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High Resolution AMR Compass

High Resolution AMR Compass. Advisor Dr. Andy Peczalski Advisor Professor Beth Stadler Pat Albersman Jeff Aymond Dan Beckvall Marcus Ellson Patrick Hermans. Honeywell. This project’s purpose is to improve the accuracy of a digital compass by using multiple compass IC’s.

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High Resolution AMR Compass

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  1. High Resolution AMR Compass Advisor Dr. Andy Peczalski Advisor Professor Beth Stadler Pat Albersman Jeff Aymond Dan Beckvall Marcus Ellson Patrick Hermans Honeywell

  2. 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. Abstract Honeywell

  3. 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/HMC105X.pdf

  4. Current Technology • Anisotropic Magnetoresistance • Wheatstone bridge Honeywell Images from http://phermans.com/w/images/9/9f/Appl_note_for_position_sensing.pdf

  5. 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 Honeywell

  6. What is the next step? • Nanowires • AMR sensing abilities • Decreased size • Decreased sensitivity Future Technology Honeywell Images from Prof. Beth Stadler

  7. 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 Project Description Honeywell

  8. 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. Project Description Honeywell

  9. Customized hardware is necessary to implement the multiple sensor system. Customized software will be required to manage the implementation. Project Description Honeywell

  10. Digital 2-axis compass • On board ADC • Modifiable sensing range • Speaks I2C • Small package • Improvable accuracy • Barber pole bridges Chosen IC: HMC 6352 Honeywell Image from http://phermans.com/w/images/9/9d/HMC6352.pdf

  11. Software & Algorithms • Firmware • MPLab & CCS Compiler Modeling & Simulations Matlab • User Interface • Visual Basic (VB) Honeywell

  12. Sensor Modeling • Goal: Parameters-> M-file -> Sensor Data • Consists of Many Sub-functions • Noise, Bridge, OpAmp, A2D • Needs to model real world situations Honeywell

  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 Honeywell

  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 Honeywell

  15. 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 Honeywell

  16. Orientation Simulations • Single IC Senor Output Wave Form: • Data Evenly Spaced • ICs at: 0, 9, 18, 27, 36, 45, 54, 63, 72, 81 Degrees Honeywell

  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 Honeywell

  18. Sensor Communication • Sensor Commands • Heading • Adjusted voltages • Raw voltages • Calibrate • Re-address • Number of Summed measurements Honeywell

  19. 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 Honeywell

  20. Weighted Averaging Honeywell

  21. Honeywell

  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 Honeywell

  23. Honeywell

  24. Visual Basic (VB) Interface Commands to perform repeatable data acquisition and benchmark tests. Honeywell

  25. Serial Serial Personal Computer (VB) PMC Controller PIC18F4520 (C) Rot. Table Parallel I2C Sensors Honeywell

  26. Hardware: Abstract • One compass, two boards • Main Board • Microcontroller • Daughter Board • Sensors Honeywell

  27. Hardware: Main Board • Essentially a controller board • Microcontroller • RS-232 Communication • I2C Communication • Interfacing • Daughter Board • Front Panel Honeywell

  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” 3.492” Honeywell

  29. Daughter Board I2C Bus Clock Data Honeywell

  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? Honeywell

  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 Honeywell Photo taken from http://www.locknest.com/newsite/products/qfn/index.htm

  32. Daughter Board Power MUX • We chose to multiplex power • Advantages • Saves power • Simplifies troubleshooting • Disadvantages • Signal loss through MUX • Other unknowns… Honeywell

  33. 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 3’s axes of sensitivity (27° and 117 °) Honeywell

  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 Honeywell

  35. Changes to Initial Design • Other changes • No laser mount • Laser mounted directly to plexi-glass case • Saves cost ($25) Honeywell

  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 Honeywell

  37. Testing • Prototype Final Honeywell

  38. Test Setup Honeywell

  39. Precision Accuracy Repeatability Compare Compare ß field Compare Honeywell

  40. Prototype Testing • Given one sensor • CCS compiler Honeywell

  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 Honeywell

  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. Honeywell

  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 Honeywell

  44. Raw voltage readings with offsets Honeywell

  45. Raw voltage readings with offsets Honeywell

  46. 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 Honeywell

  47. Results Comprise of: • Determining Specs • Comparison of Specs to Controls • Ways to improve • Future for Nanowires? Results Honeywell

  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 Honeywell

  49. 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 Honeywell

  50. Results: Specs - Precision Honeywell

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