User Manual

void PololuQTRSensors::readCalibrated(unsigned int *sensorValues, unsigned char readMode =

QTR_EMITTERS_ON)

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)

unsigned int 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 2, 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.

16. QTR Reflectance Sensors Page 55 of 65