1. Sensor’s Inside
Presented by,
Anando Kumar Paul
Secure Link Services LTD.

2. Motivation
• A common topic for ALL.
• Layman knowledgebase.
• Gains basic idea to develop
smartphone sensor based apps.
• Nothing to loose if we don’t know,
but it’s wow to know!!!

3. Sensor
• A device that measures a signal and processes
data from the signal, for real-time monitoring of a
variety of parameters.
That measures
A device
Signal
Processes data from the signal, for real-time
monitoring of a variety of parameters.

4. Sensors in Human Body
Taste
Sight Touch
Smell
Hearing

5. Sensor’s in Smartphone
Mic
Camera
Touch Screen

6. Similarity

7. Sensor’s in Smartphone
Accelerometer GPS
Proximity
Gyroscope
Ambient Light
Magnetometer

8. Gyroscope
• Detects the current orientation of the device,
or changes in the orientation
• The rotational, spinning, turning velocity in each axis.
• Measures the angular rate of how quickly the object turns.

9. How Gyroscope Works
• Also known as vibrating structure gyroscope.
• A vibrating mass is placed in the center of the chip.
• Whenever an electrical signal goes through it, mass will be
vibrated.
• Moving the phone will cause the changes of electrical signals.
• The sensors will send instructions to software.

10. Gyroscope in App
• Leveler Application
• Game consoles.
• Apple iPhone 4 in 2010

11. Accelerometer
• Measure acceleration forces.
• Static force
• Gravity pulling at your feet.
• Can find out the angle the device is tilted at with respect to the earth.
• Dynamic force
• By moving or vibrating the accelerometer.
• Can analyze the way the device is moving.
• Application
• Driving uphill or going to fall over or flying horizontally.
• Protect hard drives or deploying airbags during car crashes
• Acceleration is also measured on 3 axes.

12. How Accelerometer Works
• Uses piezoelectric effect.
• Contain microscopic crystal structures.
• Get stressed by accelerative forces.
• Causes a voltage to be generated.

13. Gyroscope Vs Accelerometer

14. Ambient Light
• Sensor, that can detect strength of light exposed.
• Used to adjust a display’s backlight.
• Improves user experience and power savings
• Brightness hence saving the battery power.
• Best-in-class
• Ultra low light sensitivity
• Low power consumption
• Ideal spectral response
• Easy to use simple output algorithm

15. How Ambient Light Works
• Made up of photocells which detect the presence of light in the
environment.

16. Proximity
• Detects how close the screen of the phone
is to your body or any object.
• Measures the distance between the phone and face
• Sense when you have brought the phone up to your ear.
• Display turns off in order to save battery.
• Deactivate touch sensor to avoid unwanted input.

17. How Proximity Works

18. Magnetometer
• Measure the
• strength and
• direction
of magnetic fields.
• Absence of strong local fields, this will measure the ambient
magnetic field of the Earth, which turns it to a digital compass.
• Determine the angle by which the device is rotated
relative to the Earth’s magnetic north pole.
• Smartphone provide raw magnetometer data and
a computed compass bearing

19. Magnetometer Application
• Compass
• Detect magnets
• Force fields
• Magnetic shield strength

20. Location Sensor
• GPS
• Triangulation of
• cell towers
• Wi-Fi networks
• Location of associated
• cell tower
• Wi-Fi network
• Challenges in Determining User Location
• Multitude of location sources
• User movement
• Varying accuracy
• Smartphone can try to automatically select the best suited
alternative location provider.

21. Steps to Detect Location
• Start application.
• Sometime later, start listening for updates from desired location
providers.
• Maintain a "current best estimate" of location by filtering out
new, but less accurate fixes.
• Stop listening for location updates.
• Take advantage of the last best location estimate.
Source: http://developer.android.com/guide/topics/location/strategies.html

22. GPS Info
• Space Segment
• GPS satellites.
• Control Segment
• Tracking stations located around the world.
• User Segment
• GPS receivers and the user community.
• Precise Positioning Service (PPS)
• Authorized users with cryptographic equipment and keys.
• Standard Positioning Service (SPS)
• Civil users worldwide use the SPS without charge.
• GPS Satellite Signals
• SVs transmit two microwave carrier signals.L1(SPS), L2(PPS)

23. GPS Satellites
• Department of Defense in 1973
• Designed to assist soldiers and military vehicles, planes, and
ships in accurately determining their locations world-wide.
24 satellites 30 total – 6 spares
Travels 20,000 km in 12 hours
Six groups of four.
Source: http://scign.jpl.nasa.gov/learn/gps2.htm

24. How GPS works
• GPS Signal consists
• Status of the transmitting satellite
• Clock / time data
• Almanac data - data to predict nearby satellites.
• Ephemeris data - calculate the location of the satellite
• Connection to
• 3 satellites is required for 2D fix (latitude / longitude)
• 4 satellites for 3D fix (altitude).
• More visible satellites increase precision of positioning

25. How GPS Receiver works
Satellite continually transmits messages using radio signals
• Time
• Satellite position
• Receiver receives the message
• Determine the transit time of each message
• Computes the distance to each satellite using the speed of light
Satellites' locations define a sphere
using each of these distances
Determine the receivers' positions (latitude, longitude, height).

26. GPS Map Plot
• Application uses these latitude, longitude and
height value to plot the location in the map.

27. Thank you