Strange problem with QTR-8A sensor readings

hi, i am trying to build a line following robot. i am using arduino rbbb(due, atmega 328) and i have 4 aa batteries 1000 mah for power supply… everything is working except the fact that my qtr sensor doesn’t read the black line correctly… i am using a a black line of 2,3 cm width on a white surface… the problem is that the first three sensors(0,1,2) are working just fine but the the last three (3,4,5) seem to change values simultaneously… for example when the robot is at the left of the line on the white surface all sensors have values near 35… when i move slightly the robot to the right then sensor1 sees the black line and it’s is value is 900+… this goes on for the second and the third sensor. when the 4th sensor sees the black line it seems that the fifth and sixth sensor see it as well, when in reality they are above the white surface… when i move it more to the right and only the sixth sensor is above the black line and five and four are above the white surface the values of the sixth sensor are very near, almost the same, to the values of the other sensors (near 30)… my sensors are connected to analog inputs of the arduino from 0-5… the ground of the arduino connects to the ground of the qtr board and to the ground of the batteries… the qtr vcc connects to arduino 5V pin… i have LEDOn connected to digital pin 10 and i have set it to HIGH… all connection seem right and i have checked them many times but i cannot see where the problem is… my baud rate is 57600 and i have changed it in the example programs (raw and callibrated values) from the qtr library… i am sendind my data to the pc wirelessly via a wixel.

please help! any idea may be very helpull!! thanx…

these are the raw values using the code from the qtr library… they show what happens when i move the robot from left to right…

at the 1st picture values from 4,5,6 seem to be correct but on the 2nd picture sensors 5,6 have values near the values from 4th sensor…






Hello.

Thank you for the detailed setup description and pictures. Some of your solder joints look very suspect, and the behavior sounds like you have a connection problem.

Can you post the code you are running? Also, can you post a picture that shows the other side of the QTR sensor? Lastly, can you use a multimeter to measure the voltage on the Arduino’s 5V output pin?

- Ben

this is the code i’m using… it’s almost the same with the callibrated_values example but i have changed the emitter_pin and the baud rate… i also have in comments the code to read the values from the analog inputs but when i do that almost every value is above 700 constantly… i also used the raw_values example with the same changes. sensors 5 and 6 follow the values of sensor 4 and i am thinking that some electrical short is causing it… my solder joints are not so good, i know it and i am going to change them, but they are not shorted anywhere… lastly i do not have a multimeter at the time so i cannot test the 5V output…

thank you for your reply!!

[code]#include <QTRSensors.h>
#define NUM_SENSORS 6 // number of sensors used
#define NUM_SAMPLES_PER_SENSOR 4 // average 4 analog samples per sensor reading
#define EMITTER_PIN 10 // emitter is controlled by digital pin 2

// sensors 0 through 5 are connected to analog inputs 0 through 5, respectively
QTRSensorsAnalog qtra((unsigned char) {0, 1, 2, 3, 4, 5},
NUM_SENSORS, NUM_SAMPLES_PER_SENSOR, EMITTER_PIN);
unsigned int sensorValues[NUM_SENSORS];

// const int analogValue0=A0;
// const int analogValue1=A1;
// const int analogValue2=A2;
// const int analogValue3=A3;
// const int analogValue4=A4;
// const int analogValue5=A5;
//
// int analog0,analog1,analog2,analog3,analog4,analog5=0;

void setup()
{

Serial.begin(57600);

Serial.begin(57600);

Serial.println("");

pinMode(EMITTER_PIN,OUTPUT);

digitalWrite(EMITTER_PIN,HIGH);

// pinMode(analogValue0,INPUT);
// pinMode(analogValue1,INPUT);
// pinMode(analogValue2,INPUT);
// pinMode(analogValue3,INPUT);
// pinMode(analogValue4,INPUT);
// pinMode(analogValue5,INPUT);

delay(500);
pinMode(13, OUTPUT);
digitalWrite(13, HIGH); // turn on Arduino’s LED to indicate we are in calibration mode
for (int i = 0; i < 400; i++) // make the calibration take about 10 seconds
{
qtra.calibrate(); // reads all sensors 10 times at 2.5 ms per six sensors (i.e. ~25 ms per call)
}
digitalWrite(13, LOW); // turn off Arduino’s LED to indicate we are through with calibration

