This document discusses sensors on Android devices. It covers an introduction to common sensors like accelerometers and gyroscopes, how sensors are used in Android applications, tips for developing sensor applications, and porting new sensors to Android. The presentation is divided into multiple parts covering the Android sensor framework, sensor hardware, developing and debugging sensor applications, and future directions for sensors on Android.

1. Sensors on Android
ChinmayVS @ DroidCON-2011

2. cvs@droidcon$ who am i
• Android >2yrs. Remember anyone?
• - sensors development. 10million+ units sold.
• Presently working @
PathPartnerTech.com
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3. Sensors on Android
PART1 : Introduction PART4: Sensor Application development.
• Sensors on Android Sample android app (code snippets)
• Famous sensor apps
• Sensors in Android apps PART5: App-dev Tips and tricks
• Sensor Hardware intro • Sensor callibration.
1. one-turn deserves another (axes-calib)
PART2 : Android Sensor Overview 2. zero-calib
• Overview • Sensor fusion (hard-way)
• Porting a new sensor onto Android • Invensense (easy-way)
• Kernel • Polling rate game/ui/fastest
• Sensor "HAL" • When to place Wakelocks
• When to register/unregister eventListener
PART3 : Porting tips and tricks
• No motion ≠ 0accel
• Accel axes 3step calibration
• Input devices & events (EV_ABS, EV_REL)
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4. “Sense-ors” on Android
A sensor (also called detector) is a device that measures
a physical quantity and converts it into a signal which can be read by
an observer or by an instrument.
1. ACCELEROMETER
2. GYROSCOPE
3. MAGNETIC_FIELD
REAL
4. LIGHT
5. PRESSURE
6. AMBIENT_TEMP
7. RELATIVE_HUMIDITY
8. PROXIMITY
VIRTUAL
9. LINEAR_ACCELERATION
10. GRAVITY
11. ROTATION_VECTOR
DEPRECEATED
12. TEMPERATURE
13. ORIENTATION
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5. “Famous” sensor apps
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6. Sensors in Android applications
• Use-cases of sensors in apps:
1. Active-Input
2. Passive-Input Application developer
3. Active-Passive
4. Auto-Rotate Android window manager
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7. Sensors in Android applications (1/4)
• Active input
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8. Sensors in Android applications (2/4)
• Passive input
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9. Sensors in Android applications (3/4)
• Active-passive
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10. Sensors in Android applications (4/4)
• Auto-rotate
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11. Sensor Hardware Intro (1/4)
• Accelerometer
+ ZERO drift
- Relatively slower response
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12. Sensor Hardware Intro (2/4)
• Gyroscope (MEMS)
+ Extremely quick response
- Gradual drift with time
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13. Sensor Hardware Intro (3/4)
• Compass (Magnetometer)
+ Obtain Yaw/Azimuth
+ Rotation with the device on a flat surface
- Picks-up surrounding magnetic noise
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14. Sensor Hardware Intro (4/4)
• Light & Proximity
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15. Android Sensors Frameworks Overview
Android App
• Use SensorManager & SensorEventListener C
O
Android Framework N D
• SensorService & SensorManager T A
R T
Android sensor “HAL” O A
L
• Links the Kernel-Drivers to the framework
Kernel Drivers
• Device drivers to control and gather data from the actual hardware.
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16. Porting a sensor onto Android
Q. My board has XYZ sensor. How do I get Android to recognise it?
 Kernel
 Device-driver
 Board File
 Userspace
 Adding New HAL
-OR-
 Modifying existing HAL
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17. Porting a sensor onto Android (kernel)
 Device-driver
 Poll/Interrupt? Hybrid-approach = Workqueues
 Early-suspend hook
 input_report_abs() / input_report_rel()
 Board File
 Interrupt, GPIO, SPI/I2C-lines
 Axes-remap to device axes platform_data
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18. Porting a sensor onto Android (kernel)
 Workqueues
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19. Porting a sensor onto Android (kernel)
 Early-Suspend hook
 Input Events
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20. Porting a sensor onto Android (userspace)
 Sensor-HAL
 Adding
– Reference Implementation : http://goo.gl/jjF3l
– Sensor-HAL implemented in : android/device/<vendor>/<device>/libsensors
– Generates library : system/lib/hw/sensors.<TARGET_BOARD_PLATFORM>.so
 Modifying
– Update sensors.cpp in sSensorList[]
– Derive a new sensor object, Include appropriate file
– Update i/p dev name in constructor
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21. Sensor Fusion
 Advantages
– Faster data samples
– Less noise in data samples
– More Accurate data samples
– Advanced Sensor data (Gestures, Glyphs, Shake-count, Step-count)
 Disadvantage
– Higher power consumption
 Implement inside App
– Register multiple sensor-listeners.
– Correlate-data.
 Implement using Custom-Library
– android/device/sample/frameworks/PlatformLibrary http://goo.gl/OI8sg
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22. Using Sensors in your app
SensorEvent http://goo.gl/hWOQu
SensorManager http://goo.gl/1DRUv
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23. App-dev Tips and tricks
 Sensor callibration.
1. one-turn deserves another (axes-calib)
2. zero-calib
 Sensor fusion
 Hard-way
 Easy-way (Invensense ) http://goo.gl/bHmDe
 Polling rate ui/normal/game/fastest?
 When to register/unregister eventListener
 When to place Wakelocks
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24. App-dev Tips and tricks
register sensorlistener
acquire wakelock
release wakelock
unregister sensorlistener
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25. What Next?
• Moving on…
– Sensor Framework on Android 4.0 (ICS)
– Sensor Drivers on Kernel 3.0
• Sensor-Fusion
– App / library
– Unified Kernel driver(sensors-class)
• Calorie-counter/Diet Advisor
“You spent 800calories since breakfast. Have a Greek-salad and a cup of milk…”
• Location-fix without GPS (using sensors  wink-wink)
http://goo.gl/ipbrL
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26. Thank You!!
Questions?
android-porting android-developers
android-kernel android-platform
CONTACT ME http://goo.gl/kKMOr
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