Sensitiveness

27 12 2013

If you are a proud owner of an iPhone you have purchased a device which is in someway much more sensitive than any human being ever can be. And it’s not the incredible SIRI I’m talking about. iPhone’s sensors know all about your movements, your finger, the distance between your ear and the device, your actual location, and even the brightness of the environment.
Your iPhone forms a liaison with you but it’s an arranged marriage, it’s a childless marriage, it’s a miscegenation, and Apple hopes that it will not get a broken marriage. And if you are an Apple freak it’s even a same-sex marriage.

The sensors …

Kinetic sensors enable the iPod touch, iPad, or iPhone’s screen to automatically switch from landscape to portrait modes and back again based on whether you’re holding the phone up and down or sideways.
The iPhone 4, 4th gen iPod touch, and iPad 2 adds another sensor: a three-axis gyroscope. When combining the gyroscope with the accelerometer, this gives these devices six axes on which it can operate. This is designed to make them more sensitive, responsive, and powerful for gaming.

Accelerometer

The accelerometer sensor measures linear acceleration along three perpendicular axes, X, Y and Z. The following schematic drawing illustrates the classical single axis mechanical accelerometer which uses a moving mass and springs. The movement of the mass along the double sided arrow measures the acceleration along that axis.
All iPhone, iPod Touch and iPad devices are equipped with a modern accelerometer that can measure acceleration in three perpendicular axes. The measurement also includes the Earth’s gravity.
Modern accelerometers utilize MEMS technology in a tiny electronic package.

Notes


Microelectromechanical systems (MEMS) is the technology of very small devices; it merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are made up of components between 1 to 100 micrometers in size (i.e. 0.001 to 0.1 mm), and MEMS devices generally range in size from 20 micrometers (20 millionths of a meter) to a millimeter (i.e. 0.02 to 1.0 mm). They usually consist of a central unit that processes data (the microprocessor) and several components that interact with the surroundings such as micro sensors.

Acceleration is the rate at which the velocity of an object changes with time. Rotations are always accelerations because the direction of the velocity changes. If an object falls down because of gravity it’s an acceleration where the velocity increases but the direction remains the same.

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Gyroscope

The gyroscope sensor measures rotational velocity along the Roll, Pitch and Yaw axes. It depends on the property of rotating mass as illustrated in the following schematic drawing of the classical mechanical gyroscope.
Like the accelerometer, gyroscope sensors for mobile devices utilize MEMS technology and may include an accelerometer.

Magnetometer

The magnetometer detects the Earth’s magnetic field along three perpendicular axes. In addition to general rotational information, the magnetometer is crucial for detecting the orientation of the device relative to the Earth’s magnetic north. Electrical appliances that generate magnetic fields disturb the magnetometer.

Linear Acceleration

The linear acceleration sensor measures the acceleration effect of the device movement, excluding the effect of Earth’s gravity on the device. It is a part of the Device-Motion information computed by the iPhone operating system from the main sensors, particularly from the accelerometer and the gyroscope.

Gravity

The gravity sensor measures the Earth’s gravity effect on the device. When the device is placed on a flat surface facing up, all of Earth’s gravity appears on the -Z axis. Tilting the device “spreads” the gravity into the X and Y axes.
The gravity sensor is a part of the Device-Motion information computed by the iPhone Operating System from the main sensors, particularly from the accelerometer and the gyroscope.
Gravity is obtained when the linear acceleration data is subtracted from the raw readings of the accelerometer.

You can compare the gravity sensor and the accelerometer as follows. Hold the device face up and make “up and down” movements. The accelerometer’s raw readings will show Earth’s gravity plus variation on the Z axis due to the movement. The gravity sensor reading will show constant Earth gravity along the Z axis regardless of the movements.

Attitude

The Attitude (rotation) sensor provides the pitch, roll and yaw (azimuth) angles of the device relative to the normal horizon.

Pitch
rotation around the Y-axis (bottom-up)
Roll
rotation Round the X-axis (left-right)
Yaw
rotation around the Z-axis which is perpendicular to the touch screen

It is a part of the Device-Motion information computed by the iPhone Operating System from the main sensors, particularly the gyroscope.
Although the gyroscope provides precise measurements of the angular rates, calculating rotations only from the gyroscope are subject to a noticeable drift due to various inherent physical phenomena like gyro precession. The Device-Motion computation automatically uses measurements from the accelerometer to minimize the drift.

Other sensors …

Proximity

This sensor can determine how close the iPhone is to your face. This sensor is what helps the iPhone turn off its screen automatically whenever you hold the phone up to your ear. This is necessary to prevent accidental button clicks by the side of your head when talking. This sensor is only on the iPhone (since the other devices don’t need it).

Ambient Light

This sensor can determine how much light is available in the area surrounding the iPhone, iPod touch, and iPad and automatically adjust the brightness of the screen in order to conserve battery life.

Moisture

The devices also contains a sensor which isn’t related to the interface. The water sensor is a little red tab that appears in the dock connector when the phone has been submerged in water. It can also appear as a red dot in the headphone jack.

