Smart Digital Magnetometer
HMR2300
The Honeywell HMR2300 is a three-axis smart digital magnetometer to
detect the strength and direction of an incident magnetic field. The three of
Honeywell’s
magneto-resistive
sensors
are oriented
in
orthogonal
directions to measure the X, Y and Z vector components of a magnetic
field. These sensor outputs are converted to 16-bit digital values using an
internal delta-sigma A/D converter. An onboard EEPROM stores the
magnetometer’s configuration for consistent operation. The data output is
serial full-duplex RS-232 or half-duplex RS-485 with 9600 or 19,200 data
rates.
Applications include: Attitude Reference, Compassing & Navigation,
Traffic
and
Vehicle
Detection,
Anomaly
Detection,
Laboratory
Instrumentation and Security Systems.
A RS-232 development kit version is available that includes a windows
compatible demo program, interface cable, AC adapter, and carrying
case.
FEATURES & BENEFITS
High Accuracy Over 1 gauss, RST = Reset Pulse
Toggle Alternates Between Set and Reset Pulse
Set Baud Rate to 9600 bps (Default)
8
9
8 or 9
7
8
7 or 8
Set Baud Rate to 19,200 bps
(8 bits, no parity, 1 stop bit)
Zero Reading Will Store and Use Current as a Negative Offset
so That the Output Reads Zero Field
*ddZR Toggles Command
The Average Reading for the Current Sample X(N) is:
Xavg=X(N)/2 + X(N-1)/4 + X(N-2)/8 + X(N-3)/16 + ...
*ddV Toggles Command
X
X
*ddY
*ddN
OK¬
OK¬
3
3
Turn the “Re-Enter” Error Response ON (*ddY) or OFF (*ddN).
OFF is Recommended for RS-485 (Default = ON)
*ddQ
{See Desc.}
62-72
Read Setup Parameters. Default: ASCII, POLLED, S/R ON,
ZERO OFF, AVG OFF, R ON, ID=00, 20 sps
*ddD
OK¬
BAUD=_9600¬
14
Change All Command Parameter Settings to Factory Default
Values
*ddRST
OK¬
BAUD=_9600¬ 14
or
BAUD=_19,200¬ 16
Change All Command Parameter Settings to the Last User
Stored Values in the EEPROM
Serial Number
*dd#
SER#_nnnn¬
22
Output the HMR2300 Serial Number
Software
Version
*ddF
S/W_vers:_
nnnn¬
27
Output the HMR2300 Software Version Number
Hardware
Version
*ddH
H/W_vers:_
nnnn¬
19
Output the HMR2300 Hardware Version Number
*ddSP
DONE¬
OK¬
8
This writes all parameter settings to EEPROM. These values will
be automatically restored upon power-up.
Too Many
Characters
Wrong
Entry
Re-enter¬
9
A command was not entered properly or 10 characters were
typed after an asterisk (*) and before a .
Missing WE
Entry
Write
Enable Off
WE_OFF¬
7
This error response indicates that this instruction requires a write
enable command immediately before it.
X
X
Format
Set/Reset
Mode
Set/Reset
Pulse
Baud Rate
Zero Reading
Average
Readings
Re-Enter
Response
Query Setup
Default
Settings
Restore
Settings
Store
Parameters
(1)
(2)
(3)
8
X
X
X
14
14
An “X” is this column means that the following command requires a Write Enable before it will execute.
All inputs must be followed by a carriage return, or Enter, key. Either upper or lower case letters may be used. The device
ID (dd) is a decimal number between 00 and 99. Device ID = 99 is a global address for all units.
The “¬” symbol is a carriage return (hex 0D). The “_” sign is a space (hex 20). The output response will be delayed from the
end of the carriage return of the input string by 2 msec (typ.), unless the command sent as a global device ID = 99.
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HMR2300
DATA FORMATS
The HMR2300 transmits each X, Y, and Z axis as a 16-bit value. The output data format can be either 16-bit signed binary
(sign plus 15 bits) or a binary coded decimal (BCD) ASCII characters. The command *ddA will select the ASCII format
and *ddB will select the binary format.