// print the calibration minimum values measured when emitters were on
for (int i = 0; i < NUM_SENSORS; i++)
{
Serial.print(qtra.calibratedMinimumOn[i]);
Serial.print(’ ');
}
Serial.println();

// print the calibration maximum values measured when emitters were on
for (int i = 0; i < NUM_SENSORS; i++)
{
Serial.print(qtra.calibratedMaximumOn[i]);
Serial.print(’ ');
}
Serial.println();
Serial.println();
delay(1000);
}

void loop()
{
// read calibrated sensor values and obtain a measure of the line position from 0 to 5000
// To get raw sensor values, call:
// qtra.read(sensorValues); instead of unsigned int position = qtra.readLine(sensorValues);
unsigned int position = qtra.readLine(sensorValues);

// print the sensor values as numbers from 0 to 1000, where 0 means maximum reflectance and
// 1000 means minimum reflectance, followed by the line position
for (unsigned char i = 0; i < NUM_SENSORS; i++)
{
Serial.print(sensorValues[i]);
Serial.print(’\t’);
}

// analog0=analogRead(analogValue0);
// analog1=analogRead(analogValue1);
// analog2=analogRead(analogValue2);
// analog3=analogRead(analogValue3);
// analog4=analogRead(analogValue4);
// analog5=analogRead(analogValue5);
//
// Serial.print("analog0= ");
// Serial.println(analog0);
//
// Serial.print("analog1= ");
// Serial.println(analog1);
//
// Serial.print("analog2= ");
// Serial.println(analog2);
//
// Serial.print("analog3= ");
// Serial.println(analog3);
//
// Serial.print("analog4= ");
// Serial.println(analog4);
//
// Serial.print("analog5= ");
// Serial.println(analog5);
//Serial.println(); // uncomment this line if you are using raw values
Serial.println(position); // comment this line out if you are using raw values

delay(250);
}[/code]


I think you should try to simplify things so we can get a better idea of what might be going wrong. My suspicion is that sensors 5 and 6 do not have a good connection to your Arduino, so the readings you get on those pins are being heavily influenced by the reading of sensor 4. There are a few ways we can test for this. First, I would like you to just try a basic program that calls analogRead() on the six sensor pins to get their raw values (don’t use the QTR library, and don’t do anything with the emitter pin). Can you post that program along with its output as you slide the array over a black line?

- Ben

ok… this is the code for the analog reading

  const int analogValue0=A0;
  const int analogValue1=A1;
  const int analogValue2=A2;
  const int analogValue3=A3;
  const int analogValue4=A4;
  const int analogValue5=A5;

  int analog[6];


void setup()
{
  
  for(int i=0;i<6;i++){
    
     analog[i]=-100; 
  }
  
  Serial.begin(57600);
  
  Serial.println("");
   
    pinMode(analogValue0,INPUT);  
    pinMode(analogValue1,INPUT);
    pinMode(analogValue2,INPUT);
    pinMode(analogValue3,INPUT);
    pinMode(analogValue4,INPUT);
    pinMode(analogValue5,INPUT);

    delay(500);
    
  }


void loop()
{
  
  analog[0]=analogRead(analogValue0);
  analog[1]=analogRead(analogValue1);
  analog[2]=analogRead(analogValue2);
  analog[3]=analogRead(analogValue3);
  analog[4]=analogRead(analogValue4);
  analog[5]=analogRead(analogValue5);
  
  for (int i = 0; i < 6; i++)
  {
    Serial.print(analog[i]);
    Serial.print('\t');
  }
  
