors between white and black Hi Technic color sensor can tell a difference between red and light pink and from solid blue to light blue So the main issue with ROS is that it is not compatible with all of the Hi Technic parts Following is the list of issues with ROS gt ROS doesn t support Hi technic color sensor To use the color sensor with ROS the user needs to be using RGB color sensor And as we know Hi technic color sensor provides larger spectrum for the color range compared to the RGB color sensor gt ROS doesn t support IR Receiver and IR Seeker sensors which are used with Electronic IR ball Y Compass sensor is another sensor that is not supported by ROS gt Multiplexer is not supported by ROS which is a very important component in lab environment where more than 4 sensors could be used on regular basis gt With ROS if one has a question that he she would like to get a response to then that person needs to rely on ROS community members response ROS s supp
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