Andreas Erben's posts : LEGO NXT, automation

Legoboto: hajimemashou, LEGO MINDSTORMS NXT, sensor eventing

Andreas Erben — Wed, 18 Apr 2007 23:45:00 GMT

In the previous posts I offered some sample code for motor movement and dealing with sensors of the LEGO MINDSTORMS NXT product used with Bram Fokke's .NET API NXT#.

One important feature of the API was not covered before: Eventing

For each sensor you can register an event handler for when the data of the event handler changes. This implies that you poll the data from the sensor of course.

Here is the sample code:

using System;
using System.Collections.Generic;
using System.Text;
using Bram.NxtSharp;
 
namespace LegoNxtConsoleSample
{
    class Program
    {
        const string c_BluetoothComPort = "COM4";
 
 
        static void pressureSensorValueChangedEventHandler(NxtSensor sensor)
        {
            if (sensor is NxtPressureSensor)
            {
                NxtPressureSensor pressureSensor = (NxtPressureSensor)sensor;
                Console.Write("Pressure rawvalue:" + pressureSensor.RawValue + " means that sensor is ");
                if (pressureSensor.IsPressed)
                    Console.WriteLine("pressed");
                else
                    Console.WriteLine("not pressed");
            }
            else
            {
                Console.WriteLine("Problem: NxtPressureSensure expected but not received");
            }
        }
 
        static void SensorEventingDemo()
        {
            Console.WriteLine("pressure sensor eventing demo, running for 30 seconds");
            NxtBrick brick = new NxtBrick();
            brick.COMPortName = c_BluetoothComPort;
            brick.AutoPoll = true;
            NxtPressureSensor pressureSensor = new NxtPressureSensor();
            pressureSensor.AutoPoll = true;
            pressureSensor.AutoPollDelay = 50;
            pressureSensor.Brick = brick;
            brick.Sensor1 = pressureSensor;
            pressureSensor.ValueChanged += new SensorEvent(pressureSensorValueChangedEventHandler);
            //best practice: connect all sensors and motors first
            brick.Connect();
            System.Threading.Thread.Sleep(30000);
            brick.Disconnect();
        }
 
 
        static void Main(string[] args)
        {
            SensorEventingDemo(); 
        }     }
}

Ohayo gozaimashita, Legoboto-san, NXT: come to your sensors (LEGO MINDSTORMS NXT)

Andreas Erben — Wed, 18 Apr 2007 23:27:00 GMT

In the previous post I offered some sample code for motor movement of the LEGO MINDSTORMS NXT product used with Bram Fokke's .NET API NXT#.

In this post I will give info about how to use the different types of sensors.

Out-of-the-box you get 4 different sensors.

Pressure (button)
Sound
Light
Sonar

Pressure, as the name says, measures how much pressure is applied. The API will pretty much treat it as a button.

Sound measures the level, the amplitude, of sound – or noise. It has two modes: a "human" mode, scaled to the human hearing, and a normal mode.

The Light sensor can find out for you if it is dark or not. It has an active (red) light you can turn on, with the reflections from that red light you can detect objects in darkness or you can tell the difference between the colors red or blue.

Sonar tells you the distance the sensor has to the next objects in the direction it is pointing. It operates with reflections from ultrasonic sound waves. Note that if you get too close you are actually blocking the sound getting out and it will not be reflected in a way that makes sense. So when you actually touch an object, it can jump to the maximum possible value suddenly.

But here goes the sample code:

using System;
using System.Collections.Generic;
using System.Text;
using Bram.NxtSharp;
 
namespace LegoNxtConsoleSample
{
    class Program
    {
        const string c_BluetoothComPort = "COM4";
 
        static void SensorDemo()
        {
            //sensors
            //the general use pattern of attaching sensors and
            //looping through sensors is similar and so not shown here
            int i = 0;
 
            NxtBrick brick;
            brick = new NxtBrick();
            brick.COMPortName = c_BluetoothComPort;
            brick.Connect();
 
 
            NxtPressureSensor pressureSensor = new NxtPressureSensor();
            pressureSensor.Brick = brick;
            brick.Sensor1 = pressureSensor;
            pressureSensor.InitSensor();
 
            NxtSoundSensor soundSensor = new NxtSoundSensor();
            soundSensor.Brick = brick;
            brick.Sensor2 = soundSensor;
            Console.WriteLine("sound sensor adjusted for human ear");
            soundSensor.AdjustForHumanEar = true;
            soundSensor.InitSensor();
            i = 0;
            while (i++ < 10)
            {
                soundSensor.Poll();
                Console.WriteLine("sound sensor raw value:" + soundSensor.Value);
                Console.WriteLine("sound sensor value:" + soundSensor.Value);
                System.Threading.Thread.Sleep(500);
            }
 