  Serial.println();
  
  
  delay(50);
}

and these are the results from right to left… same problem again…

31 27 29 28 60 75
31 27 29 28 60 75
31 27 29 28 60 75
31 27 29 28 60 75
31 27 29 28 60 75
31 27 29 28 60 75
31 27 29 28 60 75
30 27 29 28 60 75
30 27 29 28 60 75
30 27 29 28 60 75
29 27 29 28 60 75
29 27 29 28 60 75
29 27 29 28 60 75
30 27 29 28 60 75
29 27 29 28 60 75
29 27 29 28 60 75
29 27 29 28 60 75
29 27 29 28 60 75
29 27 29 28 60 75
31 27 29 28 60 75
33 27 29 28 60 75
39 27 29 28 60 75
42 27 29 28 60 75
48 27 29 28 60 75
114 27 29 28 60 75
239 27 29 28 60 75
374 27 29 28 59 75
496 27 29 28 59 74
568 27 29 28 58 74
591 27 29 28 59 74
604 27 29 28 59 74
613 27 29 28 59 74
618 27 29 28 59 74
622 27 29 28 59 74
628 28 29 28 59 74
630 28 29 28 59 74
629 27 29 28 59 74
629 27 29 28 59 74
630 28 29 28 59 74
633 28 29 28 59 74
634 28 29 28 59 74
635 28 29 28 59 74
636 28 29 28 59 74
635 27 29 28 59 74
633 27 29 28 59 74
633 28 29 28 59 74
635 28 29 28 59 74
636 28 29 28 59 74
638 28 29 28 59 74
635 27 29 28 59 74
632 27 29 28 59 74
630 27 29 28 59 74
632 27 29 28 59 74
634 28 29 28 59 74
635 28 29 28 59 74
634 28 29 28 59 74
633 28 29 28 59 74
632 27 29 28 59 74
632 27 29 28 59 74
634 28 29 28 59 74
636 28 29 28 59 74
636 28 29 28 59 74
635 28 29 28 59 74
634 28 29 28 59 74
632 28 29 28 59 74
633 28 29 28 59 74
635 28 29 28 59 74
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636 28 29 28 59 74
636 28 29 28 59 74
641 28 29 28 59 74
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644 28 29 28 59 74
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650 28 29 28 59 74
649 28 29 28 59 74
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647 28 29 28 59 74
650 28 29 28 59 74
651 28 29 28 59 74
652 28 29 28 59 74
651 28 29 28 59 74
649 28 29 28 59 74
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656 28 28 28 59 74
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665 29 28 28 59 74
666 29 28 28 59 74
669 29 28 28 59 74
670 29 28 28 59 74
672 30 28 28 59 74
676 31 28 28 59 74
679 32 28 28 59 74
684 37 28 28 59 74
691 159 28 28 59 74
693 224 28 28 59 74
697 371 28 28 59 74
700 539 28 28 58 73
697 628 28 27 58 73
691 675 28 27 58 74
685 682 28 27 58 74
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688 684 28 27 59 74
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692 698 28 27 59 74
692 702 28 27 59 74
694 704 28 27 59 74
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692 704 28 27 59 74
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690 701 28 27 59 74
691 700 28 27 59 74
695 701 28 27 59 74
697 702 28 27 59 74
696 701 28 27 59 74
692 701 28 27 59 74
690 701 28 27 59 74
692 704 28 27 59 74
693 706 28 27 59 74
692 709 28 27 59 74
690 711 28 27 58 74
687 713 28 27 58 74
685 715 28 27 58 74
685 719 28 27 58 74
685 720 28 27 58 74
685 721 28 27 58 74
683 725 28 27 58 74
679 727 28 27 58 74
675 727 29 27 58 74
673 729 29 27 58 74
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676 732 29 27 58 74
674 732 29 27 58 74
672 730 29 27 58 74
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670 730 29 27 58 74
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666 729 29 27 58 74
668 730 29 27 58 74
673 732 29 27 58 74
672 731 29 27 58 74
679 737 29 27 59 74
681 739 29 27 59 74
680 739 29 27 59 74
680 739 29 27 59 74
679 744 30 27 59 74
675 749 30 27 59 74
672 750 30 27 59 74
672 749 30 27 59 74
674 750 30 27 58 74
675 750 30 27 58 74
673 750 31 27 58 74
669 751 31 27 58 74
664 752 31 27 58 74
665 753 31 27 58 74
665 755 32 27 58 74
657 757 33 27 58 74
607 763 47 27 58 73
483 766 299 27 59 74
420 766 365 27 58 73
424 766 361 27 58 73
427 767 365 27 57 72
417 768 383 27 57 72
286 770 474 27 58 72
111 771 541 27 58 73
58 771 554 27 58 73
53 771 557 27 58 73
91 770 545 27 58 73
49 771 567 27 58 73
51 772 567 27 58 73
49 771 566 27 58 73
48 770 565 27 58 73
45 769 566 27 58 73
43 770 575 27 58 73
42 773 582 27 58 73
42 774 582 27 58 73
44 773 576 27 58 73
44 771 573 27 58 73
43 770 572 27 58 73
45 769 567 27 58 73
45 769 569 27 58 73
46 770 571 27 58 73
47 770 571 27 58 73
