High Resolution AMR Compass

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High Resolution AMR Compass
Advisor Dr. Andy Peczalski Advisor Professor Beth
Stadler Pat Albersman Jeff Aymond Dan
Beckvall Marcus Ellson Patrick Hermans
Honeywell
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Abstract
This projects purpose is to improve the accuracy
of a digital compass by using multiple compass
ICs. These will work together to collectively
improve the accuracy of the overall system.
Honeywell
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Project Motivation

• Magnetic ICs in High Demand
• Navigation
• HDD
• Proximity sensing
• Position sensing
• Increasing Accuracy is Required
• Decreasing Size is also Beneficial

Honeywell
Images from http//phermans.com/w/images/e/e2/HMC1
05X.pdf
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Current Technology

• Anisotropic Magnetoresistance
• Wheatstone bridge

Honeywell
Images from http//phermans.com/w/images/9/9f/Appl
_note_for_position_sensing.pdf
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Current Technology

• Analog
• 1, 2 or 3 axes sensing
• Direct access to bridge
• Navigational accuracy depends on ability to read
  voltages
• Digital
• 2 or 3 axes
• Internal heading calculation
• Accurate to 1 degree

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Future Technology

• What is the next step?
• Nanowires
• AMR sensing abilities
• Decreased size
• Decreased sensitivity

Honeywell
Images from Prof. Beth Stadler
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Project Description

• Feasibility study for the use of nanowires
• Not actually working with nanowires
• Trying to increase accuracy by using multiple
  bridges as would be required with nanowires
• Providing Honeywell with a new use for nanowires

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Project Description
One benchmark is to try to increase the accuracy
of the system by the number of sensors
used. Increased precision and repeatability is
also desired.
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Project Description
Customized hardware is necessary to implement the
multiple sensor system. Customized software will
be required to manage the implementation.
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Chosen IC HMC 6352

• Digital 2-axis compass
• On board ADC
• Modifiable sensing range
• Speaks I2C
• Small package
• Improvable accuracy
• Barber pole bridges

Honeywell
Image from http//phermans.com/w/images/9/9d/HMC63
52.pdf
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Software Algorithms

• Modeling Simulations
• Matlab

• Firmware
• MPLab CCS Compiler

• User Interface
• Visual Basic (VB)

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Sensor Modeling

• Goal Parameters-gt M-file -gt Sensor Data

• Consists of Many Sub-functions
• Noise, Bridge, OpAmp, A2D

• Needs to model real world situations

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MATLAB

• Successfully used to simulate single and multiple
  sensors before our hardware could be designed
• Provided a vehicle to test the performance of our
  heading calculation algorithms
• Totaled 1702 lines of MATLAB code

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Sensor Placement

• The placement of the sensors must create a system
  accurate across 360 degrees
• Each individual bridge of each sensor can be
  simulated independently in MATLAB
• Multiple arrangements can be simulated to
  determine the best implementation

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Orientation Simulations

• Single IC Senor Output Wave Form

• Data Appears Evenly Spaced
• ICs at 0, 36, 72, 108, 144, 180, 216, 252, 288,
  324 Degrees

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Orientation Simulations

• Single IC Senor Output Wave Form

• Data Evenly Spaced
• ICs at 0, 9, 18, 27, 36, 45, 54, 63, 72, 81
  Degrees

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MicroController C Code

• Written in MPLab
• Version 8.0
• CCS complier
• Version 4
• Run on PIC 18f4550
• 1326 Lines of C
• 2532 Lines of Assembly

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Sensor Communication

• Sensor Commands
• Heading
• Adjusted voltages
• Raw voltages
• Calibrate
• Re-address
• Number of Summed measurements

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Serial Communication

• Allows Compass to display results
• Very helpful in debugging
• Allows for VB to control sensor
• Easy to implement in CCS
• 115200 Baud allowable from the 20Mhz crystal

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Weighted Averaging
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Visual Basic (VB) Interface

• Provides an end-user interface
• Synchronizes the compass and the rotation table
  used to accurately measure moves
• Allows for automated data acquisition
• Provides a repeatable test benching system
• Requires a third board to handle adjusted ground
  on PMC
• Total of 4733 Lines of Code

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Visual Basic (VB) Interface
Commands to perform repeatable data acquisition
and benchmark tests.
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Serial
Serial
Personal Computer (VB)
PMC Controller
PIC18F4520 (C)
Rot. Table
Parallel
I2C
Sensors
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Hardware Abstract

• One compass, two boards
• Main Board
• Microcontroller
• Daughter Board
• Sensors

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Hardware Main Board

• Essentially a controller board
• Microcontroller
• RS-232 Communication
• I2C Communication
• Interfacing
• Daughter Board
• Front Panel

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Initial Design Daughter Board

• Three functional systems
• Sensor array
• Power MUX
• Laser
• Constraint One of the dimensions must be less
  than 3.5
• Opening of zero-gauss chamber is 3.5 in diameter

3.132
3.492
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Daughter Board
I2C Bus
Clock
Data
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Daughter Board
Power MUX

• Design challenge
• Need to assign unique address to each sensor
• Each sensor is factory installed with address
  0x42
• In order to change addresses, a command must be
  sent to a sensor on the bus
• This command message contains
• How to change address of individual sensor if
  every sensor is receiving the command?