            Console.WriteLine("sound sensor not adjusted for human ear");
            soundSensor.AdjustForHumanEar = false;
            soundSensor.InitSensor();
            i = 0;
            while (i++ < 10)
            {
                soundSensor.Poll();
                Console.WriteLine("sound sensor raw value:" + soundSensor.RawValue);
                Console.WriteLine("sound sensor value:" + soundSensor.Value);
                System.Threading.Thread.Sleep(500);
            }
 
 
            //lightsensor used uninitialized
            NxtLightSensor lightSensor = new NxtLightSensor();
            lightSensor.Brick = brick;
            brick.Sensor3 = lightSensor;
 
 
            Console.WriteLine("raw lightsensor value before poll:" + lightSensor.RawValue);
            Console.WriteLine("lightsensor value before poll:" + lightSensor.Value);
            lightSensor.Poll();
            Console.WriteLine("raw lightsensor value:"+lightSensor.RawValue);
            //note that this behaves differently when "initialized"
            //but only when brick was "off" before or different sensor was
            //used
            Console.WriteLine("lightsensor value:" + lightSensor.Value);
 
            //initSensor is done at brick.Connect(), so usually attach sensors first,
            //then connect brick!
            lightSensor.InitSensor();
            Console.WriteLine("raw initialized lightsensor value before poll:" + lightSensor.RawValue);
            Console.WriteLine("initialized lightsensor value before poll:" + lightSensor.Value);
            lightSensor.Poll();
            Console.WriteLine("raw lightsensor value:" + lightSensor.RawValue);
            Console.WriteLine("initialized lightsensor value:" + lightSensor.Value);
 
 
            //turn on ligth on lightSensor, needs InitSensor for change of lightstatus
            lightSensor.Active = true;
            lightSensor.InitSensor();
            Console.WriteLine("raw active lightsensor value before poll:"
                              + lightSensor.RawValue);
            Console.WriteLine("lightsensor active value before poll:"
                + lightSensor.Value);
            lightSensor.Poll();
            Console.WriteLine("raw active lightsensor value:" + lightSensor.RawValue);
            Console.WriteLine("active lightsensor value:" + lightSensor.Value);
 
            //turnoff light
            lightSensor.Active = false;
            lightSensor.InitSensor();
 
            //autopolling lightsensor 
            brick.AutoPoll = true;
            lightSensor.AutoPoll = true;
            lightSensor.AutoPollDelay = 1000;
            //note that usually you will set up
            //sensors and autopoll before first brick.Connect()
            //which will do StartPolling for you
            brick.StartPolling();
            while (i++ < 20)
            {
                //this should show that AutoPollDelay matters
                Console.WriteLine("Light sensor raw value:"+lightSensor.RawValue);
                System.Threading.Thread.Sleep(500);
            }
            brick.StopPolling();
 
 
            //sonar sensor measures distance
            NxtSonar sonarSensor = new NxtSonar();
            sonarSensor.Brick = brick;
            brick.Sensor4 = sonarSensor;
            sonarSensor.InitSensor();
            i = 0;
            while (i++ < 20)
            {
                sonarSensor.Poll();
                Console.WriteLine("Sonar sensor raw value:"+sonarSensor.RawValue);
                System.Threading.Thread.Sleep(500);
            }
 
 
            //disconnect Sensor2
            brick.Sensor2 = null; 
            foreach(NxtSensorPort sensorPort in brick.SensorPorts())
            {
                Console.Write(sensorPort.ToString()+" ");
                if (brick.GetSensor(sensorPort) == null)
                    Console.WriteLine("is not connected");
                else
                    Console.WriteLine("is connected with a "
                        + brick.GetSensor(sensorPort).ToString());
            }
 
 
            foreach(NxtSensor sensor in brick.ConnectedSensors())
            {
                sensor.Poll();
                Console.WriteLine(sensor.GetType().Name + " is connected to port " + sensor.Port.ToString() + " and has value " + sensor.RawValue);
            }
            //of further interest could be:
            //sensor.LastResult of type NxtGetInputValues
 
 
            brick.Disconnect();
        }
 
        static void Main(string[] args)
        {
            SensorDemo();
        }
    }
}

Domo arigato, Mr. Legoboto NXT#, turn the motor on (LEGO MINDSTORMS NXT)

Andreas Erben — Wed, 18 Apr 2007 22:53:00 GMT

We found that LEGO did a great job in delivering the MINDSTORMS NXT products (note that this link might point to the next version of MINDSTORMS products in the future and not to NXT anymore).

It is a great for learning purposes and can actually be used with Microsoft Robotics Studio. However, you might want to have a more basic way of controlling the robot, but there is no native C# interface available right now.

