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

7

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

9

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

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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

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