1. LEGO NXT Robot Programming
Introduction to Programming a Lego NXT robot in C#

2. Objectives Introduction to the NXT Robot
Hardware/Software Requirements
Setting up a Bluetooth connection
Connecting to a robot from a C# application
Getting the robot to move
Obtaining information from sensors
Touch
Ultrasonic
Light

3. The NXT Tribot Robot
Sound
Ultrasonic
Touch
Wheels (x 2)
Grabber
Light

4. Software/Hardware Requirements
NXT Mindstorms Lego robot
Bluetooth adapter (USB)
Software
Lego NXT Driver software (CD provided with robot)
Visual Studio (C#)
MindSqualls API

5. Setting up a Bluetooth connection
On the NXT robot
Ensure bluetooth is switched on
Ensure it is “visible”
On the PC
Add a “new” bluetooth device
Attach it to your NXT (should be discovered automatically)
Passcode will be required on both the NXT and the PC
Need to record which COM port is being used
For detailed instructions see the document Connecting NXT via Bluetooth.docx

6. Preparing a C# project Create a new forms project
Add the MindSqualls library to the project
Right click the project (in the solution explorer) and select “Add”
Choose “Existing item”
Browse for NKH.MindSqualls.dll and press “Add”
Add a reference to this library
Right click references (in the solution explorer) and select “Add Reference”
Select the “Browse” tab
Select the file NKH.MindSqualls.dll and press “OK”
Add the following line to the top of the form code
using NKH.MindSqualls;

7. Connecting to the robot
The robot is controlled via an object of the class NxtBrick
When a brick object is created it needs to be passed a string parameter containing the COM port for the bluetooth connection
The brick object must then be connected:
NxtBrick brick = new NxtBrick(sComPort);
brick.Connect();

8. Disconnecting the robot
Before closing the application the brick should be disconnected
The brick object should also be deleted
brick.Disconnect();
brick = null;
To check if a robot is connected or not
if (brick != null && brick.IsConnected)

9. “Talking” to the NxtBrick
Status and other information can be obtained from the NxtBrick via properties
brick.Name
brick.BatteryLevel
Sounds can be sent to the NxtBrick (1st param is frequency, 2nd param is time in milliseconds)
brick.PlayTone(500, 250);
Thread.Sleep(250); // pause to allow tone to play
brick.PlayTone(1000, 500);
Note that if you are using the Thread.Sleep method you need to add the following at the top of your code:
using System.Threading;

10. Demonstration
HelloNXT.sln

11. NXT Tribot Ports 3 Motors 4 Sensor Ports MotorA: Right wheel
MotorB: Grabber
MotorC: Left wheel
4 Sensor Ports
Sensor1: Touch sensor
Sensor2: Light sensor
Sensor3: Sound sensor
Sensor4: Ultrasonic sensor

12. Getting the robot to move
Create Motor objects and attach to motor ports
brick.MotorA = new NxtMotor();
brick.MotorC = new NxtMotor();
Motors can be set to run at a power level (speed) for a particular number of degrees rotation
brick.MotorA.Run(20, 360);
brick.MotorC.Run(20, 360);
Power values range from (% power of motor)
Rotation values range from 0-unlimited (0 runs continuously)
To turn run one motor only (or both at different speeds)
To reverse set use a negative power value

13. Stopping the robot
If the motors are set to run continuously then your code must provide the instruction to stop
The robot can be stopped by setting the motors into “idle” mode
brick.MotorA.Idle();
brick.MotorC.Idle();
Another option is to “brake” the motors but in this case power is still used to hold the motor in position (e.g. On a hill)

14. Sequencing issues
The C# code runs sequentially, issuing instructions to the robot as specified
If an instruction tells the robot to do something which will take some time then the code does not wait for that operation to complete
What will happen if the following code is used?
brick.MotorA.Run(20, 3600);
brick.MotorC.Run(20, 3600);
brick.MotorA.Run(-20, 3600);
brick.MotorC.Run(-20, 3600);