Water damage is a common problem with cell phones that can cause a significant drop in value, and can often void any warranties you may have. Most mobile phones, including the iPhone, have some sort of water damage indicator.

The 4S has indicators both in the headphone jack, and on the bottom of the dock-connector housing. The new iPhone 5 features one water damage indicator on the inside of the nano SIM card slot.

The best way to look at the indicator is by aiming a flashlight or lighted magnifying glass into the jack. If the iPhone has been submerged in liquid, or has liquid damage, this circular indicator would be triggered and colored red or pink. If the indicator has been triggered, the repair is most likely not covered by the warranty.

NOTE
What to do if your iPhone gets wet …

Immediately turn off the phone. Do not turn it back on, charge it, or connect it to a computer or other device.
Second, hand dry your phone as best you can with a soft cloth. Remove your SIM card and pat down any excess moisture and wipe out the headphone and charge ports.
Next, quickly place the phone in a bag of uncooked rice and let it sit for 48 hours in a dry place. You can also add silica packages to the rice to help the absorption process. The rice will absorb any moisture that remains in the phone.
After 48 hours have passed remove your phone, re-insert the SIM, and try turning it back on. With a little bit of luck you may have saved your iPhone from a watery fate.

Touch Screen

This is doubtlessly the most important sensor of your device. It should work fast, precise, and even if there are fat deposits.

The iPhone’s processor and operating system interpret the input from the touch screen. The capacitive material sends raw touch-location data to the iPhone’s processor. The processor uses software to interpret the raw data as commands and gestures.

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Here’s what happens:

In the nanosecond between the time you touch the iPhone’s screen and the display reacts, several calculations and signals are sent from the touch screen to the software.

  • 1 Signals travel from the touch screen to the processor as electrical impulses.
  • 2 The processor uses software to analyze the data and determine the features of each touch. This includes size, shape, and location of the affected area on the screen. If necessary, the processor arranges touches with similar features into groups. If you move your finger, the processor calculates the difference between the starting and ending point of your touch.
  • 3 The processor uses its gesture-interpretation software to determine which gesture you made. It combines your physical movement with information about which application you were using and what the application was doing when you touched the screen.
  • 4 The processor relays your instructions to the program in use. If necessary, it also sends commands to the iPhone’s screen (e.g. when pinch-to-zoom is registered) and other hardware components. If the raw data doesn’t match any applicable gestures or commands, the iPhone disregards it as an extraneous touch.

All these steps happen in a nanosecond and you see changes in the screen based on your input almost instantly. This process allows you to access and use all of the iPhone’s applications with your fingers.

The M7 motion processor …

With the release of the iPhone 5S Apple implemented an additional processor, the A7 motion processor.

The M7 is an ARM Cortex-M3 part from NXP running at 180 MHz. The chip allows for low-power collection of motion data drawn from a Bosch Sensortec accelerometer, an STMicroelectronics gyroscope, and an AKM magnetometer.
After collecting information from the accelerometer, gyroscope, and magnetometer, the M7 performs some matrix math processing magic to produce an absolute orientation of the phone relative to the world. This data is then passed to the A7 in a neat package, probably in the form of three headings (roll, pitch, and yaw).

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Using the A7 main processor to monitor this sort of data would be mega-stress, so the M7 was introduced to maintain a constant, low-power watch over these sensors even if the device is asleep.

The M7 is accessible to applications through the Core Motion API in iOS 7, so it will, for example, allow fitness apps that track physical activity and access data from the M7 without constantly engaging the main A7 CPU. It will enable applications to be aware of what type of movement the user is experiencing, such as driving, walking, running or sleeping. Another application could be the ability to do indoor tracking and mapping.

All sensors …

This mind map shows you all sensors implemented in the iPhone 5S.

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The app Sensor Kinetics …

Sensor Kinetics is an advanced viewer and monitor for all the sensors available in your iPhone, iPad, or iPod Touch device. Written by Dr. David Y. Feinstein, one of the pioneers in the use of accelerometers and gyroscopes within the modern smartphone, the app provides a comprehensive view of the total dynamics of the device’s sensors.

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Sensor Kinetics interacts with the six sensors relating to movement in your device: the Accelerometer, the Gyroscope, the Magnetometer, the Linear Acceleration Sensor, the Gravity Sensor and the Attitude Sensor.
When first activated, Sensor Kinetics: shows you which sensors are available on your device. The main screen captures data from all the sensors and employs graphical windows to illustrate the sensor’s operation.

Summary …

Keep in mind that all these incredible micro machines won’t help you if you have to explain your wife that you again forget her birthday. And don’t try to explain your own failure with a failure of one of the sensors of your iPhone. If she reads this blog she will call you a brazen-faced liar because Apple’s Reminder app doesn’t use any sensor (except you used the option ‘Remind me at a location’). It’s just your brain which was buggy.

Note
Some sensor descriptions are taken from the app Sensor Kinetics.

Thanks for surfing by.


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