The order of ouput for the binary format is Xhi, Xlo, Yhi, Ylo, Zhi, Zlo. The binary format is more efficient for a computer to
interpret since only 7 bytes are transmitted. The BCD ASCII format is easiest for user interpretation but requires 28 bytes
per reading. There are limitations on the output sample rate (see table below) based on the format and baud rate
selected. Examples of both binary and BCD ASCII outputs are shown below for field values between 2 gauss.
Field
(gauss)
+2.0
+1.5
+1.0
BCD ASCII
Value
30,000
22,500
15,000
+0.5
0.0
-0.5
-1.0
-1.5
-2.0
7,500
00
-7,500
-15,000
-22,500
-30,000
Binary Value (Hex)
High Byte
Low Byte
75
30
57
E4
3A
98
1D
00
E2
C3
A8
8A
4C
00
B4
74
1C
D0
Binary Format: 7 Bytes
XH | XL | YH | YL | ZH | ZL |
XH = Signed Byte, X axis
XL = Low Byte, X axis
= Carriage Return (Enter key), Hex Code = 0D
ASCII Format: 28 Bytes
SN | X1 | X2 | CM | X3 | X4 | X5 | SP | SP | SN | Y1 | Y2 | CM | Y3 | Y4 | Y5 | SP | SP | SN | Z1 | Z2 | CM | Z3 | Z4 | Z5 | SP
| SP |
The ASCII characters will be readable on a monitor as sign decimal numbers. This format is best when the user is
interpreting the readings.
PARAMETER SELECTION VERSUS OUTPUT SAMPLE RATE
Sample
Rate
(sps)
10
20
25
30
40
50
60
100
123
154
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ASCII
9600
yes
yes
yes
yes
no
no
no
no
no
no
19,200
yes
yes
yes
yes
yes
yes
no
no
no
no
Binary
9600
yes
yes
yes
yes
yes
yes
yes
yes
no
no
19,200
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
f3dB
Notch
(Hz)
17
17
21
26
34
42
51
85
104
131
(Hz)
50/60
50/60
63/75
75/90
100/120
125/150
150/180
250/300
308/369
385/462
Command Input
Rate – min.
(msec)
20
20
16
14
10
8
7
4
3.5
3
9
HMR2300
DEVICE ID
The Device ID command (*ddID=nn) will change the HMR2300 ID number. A Write Enable (*ddWE) command is required
before the device ID can be changed. This is required for RS-485 operation when more than one HMR2300 is on a
network. A Device ID = 99 is universal and will simultaneously talk to all units on a network.
BAUD RATE COMMAND
The Baud Rate command (*dd!BR=F or S) will change the HMR2300 baud rate to either fast (19,200 baud) or slow (9600
baud). A Write Enable (*ddWE) command is required before the baud rate can be changed. The last response after this
command has been accepted will be either BAUD=9600 or BAUD=19,200. This will indicate to the user to change to the
identified new baud rate before communications can resume.
ZERO READING COMMAND
The Zero Reading command (*ddZN) will take a magnetic reading and store it in the HMR2300’s microcontroller. This
value will be subtracted from subsequent readings as an offset. The zero reading will be terminated with another
command input(*ddZF) or a power down condition. This feature is useful for setting a reference attitude or nulling the
earth’s field before anomaly detection.
SET/RESET AND AVERAGE COMMANDS
The set-reset function generates a current/magnetic field pulse to each sensor to realign the permalloy thin film
magnetization. This yields the maximum output sensitivity for magnetic sensing. This pulse is generated inside the
HMR2300 and consumes less than 1mA typically. The Set/Reset Mode command (*ddTN or *ddT) activates an internal
switching circuit that flips the current in a “Set” and “Reset” condition. This cancels out any temperature drift effects and
ensures the sensors are operating in their most sensitive region.
Fluctuations in the magnetic readings can be reduced by using the Average Readings commands (*ddVN or *ddV). These
commands provide a low pass filter effect on the output readings that reduces noise due to Set/Reset switching and other
environmental magnetic effects. The two figures below show the average readings effect for step and impulse responses.
