AVR Library Command Reference

Reference

C++ and Arduino methods are shown in red.

C functions are shown in green.

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

QTR_EMITTERS_ON)

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

Reads the raw sensor values into an array. There MUST be space for as many values as there were sensors

specified in the constructor. The values returned are a measure of the reflectance in units that depend on the type

of sensor being used, with higher values corresponding to lower reflectance (a black surface or a void). QTR-xA

sensors will return a raw value between 0 and 1023. QTR-xRC sensors will return a raw value between 0 and the

timeout argument provided in the constructor (which defaults to 4000). The units will be in Timer2 counts, where

Timer2 is running at the CPU clock divided by 8 (i.e. 2 MHz on a 16 MHz processor, or 2.5 MHz on a 20 MHz

processor).

The functions that read values from the sensors all take an argument readMode, which specifies the kind of read

that will be performed. Several options are defined: QTR_EMITTERS_OFF specifies that the reading should be

made without turning on the infrared (IR) emitters, in which case the reading represents ambient light levels near

the sensor; QTR_EMITTERS_ON specifies that the emitters should be turned on for the reading, which results in

a measure of reflectance; and QTR_EMITTERS_ON_AND_OFF specifies that a reading should be made in both

the on and off states. The values returned when the QTR_EMITTERS_ON_AND_OFF option is used are given

by on + max – off, where on is the reading with the emitters on, off is the reading with the emitters off, and max

is the maximum sensor reading. This option can reduce the amount of interference from uneven ambient lighting.

Note that emitter control will only work if you specify a valid emitter pin in the constructor.

Example usage:

unsigned int sensor_values[8];

sensors.read(sensor_values);

void PololuQTRSensors::emittersOn()

void qtr_emitters_on()

Turn the IR LEDs on. This is mainly for use by the read method, and calling these functions before or after the

reading the sensors will have no effect on the readings, but you may wish to use these for testing purposes. This

method will only do something if a valid emitter pin was specified in the constructor.

void PololuQTRSensors::emittersOff()

void qtr_emitters_off()

Turn the IR LEDs off. This is mainly for use by the read method, and calling these functions before or after the

reading the sensors will have no effect on the readings, but you may wish to use these for testing purposes.

void PololuQTRSensors::calibrate(unsigned char readMode = QTR_EMITTERS_ON)

void qtr_calibrate(unsigned char readMode)

Reads the sensors for calibration. The sensor values are not returned; instead, the maximum and minimum values

found over time are stored internally and used for the readCalibrated() method. You can access the calibration

(i.e raw max and min sensor readings) through the public member pointers calibratedMinimumOn,

calibratedMaximumOn, calibratedMinimumOff, and calibratedMaximumOff. Note that these pointers will point

to arrays of length numSensors, as specified in the constructor, and they will only be allocated after calibrate() has

been called. If you only calibrate with the emitters on, the calibration arrays that hold the off values will not be

allocated.

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

QTR_EMITTERS_ON)

11. QTR Reflectance Sensors Page 27 of 35