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QTI Sensors on BOE-BOT — Parallax Forums

QTI Sensors on BOE-BOT

Joe FishbackJoe Fishback Posts: 99
edited 2007-04-03 14:03 in Robotics
I have installed Line Following app using 3 QTI sensors to my BOE-BOT. Everything runs fine. Using the spacers that come with the sensors give a ground clearance between sensors and·ground·of about 1/4". This works fine, but I would like a little more clearance. Does anybody know what the maximum·clearance distance that the Parallax QTI sensors will work following a line.·I·know I can just cut off the spacers that·I have till the sensors do not work, but I thought may somebody could save me some time (OK I am lazy).






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······ Joe Fishback

-Robots are my friends-

Comments

  • Bruce BatesBruce Bates Posts: 3,045
    edited 2006-09-01 06:11
    Joe -

    I'm doing this from memory, but I don't think you can raise them much, if at all.

    Regards,

    Bruce Bates

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  • dandreaedandreae Posts: 1,375
    edited 2006-09-01 14:43
    The reason that you don't want to raise the QTI sensors above a 1/4", is due to the fact light will interfere with the sensor's ability to read properly.


    Dave

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    Dave Andreae

    Tech Support
    dandreae@parallax.com
    Http://www.parallax.com

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  • Andy Lindsay (Parallax)Andy Lindsay (Parallax) Posts: 1,919
    edited 2006-09-01 16:20
    The idea behind the QTI line sensor is to have it close to the surface to reduce ambient light's ability to interfere and to increase surface reflections of its built-in IR LED. When it's mounted far away from the surface, it reduces the effectiveness of its IR LED and increases interference from other sources like the sun and incandescent lights. 1/4 inch is pretty far. The QTI's QRD1114 is optimal at 20 to 30 mils (http://www.fairchildsemi.com/ds/QR/QRD1114.pdf).

    Try out the four QTI system too. I think it's a better circuit and algorithm, both faster and more reliable. See A Faster QTI Subroutine for Boe-Bot Line Following in the Stamps in Class "Mini Projects"·section.

    For clearance and immunity to ambient light, I would experiment with the Boe-Bot's IR object detection system. By mounting a section of straw or shrink wrap tubing over both the IR LED and the detector, you can focus the detection beam on an area that's much narrower than Chapter 8, Activity #3 in Robotics with the Boe-Bot (.pdf). Make sure both tubes are pointing at the same spot. I haven't tried it, but I'm guessing you'll be able to get pretty good performance at 3/8 or even 1/2 inch from the end of the straw/tubing. This will take some tinkering. The resistance in series with the IR LED will have to be adjusted, as will the length of the tubing and the distance from the end of the tubing to the surface.

    Post Edited (Andy Lindsay (Parallax)) : 9/1/2006 4:25:00 PM GMT
  • Lmiller1708Lmiller1708 Posts: 12
    edited 2007-04-03 04:19
    Hi all,
    I was wondering if anyone has tried this method of covering the sensors?
    If that does not work would changing the resistor to a smaller value help?
    I was running into the same problem of not enough ground clearance.
    Thanks,
    Lance
  • sailman58sailman58 Posts: 162
    edited 2007-04-03 14:03
    Maybe it is like the Bumble bee that isn't supposed to fly, but I have removed the plastic spacers from my 3 QTI sensor setup and it works fine. I lost one in the bowels of my recliner chair, and rarher than tear the chair apart I removed the spacers from the other two sensors. They are only about 1/8 ".

    Ron
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