Switching the set-reset state is not required to sense magnetic fields. A single Set (or Reset) pulse will maximize the
output sensitivity and it will stay that way for months or years. To turn off the internal switching, enter the command *ddTF
or *ddT. In this state the sensors are either in a Set or Reset mode. If the HMR2300 is exposed to a large magnetic field
(>10 gauss), then another set pulse is required to maximize output sensitivity.
In the Set mode, the direction of the sensitive axis’ are shown on the enclosure label and the board dimensions figure. In
the Reset mode, the sensitive field directions are opposite to those shown. By typing *dd], the user can manually activate
a Set or Reset pulse. The S/R pulse commands can be used the continuous read mode to flip between a Set and Reset
state. Note that the first three readings immediately after these commands will be invalid due to the uncertainty of the
current pulse to the sensor sample time.
DEFAULT AND RESTORE COMMANDS
The Defaut Settings command (*ddD) will force the HMR2300 to all the default parameters. This will not be a permanent
change unless a Store Parameter command (*ddSP) is issued after the Write Enable command. The Restore Settings
command (*ddRST) will force the HMR2300 to all the stored parameters in the EEPROM.
10
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HMR2300
OUTPUT SAMPLE RATES
The sample rate can be varied from 10 samples per second (sps) to 154 sps using the *ddR=nnn command. Each sample
contains an X, Y, and Z reading and can be outputted in either 16-bit signed binary or binary coded decimal (BCD) ASCII.
The ASCII format shows the standard numeric characters displayed on the host computer display. Some sample rates
may have restrictions on the format and baud rate used, due to transmission time constraints.
There are 7 Bytes transmitted for every reading binary format and 28 Bytes per reading in ASCII format. Transmission
times for 9600 baud are about 1 msec/Byte and for 19,200 baud are about 0.5msec/Byte. The combinations of format and
and baud rate selections are shown in the above Table. The default setting of ASCII format and 9600 baud will only
transmit correctly up to 30 sps. Note the HMR2300 will output a higher data settings, but the readings may be incorrect
and will be at alower output rate than selected.
For higher sample rates (>60 sps), it is advised that host computer settings for the terminal preferences be set so a line
feed is not appended to the sent commands. This slows down the reception of data, and it will not be able to keep up
with the incoming data stream.
INPUT SIGNAL ATTENUATION
Magnetic signals being measured will be attenuated based on the sample rate selected. The bandwidth, defined by the
3dB point, is shown in the above Table for each sample rate. The default rate of 20 sps has a bandwidth of 17Hz. The
digital filter inside the HMR2300 is the combination of a comb filter and a low pass filter. This provides a linear phase
response with a transfer function that has zeros in it.
When the 10 or 20 sps rate is used, the zeros are at the line frequencies of 50 and 60 Hz. These zeros provide better than
125 dB rejection. All multiples of the zeros extend throughout the transfer function. For example, the 10 and 20 sps rate
has zeros at 50, 60, 100, 120, 150, 180, ... Hz. The multiples of the zeros apply to all the sample rates against the stated
notch frequencies in the above Table.
COMMAND INPUT RATE
The HMR2300 limits how fast the command bytes can be recieved based on the sample rate selected. The above Table
shows the minimum time between command bytes for the HMR2300 to correctly read them. This is usually not a problem
when the user is typing the commands from the host computer. The problem could arise from an application program
outputting command bytes too quickly.
CIRCUIT DESCRIPTION
The HMR2200 Smart Digital Magnetometer contains all the basic sensors and electronics to provide digital indication of
magnetic field strength and direction. The HMR2300 has all three axis of magnetic sensors on the far end of the printed
circuit board, away from the J1 and J2 connector interfaces. The HMR2300 uses the circuit board mounting holes or the
enclosure surfaces as the reference mechanical directions. The complete HMR2300 PCB assembly consists of a mother
board, daughter board, and the 9-pin D-connector (J1).
