Hello,
I have been working with the QTR-8A sensor with an Arduino UNO in an attempt to create a line following robot. To test the QTR-8A sensor I have been using the “QTRAExample” (as seen below) file provided with the Polulu QTR-sensor-library. The issue that I have been having is that sensor 5 and 6 will print out inaccurate values when calibrating over a white piece of paper, and a standard piece of electrical tape (all other sensors calibrate to a value between 500-600, while sensor 5 and 6 calibrate between 800-900).
#include <QTRSensors.h>
// This example is designed for use with six QTR-1A sensors or the first six sensors of a
// QTR-8A module. These reflectance sensors should be connected to analog inputs 0 to 5.
// The QTR-8A's emitter control pin (LEDON) can optionally be connected to digital pin 2,
// or you can leave it disconnected and change the EMITTER_PIN #define below from 2 to
// QTR_NO_EMITTER_PIN.
// The setup phase of this example calibrates the sensor for ten seconds and turns on
// the LED built in to the Arduino on pin 13 while calibration is going on.
// During this phase, you should expose each reflectance sensor to the lightest and
// darkest readings they will encounter.
// For example, if you are making a line follower, you should slide the sensors across the
// line during the calibration phase so that each sensor can get a reading of how dark the
// line is and how light the ground is. Improper calibration will result in poor readings.
// If you want to skip the calibration phase, you can get the raw sensor readings
// (analog voltage readings from 0 to 1023) by calling qtra.read(sensorValues) instead of
// qtra.readLine(sensorValues).
// The main loop of the example reads the calibrated sensor values and uses them to
// estimate the position of a line. You can test this by taping a piece of 3/4" black
// electrical tape to a piece of white paper and sliding the sensor across it. It
// prints the sensor values to the serial monitor as numbers from 0 (maximum reflectance)
// to 1000 (minimum reflectance) followed by the estimated location of the line as a number
// from 0 to 5000. 1000 means the line is directly under sensor 1, 2000 means directly
// under sensor 2, etc. 0 means the line is directly under sensor 0 or was last seen by
// sensor 0 before being lost. 5000 means the line is directly under sensor 5 or was
// last seen by sensor 5 before being lost.
#define NUM_SENSORS 6 // number of sensors used
#define NUM_SAMPLES_PER_SENSOR 4 // average 4 analog samples per sensor reading
#define EMITTER_PIN QTR_NO_EMITTER_PIN // 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];
void setup()
{
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
Serial.begin(9600);
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');
}
//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);
}
Here is a small section of the output following calibration:
512 494 504 502 924 899
1023 1023 1023 1023 1023 1023
986 971 982 971 929 814 2411
984 964 818 973 767 0 1905
929 996 942 925 545 798 2302
939 950 917 909 494 983 2388
972 973 971 959 848 870 2419
677 633 747 735 0 709 2249
677 661 695 1000 1000 0 2244
518 850 1000 865 0 419 2064
816 1000 1000 909 151 564 2061
886 992 913 877 0 483 1894
1000 899 894 898 525 540 2140
841 879 822 842 484 669 2276
992 977 996 963 969 983 2491
I have tried multiple QTR-8A sensors and the problem is the same with the other modules. I have also been calibrating the sensor at 3mm height from the piece of paper, as recommended in the user’s guide. I have also tried switching out the wires running from the sensor to the Arduino, and the problem still consists. I have been powering the sensor from a power supply at 5V and it is pulling .09A. Lastly, I checked if the IR sensors were emitting properly by turning off the lights, and using the front facing camera of my phone, and they were all emitting properly. I can send pictures if they are needed.
Thank You in advance and I look forward to what you have to say! =)