TruePoint™ Compass Module
HMR3500
The HMR3500 TruePoint™ compass module is a 3-axis
digital compass solution with a customizable coordinate
system for mounting in any desired orientation. Three
Anisotropic Magneto-Resistive sensors and three MEMs
accelerometers are combined to provide compass heading
as well as pitch and roll angles.
The HMR3500 has provisions for hard and soft-iron
correction algorithms to handle magnetic distortion effects.
In addition a World Magnetic Model feature is provided to
automatically add declination angle corrections for
reference to true north (geographic north).
Honeywell provides 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
products provide real solutions you can count on.
FEATURES BENEFITS
4
Precision Compass Accuracy
4
Better Than 1° Nominal Heading Accuracy (1 σ), 0.1° Resolution
4
Tilt-Compensated
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±89° Pitch and Roll, 360° Continuous Roll Capabilit y
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Update Rate to 25Hz
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Rapid Heading Computations for Guidance Applications
4
Compact Solution in a 1.97” by 1.65” by
0.52” PCB Assembly
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Small Size for Tight Mounting Conditions, Minimal Layout Constraints
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Hard and Soft-Iron Compensation
Routines
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User Driven Calibration to Null Stray Fields. A Single Routine for Both
Hard and Soft Iron Corrections
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World Magnetic Model Included
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Choice of True North or Magnetic North References
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-40° to +85°C Operating Temp Range
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Consumer and Industrial Environment Uses
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+5 DC Supply Voltage Range
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Customizable to a Wide Variety of Power Sources
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Light Weight
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3.0 oz with Aluminum Housing, 0.6 oz PCB only
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Customizable Coordinate System
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24 Custom Coordinate Orientations
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All Solid State Components
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Rugged for User-Defined Orientation Plane
HMR3500
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SPECIFICATIONS
Characteristics Conditions Min Typ Max Units
Heading
Accuracy (Clean Magnetic Environment)
Level
Pitch 0° to ±30°
Roll 0° to ±30°
-
0.5
0.75
0.75
1
(1 σ)
Resolution 0.1 deg
Repeatability 3 sweeps, 0º to 360º, level 0.2 deg σ
Pitch and Roll
Roll Range Default orientation, rotation about X-axis ±180° deg
Pitch Range Default orientation, rotation about Y-axis ±80° deg
Accuracy Roll ±30º, Pitch ±30º 0.5 1 deg σ
Null Accuracy
1
Level ±0.5 deg
Resolution Level, 1-sigma, 100 readings 0.04 deg
Roll Repeatability Roll ±70º
Pitch ±70º 0.2
0.2 deg σ
Pitch Repeatability
Roll ±70º
Pitch ±70º 0.1
0.1 deg σ
Magnetic Field
Range Maximum Magnetic Flux Density 0.7 gauss
Resolution 1-sigma, 100 readings 0.45 milli-
gauss
Dip Angle Earth’s Vertical Field Component -70 +70 deg
Linearity 0.2 %FS
Electrical
Input Voltage
Standard Product 2.5 5.0 5.2 volts DC
Power Input Voltage 2.5 to 5.2V 300 mW
Digital Interface
UART ASCII 4800 9600 38,400 Baud
Update Rate Continuous Heading Updates 0.05 10 25 Hz
Format Bi-directional binary packet data protocol. RS-232 -
Physical
Dimensions Circuit Board Assembly 1.97 x 1.65
x 0.52 inches
Weight HMR3500 PCB only
HMR3500 with case, no cable 0.6
3.0 ounce
ounces
Connector 5-pin, 2mm pin spacing -
Environment
Temperature Operating
Storage (OEM only) -40
-55 -
- +85
+125 °C
°C
1
Null zeroing prior to use of the HMR3500 and upon exposure to temperature excursions beyond the Operating
Temperature limits is required to achieve highest performance.
* Tested at 25°C unless stated otherwise.
HMR3500
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PIN CONFIGURATION
Pin Number Pin Name Description
1 Ground Power Supply Return and Ground Reference
2 RXD RS-232 Receive Data
3 TXD RS-232 Transmit Data
4 +Vin Positive Power Supply Voltage Input
5 Ground Ground Reference (for twisted pair routing with +Vin)
BASIC DEVICE OPERATION
The HMR3500 TruePoint™ Compass Module includes 3-axis Anisotropic Magneto-Resistive (AMR) sensors, 3-axis
MEMS accelerometers, a temperature sensor, and 16-bit microprocessor with onboard Analog to Digital Converter (ADC).
The HMR3500 is available as a printed circuit board assembly, or assembled in a black aluminum case with cable
assembly. Additionally, the cable assembly can be ordered separately. A demonstration kit of the HMR3500 is available
with the case, cable assembly, a CD of the CompassHost windows utility software for the user’s personal computer.
The HMR3500 requires an external DC power supply for the red (positive) and black (ground) wires of the cable
assembly. By feeding 5 volts at about 50 milli-amperes into the HMR3500, the compass will operate, and a red LED on
the printed circuit board assembly will begin blinking at a 1Hz rate. Lack of a blinking LED or at a rapid rate is an
indication of an error, and action should taken to cycle power on the compass electronics to reset the module.
As a factory default, the RS-232 interface is set at 9600 baud with one start bit, 8 data bits, one stop bit, and no parity bits.