46 770 569 27 58 73
46 769 567 27 58 73
46 769 566 27 58 73
46 770 567 27 58 73
49 771 566 27 58 73
49 771 568 27 58 73
48 771 568 27 58 73
46 770 566 27 58 73
46 769 565 27 58 73
46 769 565 27 58 73
47 770 566 27 58 73
49 770 567 27 58 73
39 770 591 27 58 73
32 768 637 27 58 73
29 767 670 27 58 73
28 766 679 27 58 74
27 767 695 27 58 74
26 766 708 27 59 74
26 766 712 27 59 74
26 766 713 27 59 74
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25 766 719 27 59 74
25 765 721 27 59 74
25 762 729 27 59 74
24 758 740 27 59 74
24 751 753 27 59 74
24 746 763 27 59 74
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24 748 764 27 59 74
24 748 764 27 59 75
24 742 766 28 59 75
24 739 768 28 59 75
24 732 774 28 59 75
24 728 778 28 60 75
24 722 783 29 60 75
24 716 786 30 60 75
24 700 790 31 61 76
24 678 793 34 63 77
24 670 795 35 64 78
24 673 796 35 64 79
24 672 797 35 64 79
24 662 798 36 65 79
24 660 798 36 66 80
24 659 797 36 65 80
24 659 797 36 66 80
24 660 798 36 65 80
24 661 799 37 66 80
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24 655 797 37 66 80
24 656 798 37 66 80
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24 655 797 37 66 80
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24 658 798 37 66 80
24 657 798 37 66 80
24 656 797 37 66 80
24 657 797 37 66 80
24 659 798 37 66 80
24 661 799 37 66 80
24 662 800 37 66 80
24 663 800 37 66 80
24 650 800 38 67 81
24 625 801 43 69 82
24 588 803 77 90 95
24 516 806 203 173 150
24 354 809 357 294 243
24 79 812 481 410 346
24 34 811 571 507 443
24 30 809 627 577 521
24 29 808 652 618 575
24 30 820 654 634 606
25 33 836 658 642 622
26 33 837 658 645 631
26 33 836 656 644 634
25 33 835 656 644 635
25 33 835 657 645 636
26 33 836 659 646 637
26 33 837 660 647 638
25 33 836 659 647 639
25 33 835 658 646 638
25 33 835 656 645 638
25 33 835 657 645 637
25 33 836 658 646 638
26 33 837 660 647 639
26 33 836 659 647 639
25 33 835 657 646 639
25 33 835 656 645 638
25 33 835 657 645 637
26 33 836 659 646 638
26 33 837 660 648 639
25 33 836 659 648 639
25 33 836 658 647 639
25 33 835 656 645 638
25 33 835 657 645 638
26 33 836 659 647 638
26 33 837 660 648 639
26 33 837 659 648 640
26 33 836 657 647 639
25 33 835 656 646 638
25 33 835 657 646 638
26 33 836 658 647 639
26 33 837 660 648 640
26 33 837 659 648 640
26 33 836 658 647 639
25 33 835 656 646 638
25 33 835 657 646 638
25 33 836 659 647 639
25 32 835 669 654 643
25 32 834 675 660 649
25 32 831 683 667 655
25 31 825 701 682 667
25 31 824 703 687 674
25 31 825 705 691 679
25 31 826 706 692 682
25 31 826 706 693 683
25 30 823 707 694 684
25 30 819 715 699 688
25 30 810 733 712 698
25 29 801 748 725 709
25 29 801 750 730 716
25 29 800 750 732 720
25 29 797 751 734 722
25 29 790 757 738 726
25 29 765 776 751 735
25 29 721 795 767 748
25 28 686 803 776 759
25 28 676 804 780 764
25 28 668 803 781 767
25 28 665 803 781 768
25 28 666 803 781 768
25 28 668 804 782 769
25 28 657 806 783 770
25 28 638 807 784 771
25 28 620 807 784 772
25 28 582 808 786 773
25 28 516 811 789 776
25 28 349 815 793 779
25 28 79 815 792 779
25 28 39 812 789 778
25 28 37 810 787 776
25 28 36 808 785 774
25 28 35 807 784 773
25 28 35 808 784 772
25 28 34 807 784 772
25 28 34 806 784 772
25 28 33 801 780 769
25 28 32 795 775 765
25 27 31 791 771 761
25 27 31 784 766 757
25 27 31 777 760 752
25 27 30 763 749 743
24 27 30 745 735 731
24 27 30 722 716 715
24 27 29 692 691 695
24 27 29 663 665 671
24 27 29 630 635 644
24 27 29 588 598 611
24 27 29 551 561 576
24 27 29 529 534 545
24 27 29 496 503 515
24 27 29 432 451 471
24 27 29 316 359 398
24 27 29 116 201 272
24 27 29 37 107 171
24 27 29 33 76 119
23 27 29 31 66 95
23 27 28 30 63 84
23 27 28 29 61 79
23 27 28 29 61 77
23 27 28 29 60 76
23 26 28 28 60 76
23 26 28 28 59 75
23 26 28 28 58 74
23 26 28 28 58 74
23 26 28 28 57 73
23 26 28 28 59 74
23 26 28 28 59 75
23 26 28 28 60 75
23 26 28 27 60 75
23 26 28 27 60 75
23 26 28 27 60 75
23 26 28 27 59 75
23 26 28 27 59 75
23 26 28 27 59 75
23 26 28 27 59 74
23 25 28 27 59 74
23 26 28 27 59 73
23 25 27 27 58 72
23 25 27 27 58 72
22 25 27 27 59 74
22 25 27 27 59 74

