/** Power on and prepare for general usage.
* This will prepare the magnetometer with default settings, ready for single-
* use mode (very low power requirements). Default settings include 8-sample
* averaging, 15 Hz data output rate, normal measurement bias, a,d 1090 gain (in
* terms of LSB/Gauss). Be sure to adjust any settings you need specifically
* after initialization, especially the gain settings if you happen to be seeing
* a lot of -4096 values (see the datasheet for mor information).
*/
void HMC5883L::initialize() {
// write CONFIG_A register
setSampleAveraging(HMC5883L_AVERAGING_8);
setMeasurementBias(HMC5883L_BIAS_NORMAL);
setDataRate(HMC5883L_RATE_15);
// write CONFIG_B register
setGain(HMC5883L_GAIN_1090);
// write MODE register
setMode(HMC5883L_MODE_SINGLE);
}
bool HMC5883L::calibrate(int8_t testGain) {
// Keep the current status ...
uint8_t previousGain = getGain();
// Set the gain
if (testGain < 0) {
testGain = gain;
}
setGain(testGain);
// To check the HMC5883L for proper operation, a self test
// feature in incorporated in which the sensor offset straps
// are excited to create a nominal field strength (bias field)
// to be measured. To implement self test, the least significant
// bits (MS1 and MS0) of configuration register A are changed
// from 00 to 01 (positive bias) or 10 (negetive bias)
setMeasurementBias(HMC5883L_BIAS_POSITIVE);
// Then, by placing the mode register into single-measurement mode ...
setMode(HMC5883L_MODE_SINGLE);
// Two data acquisition cycles will be made on each magnetic vector.
// The first acquisition will be a set pulse followed shortly by
// measurement data of the external field. The second acquisition
// will have the offset strap excited (about 10 mA) in the positive
// bias mode for X, Y, and Z axes to create about a ±1.1 gauss self
// test field plus the external field.
// The first acquisition values will be subtracted from the
// second acquisition, and the net measurement will be placed into
// the data output registers.
int16_t x,y,z;
getRawHeading(&x,&y,&z);
// In the event the ADC reading overflows or underflows for the
// given channel, or if there is a math overflow during the bias
// measurement, this data register will contain the value -4096.
// This register value will clear when after the next valid
// measurement is made.
if (min(x,min(y,z)) == -4096) {
scaleFactors[testGain][0] = 1.0f;
scaleFactors[testGain][1] = 1.0f;
scaleFactors[testGain][2] = 1.0f;
return false;
}
getRawHeading(&x,&y,&z);
if (min(x,min(y,z)) == -4096) {
scaleFactors[testGain][0] = 1.0f;
scaleFactors[testGain][1] = 1.0f;
scaleFactors[testGain][2] = 1.0f;
return false;
}
// Since placing device in positive bias mode
// (or alternatively negative bias mode) applies
// a known artificial field on all three axes,
// the resulting ADC measurements in data output
// registers can be used to scale the sensors.
float xExpectedSelfTestValue =
HMC5883L_SELF_TEST_X_AXIS_ABSOLUTE_GAUSS *
HMC5883L_LSB_PER_GAUS[testGain];
float yExpectedSelfTestValue =
HMC5883L_SELF_TEST_Y_AXIS_ABSOLUTE_GAUSS *
HMC5883L_LSB_PER_GAUS[testGain];
float zExpectedSelfTestValue =
HMC5883L_SELF_TEST_Z_AXIS_ABSOLUTE_GAUSS *
HMC5883L_LSB_PER_GAUS[testGain];
scaleFactors[testGain][0] = xExpectedSelfTestValue/x;
scaleFactors[testGain][1] = yExpectedSelfTestValue/y;
scaleFactors[testGain][2] = zExpectedSelfTestValue/z;
setGain(previousGain);
setMeasurementBias(HMC5883L_BIAS_NORMAL);
return true;
}
