AK8975 Class Reference

API for the AK8975 magnetometer. More...

Detailed Description

• ID: ak8975
• Name: 3-axis Magnetometer
• Other Names: AK9875
• Category: compass
• Manufacturer: seeed
• Connection: i2c
• Link: http://www.akm.com/akm/en/file/datasheet/AK8975.pdf

This is a 3-axis magnetometer, which can be used alone, or coupled with another device (such as the mcu9150 9-axis motion sensor).

    upm::AK8975 sensor;

    sensor.init();

    while (shouldRun) {
        sensor.update();

        float x, y, z;

        sensor.getMagnetometer(&x, &y, &z);
        cout << "Magnetometer:  ";
        cout << "MX = " << x << " MY = " << y << " MZ = " << z << endl;

        cout << endl;

        upm_delay_us(500000);
    }

Public Types
enum	AK8975_REG_T {   REG_WIA = 0x00, REG_INFO = 0x01, REG_ST1 = 0x02, REG_HXL = 0x03,   REG_HXH = 0x04, REG_HYL = 0x05, REG_HYH = 0x06, REG_HZL = 0x07,   REG_HZH = 0x08, REG_ST2 = 0x09, REG_CNTL = 0x0a, REG_ASTC = 0x0c,   REG_ASAX = 0x10, REG_ASAY = 0x11, REG_ASAZ = 0x12 }
enum	ST1_BITS_T { ST1_DRDY = 0x01 }
enum	ST2_BITS_T { ST2_DERR = 0x04, ST2_HOFL = 0x08 }
enum	CNTL_MODES_T { CNTL_PWRDWN = 0x00, CNTL_MEASURE = 0x01, CNTL_SELFTEST = 0x08, CNTL_FUSE_ACCESS = 0x0f }
enum	ASTC_BITS_T { ASTC_SELF = 0x40 }

Public Member Functions
	AK8975 (int bus=AK8975_I2C_BUS, uint8_t address=AK8975_DEFAULT_I2C_ADDR)
	~AK8975 ()
bool	init ()
bool	setMode (CNTL_MODES_T mode)
bool	isReady ()
bool	waitforDeviceReady ()
bool	update (bool selfTest=false)
bool	selfTest ()
void	getMagnetometer (float *x, float *y, float *z)

Protected Member Functions
float	adjustValue (float value, float adj)

Protected Attributes
float	m_xCoeff
float	m_yCoeff
float	m_zCoeff
float	m_xData
float	m_yData
float	m_zData

Member Enumeration Documentation

enum AK8975_REG_T

AK8975 registers

enum ST1_BITS_T

ST1 bits

enum ST2_BITS_T

ST2 bits

enum CNTL_MODES_T

CNTL register, operating mode values

enum ASTC_BITS_T

ASTC (self test control) bits

Constructor & Destructor Documentation

AK8975	(	int	bus = AK8975_I2C_BUS,
		uint8_t	address = AK8975_DEFAULT_I2C_ADDR
	)

ak8975 constructor

Parameters

bus	i2c bus to use
address	the address for this device

~AK8975

(

)

AK8975 Destructor

Member Function Documentation

bool init

(

)

set up initial values and start operation

Parameters

dsr	the data sampling rate: one of the DSR_BITS_T values

Returns

true if successful

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bool setMode

(

CNTL_MODES_T

mode

)

put the chip into a specific mode

Parameters

mode	one of the CNTL_MODES_T values

Returns

true if successful

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bool isReady

(

void

)

check to see if the ST1_DRDY bit is set, indicating the device can accept commands

Returns

true if device is ready, false otherwise

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bool waitforDeviceReady

(

)

check to see if device is ready and sleep/retry if not. Returns once device indicates it's ready.

Returns

true if device is ready, false if retries exhausted

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bool update

(

bool

selfTest = false

)

take a measurement

Parameters

selfTest

true if we are running a self test, false (default) otherwise.

Returns

true if successful, false otherwise

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bool selfTest

(

)

do a self test sequence. When self test is executed, the device activates internal calibrated magnets, and measures them, updating the measurement registers. Once complete, the data can be read as usual (getMagnetometer()) and the returned values compared against the following limits to determine correctness:

-100 < X < +100; -100 < Y < +100; -1000 < Z < -300

Returns

true if successful, false otherwise

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void getMagnetometer	(	float *	x,
		float *	y,
		float *	z
	)

return the compensated values for the x, y, and z axes. The unit of measurement is in micro-teslas (uT).

Parameters

x	pointer to returned X axis value
y	pointer to returned Y axis value
z	pointer to returned Z axis value

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float adjustValue ( float  value, float  adj  )

protected

compute a compensated magnetometer axis value, based on the raw axis value and a per-device, per-axis adjustment coefficient that was read and stored at init() time.

Parameters

value	the raw axis value to compensate
adj	the adjustment coefficient

Returns

true if successful

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The documentation for this class was generated from the following files:

• src/mpu9150/ak8975.hpp
• src/mpu9150/ak8975.cxx