The HMR3500 does not require any hardware or software handshaking or related features. The baud rate can be
changed by command after initial communication at the current baud rate.
The CompassHost utility software is a 32-bit Windows® application program that is provided with the HMR3500
demonstration kit, and can be used to evaluate the HMR3500’s performance and demonstrate the compass features. With
exception of the baud rate change command, the CompassHost is capable of sending and receiving all of the commands
of the compass/computer interface. Host computers should be capable of running Windows 9x, ME, NT, 2000, XP and
follow-on operating systems. An install program loads the executable file CompassHost.exe and ActiveX components. A
readme.txt file is also included to describe the installation process.
PHYSICAL CHARACTERISTICS
The circuit board for the HMR3500 is 1.57 by 1.97 by 0.52 inches and composed of multi-layer, fiberglass-epoxy printed
boards, with the main board horizontal and a vertical board for mounting the z-axis magnetic sensor and accelerometer.
The vertical board is held orthogonal to the main board by two brass hardware blocks to ensure mechanical orthogonality.
1.57
1.97
1.00
0.150
1.65
0.150 0.170
φ
0.116
4 PLCS
Forward
Direction
X
Y
Pin 1
1.57
1.97
1.00
0.150
1.65
0.150 0.170
φ
0.116
4 PLCS
Forward
Direction
X
Y
Pin 1
Figure 1
HMR3500 Top View and Dimensions
HMR3500
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MOUNTING CONSIDERATIONS
The following is the recommend printed circuit board (PCB) footprint for the HMR3500. The reference direction (forward)
is the right PCB assembly edge shown in Figure 1. Left to right, the interface connector is numbered pin 1 to pin 5 per the
pin configuration table.
UNC 4-40 fastening hardware is recommended for mounting the printed circuit board with at least 0.125 inch nylon
spacers to stand off the board from the mounting surface. Fastener hardware must be non-ferrous for full compass
performance with brass or nylon screws the usual materials of choice.
CASE DIMENSIONS
(in inches)
CIRCUIT DESCRIPTION
The HMR3500 circuit design starts with a microprocessor powered by power supply sub-circuit that takes the input
voltage and creates regulated power for the various other circuits in the HMR3500. Two 2-axis MEMS accelerometers are
mounted horizontally and vertically to combine into a 3-axis tilt sensing sub-circuit. Each accelerometer outputs a Pulse-
Width-Modulated (PWM) digital signal that the microprocessor measures for pitch and roll angles.
Besides an integral temperature sensor, a 2-axis and 1-axis magnetic sensor devices are mounted horizontally and
vertically to create a 3-axis measurement of the incident magnetic field upon the sensors. Each sensor output is amplified
and sent to a multiplexed input ADC residing inside the microprocessor. After digitizing, the magnetic signals are
corrected for hard and soft-iron magnetic errors created by the environment to which the compass is attached.
Heading computation uses the magnetic and tilt information inputs after compensation for errors. From the basic magnetic
heading, a declination value may be added to arrive at a geographic north referenced heading. An index offset value may
also be added to correct for mechanical installation misalignment on the target platform.
Figure 2
HMR3500 Case Dimensions
HMR3500
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Figure 3
HMR3500 Block Diagram
UART COMMUNICATION INTERFACE
The 5-pin power supply and UART interface connector on the HMR3500, mates with a Harwin latching connector (Part #
M80-8980505) per the pin configuration table earlier in this document. The interface hardware protocol is RS-232 without
any further handshaking or hardware control lines.
Further HMR3500 interface commands and protocol are in the HMR3500 user’s guide document.
TEST SOFTWARE DESCRIPTION
Computer test software is provided in the HMR3500 demonstration kit that will permit a thorough evaluation and
demonstration of the compass capabilities. CompassHost is a 32-bit Windows test program. It is capable of sending and
receiving all messages described in this manual except the BAUD message. It can display all messages received from the
module in the main window with scrolling text. It has a small window summarizing the current status of the module and a
graphic display of the current compass heading, roll, and pitch.
CompassHost can be run under Windows 9x, ME, NT 4.0, 2000 or their successors. One available serial port is required
for communicating with the compass. Processor, memory, and disk space requirements are minimal.
The CompassHost software is not described in this datasheet, but given in depth description in the HMR3500 user’s guide
document.
Temp
Sensor
X
Y
Z
Magnetic
Sensors
Accels
X
Y
Z
Power
Supply
16 – Bit
Microcontroller
T
R
RS-232
I/O
Temp
Sensor
X
Y
Z
Magnetic
Sensors
Accels
X
Y
Z
Power
Supply
16 – Bit
Microcontroller
T
R
RS-232
I/O
HMR3500
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Figure 4
Compass Test Evaluation Software Display
ORDERING INFORMATION
Ordering Number Product
HMR3500
HMR3500 Demo
TruePoint Compass Module PCB Only (RS232)
TruePoint Compass Demonstration Kit
FIND OUT MORE
For more information on Honeywell’s Magnetic Sensors visit us online at www.magneticsensors.com 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
Form #900329
November 2008
©2007 Honeywell International Inc.
Honeywell
12001 Highway 55
Plymouth, MN 55441
Tel: 800-323-8295
www.honeywell.com/magneticsensors