Start Address Ack Command Ack Stop
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Daughter Board
Power MUX

• Solution Need to isolate communication to
  individual sensor
• How?
• Burn-in Socket
• Use a network of jumpers
• Multiplex I2C to each sensor
• Multiplex power to each sensor

Honeywell
Photo taken from http//www.locknest.com/newsite/p
roducts/qfn/index.htm
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Daughter Board
Power MUX

• We chose to multiplex power
• Advantages
• Saves power
• Simplifies troubleshooting
• Disadvantages
• Signal loss through MUX
• Other unknowns

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Problems with Initial Design

• Problems
• Main Board
• None
• Daughter Board
• I2C bus
• When powered off, the sensors interfere with I2C
  bus
• 5V data signal is pulled down to 2.5V
• Therefore communication will not work
• Problems not related to design
• Sensor 3 will not communicate
• Will not hinder project algorithm will still
  work
• Slight loss of sensitivity at sensor 3s axes of
  sensitivity (27 and 117 )

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Changes to Initial Design

• I2C bus fix
• Remove MUX and feed power to all sensors
• Cut I2C traces
• Add jumpers to I2C vias and address them one by
  one
• Connect all jumpers to I2C bus

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Changes to Initial Design

• Other changes
• No laser mount
• Laser mounted directly to plexi-glass case
• Saves cost (25)

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Proposed Final Design

• Due to I2C bus issues, our current design does
  not work
• Two options
• Power all sensors and use burn-in or jumpers
  socket to isolate sensors
• Multiplex I2C bus
• Add Physical Jumpers to the I2C bus to individual
  connect one sensor at a time

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Testing

• Prototype Final

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Test Setup
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Accuracy
Precision
Repeatability
Compare
Compare
ß field
Compare
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Prototype Testing

• Given one sensor

• CCS compiler

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Final Testing

• Elements of Final testing
• Pretesting to determine zero gauss values
• Pretesting to determine IC positional offsets
• Testing to obtain compass specs
• Accuracy, Precision, Repeatability

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Pre-testing (zero gauss)

• Place sensors in the zero gauss chamber
• Rotate 360 deg. while taking readings
• Analyze data and get zero gauss values
• This determines what value we should see when the
  IC is experiencing zero gauss, aka parallel to
  the field direction.

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Pre-testing (offsets)

• Place sensors in artificial magnetic field
• Run VB script that finds sensor locations
• Uses the zero gauss value of each chip
• Works using relativity, sensor 1 0, sensor2 ?
  From 1
• Bang bang control
• Analyze data and find chip placements
• Hardcode this to software

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Raw voltage readings with offsets
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Raw voltage readings with offsets
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Accuracy

• Test Procedure
• Determine the B field
• Find the zero crossing on each axis
• B field should be 90 degrees from zero crossing
• Average the 20 axes results
• Take measurement
• Compare result to actual
• Rotate to different position
• Repeat steps 2-5

113 deg
23 deg
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Results

• Results Comprise of
• Determining Specs
• Comparison of Specs to Controls
• Ways to improve
• Future for Nanowires?

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Results Control Comparisons

• First Control is the Sensor Heading output
• We Dont know how they compute this
• Second Control is performing arctan(x/y) on a
  single designated sensor
• These will be compared with our computation of
  arctan(x/y) of multiple sensors averaged

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Results Specs - Repeatability

• Comprised of 5 readings taken at 0, 90, 180,270
• Our Product Min - 0.015 Max -0.089
• Control Min - 0.033 Max -0.051
• Honeywell Min - 0.030 Max - 0.120

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Results Specs - Precision
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Results Specs - Accuracy
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How Can We Improve

• Currently using arcTan(x/y) to compute heading
• This assumes we have X and Y which need to be 90
  degrees apart
• In practice this is not true, we found this is
  actually only within -8 degrees
• Use different algorithms, better weighting
• More Sensors

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Future For Nanowires?

• Nanowires are inherently less accurate
• Means greater room for improvement
• Small enough to use more than 10 bridges
• Weighting should have more of an effect
• Will have completely different obstacles
• All in all, from the results of this feasibility
  test they look very promising

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Conclusion

• Questions/ Comments?
• Thanks for your Attention and Time!

Honeywell