HMC5883
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SELF TEST OPERATION
To check the HMC5883 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 this self test, the least significant bits
(MS1 and MS0) of configuration register A are changed from 00 to 01.
Then, by placing the mode register into single-measurement mode (0x01), 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 5.5mA) in the positive bias mode for X and Y axes and the
negative bias mode for Z axis to create about a ±0.6 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.
If the configuration register B is left at the factory default value of 0x20, values around +655 ADC counts (0.64 Ga * 1024
counts/Ga) will be placed in the X and Y data output registers (around -604 in Z data output register). To leave the self
test mode, change MS1 and MS0 bit of the configuration register A back to 00. Also change the mode register if single-
measurement mode is not the intended mode of operation.
SCALE FACTOR CALIBRATION
Using the method described above in section SELF TEST OPERATION, user can scale sensors’ sensitivity to match each
other. Since placing device in positive bias mode (or alternatively negative bias mode) applies a known artificial field on
all three axes, the resulting ADC measurement in data output registers can be used to scale the sensors.
Alternatively, the built-in self test can be used to periodically compensate the scaling errors due to temperature variations.
A compensation factor can be found by comparing the self test outputs with the ones obtained at a known temperature.
For example, if the self test output is 615 at room temperature and 630 at the current temperature then a scale factor of
(615/630) should be applied to all current magnetic readings. A temperature sensor is not required using this method.
EXTERNAL CAPACITORS
The two external capacitors should be ceramic type construction with low ESR characteristics. The exact ESR values are
not critical but values less than 200 milli-ohms are recommended. Reservoir capacitor C1 is nominally 4.7 µF in
capacitance, with the set/reset capacitor C2 nominally 0.22 µF in capacitance. Low ESR characteristics may not be in
many small SMT ceramic capacitors (0402), so be prepared to up-size the capacitors to gain Low ESR characteristics.
ORDERING INFORMATION
3-Axis Digital Compass IC
Tape and Reel 2.5k pieces/reel
FIND OUT MORE
For more information on Honeywell’s Magnetic Sensors visit us online at www.honeywell.com/magneticsensors or contact
us at 800-323-8295 (763-954-2474 internationally).
The application circuits herein constitute typical usage and interface of Honeywell product. Honeywell does not warranty or assume liability of customer-
designed circuits derived from this description or depiction.
Honeywell reserves the right to make changes to improve reliability, function or design. Honeywell does not assume any liability arising out of the
application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.
U.S. Patents 4,441,072, 4,533,872, 4,569,742, 4,681,812, 4,847,584 and 6,529,114 apply to the technology described
Honeywell
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Plymouth, MN 55441
Tel: 800-323-8295
www.honeywell.com/magneticsensors
Form # 900405 Rev A
March 2010
©2010 Honeywell International Inc.
