High Resolution AMR Compass

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Dr. Andy PeczalskiProfessor Beth StadlerPat AlbersmanJeff AymondDan BeckvallMarcus EllsonPatrick Hermans

Agenda

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•Introduction/Abstract – Marcus E•MATLAB Simulations – Marcus E•Software – Pat H•Hardware – Jeff A•Testing – Pat A•Results – Dan B

Abstract

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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

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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.

Abstract

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Customized hardware is necessary to implement the multiple sensor system.

Customized software to manage the implementation is also necessary.

MATLAB

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• 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

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:

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

0 50 100 150 200 250 300 350 400-600

-400

-200

0

200

400

600ICs Binary Outputs

B Field Angle

ICs B

inary

Outp

uts

0 50 100 150 200 250 300 350 400-600

-400

-200

0

200

400

600ICs Binary Outputs

B Field Angle

ICs B

inary

Outp

uts

Orientation Simulations

• Single IC Senor Output Wave Form:

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

0 50 100 150 200 250 300 350 400-600

-400

-200

0

200

400

600ICs Binary Outputs

B Field Angle

ICs B

inary

Outp

uts

0 50 100 150 200 250 300 350 400-600

-400

-200

0

200

400

600ICs Binary Outputs

B Field Angle

ICs B

inary

Outp

uts

Software

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Three software realms involved with this project:

MATLABC

VB

C

• 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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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

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Personal Computer(VB)

PIC18F4520(C)

PMC Controller

Rot. Table

Sensors

Serial Serial

I2C

Parallel

Final Hardware

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• Abstract• Initial Design• Problems with Initial Design• Changes Made• Proposed Final Design

Abstract

• One compass, two boards– Main Board

• Microcontroller

– Daughter Board• Sensors

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Initial Design

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Main Board

Main Board

• Essentially a controller board– Microcontroller– RS-232 Communication– I2C Communication– Interfacing

• Daughter Board• Front Panel

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Initial Design

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Daughter Board

Daughter Board

• Three functional systems– Sensor array– Power MUX– Laser

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• Constraint: One of the dimensions must be less than 3.5” – Opening of zero-gauss chamber is 3.5” in diameter

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3.132”

Daughter BoardDimensions

• Constraint: One of the dimensions must be less than 3.5” – Opening of gauss-free chamber is 3.5” in diameter

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3.132”

0.73”

The Daughter Board meets size requirements

Daughter BoardDimensions

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GroundData

Clock

Power

Feedback Networks

Decoupling Capacitor

LED

Daughter BoardHMC6352

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Daughter BoardI2C Bus

Data

Clock

• 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?

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Daughter BoardPower MUX

Start Address [Ack] Command [Ack] Stop

• 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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Daughter BoardPower MUX

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

• We chose to multiplex power– Advantages

• Saves power• Simplifies troubleshooting

– Disadvantages• Signal loss through MUX• Other unknowns…

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Daughter BoardPower MUX

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 °)

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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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Changes to Initial Design

• Other changes– Main Board Layout

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Before After

Proposed Final Design

• Due to I2C bus issues, our current design does not work

• Two options1. Power all sensors and use burn-in or jumpers

socket to isolate sensors2. Multiplex I2C bus

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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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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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Proposed Final Design

• 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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Testing

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Prototype Final

Test Setup

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Accuracy

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Precision

RepeatabilityCompare

Compare

ß field

Compare

Prototype Testing

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•Given one sensor

•CCS compiler

Final Testing

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Elements of Final testing

•Pretesting (zero gauss values)

•Pretesting (offsets)

•Testing (accuracy, precision, repeatability)

Pre-testing (zero gauss)

1. Place sensors in the zero gauss chamber2. Rotate 360 deg. while taking readings3. Analyze data and get zero gauss values

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Pre-testing (offsets)

1. Place sensors in artificial magnetic field2. Run VB script that finds sensor locations

• Finds zero gauss value of each chip• Works using relativity• Bang bang control

3. Analyze data and find chip placements 4. Hardcode this to software

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Accuracy

Test Procedure1. 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

2. Take measurement 3. Compare result to actual4. Rotate to different position5. Repeat steps 2-5

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23 deg

113 deg

Results

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Results Comprise of:

•Determining Specs

•Comparison of Specs to Controls

•Ways to improve

•Future for Nanowires?

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 = +- 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

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•Questions/ Comments?

•Demo Upstairs?