HMR3300 Datasheet, PDF (4/11 Pages) Honeywell Solid State Electronics Center – Digital Compass Solutions

HMR3200/3300
pair of sensors for compassing (flat or upright). The HMR3300 uses all three magnetic sensors plus includes an
accelerometer to provide tilt (pitch and roll) sensing relative to the board’s horizontal (flat) position.
The HMR3200/HMR3300 circuit starts with Honeywell HMC1021Z and HMC1022 single and two-axis magnetic sensors
providing X, Y, and Z axis magnetic sensing of the earth’s field. The HMC1022 provides the horizontal components (X and
Y), and HMC1021Z provides the vertical (Z) axis component of the incident magnetic field into cartesian magnitudes at
orthognal angles. These sensors are supplied power by a constant current source to maintain best accuracy over
temperature. The sensor output voltages and constant current sensor supply voltage are provided to a multiplexed 16-bit
Analog to Digital Converter (ADC) integrated circuit. A microcontroller integrated circuit periodically queries the
multiplexed ADC and performs the offset corrections and computes the heading. This microcontroller also performs the
external serial data interface and other housekeeping functions such as the calibration routine. An onboard EEPROM
integrated circuit is employed to retain necessary data variables for best performance.
For the HMR3200, the three magnetic sensors (XYZ) are included and no accelerometer is present. The *L (level) and *U
(upright) are available for horizontal and vertical circuit board orientations respectively. At level, the XY sensors are used
to compute heading; and upright, the YZ sensors are used to compute heading.
For the HMR3300, an additional pair of data inputs from the ±2g accelerometer (Analog Devices ADXL213) is received by
the microcontroller. These tilt inputs (pitch and roll) are added to sensor data inputs to form a complete data set for a three
dimensional computation of heading. If the board is held horizontal, the pitch and roll angles are zero and the X and Y
sensor inputs dominate the heading equation. When tilted, the Z magnetic sensor plus the accelerometer’s pitch and roll
angles enter into heading computation.
The power supply for the HMR3200/HMR3300 circuit is regulated +5 volt design allowing the user to directly provide the
regulated supply voltage or a +6 to +15 volt unregulated supply voltage. If the unregulated supply voltage is provided,
then the linear voltage regulator integrated circuit drops the excess supply voltage to a stable +5 volts. The power supply
is a dual ground (analog and digital) system to control internal noise and maximize measurment accuracy.
ELECTRICAL INTERFACE PINOUT
Pin Number
1
2
3
4
5
6
7
8
Pin Name
SCK
RX
TX
CS
Cal
+5
GD
V+
Description
Synchronous Data Clock (Pulled high in UART mode and left open)
Receive Data, 5V CMOS Input
Transmit Data, 5V CMOS Output
Chip Select (Pulled high in UART mode and left open)
Calibration Input (No connection normally, consult for details)
+5 Volt Regulated Power Input (SW1 must be fully CCW)
Logic and Power Return (Ground)
Unregulated Power Input (+6 to +15 volts, factory default, SW1 must be CW)
APPLICATION NOTES
When To Calibrate
The HMR3200/HMR3300 comes with an optional user hard-iron calibration routine to null modest intensity hard-iron
distortion. For many users in cleaner magnetic environments, the factory calibration will be better and yield more accurate
readings than after a user calibration.
The calibration routine is not cure-all for nasty magnetic environments. If a needle compass is thrown off from true
readings, then it is very likely the HMR3200 and HMR3300 will have poor accuracy too. Most compass error sources
come from ferrous metals (steel, iron, nickel, cobalt, etc.) located too close to the compass location and are known as
soft-irons creating soft-iron distortion. Soft-iron distortion will change the intensity and direction of the magnetic fields on
any nearby compass, and the calibration routine can not remove these flux concentration and bending errors. A good rule
of thumb is to keep soft-irons at least two largest dimensions away from the compass. For example, a half-inch stainless
steel panhead bolt should be at least an inch away from the HMC1021Z and HMC1022 sensor locations.
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