1. High Resolution AMR Compass
Advisor Dr. Andy Peczalski
Advisor Professor Beth Stadler
Pat Albersman
Jeff Aymond
Dan Beckvall
Marcus Ellson
Patrick Hermans
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2. Abstract
This project’s purpose is to improve the accuracy of a digital compass by using multiple compass IC’s.
These will work together to collectively improve the accuracy of the overall system.
Using the HMC6532 compass (discussed later)
Using most accurate regions of each IC (discussed later)
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3. Project Motivation Magnetic ICs in High Demand
Navigation
HDD
Proximity sensing
Position sensing
Increasing Accuracy is Required
Decreasing Size is also Beneficial
Why Do We Want to Do This? (why are we making a hyper-accurate compass?)
Before further project explanation, a review of magnetic sensing
Magnetic Ics are becoming more heavily used.
Go through other applications
Like most other sensors and embedded systems they are decreasing in size and increasing in accuracy
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Images from

4. Current Technology Anisotropic Magnetoresistance Wheatstone bridge
What is arleady on the market?
Most sensing is done using these.
Explain
Go over resistance change as field direction changes
Go over how this works in the Wheatstone bridge, give example relating to change in resistance.
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5. Current Technology Analog Digital Honeywell 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
The bridges are often found in all in one IC’s that eitehr output anlog voltages or can be found packeged with A2D’s and other processing technology
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6. Future Technology What is the next step? Nanowires Honeywell
AMR sensing abilities
Decreased size
Decreased sensitivity
Nanowires allows for a much smaller sensing element therefore a much smaller sensor. However they are less accurate therefore to get comparable or higher accuracy many more sensing elements must be used.
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Images from Prof. Beth Stadler

7. 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
We are doing a feasibility study to hopefully prove that multiple wheatstone bridges will greatly improve accuracy.
If this can be proved it can than be implemented with nanowire technology to reduce the size of current compass IC’s and perhaps incrase accuracy as well.
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8. Increased precision and repeatability is also desired.
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.
In our case, 10 sensors in an attempt to have 10x accuracy.
Precision and repeatability to be discussed later.
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9. Customized software will be required to manage the implementation.
Project Description
Customized hardware is necessary to implement the multiple sensor system.
Customized software will be required to manage the implementation.
Do a brief overview of the design, such that the software sections make sense,
State, we will be using a micro processor to communicate to chosen sensors and obtain data.
The micro will also be able to display the data to use via serial communication and HyperTerminal
A VB program can then be written to interface to the device as well, useful for data collection.
These will all be discussed in more detail shortly.
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10. Chosen IC: HMC 6352 Digital 2-axis compass On board ADC
Modifiable sensing range
Speaks I2C
Small package
Improvable accuracy
Barber pole bridges
Gives access to heading and bridge voltage data.
Discuss I2C, it is a serial communication protocol that uses a data line and a clock line. Used to transmit digital data.
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11. Modeling & Simulations Matlab
Software & Algorithms
Modeling & Simulations
Matlab
Firmware
MPLab & CCS Compiler
User Interface
Visual Basic (VB)
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12. Sensor Modeling Goal: Parameters-> M-file -> Sensor Data
Consists of Many Sub-functions
Noise, Bridge, OpAmp, A2D
- - the globe pic,
-Matlab icon
-Sensor from our wiki
The rest I drew
Needs to model real world situations
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13. 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
Image from mathworks
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14. 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
2 bridges per sensor offset 90 degrees from each other.
Linear region is the most accurate.
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15. Orientation Simulations
Single IC Senor Output Wave Form:
Start by showing the singe IC output. Describe in some detail the linear and non linear region and why the non linear region is bad.
First Spacing idea was that it takes the wave from 360 degrees to repeat and we want to space NumICs in that region. Therefore:
360/NumIC = 360/10 = 36 Degree Spacing
This creates what appears to be an evenly distributed field, but note that optimal axes intersect (draw a line at zero) and are spaced 18 degrees apart.
Data Appears Evenly Spaced
ICs at: 0, 36, 72, 108, 144, 180, 216, 252, 288, 324 Degrees
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16. Orientation Simulations
Single IC Senor Output Wave Form:
Next we realized that if we space each linear region (aka each color) evenly and such that none overlapped we should create a more dense and evenly spaced region of linear regions.
Since there is a linear region every 90 degrees and we have:
90/NumICs = 90/10 = 9 Degree Spacing
Data Evenly Spaced
ICs at: 0, 9, 18, 27, 36, 45, 54, 63, 72, 81 Degrees
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17. 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
Ccsinfo.com
Microchip.com
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18. Sensor Communication Sensor Commands Heading Calibrate Re-address
Adjusted voltages
Raw voltages
Calibrate
Re-address
Number of Summed measurements
Talk on the ability to change ram and EEPROM values
Image from philips
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19. Serial Communication Allows Compass to display results
Very helpful in debugging
Allows for VB to control sensor
Easy to implement in CCS
Baud allowable from the 20Mhz crystal
Baud of from the 20Mhz crystal
Image from wikipedia
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20. Weighted Averaging Honeywell
Don’t Describe this in detial, just state we are perofrming a weighted average
The weights are bassed upon when arctan is most accurate and when our data is most accurate
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21. As shown here, weights are high when everything is fairly accurate, and really low when something is supper in accurate
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22. 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
Done by dan
Pmc interface voltage problem, took a week to fix,
Problems like this are what cause delays in the real work force and need to be planned for
As Randy would say: You don’t know what you don’t know.
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23. Honeywell PMC Interface and controls, includes a mini terminal windows
Done by dan
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24. Visual Basic (VB) Interface
Done by dan
Commands to perform repeatable data acquisition and benchmark tests.
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25. Honeywell Serial Serial Personal Computer (VB) PMC Controller
PIC18F4520
(C)
Rot. Table
Parallel
I2C
Sensors
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26. Hardware: Abstract One compass, two boards Main Board Daughter Board
Microcontroller
Daughter Board
Sensors
MB is the brains
DB has the sensors
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27. Hardware: Main Board Essentially a controller board Microcontroller
RS-232 Communication
I2C Communication
Interfacing
Daughter Board
Front Panel
Features
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28. 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”
Features
3.492”
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29. Daughter Board I2C Bus Honeywell Clock Data
I2C bus – these are all on the bottom!
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30. 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
Stop
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31. 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
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Photo taken from

