AVR Library Command Reference

void qtr_read_calibrated(unsigned int *sensorValues, unsigned char readMode)

Returns sensor readings calibrated to a value between 0 and 1000, where 0 corresponds to a reading that is less

than or equal to the minimum value read by calibrate() and 1000 corresponds to a reading that is greater than or

equal to the maximum value. Calibration values are stored separately for each sensor, so that differences in the

sensors are accounted for automatically.

unsigned int PololuQTRSensors::readLine(unsigned int *sensorValues, unsigned char readMode =

QTR_EMITTERS_ON, unsigned char whiteLine = 0)

void qtr_read_line(unsigned int *sensorValues, unsigned char readMode)

Operates the same as read calibrated, but with a feature designed for line following: this function returns an

estimated position of the line. The estimate is made using a weighted average of the sensor indices multiplied by

1000, so that a return value of 0 indicates that the line is directly below sensor 0, a return value of 1000 indicates

that the line is directly below sensor 1, 2000 indicates that it’s below sensor 2000, etc. Intermediate values

indicate that the line is between two sensors. The formula is:

0*value0 + 1000*value1 + 2000*value2 + ...

--------------------------------------------

value0 + value1 + value2 + ...

As long as your sensors aren’t spaced too far apart relative to the line, this returned value is designed to be

monotonic, which makes it great for use in closed-loop PID control. Additionally, this method remembers where

it last saw the line, so if you ever lose the line to the left or the right, it’s line position will continue to indicate the

direction you need to go to reacquire the line. For example, if sensor 4 is your rightmost sensor and you end up

completely off the line to the left, this function will continue to return 4000.

By default, this function assumes a dark line (high values) surrounded by white (low values). If your line is light

on black, set the optional second argument whiteLine to true. In this case, each sensor value will be replaced by

the maximum possible value minus its actual value before the averaging.

unsigned int* PololuQTRSensors::calibratedMinimumOn

unsigned int* qtr_calibrated_minimum_on()

The calibrated minumum values measured for each sensor, with emitters on. The pointers are unallocated and set

to 0 until calibrate() is called, and then allocated to exactly the size required. Depending on the readMode

argument to calibrate(), only the On or Off values may be allocated, as required. This and the following variables

are made public so that you can use them for your own calculations and do things like saving the values to

EEPROM, performing sanity checking, etc. The calibration values are available through function calls from C.

unsigned int* PololuQTRSensors::calibratedMaximumOn

unsigned int* qtr_calibrated_maximum_on()

The calibrated maximum values measured for each sensor, with emitters on.

unsigned int* PololuQTRSensors::calibratedMinimumOff

unsigned int* qtr_calibrated_minimum_off()

The calibrated minimum values measured for each sensor, with emitters off.

unsigned int* PololuQTRSensors::calibratedMaximumOff

unsigned int* qtr_calibrated_maximum_off()

The calibrated maximum values measured for each sensor, with emitters off.

PololuQTRSensors::~PololuQTRSensors()

The destructor for the PololuQTRSensors class frees up memory allocated for the calibration arrays. This feature

is not available in C.

PololuQTRSensorsRC::PololuQTRSensorsRC()

11. QTR Reflectance Sensors Page 28 of 35