The HMR2300 circuit starts with Honeywell HMC2003 3-Axis Magnetic Sensor Hybrid to provide X, Y, and Z axis
magnetic sensing of the earth’s field. The HMC2003 contains the AMR sensing bridge elements, a constant current
source bridge supply, three precision instrumentation amplifiers, and factory hand-selected trim resistors optimized for
performance for magnetic field gain and offset. The HMC2003 is a daughter board that plugs into the HMC2300
motherboard, and the hybrid analog voltages from each axis is into analog multiplexors and then into three 16-bit Analog
to Digital Converters (ADCs) for digitization. No calibration is necessary as the HMC2003 hybrid contains all the
compensation for the sensors, and the set/reset routine handles the temperature drift corrections. A microcontroller
integrated circuit receives the digitized magnetic field values (readings) by periodically querying the ADCs and performs
any offset corrections. This microcontroller also performs the external serial data interface and other housekeeping
functions. An onboard EEPROM integrated circuit is employed to retain necessary setup variables for best performance.
The power supply for the HMR2300 circuit is regulated +5 volt design (LM2931M) with series polarity power inputs diodes
in case of accidental polarity reversal. A charge pump circuit is used to boost the regulated voltage for the set/reset pulse
function going to the set/reset straps onboard the HMC2003. Transient protection absorbers are placed on the TD, RD,
and V+ connections to J1.
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11
HMR2300
APPLICATIONS PRECAUTIONS
Several precautions should be observed when using magnetometers in general:
The presence of ferrous materials, such as nickel, iron, steel, and cobalt near the magnetometer will create
disturbances in the earth’s magnetic field that will distort the X, Y, and Z field measurements.
The presence of the earth’s magnetic field must be taken into account when measuring other magnetic fields.
The variance of the earth’s magnetic field must be accounted for in different parts of the world. Differences in the
earth’s field are quite dramatic between North America, South America and the Equator region.
Perming effects on the HMR2300 circuit board need to be taken into account. If the HMR2300 is exposed to
fields greater than 10 gauss, then it is recommended that the enclosure/circuit boards be degaussed for highest
sensitivity and resolution. A possible result of perming is a high zero-field output indication that exceeds
specification limits. Degaussing wands are readily available from local electronics tool suppliers and are
inexpensive. Severe field offset values could result if not degaussed.
NON-FERROUS MATERIALS
Materials that do not affect surrounding magnetic fields are: copper, brass, gold, aluminum, some stainless steels, silver,
tin, silicon, and most non-metals.
HANDLING PRECAUTIONS
The HMR2300 Smart Digital Magnetometer measures fields within 2 gauss in magnitude with better than 0.1 milli-gauss
resolution. Computer floppy disks (diskettes) store data with field strengths of approximately 10 gauss. This means that
the HMR2300 is many times more sensitive than common floppy disks. Please treat the magnetometer with at least the
same caution as your diskettes by avoiding motors, CRT video monitors, and magnets. Even though the loss of
performance is recoverable, these magnetic sources will interfere with measurements.
DEMONSTRATION PCB MODULE KIT
The HMR2300 Demonstration Kit includes additional hardware and Windows software to form a development kit for with
the smart digital magnetometer. This kit includes the HMR2300 PCB and enclosure, serial port cable with attached AC
adapter power supply, and demo software plus documentation on a compact disk (CD). The figure below shows the
schematic of the serial port cable with integral AC adapter. There will be three rotary switches on the AC adapter. These
should be pointed towards the positive (+) polarity, +9 volts, and 120 or 240 VAC; depending your domestic supply of
power.
D9-F
D9-F
data
2
3
2
3
data
5
5
ground
9
9
GRY
+9vdc
BLK
AC adapter
12
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HMR2300
ORDERING INFORMATION
Ordering Number
Product
HMR2300-D00-232
HMR2300-D00-485
PCB Only (No Enclosure), RS-232 I/O
PCB Only (No Enclosure), RS-485 I/O
HMR2300-D21-232
HMR2300-D21-485
Extended-Base Enclosure, RS-232 I/O
Extended-Base Enclosure, RS-485 I/O
HMR2300-D21-232-DEMO
HMR2300-D21-485-DEMO
Demo Kit, Extended-Base Enclosure, RS-232 I/O
Demo Kit, Extended-Base Enclosure, RS-485 I/O
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.
The application circuits herein constitute typical usage and interface of Honeywell product. Honeywell does not warranty or assume liability of customerdesigned 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
12001 Highway 55
Plymouth, MN 55441
Tel: 800-323-8295
www.magneticsensors.com
www.honeywell.com
PDS-42008
February 2016
13