32. 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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33. Problems with Initial Design
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 3’s axes of sensitivity (27° and 117 °)
Sensors interfere with I2C bus because when they are powered off, they have a low resistance (because of the PIC?)
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34. 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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35. Changes to Initial Design
Other changes
No laser mount
Laser mounted directly to plexi-glass case
Saves cost ($25)
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36. 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
Briefly state, these are fixes that could be made and each have there own advantages and disadvantages that would need to be analyzed
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37. Testing
Prototype Final
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38. Test Setup
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39. Precision Repeatability Accuracy ß field Honeywell Compare Compare
Talk about the zero gauss chamber
Rotating sensor array to find the B field with each sensor.
ß field
Compare
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40. Prototype Testing Given one sensor CCS compiler Honeywell
For testing we only had one sensor to test with and could not test to see if I2C bus communications would work with multiple sensors.
We did however, get it to work and obtained data that matched our Matlab models
CCS compiler
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41. 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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42. 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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43. 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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44. Raw voltage readings with offsets
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45. Raw voltage readings with offsets
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46. Accuracy Test Procedure Determine the B field Take measurement
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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47. Results Results Comprise of: Determining Specs
Comparison of Specs to Controls
Ways to improve
Future for Nanowires?
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48. Results: Control Comparisons
First Control is the Sensor Heading output
We Don’t 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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49. Results: Specs - Repeatability
Comprised of 5 readings taken at 0, 90, 180,270
Our Product: Min = Max =
Control: Min = Max =
Honeywell: Min = Max =
These are in degrees, as you can see ours is not the best, but do notice the min was much better than all others. This is due to the fact we have an inaccurate region that needs to be fixed still. As shown next…
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50. Results: Specs - Precision
This is for rotating 1 Deg for full 360, and graphed is the error in displayed amount moved
The error is due to roll over of the heading, 359-> 0 next and we are having problems with averaging 359 heading of some sensors and 0 from other sensors, this is easily fixable.
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51. Results: Specs - Accuracy
THe PMC is set to be with respect to true direction, the error in respected headings is graphed
The accraucy will be the worst of these errors.
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52. 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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53. 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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54. Conclusion Questions/ Comments? Thanks for your Attention and Time!
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