Digital Compass Solutions
HMR3200/HMR3300
The Honeywell HMR3200/HMR3300 are digital compass
solutions for use in precision heading applications.
Honeywell’s magnetoresistive sensors are utilized to
provide the reliability and accuracy of these small, solid
state compass designs. These compass solutions are
designed for generic precision compass integration into
customer systems using a 5-voltage logic level serial data
interface with commands in ASCII format.
The HMR3200 is a two-axis precision compass with three
orthogonal magnetoresistive sensors, and can be used in
either vertical or horizontal orientations.
The HMR3300 includes a MEMS accelerometer for a horizontal three-axis, tilt compensated precision compass for
performance up to a
±60°
tilt range.
Honeywell continues to maintain product excellence and performance by introducing innovative solid-state magnetic
sensor solutions. These are highly reliable, top performance products that are delivered when promised. Honeywell’s
magnetic sensor solutions provide real solutions you can count on.
FEATURES
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Compact Solution on a 1.0” by 1.5” PCB
Precision Compass Accuracy
Tilt-Compensated (HMR3300 only)
0.5° Repeatability
8 Hz Continuous Update Rate
Hard-Iron Compensation Routine
-40° to +85°C Operating Temp Range
Demonstration Kit Available
UART and SPI Communication
BENEFITS
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Small Size and Pin Interface for Daughter/Motherboard Integration
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±1° at Level Heading Accuracy, ±0.1° Resolution
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Up to ±60° of Pitch and Roll Angles Using a MEMS Accelerometer
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Magnetoresistive Sensor Technology for Consistency
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Rapid Heading Computations for Control System Applications
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User Driven Calibration to Null Stray Fields
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Consumer and Industrial Environment Uses
RS-232 Motherboard PCB, Cable,
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Includes Software, and a Carrying Case 9-volt power supply, PC
Demo
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Intuitive Command Language
HMR3200/3300
SPECIFICATIONS
Characteristics
Heading
Accuracy
Level
0° to
±30°
(HMR3300 only)
±30°
to
±60°
(HMR3300 only)
HMR3200
HMR3300
HMR3200
HMR3300
(HMR3300 only)
Roll and Pitch Range
0° to
±
30°
±
30° to
±
60°
Level
-20° to +70°C Thermal Hysterisis
-40° to +85°C Thermal Hysterisis
0.4
1.0
0.4
1.0
5.0
0.1
0.2
0.2
Maximum Magnetic Flux Density
±
2
0.1
Unregulated
Regulated
HMR3200
HMR3300
ASCII (1 Start, 8 Data, 1 Stop,
0 Parity) User Selectable Baud Rate
CKE = 0, CKP = 0 Psuedo Master
Continuous/Strobed/Averaged
HMR3200
HMR3300
In-Line 8-Pin Block (0.1” spacing)
Circuit Board Assembly
HMR3200
HMR3300
25.4 x 36.8 x 11
7.25
7.50
mm
grams
15
8
Hz
2400
6
4.75
-
-
18
22
-
0.5
15
5.25
20
24
19200
±
60
0.5
1.2
deg
deg
deg
1.0
3.0
4.0
0.1
0.1
0.2
0.1
0.2
0.2
0.4
0.2
0.4
deg RMS
Conditions
Min
Typ
Max
Units
Resolution
Hysteresis
Repeatability
Pitch and Roll
Range
Accuracy
Null Accuracy*
deg
deg
deg
Resolution
Hysteresis
Repeatability
Magnetic Field
Range
Resolution
Electrical
Input Voltage
Current
Digital Interface
UART
SPI
Update
deg
deg
deg
gauss
milli-gauss
volts DC
mA
Baud
Connector
Physical
Dimensions
Weight
Environment
Operating (HMR3200)
-40
-
+85
°C
Operating (HMR3300)
-20
-
+70
Storage
-55
+125
* Null zeroing prior to use of the HMR3300 and upon exposure to temperature excursions beyond the Operating
Temperature limits is required to achieve highest performance.
Temperature
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HMR3200/3300
PHYSICAL CHARACTERISTICS
The circuit board for the HMR3200/HMR3300 Digital Compassing Solutions is approximately 1.45 by 1 inches. An 8-Pin
header protrudes down on the rear edge of the compass circuit board for the user electrical interface to the motherboard.
The header pins extend 5/16” below the board plane with the bottom-side mounted magnetic sensor integrated circuits
(HMC1021Z and HMC1022) extending 3/16” below the board plane. Components on the top-side have a maximum height
of 1/8”.
In addition two single pins, identical to the 8 header pins, are placed on the sides toward the forward edge of the circuit
board (HMC1021Z is at the magnetic front or north reference). These single pins are for mechanical mounting and do not
have electrical connections to the compass electronics.
POWER SUPPLY INTERFACE
Rotary switch (SW1) is located near pins 6 and 7, and is used to select the customer provided power supply voltage type.
The HMR3200/3300 is factory set with this switch fully clockwise, for selection of unregulated input (+6 to+15) voltage
from the V+ pin (pin 8). By rotating the switch fully counter-clockwise, users may provide a regulated +5 volt supply to the
+5 pin (pin 6) as an alternative. Incorrect switch settings may cause no response or faulty responses. Upon correct power
application, light emitting diode D2 turns on for about one second afterwards to indicate the execution of the initialization
firmware. Do not use both power inputs simultaneously.
