No se pueden leer los valores de Pololu QTR 8RC

Estoy utilizando la matriz de sensores Pololu QTR 8RC. Estoy usando sólo 5 sensores. He conectado los sensores a arduino en pines digitales 3 hasta 7 + VCC y GND. Estoy usando el bosquejo de ejemplo. Si uso la función "leer" obtengo alguna variación en los valores de los sensores. Pero si uso la función "readLine" obtengo todo 0 en las lecturas. También después de la calibración, los valores calibrados mínimo y máximo son 2500.

#include <QTRSensors.h>

// This example is designed for use with eight QTR-1RC sensors or the eight sensors of a
// QTR-8RC module.  These reflectance sensors should be connected to digital inputs 3 to 10.
// The emitter control pin 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 pin 13 LED while calibration is going on.  During this phase, you should expose each
// reflectance sensor ot 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
// (pulse times from 0 to 2500 us) 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 9 (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   5     // number of sensors used
#define TIMEOUT       2500  // waits for 2500 us for sensor outputs to go low
#define EMITTER_PIN   QTR_NO_EMITTER_PIN     // emitter is controlled by digital pin 2

// sensors 0 through 7 are connected to digital pins 3 through 10, respectively
QTRSensorsRC qtrrc((unsigned char[]) {3, 4, 5, 6, 7, 8, 9, 10},
  NUM_SENSORS, TIMEOUT, EMITTER_PIN); 
unsigned int sensorValues[NUM_SENSORS];


void setup()
{
  delay(500);
  int i;
  pinMode(13, OUTPUT);
  digitalWrite(13, HIGH);    // turn on LED to indicate we are in calibration mode
  for (i = 0; i < 400; i++)  // make the calibration take about 10 seconds
  {
    qtrrc.calibrate();       // reads all sensors 10 times at 2500 us per read (i.e. ~25 ms per call)
  }
  digitalWrite(13, LOW);     // turn off LED to indicate we are through with calibration

  // print the calibration minimum values measured when emitters were on
  Serial.begin(9600);
  for (i = 0; i < NUM_SENSORS; i++)
  {
    Serial.print(qtrrc.calibratedMinimumOn[i]);
    Serial.print(' ');
  }
  Serial.println();

  // print the calibration maximum values measured when emitters were on
  for (i = 0; i < NUM_SENSORS; i++)
  {
    Serial.print(qtrrc.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, where 0 means directly under sensor 0 or the line was lost
  // past sensor 0, 1000 means directly under sensor 1, 200 means directly under sensor 2, etc.
  // Note: the values returned will be incorrect if the sensors have not been properly
  // calibrated during the calibration phase.  To get raw sensor values, call:
  //  qtra.read(sensorValues);
  unsigned int position = qtrrc.readLine(sensorValues);

  //qtrrc.read(sensorValues);

  // print the sensor values as numbers from 0 to 9, where 0 means maximum reflectance and
  // 9 means minimum reflectance, followed by the line position
  unsigned char i;
  for (i = 0; i < NUM_SENSORS; i++)
  {
    Serial.print(sensorValues[i] * 10 / 1001);
    Serial.print(' ');
  }
  Serial.print("    ");
  Serial.println(position);

  delay(250);
}