Bram Fokke did a great job in actually writing a C# based interface for controlling MindStorms NXT named NXT#. Even though I would not agree with every little implementation detail, he deserves a lot of respect and credit for that.
However, there could be more sample code.

The API offers a LOT more than what I will discuss here. I only deal with the basic features: How to control the motors and maybe later how to read the sensors. So I recommend you check it out yourself.

There are a lot of issues when controlling the robot. So expect funny behavior. Like for example when sending two identical commands to the robot in some time delay so that the first command actually executed already, it might just refuse to execute the second one. Also some other commands resulted in a "non"-movement, even so they should have done something. So – please feel free to experiment, and please add own exception-handling code. After all this is about experimenting and learning.

But how did we get into LEGO MINDSTORMS NXT in the first place? Well, partially it was also a collateral from dealing with RFID. RFID is all about sensors and reacting to it. So, we wanted to look around a little and ended up with a toy that proved to be a lot more than just a toy.

In fact, if we are dealing with hands-on-people, we like to use this product sometimes to do customer demos with it, since it makes some business-integration or business process scenarios suddenly so much more interesting, when you actually see something happening in the physical world.

This first session will only deal with controlling the motor.

Preparations: You have to pair your LEGO MINDSTORMS NXT brick with your bluetooth interface. You have to assign an outgoing com-port to your robot. Then you need to remember the actual name of the COM-port and put it in the code. The code-sample has a COM-port "COM4" but it could be entirely different and easily be a number of COM10 or higher.
The LEGO MINDSTORMS NXT brick has to be turned on before you connect. And finally - be sure you have enough batteries. One set will probably last only a day or so when you play around for a longer while.

Here comes the sample code:

using System;
using System.Collections.Generic;
using System.Text;
using Bram.NxtSharp;
 
namespace LegoNxtConsoleSample
{
    class Program
    {
        const string c_BluetoothComPort = "COM4";
 
        static void MotorDemo()
        {
            NxtBrick brick;
            brick = new NxtBrick();
            brick.COMPortName = c_BluetoothComPort;
            brick.Connect();
 
 
            //select MotorB and turn 180 degrees
            NxtMotor motor1;
            motor1 = new NxtMotor();
            //unfortunately this is necessary, should be wrapped by the API
            //e.g. by "AttachMotor"
            motor1.Brick = brick;
            //that will actually reattach motor to different port
            //if port was already set
            brick.MotorB = motor1;
            //brick.MotorB=motor1 wraps
            //brick.AttachMotor(NxtMotorPort.PortB, motor1);
            Console.WriteLine("turn motor B 180 degrees backwards");
            motor1.Turn(-50, 180);
            System.Threading.Thread.Sleep(2000);
            //will not stop the motor apruptly
            Console.WriteLine("coast motor B");
            motor1.Coast();
            System.Threading.Thread.Sleep(2000);
            Console.WriteLine("turn motor B 180 degrees");
            //turns the other direction and let the other motor start after that
            motor1.Turn(75, 180);
 
 
            //attach MotorC in a different way and turn
            NxtMotor motor2 = new NxtMotor();
            motor2.Brick = brick;
            //will also use "AttachMotor" internally
            motor2.Port = NxtMotorPort.PortC;
            Console.WriteLine("turn motor C until break or coast is sent");
            motor2.Turn(60, 0);
            System.Threading.Thread.Sleep(2000);
            Console.WriteLine("brake motor C");
            motor2.Brake();
 
            //break MotorB also if still running
            Console.WriteLine("brake motor B if still running");
            motor1.Brake();
 
 
            //use SetOutputState for motor C
            Console.WriteLine("turn motor C with granular control, " +
                               "flip first (should change direction)");
            motor2.Flip = !motor2.Flip;
            motor2.SetOutputState(50, NxtMotorMode.MotorOn | NxtMotorMode.Regulated,
            NxtMotorRegulationMode.MotorSpeed, 0, NxtMotorRunState.Running, 1000);
            System.Threading.Thread.Sleep(2000);
            Console.WriteLine("brake motor C");
            motor2.Brake();
 
 
            //iterate through Motorports, not depending on connection state
            foreach (NxtMotorPort motorPort in brick.MotorPorts())
            {
                motor1 = brick.GetMotor(motorPort);//returns null when motor not set
                if (motor1 != null)
                {
                    Console.WriteLine(motorPort.ToString() + " is connected");
                }
                else
                {
                    Console.WriteLine(motorPort.ToString() + " is not connected");
                }
            }
 
 
            //only motors where the brick and port were set are shown here.
            foreach (NxtMotor motor in brick.ConnectedMotors())
            {
                Console.WriteLine("reset motorposition for motor with port " + motor.Port.ToString());
                motor.ResetPosition(false);
            }
 
 
            brick.Disconnect();
        }
 
        static void Main(string[] args)
        {
            MotorDemo();
        }     }
}