Digital GyroscopesBrian Margosian Connor Donker
Nick Tountasakis
Tuesday, November 5th, 2013
https://learn.sparkfun.com/tutorials/gyroscope
Agenda
What is a gyroscope? Why are they useful? Project usage Error compensation Types of gyroscopes / interfacing Question / Answer
1
What is a Gyroscope?
Device used to measure rotational velocity
https://learn.sparkfun.com/tutorials/accelerometer-basics/all
2
Mechanical Gyro Spinning wheel with fixed axle
Mounted in 2 or 3 gimbals to allow rotation
Resists external torque
http://en.wikipedia.org/wiki/File:Gyroscope_operation.gifDetailed explanation of the physics involved in a mechanical gyroscope can be found at.. http://www.real-world-physics-problems.com/gyroscope-physics.html
3
MEMS Gyro
Small oscillating mass http://sensorwiki.org/doku.php/sensors/gyroscope
Low-current electric signals produced
One mass per axis
Utilize Coriolis force
4http://electroiq.com/blog/2010/11/introduction-to-mems-gyroscopes/
MEMS Gyro Cont.
5
http://sensorwiki.org/doku.php/sensors/gyroscope
Why are they useful?
Measure angular velocity Projects
Aviation Stability control Image on spinning disc Motion detection
6
http://www.eecs.umich.edu
Sources of ErrorGyro Drift:
Defined as gyro at resting state producing non-zero values
Drift seen at all rotational velocities, on all axes
Caused by heating up of gyroscope during operation
Unsteady input power source voltages contributes
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Visualization of Gyro Drift
http://nxttime.wordpress.com/category/sensors/gyro-sensor/
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How to CompensateMultiple Options:
More expensive (+$5 - $10) premium on-chip temperature compensation
Wait until sensor reaches maximum temperature, calculate offset Drift not exactly constant, high accuracy requires moving
average calculation
Run gyroscope off of quality power supply Can get by with batteries and voltage regulator
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Gyros vs. Accelerometers
GyroscopesRotational motion
AccelerometersLinear motion
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https://learn.sparkfun.com/tutorials/accelerometer-basics/all https://learn.sparkfun.com/tutorials/accelerometer-basics/all
Gyros vs. Accelerometers cont.Gyros: Integrate rotational velocity to determine angular displacement Susceptible to gyro drift More resistant to external noise than accelerometers
Accelerometers: Integrate linear acceleration to determine linear displacement Measures linear motion with inertial resistive forces Must continually compensate for gravity
IMU (Inertial Measurement Unit) - combination plus magnetometer
Detailed explanation how to combine data to determine full orientation:http://www.instructables.com/id/Accelerometer-Gyro-Tutorial/#step1
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So you want to add a gyroscope?
Range Interface Number of axes Power Bonus features
Interrupts Temperature sensing Internal LPF
https://www.sparkfun.com/products/9446
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Device comparisonDevice Range Interface Price Axes Power Bonus Features
LPY503AL 30/s (4x output) or 120/s
Analog $30 2 2.7-3.6V6.8mA or1-5uA
Self-test, power-down, 1x and 4x outputs
L3G4200D 250/s, 500/s or 2000/s
SPI and I2C
$50 3 2.4-3.6V6.1mA or5uA
Power-down and sleep mode, temperature sensor, High shock survivability
ITG-3200 2000/s I2C $20 3 2.1-3.6V6.5mA or5uA
Programmable low pass filter, optional external clock input for better clock accuracy, 1 interrupt output, temperature sensor
Images and data courtsey of sparkfun.com 13
Analog Interfacing
Analog Gyro
Z axis ADC
X axis ADC
Y axis ADC Microcontroller
Pros:CheaperEasier to interpret dataPrecision
Cons:More partsMore pin usage (dependant on ADCs)Often higher power
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Digital Interfacing
Digital Gyro Microcontroller
Pros:Smaller packageLess power use (fewer running components)Fewer pins
Cons:Often marginally more expensiveCan be harder to interface
X axis ADCY axis ADCZ axis ADC
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Sample I2C Transaction
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X data Y data Z data
0x28
0x2A 0x2B 0x2C 0x2D0x290x28L L LH H H
Sample I2C Transaction
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X data Y data Z data
0x28
0x2A 0x2B 0x2C 0x2D0x290x28L L LH H H
Sample I2C Transaction
16
X data Y data Z data
0x28
0x2A 0x2B 0x2C 0x2D0x290x28L L LH H H
Sample I2C Transaction
16
X data Y data Z data
0x28
0x2A 0x2B 0x2C 0x2D0x290x28L L LH H H
Sample I2C Transaction
16
X data Y data Z data
0x28
0x2A 0x2B 0x2C 0x2D0x290x28L L LH H H
Sample I2C Transaction
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X data Y data Z data
0x28
0x2A 0x2B 0x2C 0x2D0x290x28L L LH H H
IMUs
http://www.pololu.com/product/1268/
Gyro, accelerometer, magnetometer on board
Always digital Degrees of freedom Some come with onboard
processors Can be pricey ($50-$125)
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Summary
Gyroscope basics What is a gyro? Mechanical vs MEMS
Uses of Gyroscopes in projects Gyro drawbacks
Gyro drift Compensation
Interfacing Analog Digital
18Image from: http://www.eeherald.com/section/design-guide/mems_application.html
But wait, theres more! (References)High-level gyro usage/description:https://learn.sparkfun.com/tutorials/gyroscope
Low-level description of MEMS Gyro:http://en.wikipedia.org/wiki/Vibrating_structure_gyroscope#MEMS_gyroscope
Explanation of gyro drift and how to compensate:http://nxttime.wordpress.com/category/sensors/gyro-sensor/
Detailed explanation how to combine data to determine full orientation:http://www.instructables.com/id/Accelerometer-Gyro-Tutorial/#step1
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Digital GyroscopesBrian Margosian Connor Donker
Nick Tountasakis
Tuseday, November 5th, 2013
https://learn.sparkfun.com/tutorials/gyroscope
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