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path following between two lines with one light sensor-help 
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Post path following between two lines with one light sensor-help
hello, i started working with robotC just about a week and a half ago...ive also never programmed in my life before. i understand the basics (i think) from some of the tutorials found on the robotC website , but im stuck on one particular problem that i just cant seem to figure out.

the problem involves using one light sensors and two servo motors.

i need to program the robot i have built to travel along a path between two black lines. what i want the robot to do is this:

travel forward at a 45° angle from the start until it hits the black line on the right. then turn 90° to the LEFT and travel straight again until it hits the black line on the left. now i need the robot to turn RIGHT and travel straight until it hits the line on the right, turn 90° to the LEFT....and so on and so forth.

what i need help with is programming the light sensor so that when it hits the line the first time it turns the robot left and the second time turns right. Or programming the light sensor so that it will turn the robot left when the light sensor reads the black line on the odd counts (1,3,5 etc.) and turns the robot right on the even counts (2,4,6) of the light sensor reading the black line. any idea's?

if i had two light sensors this problem wouldn't be a problem, but i only have one. basically what i need to do is use one light sensor to do run two tasks alternatingly.

if there is another simpler approach to this problem, please let me know.


Thu Jan 08, 2009 9:29 pm
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Post Re: path following between two lines with one light sensor-help
Following a line with one light sensor is tricky and if you want to make an exact solution your program can be quite complex. If you are new to computer programming, I don't suggest to start with this task. Not because you could not understand it, but because of the traps might be well hidden in it.

The idea behind the single sensor line follower canbe like this.

If you mount the light sensor on your robot on such a way that it is close but not very close to the surface, the red light will illuminate up to a square inch on the paper. If you just check the light sensor reading within the "Try me" menu as you gently push your robot to cross the black stripe, you can see the sensor reading is continuously change as the illuminated area reaches the black stripe.

Exploiting this smooth transition you can make a program that tries to steer the robot to keep sensor reading within a "gray" range i.e. the robot will follow the edge of the black stripe.

If you want to make a decision whether your robot hit the left or right edge of the black stripe you will have to drive the robot very slowly a bit left and a bit right, as if a mouse were just "sniffing around". Should a subtle left turn "blacken" (and a subtle right turn lighten) the sensor reading the robot met the right edge of the black stripe.


Fri Jan 09, 2009 7:06 pm
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Post Re: path following between two lines with one light sensor-help
You should start with giving your robot a state that describes its current position in respect to the two lines. You could use these states: To the left, on the left line, in the middle, on the right line, to the right.
Then u must decide from which to which state you can go: from in the middle to to the left, etc.
Then you must detect when you go from one state to another. Say light sensor reports less light.
Then you must decide how to react to it. I would suggest, turn left.
Then, start all over again, apply what you have learned and code it well this time.

The last one is just personal experience.

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Fri Jan 09, 2009 7:37 pm
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Post Re: path following between two lines with one light sensor-help
thanks for your input guys =)

After looking over the tutorial video's and PDF's (found on the robotC website) about a hundred more times, i came up with this..and it works! =) .....at least i think so..when i tested it out on the course it worked. (attachment)

please, if you will, leave comments and critique on how i can make this better. Thanks. :D


Attachments:
File comment: drawing of what robot does
robot track code.jpg
robot track code.jpg [ 28.75 KiB | Viewed 2614 times ]
File comment: CODE
robot track code.c [2.75 KiB]
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Sat Jan 10, 2009 1:17 am
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Post Re: path following between two lines with one light sensor-help
sry, here's the code so you dont have to download.

Code:
#pragma config(Sensor, S1,     lightsensor,         sensorLightActive)
#pragma config(Sensor, S2,     touchsensor,         sensorTouch)  //other sensors will be used later
#pragma config(Sensor, S3,     sonar,               sensorSONAR)  //in different sections of the course
#pragma config(Sensor, S4,     sound,               sensorSoundDB)
//*!!Code automatically generated by 'ROBOTC' configuration wizard               !!*//

task main()
{
  int lightcount = 0; //a counter for the light sensor? or a counter used for tasks with the light sensor?

  nMotorPIDSpeedCtrl[motorA] = mtrSpeedReg;  //keep the wheels going the same speed (no unwanted turning! finally =) )
  nMotorPIDSpeedCtrl[motorB] = mtrSpeedReg;

  nMotorEncoder[motorA] = 0;        //for turning control, probably not going to be used now..yet..maybe
  nMotorEncoder[motorB] = 0;

  while(nMotorEncoder[motorA] < 10800)  //motor A (right motor) turns 30 times before stopping
  {
     if(lightcount == 0)  //the counter starts at zero...should this be an "if" statement or a "while" statement?
     {
        if(SensorValue(lightsensor) > 49)  //light sensor reads lights object (white table)
        {
          motor[motorA] = 50;              //and so it moves forward at half speed...until...
          motor[motorB] = 50;
        }
        else                               //it hits the black line
        {
          motor[motorA] = 50;              //so it turns to the right, off of the blasck line
          motor[motorB] = -50;
          wait1Msec(350);
          lightcount = lightcount + 1;     // and adds "1" (one) to the lightcount value
        }
        if(lightcount == 1)  //now since the lightcount value is = 1, this next peice of code should run.
        {                    //should i use "if(lightcount == 1)" or "while(lightcount == 1)" here?  does it matter?
          if(SensorValue(lightsensor) > 49)
           {                                //so the light sensors reads a light value, and tells the robot to move forward
             motor[motorA] = 50;
             motor[motorB] = 50;
           }
           else                             // this time when the light sensor reads a dark value....
           {
             motor[motorA] = -50;           // it turns the opposite direction as before
             motor[motorB] = 50;
             wait1Msec(350);
             lightcount = lightcount -1;    //and reducing the lightcount value back to zero, so the first code can run again. =)
           }
        }
    }
  }
}
//conclusion:
//the robot zigzags in between the lines via two motors and one light sensor.
//going forward on a light surface and turning one way on a dark surface
//and turning the opposite way when it hits another dark surface
// comments, and helpful critic is very much appretiated


Sat Jan 10, 2009 2:30 am
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Post Re: path following between two lines with one light sensor-help
wow.

really.


Sat Jan 10, 2009 8:40 am
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