Andrew

package linefollower;

import lejos.nxt.Button;
import lejos.nxt.LCD;
import lejos.nxt.LightSensor;
import lejos.nxt.MotorPort;
import lejos.nxt.SensorPort;

public class LineFollower {



    /**

     * The light sensor should be connected to port 3. The
     * left motor should be connected to port C and the right
     * motor to port B. thanks to  Ole Caprani for some bits of code

     */


        public static void main (String[] aArg)
        throws Exception
        {


            LightSensor light = new LightSensor(SensorPort.S3);
            final int blackWhiteThreshold = 50;
               final int sampleInterval = 10;  // ms

            final int forward = 1;
            final int stop = 3;
            final int flt = 4;
            final int power = 80;


            light.setFloodlight(true);


            // Follow line until ESCAPE is pressed
            LCD.drawString("Press ESCAPE", 0, 2);
            LCD.drawString("to stop ", 0, 3);
            while (! Button.ESCAPE.isDown())
            {

                if (light.readValue() > blackWhiteThreshold)
                {
                    // On white, turn right

                    MotorPort.B.controlMotor(0,stop);
                    MotorPort.C.controlMotor(power, forward);
                }
                else
                {
                    // On black, turn left

                    MotorPort.B.controlMotor(power, forward);
                    MotorPort.C.controlMotor(0,stop);
                }
                LCD.drawInt(light.readValue(), 3, 9, 0);

                Thread.sleep(sampleInterval);

            }

            // Stop car gently with free wheel drive
            MotorPort.B.controlMotor(0,flt);
            MotorPort.C.controlMotor(0,flt);

            LCD.drawString("Program stopped", 0, 0);
            Thread.sleep(2000);
        }
    }