HMR3100
Advanced Information
SENSOR PRODUCTS
HMR3100
Digital Compass Solution
User's Guide
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HMR3100
Advanced Information
SENSOR PRODUCTS
TABLE OF CONTENTS
INTRODUCTION ............................................................................................................................................................................3
SPECIFICATIONS ..........................................................................................................................................................................3
PIN CONFIGURATION..................................................................................................................................................................4
PHYSICAL CHARACTERISTICS ................................................................................................................................................4
CIRCUIT DESCRIPTION ..............................................................................................................................................................5
USART COMMUNICATION PROTOCOL .................................................................................................................................5
Normal Mode..................................................................................................................................................................................5
Continuous Mode............................................................................................................................................................................6
Calibration Mode ............................................................................................................................................................................7
Data Description .............................................................................................................................................................................7
DEVELOPMENT KIT.....................................................................................................................................................................8
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HMR3100
Advanced Information
SENSOR PRODUCTS
INTRODUCTION
The Honeywell HMR3100 is a electronic compassing solution for use in consumer electronics and personal
navigation products. Honeywell's magnetoresistive sensors are utilized to provide enhanced reliability and accuracy
in a small, solid state compass design. This compass solution is easily integrated into systems using a UART or SPI
interface in ASCII format. Performance is optimized for a horizontal orientation.
SPECIFICATIONS
Characteristics
Conditions
Min
Typ
Max
Units
Heading
Accuracy
Level
5
deg RMS
Resolution
0.5
deg
Repeatability
3
deg
Magnetic Field
Range
Maximum Magnetic Flux Density
2
gauss
Resolution
6
milli-gauss
Electrical
Input Voltage
Unregulated
2.6
3
5
volts DC
Current
Normal Mode (Average)
Sleep Mode
Calibration
0.1
6.1
0.2
7.3
0.5
1
17.3
mA
A
mA
Digital Interface
USART
USART 9600.N.8.1
2400
9600
19200
Baud
Update
Continuous or Polled
-
2
20
Hz
Connector
8-Pin
-
Physical
Dimensions
Circuit Board Assembly
19 x 19 x
4.5
mm
Weight
2.3
grams
Environment
Temperature
Operating
Storage
0
-40
-
-
+70
+110
C
C
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HMR3100
Advanced Information
SENSOR PRODUCTS
PIN CONFIGURATION
Pin Number
Pin Name
Description
1
VCC
Power Supply Input
2
NC
No Connection
3
RTS
Ready To Send Input
4
NC
No Connection
5
TXD
Transmit Data Output
6
RXD
Receive Data Input
7
GND
Power and Signal Ground
8
NC
No Connection
PHYSICAL CHARACTERISTICS
The circuit board for the HMR3100 Digital Compassing Solutions is approximately 0.77 by 0.77 inches. Two 4-Pin
headers protrude down on each edge of the board for a total of eight pins to become the user interface or the
development kit intermediate board interface. Figure 1 shows a typical circuit board with dimensions.
Figure 1
HMR3100 Pinout
0.77"
0.77"
C
xtal
Pin 1
Pin 4
Top Side
Pin 5
Pin 8
J1 J2 J3 J4
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HMR3100
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CIRCUIT DESCRIPTION
The HMR3100 Digital Compass Solution circuit board includes the basic magnetic sensors and electronics to provide
a digital indication of heading. The HMR3100 has a Honeywell HMC1022 two-axis magnetic sensor on board. The
HMR3100 allows uses to derive compassing (heading) measuriments when the board is in a horizontal (flat) position.
The HMR3100 circuit starts with the HMC1022 two-axis magnetic sensors providing X and Y axis magnetic sensing of
the earth's field. These sensors are supplied power by a switching transistor to conserve power with battery operated
products. The sensor output voltages are provided to a dual operational amplifier and then to analog to digital
converters (ADC) onboard a microcontroller (
C) integrated circuit. A microcontroller integrated circuit periodically
samples the amplified sensor voltages, 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.
The power supply for the HMR3100 circuit board is to be about a +3 to +5 volt range allowing the user to provide a
single lithium battery to logic level supply voltages. The power supply architecture is a single ground system for single
ended supply sources (+ and ground return)
USART COMMUNICATION PROTOCOL
HMR3100 module communicates through binary data and ASCII characters at four selectable baud rates of 2400,
4800, 9600, or 19200. The default data bit format is USART 9600.N.8.1. The baud rate selection is determined by
the position of jumpers J1 and J3. These jumpers are zero ohm SMT resistors (jumpers) and are normally high (logic
1) when removed, and grounded (logic 0) when in place. At 2400 baud, no jumpers are present for a 1,1 logic
presentation. At 4800 baud J3 is present for a 1,0 logic presentation. The factory default setting of 9600 baud is
created by a jumper present on J1 for a 0,1 logic presentation. With J1 and J3 jumpers present for a 0,0 logic
presentation, the compass module works at 19200 baud. See Figure 1 for jumper locations. Jumper J2 is for factory
testing, and J4 is for X-axis inverse should the end-item mount the HMR3100 module upside down.
