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Qti sensors — Parallax Forums

Qti sensors

TebosTebos Posts: 11
edited 2009-05-03 03:50 in Robotics
Hello, Im trying to make by own version of the QTI circuit but am having some trouble.· I am using some QRD1113 http://www.fairchildsemi.com/ds/QR/QRD1113.pdf·I see that the QTI sensors use QRD1114 but dont see how to modify my 1113's to behave like the QTI.· I construcyed to circuit and tried testing them with the code but I am not getting a value change at the input pin.· Right now it only gives me a value of 7 and changes to 8 when something is right on top of it (black tape).· I am using a peace of white paper alternating with black electrical tape.· I am trying to use these sensors for a·maze navagating robot but was unable to make them work properly b/c of the florscent lighting in the room.· So now·Im trying to·detect the top of the walls like a QTI.· Any info would be greatly
appreciated.

Robot specs:
BS2
Supper carrier / boe-bot chass
Continuous rotation servos

Comments

  • kwinnkwinn Posts: 8,697
    edited 2009-05-02 21:04
    The problem with using this reflective sensor is the lack of sensitivity. The features of the spec sheet include "Phototransistor Output" and "Unfocused for sensing diffused surfaces" which means it is meant to work close to the reflective surface. If you look at Fig. 5 Normalized Collector Current vs. Distance on the spec sheet it shows that the peak sensitivity is at 35 mils and is nearly zero at 250 mils (1/4 inch). Not a good choice for this application.
  • TebosTebos Posts: 11
    edited 2009-05-02 22:49
    I found that out the hard way (hrs of trying to make them work to detect a wall)· but now since i know that they are only good for close distances and want them to work like a QTI.· In this case it would be the top of the maze, which i would fix to be close enough to top.··My problem is making them return a high or low number with RCTIME.· ·
  • kwinnkwinn Posts: 8,697
    edited 2009-05-03 03:50
    You will probably need to get them to within about a tenth of an inch or less from the surface to work. An RC timing circuit is possible by having a capacitor from the collector to +V, having the pin set to output to charge the cap through a resistor, changing the pin to an input and measuring the time it takes to discharge.
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