1. High Resolution AMR Compass
Dr. Andy Peczalski
Professor Beth Stadler
Pat Albersman
Jeff Aymond
Dan Beckvall
Marcus Ellson
Patrick Hermans
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2. Agenda Introduction/Abstract – Marcus E MATLAB Simulations – Marcus E
Software – Pat H
Hardware – Jeff A
Testing – Pat A
Results – Dan B
Will just go down the line
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3. 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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4. Increased precision and repeatability is also desired.
Abstract
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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5. Customized software to manage the implementation is also necessary.
Abstract
Customized hardware is necessary to implement the multiple sensor system.
Customized software to manage the implementation is also necessary.
Hardware to be discussed later.
Software to be discussed later as well.
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6. MATLAB
Used to simulate single and multiple sensors before our hardware was complete
Provided a vehicle to test the performance of our heading calculation algorithms
1702 lines of MATLAB simulations
Image from mathworks
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7. 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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8. 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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9. 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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10. MATLAB C VB Software Three software realms involved with this project:
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11. C Written in MPLab CCS complier Run on PIC 18f4550 1326 Lines of C
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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12. 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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13. 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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14. Honeywell

15. Honeywell

16. Weighted Averaging Honeywell Baud of 115200 from the 20Mhz crystal
Image from wikipedia
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17. Baud of 115200 from the 20Mhz crystal
Image from wikipedia
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18. VB Provides an end-user interface
Synchronizes the compass and the rotation table
Allows for automated data acquisition
Provides a repeatable test benching system
Requires a third board to handle adjusted ground on PMC
4733 Lines
Done by dan
Pmc interface voltage problem
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19. Done by dan
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20. Done by dan
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21. Honeywell Serial Serial Personal Computer (VB) PMC Controller
PIC18F4520
(C)
Rot. Table
Parallel
Sensors
I2C
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22. Final Hardware Abstract Initial Design Problems with Initial Design
Changes Made
Proposed Final Design
First look at high level overview of HW
Brief look at our initial design
Describe what problems we ran into with the hardware
Talk about changes made
Give a proposed final design
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23. 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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24. Initial Design
Main Board
This is what MB looks like
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25. Main Board Essentially a controller board Microcontroller
RS-232 Communication
I2C Communication
Interfacing
Daughter Board
Front Panel
Features
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26. Initial Design
Daughter Board
This is what DB looks like
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27. Daughter Board Three functional systems Sensor array Power MUX Laser
Features
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28. Daughter Board Dimensions
Constraint: One of the dimensions must be less than 3.5”
Opening of zero-gauss chamber is 3.5” in diameter
3.132”
Zero Gauss Chamber provided by Honeywell
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3.492”

29. The Daughter Board meets size requirements
Dimensions
Constraint: One of the dimensions must be less than 3.5”
Opening of gauss-free chamber is 3.5” in diameter
0.73”
Laser mount height is 0.73”
3.132”
The Daughter Board meets size requirements
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30. Daughter Board HMC6352 Honeywell Feedback Networks Power LED Clock
Look at HMC6352
Ground
Data
Decoupling Capacitor
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31. Daughter Board
I2C Bus
Clock
Data
I2C bus
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32. 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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33. 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

34. 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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35. 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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36. 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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37. Changes to Initial Design
Other changes
No laser mount
Laser mounted directly to plexi-glass case
Saves cost ($25)
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38. Changes to Initial Design
Other changes
Main Board Layout
Before
After
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39. 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
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40. Proposed Final Design
Option 1: Power all sensors and use socket/jumpers
Advantages
No MUX needed
Reduces surface area of board
Reduces signal loss of MUX
Sleep mode on sensors
Save power
I2C bus has not been tested in this mode
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41. Proposed Final Design
Option 1: Power all sensors and use socket/jumpers
Disadvantages
Sockets can be expensive
Footprint of HMC6352 is not common
Hard to find socket
No disadvantages if we add jumpers
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42. Proposed Final Design Advantages Disadvantages
Option 2: Multiplex I2C bus
Advantages
No need for a socket
Sleep mode to save power (not tested)
Disadvantages
Side effects of multiplexing I2C unknown
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43. Testing
Prototype Final
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44. Test Setup
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45. 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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46. Prototype Testing
Given one sensor
CCS compiler
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47. Final Testing Elements of Final testing Pretesting (zero gauss values)
Pretesting (offsets)
Testing (accuracy, precision, repeatability)
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48. Pre-testing (zero gauss)
Place sensors in the zero gauss chamber
Rotate 360 deg. while taking readings
Analyze data and get zero gauss values
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49. Pre-testing (offsets)
Place sensors in artificial magnetic field
Run VB script that finds sensor locations
Finds zero gauss value of each chip
Works using relativity
Bang bang control
Analyze data and find chip placements
Hardcode this to software
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50. Raw voltage readings with offsets
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51. Raw voltage readings with offsets
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52. 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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53. Results Results Comprise of: Determining Specs
Comparison of Specs to Controls
Ways to improve
Future for Nanowires?
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54. Results: Specs - Repeatability
Comprised of 5 readings taken at 0, 90, 180,270
Our Product: Min = Max =
Control: Min = Max =
Honeywell = Max =
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55. Results: Specs - Precision
This is for rotating 1 Deg for full 360, and graphed is the error in displayed amount moved
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56. 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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57. 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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58. 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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59. Conclusion
Questions/ Comments?
Demo Upstairs?
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