Can you tell me what the output is if you run the following program? (The only change I made was to enable internal pull-ups on your analog inputs.)

[code]
const int analogValue0=A0;
const int analogValue1=A1;
const int analogValue2=A2;
const int analogValue3=A3;
const int analogValue4=A4;
const int analogValue5=A5;

int analog[6];

void setup()
{

for(int i=0;i<6;i++){

 analog[i]=-100; 

}

Serial.begin(57600);

Serial.println("");

pinMode(analogValue0,INPUT_PULLUP);  
pinMode(analogValue1,INPUT_PULLUP);
pinMode(analogValue2,INPUT_PULLUP);
pinMode(analogValue3,INPUT_PULLUP);
pinMode(analogValue4,INPUT_PULLUP);
pinMode(analogValue5,INPUT_PULLUP);

delay(500);

}

void loop()
{

analog[0]=analogRead(analogValue0);
analog[1]=analogRead(analogValue1);
analog[2]=analogRead(analogValue2);
analog[3]=analogRead(analogValue3);
analog[4]=analogRead(analogValue4);
analog[5]=analogRead(analogValue5);

for (int i = 0; i < 6; i++)
{
Serial.print(analog[i]);
Serial.print(’\t’);
}

Serial.println();

delay(50);
}[/code]

Another thing you might try is reading the sensors in the reverse order and see if that affects the output.