Figure 1 shows a typical HMR3200/HMR3300 circuit board assembly with the basic dimensions.
1.45”
0.15”
.037”
SW1
8
7
6
5
4
3
2
1
1.00”
8-PIN
HEADER
(0.1” SPACING)
Pitch Axis
Pitch Axis
.037”
.094”
+
-
-
-
REF PINS
(2)
Forward Direction
~0.30” Tall
1.22”
+
Roll Axis
-
Figure 1
MOUNTING CONSIDERATIONS
The HMR3200/HMR3300 precision compasses use the ten integrated circuit style pins to plug into compatible
motherboards for electrical interface, and to be orientated mechanically. The pins are nominally 0.030” in diameter and
0.200 in length. Trimming the pin lengths or removing the pins voids the warranty, as Honeywell can not retest the
modified compasses (socketized test fixtures). Wires can be substituted for the pins, but caution should be used in
soldering to not damage the pin solder pads.
The HMC1021Z part is an 8-pin SIP device that is shipped carefully in a nearly perfectly vertical orientation with respect to
the horizontal referenced circuit board. Do not bend or reposition this part, or the factory magnetic calibration will be no
longer valid. Should the part be accidentally bent, return for recalibration is possible or align the part vertical to recapture
most of the accuracy. Correct flat orientation of the compass modules is with the pins pointing downward.
CIRCUIT DESCRIPTION
The HMR3200/HMR3300 Digital Compass Solutions include all the basic sensors and electronics to provide a digital
indication of heading. The HMR3200 has all three axis of magnetic sensors on board, but allows the user to select which
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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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HMR3200/3300
Other nasty magnetic environments are man-made AC and DC magnetic fields created from nearby motors and high
current conductors. These fields should also require compass or source relocation when possible. In some cases, ferrous
metal shielding may help if the shield material is thin and far enough away from the compass.
Hard-iron distortion can be calibrated out, and is composed of soft-irons that are also magnetized and create remnant
(stray) magnetic flux. Classic hard-iron distortion typically comes from large vehicle chassis components and engine
blocks that have up to
±2
gauss on the parts. Locating the compass away from hard and soft-irons is the first line of
defense to preserve accuracy, and the calibration routine will null out the remaining hard-iron influences.
Calibration Procedure
For the HMR3200, one complete turn in a level plane is the best way to expose the sensors to all headings to compute
the calibration offsets. Since the compass collects data at a 15 samples per second rate, a sample per degree of rotation
or slower is a good guideline. If slow turns are not possible, multiple faster turns are a good substitute. The goodness of
the calibration or the amount of hard-iron present is found by checking the Xof, Yof, and Zof values after the calibration
routine is complete. In known clean magnetic environments, the horizontal values (XY = level, YZ = upright) should be
±200
ADC counts or less in these offset variables. Sending these Xof, Yof, and Zof values back to zero returns the
compass to the factory calibration state. The vertical axis values can be zero set or ignored for the HMR3200.
For the HMR3300, the above described level turns will calibrate the XY axis’, but the Z-axis must also be calibrated as
well One full rotation with as much pitch and roll variation included as application allows. If only mild pitch and roll
variations are possible, complete the level rotations, exit the calibration routine, and force the Zof value to zero. Some
accuracy maybe lost in this zeroing, but the mild tilt would likely never cause serious tilt-compensation heading error.
UART COMMUNICATION PROTOCOL
HMR3200/HMR3300 modules communicate through ASCII characters with the * or # characters as start bytes. The data
bit format is 1 Start, 8 Data, 1 Stop, and No parity bits. Factory baud rate is set to 19,200. Asynchronous communication
has the complete menu of commands. Synchronous communication is limited to direct heading queries and no other
commands.
POWER-ON/RESET
The compasses require a hard power-on transition on the power supply voltage to serve as an internal hardware reset
and clock-start. Some bench power supplies may create a soft-start condition and the HMR3200/HMR3300 my react with
a constant-on LED illumination if not reset suddenly. An in-line power supply switch (mechanical or electrical) may be
required when prototyping to avoid soft-starts.
Upon application of power or after a Reset Command, the HMR3200/HMR3300 will run about an 800 milli-second
initialization routine to set the onboard hardware and grab EEPROM variables and shadow them in controller RAM
locations for operation. The LED will illuminate during the routine and extinguish upon completion.
INITIAL STATUS OUTPUT
The HMR3200/HMR3300 will begin sending ASCII characters immediately after the initialization routine ends and the LED
extinguishes. The first line of text will be the model number of the compass and the internal firmware revision number. For
the HMR3300, a second response string will be sent, starting with a # character and either the N, W or A characters. The
#N response indicates normal operation and is the always expected response from the HMR3200. The #W and #A
responses are only for the HMR3300, and indicate the low temperature warning and alarm environments had been
encountered. These responses will be reset to normal when the user sends the pitch and roll re-zero commands to re-
calibrate the MEMS accelerometer for best tilt-compensation performance and accurate tilt indications.
After initialization, the compasses automatically begin streaming heading or magnetometer output data at 15Hz
(HMR3200) or 8Hz (HMR3300). Users must send a start/stop command (*S) to exit continuous streaming data, and to get
the controller’s full attention to the next commands.
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