15. Solving the problem
There are a number of ways to solve sequencing problems
Ideally you would obtain information from the robot to indicate when it is finished
This can be quite complicated
A crude but simple approach is to add code to make the program “sleep” for enough seconds to let the robot complete its operation
brick.MotorA.Run(20, 3600);
brick.MotorC.Run(20, 3600);
Thread.Sleep(5000); //sleep for 5 seconds
brick.MotorA.Run(-20, 3600);
brick.MotorC.Run(-20, 3600);

16. Synchronising the motors
Setting both motors to run separately will inevitably affect the straightness of motion
One motor will start fractionally before the other (depending on the order of code statements)
This will cause the robot to start with a slight turn (and finish with a turn in the opposite direction)
This can be avoided by creating a synchronised pair of motors and controlling them as a pair

17. Controlling synchronised motors
Create an NXTSyncMotor object from the required motors
NxtMotorSync motorPair;
motorPair = new NxtMotorSync(brick.MotorA,
brick.MotorC);
To run the motors as a pair use:
motorPair.Run(20, 180, 0);
This time a third parameter is required to control turning. It ranges from -100 to 100 (0 moves straight)
As before an angle of 0 moves the robot continuously
To stop both motors use
motorPair.Idle();

18. Controlling the Tribot grabber
The grabber on the Tribot robot is controlled by a motor
Running the motor in the forward direction opens the grabber
brick.MotorB.Run(5, 45);
Running the motor in the backward direction closes the grabber
brick.MotorB.Run((sbyte)(-5), 45);
A cast is required here to ensure the correct data type is used
Note that only small angles of rotation are required. Turn too far and your grabbers will fall off the robot!!

19. Demonstration
NXTMove.sln

20. Interacting with sensors
Objects can be created for each sensor type and attached to the appropriate port
A poll command is issued to the sensor and this enables data recorded by the sensor to be returned
Appropriate methods exist (depending on the sensor type) to retrieve this data
A timer control on your form can be used to repeatedly poll and retrieve data
The timer tick event can then be used to perform necessary actions depending on the data retrieved

21. The touch sensor
Creating and attaching a touch sensor (should be done before connecting the brick):
touchSensor = new NxtTouchSensor();
brick.Sensor1 = touchSensor;
Determining whether the touch sensor is pressed or not:
touchSensor.Poll();
if (touchSensor.IsPressed == true) {
// code to excecute if sensor is pressed }

22. Demonstration
TouchTest.sln

23. The light sensor (not NXT2)
Creating and attaching a light sensor (should be done before connecting the brick):
lightSensor = new NxtLightSensor();
brick.Sensor2 = lightSensor;
Determining the intensity of light recorded by the sensor:
lightSensor.Poll();
int iIntensity = (int)lightSensor.Intensity;
The light sensor can generate a light of its own which reflects objects and makes recording more accurate:
lightSensor.GenerateLight = true;

24. Demonstration
LightTest.sln

25. The sound sensor (not NXT2)
Creating and attaching a sound sensor (should be done before connecting the brick):
soundSensor = new NxtSoundSensor();
brick.Sensor3 = soundSensor;
Determining the level of sound recorded by the sensor:
soundSensor.Poll();
int iSound = (int)soundSensor.SoundLevel;
Note that this sensor records only sound levels, it cannot be used to determine the frequency of the sound (i.e. It cannot be used for sound recognition)

26. Demonstration
SoundTest.sln

27. The ultrasonic sensor
Sends out an ultrasonic wave which is deflected by an object in front of the sensor
The time to return enables the distance to be calculated
Creating and attaching an ultrasonic sensor (should be done before connecting the brick):
ultrasonicSensor = new NxtUltrasonicSensor();
brick.Sensor4 = ultrasonicSensor;
Determining the distance (in cm) recorded by the sensor:
ultrasonicSensor.Poll();
int iDist = (int) ultrasonicSensor.DistanceCm;
If there is no object in range a distance value of 255 is returned

28. Demonstration
UltrasonicTest.sln