- Ben

ben i tested the code with the INPUT_PULLUP and here are the results… 5 and 6’s values are constantly near 1016… i don’t what this means…

49 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 59 60 51 1016 1016
50 60 60 51 1016 1016
50 59 61 51 1016 1016
49 59 61 51 1016 1016
49 58 60 51 1016 1016
49 58 60 51 1016 1016
48 57 60 51 1016 1016
48 57 61 52 1016 1016
47 56 63 52 1016 1016
47 56 66 53 1016 1016
47 55 74 53 1016 1016
46 53 65 52 1016 1016
46 53 66 53 1016 1016
46 52 66 53 1016 1016
47 53 70 53 1016 1016
47 53 84 54 1016 1016
48 53 88 55 1016 1016
47 52 73 54 1016 1016
48 52 78 54 1016 1016
51 53 89 55 1016 1016
277 52 65 54 1015 1015
758 52 62 55 1017 1017
843 53 60 55 1018 1018
864 55 60 56 1018 1018
881 61 61 56 1018 1018
895 255 61 56 1017 1017
901 573 62 56 1013 1013
908 762 65 56 1018 1018
914 860 96 57 1019 1019
909 890 87 55 1019 1020
907 903 114 54 1019 1020
901 912 178 54 1019 1020
894 917 274 54 1018 1018
888 918 318 54 1017 1017
884 918 338 54 1016 1016
881 921 415 55 1014 1014
846 922 586 54 1015 1015
672 924 805 54 1017 1017
436 921 858 55 1014 1014
420 921 860 55 1014 1015
417 921 861 55 1014 1015
237 921 882 54 1019 1019
60 918 898 55 1020 1020
55 914 904 55 1020 1020
52 906 912 55 1019 1020
52 894 921 73 1020 1020
52 852 929 468 1012 1012
52 651 934 778 1017 1017
51 351 931 855 1017 1017
51 168 928 880 1020 1020
51 93 921 892 1020 1020
51 69 909 904 1020 1020
51 64 878 914 1020 1020
51 60 766 916 1019 1019
50 58 500 911 1010 1010
50 57 255 911 1017 1017
50 56 174 902 1018 1018
50 56 149 890 1018 1018
50 56 129 852 1018 1018
50 56 119 736 1016 1017
49 56 89 506 1007 1007
49 55 73 210 1016 1016
49 56 70 70 1016 1016
49 56 69 61 1016 1016
49 55 66 59 1016 1016
49 55 64 58 1016 1016
48 54 64 57 1016 1016
48 54 63 56 1016 1016
48 53 64 55 1016 1016
48 53 63 54 1016 1016
48 52 62 54 1016 1016
47 52 61 54 1016 1016
47 52 59 53 1016 1016
46 51 58 53 1016 1016
46 51 56 53 1016 1016
45 51 56 54 1016 1016
45 50 55 53 1016 1016
44 50 54 53 1016 1016
44 49 54 52 1016 1016
43 48 54 52 1016 1016
43 48 53 51 1016 1016
43 47 53 51 1016 1016
42 47 53 51 1016 1016
43 47 53 50 1016 1016
42 47 53 51 1016 1016
42 47 53 51 1016 1016
42 47 53 51 1016 1016
42 47 53 51 1016 1016
42 47 53 51 1016 1016
42 47 53 51 1016 1016
42 47 53 51 1016 1016
43 47 53 51 1016 1016
42 47 53 51 1016 1016
43 47 53 51 1016 1016
42 47 53 51 1016 1016
42 47 53 51 1016 1016
42 47 53 50 1016 1016
42 47 52 50 1016 1016
42 47 52 50 1016 1016
42 47 52 50 1016 1016
42 47 52 50 1016 1016
43 47 53 51 1016 1016
43 47 53 51 1016 1016
42 47 53 51 1016 1016
42 47 53 51 1016 1016
42 47 53 51 1016 1016
43 47 53 51 1016 1016
42 47 52 50 1016 1016

That is a very strong indication that analog pins 5 and 6 are not electrically connected to the QTR array. If you disable the pull-ups and read the sensors in a different orders, you will probably read values for 5 and 6 that approximately match the values of whatever sensor you read right before them.

I think at this point you should invest in a multimeter (they are not very expensive, and they are pretty much an essential tool if you are going to be working with electronics like this). I suggest you disconnect the QTR sensor array from the Arduino entirely and just use a multimeter to see what the voltages are on the channels as you pass the array over the line. If you probe at various points, you should be able to determine where your connection is broken.

- Ben

ben i solved it… i found that the analog pins of the atmega chip were not soldered correctly. i reheated the pins added some solder and now they work…

thank you very much for your help!

That’s great to hear; thank you for letting us know what the problem was.

- Ben