Sensor’s InsidePresented by,Anando Kumar PaulSecure Link Services LTD.
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!!!
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 SignalProcesses data from the signal, for real-timemonitoring of a variety of parameters.
Sensors in Human BodyTaste Sight Touch Smell Hearing
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.
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.
Gyroscope in App• Leveler Application• Game consoles.• Apple iPhone 4 in 2010
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.
How Accelerometer Works• Uses piezoelectric effect.• Contain microscopic crystal structures.• Get stressed by accelerative forces.• Causes a voltage to be generated.
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
How Ambient Light Works• Made up of photocells which detect the presence of light in the environment.
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.
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
Magnetometer Application• Compass• Detect magnets• Force fields• Magnetic shield strength
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.
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
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)
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
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
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).
GPS Map Plot• Application uses these latitude, longitude and height value to plot the location in the map.