E0-245: ASP

Lecture 16+17: Physical Sensors

Dipanjan Gope

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• Location Sensors - Theory of location sensing

- Package android.location

• Physical Sensors - Sensor Manager

- Accelerometer

- Gyroscope

- Magnetometer

- Sensor fusion

• Multimedia - Camera

- Microphone

• NFC

Module 2: Android Sensor Applications

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Activity

Views

Intent

ContentProvider

BroadcastReceiver

Service

Coverage

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• Greg Milette, Adam Stroud: Professional Android Sensor Programing, 2012, Wiley India

References

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Popular Apps with Physical Sensors

MAGNETOMETER APPS

GYROSCOPE GAMING ACCELEROMETER FITNESS

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Classification based on source of data

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Raw Sensor Data

http://developer.android.com/guide/topics/sensors/sensors_overview.html

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Raw Sensor Data

http://developer.android.com/guide/topics/sensors/sensors_overview.html

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Synthetic Sensor Data

http://developer.android.com/guide/topics/sensors/sensors_overview.html

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Classification based on application

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• Motion - Accelerometer

- Gyroscope

- Linear acceleration

- Gravity

• Position - Magnetic field

- Proximity

- Rotation vector

• Environment - Light

- Barometer

- Ambient temperature

- Relative humidity

Physical Sensors

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Smart Watches Today

https://www.google.co.in/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http%3A%2F%2Fwww.slideshare.net%2FLeybzon%2Fapple-iwatch-android-wear-and-other-wristbased-sensor-platforms&ei=J-EQVe6sDNWdugS84oGwBg&psig=AFQjCNFwN3VY9DQjg7lYqPiWdZqxh0qR8A&ust=1427255772724923

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Sensor Hardware

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Accelerometer

F=mA MEMS Capacitive-based SIP

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/DM00037200.pdf

https://www.youtube.com/watch?v=i2U49usFo10

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Gyroscope

F=-2m Ω x v MEMS Capacitive based SIP

Ref: MEMS gyroscopes - A revolutionary way to interface with the real world, STMicroelectronics

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Magnetic Field

Anonymous, 400BC

http://en.wikipedia.org/wiki/Hall_effect

Lorentz Force

Asahi Kasei: AK8975C Others: Anisotropic Magneto Resistance

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Android Sensor Data Structures

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Class:

• SensorManager

• Sensor

• SensorEvent

Interface:

• SensorEventListener

Android.hardware

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Package: Android.location

LocationManager

LocationProvider LocationListener

Location

Criteria

Enables Notifies with location data

Produces Consumed

Reads LocationProvider Requirements

Greg Milette, Adam Stroud: Professional Android Sensor Programing, 2012, Wiley India

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Package: Android.hardware

SensorManager

Sensor SensorEventListener

SensorEvent

Produces Consumed

Specifies

Event Values

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<uses-feature android:name="android.hardware.sensor.accelerometer"

android:required="true" />

<uses-feature android:name="android.hardware.sensor.compass"

android:required="false" />

Manifest File

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• android.hardware.sensor.accelerometer

• android.hardware.sensor.gyroscope

• android.hardware.sensor.compass

• android.hardware.sensor.barometer

• android.hardware.sensor.light

• android.hardware.sensor.proximity

Manifest File

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• private SensorManager sensorManager;

• sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);

• List<Sensor> sensors = sensorManager.getSensorList(Sensor.TYPE_****);

• Sensor = sensorManager.getDefaultSensor(Sensor.TYPE_***);

SensorManager

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• Maximum range

• Minimum delay

• Name

• Power

• Resolution

• Type

• Vendor

• Version

Sensor Class

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• Accuracy - SENSOR_STATUS_ACCURACY_HIGH

- SENSOR_STATUS_ACCURACY_MEDIUM

- SENSOR_STATUS_ACCURACY_LOW

- SENSOR_STATUS_ACCURACY_UNRELIABLE

• Sensor

• Timestamp

• Values

SensorEvent

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• onAccuracyChanged

- when the accuracy from the sensor changes

• onSensorChanged

- when the values from the sensor changes

SensorEventListener

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Sensor Data Reference

http://developer.android.com/guide/topics/sensors/sensors_overview.html

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Lets Code …

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1. Determine Available Sensors

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• Move from one screen (activity) to another

• Can also open other applications

• 3 main: start an activity/service/broadcast

• Asynchronous

• Bound at run-time

• Explicit or implicit

Building Block: Intent

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Implicit Intent

http://developer.android.com/guide/components/intents-filters.html

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• Primitive

Passing Data: Extras

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• Persistent Objects

Passing Data: Application

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2. Determine Sensor Range and Resolution

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• Acceleration: m/s2

• Gyroscope: Deg/s or Rad/s

• Magnetic Field: uT

• Min Delay: us

• Power: mA

Units

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• SENSOR_DELAY_FASTEST 0ms

• SENSOR_DELAY_GAME 20ms

• SENSOR_DELAY_UI 67ms

• SENSOR_DELAY_NORMAL 200ms

3. Define Sensor Rate

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Sensor Results Display

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4. Register/Unregister SensorListeners

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Signal Processing and Sensor Fusion

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Accuracy and Precision

Greg Milette, Adam Stroud: Professional Android Sensor Programing, 2012, Wiley India

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• Noise

• Drift

Type of Error

Accelerometer Drift

Paul Lawitski, Sensor fusion

Gyroscope Drift

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• Low-pass filter

Filtering

• High-pass filter to filter noise in gravity

• Kalman filter

- systems dynamic model and constraints

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Sensor Fusion

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Acceleration in Earth’s axis

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Activity

Views

Intent

ContentProvider

BroadcastReceiver

Service

Coverage