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Line trackers not returning large values when measuring dark
http://robotc.net/forums/viewtopic.php?f=11&t=4501
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Author:  ebartz [ Sat May 05, 2012 3:53 pm ]
Post subject:  Line trackers not returning large values when measuring dark

I am trying to set up the swervebot linetrackers following the robotc traning videos...The values I am getting for all three line trackers go from about 150 for white and 165 for black....Even with the lights off, I can't get a value much larger...I should be getting much larger values for Black....any Ideas why?

Author:  magicode [ Sat May 05, 2012 4:21 pm ]
Post subject:  Re: Line trackers not returning large values when measuring

Do you have the Cortex connected to a battery and turned on while measuring these values, or is it just being powered by the USB cable?

Author:  ebartz [ Sat May 05, 2012 4:30 pm ]
Post subject:  Re: Line trackers not returning large values when measuring

Yes, it is connected to a charged barrery and turned on. using vexnet I downloaded the program per the instruction on the video trainer to use the debugger window to find the threshold value between the sensor values returned over light and dark surfaces...

Author:  Spiked3 [ Sun May 06, 2012 4:56 am ]
Post subject:  Re: Line trackers not returning large values when measuring

Just a wild off the wall guess, but I recently heard of someone who had this problem. Turned out to be shiny black tape used for the black line and a near perfect 90 degree angle on the sensor. He offset the angle a half a degree and it fixed it.

Author:  ebartz [ Wed May 09, 2012 7:00 pm ]
Post subject:  Re: Line trackers not returning large values when measuring

Found the solution....I had slipped a piece of black construction paper under the line trackers to measure the values....evidently not all black colors are equal....I tried putting it over black electical tape and it worked like it is suppose to. Just to double check I tried the black constructiion paper again and got the same bad readings.....did I miss something in the instrucions?

Author:  jbflot [ Fri May 11, 2012 9:17 am ]
Post subject:  Re: Line trackers not returning large values when measuring

You should always take your measurements for the threshold using the surfaces that you're tracking - if you're tracking black electrical tape, use black electrical tape.

Remember that the sensors work based off of reflected infrared light. Dull construction paper and shiny electrical tape are going to reflect totally different amounts of light, even if they're both black.

Author:  ebartz [ Sun May 13, 2012 6:20 pm ]
Post subject:  Re: Line trackers not returning large values when measuring

yeah, I didn't have my challange board made but I wanted to start writting the code so i thought that I would get some reading on "dark" and "light" surfaces so I could start. I guess what was messing me up was that white card stock and black construction paper were vertually identical....I thought that I have installed them wrong or that I missed something on the setutup...

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