The HMR3100 is ready to output heading information when the board is powered up. Note that when the device is first
powered up, it may need calibration. The HMR3100 has three modes of operation described as normal, continuous,
and calibration.
Normal Mode
When the host processor (external to the HMR3100) sends a RTS low pulse to the RTS pin, the HMR3100 will send
the heading data via the TXD pin. The host shall hold the RXD pin high during this mode. The RTS shall be held high
when not pulsed. The HMR3100 will return to sleep status when RTS is left high after the data is sent. Up to 20
heading queries per second can be accomplished given fast enough baud rates. A caution is advised that average
current draw is proportional to supply voltage and amount of queries handled. At the 20 Hz rate, 1 to 5 milliamperes of
current is consummed with lesser query rates taking advantage of the less than one microampere sleep mode current
draw between queries. Figure 2 shows the normal mode timing diagram.
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HMR3100
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Figure 2
Normal Mode Timing Diagram
Continuous Mode
When the host processor sets the RTS pin to a low level position, the HMR3100 will continuously stream heading data
via the TXD pin. Note that the processor does not return to sleep mode and outputs heading slightly below a 2 Hz
rate. Figure 3 shows the continuous mode timing diagram.
Figure 3
Continuous Mode Timing Diagram
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HMR3100
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.
Calibration Mode
When the host processor pulses the RTS pin, and sends the RXD pin to a low logic level, the HMR3100 is in
calibration mode. At a moderate rate (2 to 5 seconds per rotation), rotate the HMR3100/host assembly two complete
circles to allow the HMR3100 to take measurements for compass calibration. At the completion of the rotations, return
the RXD to a high logic level. The HMR3100 will return to sleep status until another mode has been initiated. Upon
initiation of the calibration mode, the microcontroller shall output a STA (53 54 41 hex) indicating a start of calibration
and then RDY (52 44 59 hex) at the completion of the rotations and the RXD line returning high. Figure 4 shows the
calibration mode timing diagram.
Figure 4
Calibration Mode Timing Diagram
Data Description
The HMR-3100 host processor uses a three byte reply as the RTS line is brought low. The data is formatted in
hexadecimal (hex) fashion with the first byte being either 80(hex) or 81(hex). If that first byte LSbit is flagged high (81
hex), it means magnetic distortion maybe present and a calibration should be performed. The remaining two bytes are
the heading (in degrees) in MSB to LSB format. There is some data interpretation needed to derive the heading. For
example, an 80 02 85 (hex) Byte pattern correlates to 322.5 degrees.
This is done by taking the MSB hex value, converting it to decimal representation (e.g. 02 decimal) and multiplying it
by 256. Then the LSB is decimalized (e.g. 85(hex) to 133(decimal)) and added to the 512(decimal) MSB. The total
(512+133=645) is then divided by two to arrive at a 322.5 degree heading. This data format permits the 0.5
resolution.
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HMR3100
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SENSOR PRODUCTS
DEVELOPMENT KIT
The HMR3100 Development Kit includes additional hardware and Windows demo program software to form a
development kit for electronic compassing. This kit includes the appropriate HMR3100 Printed Circuit Board (PCB)
module soldered to an intermediate circuit board using a wide DIP-style (0.8" spacing) pin arrangement. The
intermediate board assembly plugs into an RS-232 motherboard with a serial port connector. In addition, a four-foot
serial port cable (RJ-11 to D-9F), nine-volt battery clip, demo program software, and this user's guide is included. The
RS-232 motherboard incorporates a 5-volt regulator integrated circuit to provide the necessary voltages to the
onboard RS-232 converter integrated circuit and the HMR3100 daughter-board. A nine-volt battery clip is included,
but other DC input voltages between 7 and 15 volts may be used. Supply currents are nominally around 8
milliamperes plus the HMR3100 current draw.
The RS-232 motherboard also contains a six-contact modular jack (RJ-11) for a compact RS-232 interface to a
personal computer serial port. Ground, RTS, RXD, and TXD data lines are brought out to the jack with two contacts
left open. Figure 5 shows the kit board assemblies.
Figure 5
HMR3100 Kit Hardware
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.
900284 12 2001 Rev
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