Strange problem with QTR-8A sensor readings

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#1

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…

callibrated_values.png1280×800 53.5 KB


20130901_183706.jpg1312×984 427 KB


20130901_183609.jpg1228×1664 491 KB

#2

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

#3

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]

20130902_231449.jpg2560×1920 802 KB

#4

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

#5

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
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25 28 32 795 775 765
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24 27 29 37 107 171
24 27 29 33 76 119
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#6

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

#7

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
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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

#8

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

#9

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!

#10

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

- Ben