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Accelerometers Unveiled!!

Aren’t you surprised seeing smartphone users spending more time on the applications these phones afford rather than talking on these devices. Reason being the Smartphones come with so many applications which extend their features and functionalities. With the advent of iPhone, Apple introduced a catchy feature known as Accelerometer.  Today you can find this feature in variety of Motorola, Samsung and LG phones. Naming a few Omnia, Wave, Galaxy S, Nexus, etc.

So What the heck is an accelerometer?

Today many smartphone users have become powerusers. Many smartphone companies give away free SDK’s. Technically speaking smartphones have become small PC for which you can develop your own application and even commercialize it  if you want to make money out of it.

Coming back to the topic: The accelerometer is a feature in smart phones which makes it possible to rotate the display (in a very vague term) of the phone when you rotate the phone from portrait to landscape and from landscape to portrait. This means if you hold your phone in a normal position just as you hold other phones, the display it takes is portrait. It adjusts to landscape when the phone is rotated. In iPhone iTouch accelerometer makes possible better display and control in playing games, better readability and viewing angle during reading,
listening to music, watching videos etc. These applications are developed in a way that they make use of the accelerometer for giving better experience to the users. The accelerometer is vastly leveraged by game applications. The wide screen not only gives a larger display for enhanced gaming experience but also afford more control touch buttons which intensifies a player’s involvement in the game.

Technical Aspects

An accelerometer is nothing but a Gyroscope:
“A device for measuring or maintaining orientation, based on the principles of conservation of angular momentum.” Wow!! that was some pure physics definition.

Anyways in layman term: “It is used for measuring or maintaining orientation, which is the exact reason an iPhone contains one of these gizmos.”

Since a mechanical gyroscope makes smartphones bulky, electronic gyroscopes are used. In particular the iPhone utilizes a microscopic, electronic version of a vibrational gyroscope, also called a MEMS gyroscope.
A basic MEMS device consists of an ASIC (application-specific integrated circuit) and a micro-machined silicon sensor. The type AGD1 2022 FP6AQ (Topmost picture) chip found in the iPhone 4 is a MEMS gyroscope designed by STMicroelectronics which is similar to their L3G4200D gyroscope.

Anatomy of GK10A MEMS Die

The GK10A is comprised of a plate, called the “proof mass,” that vibrates (oscillates) when a drive signal is applied to set of drive capacitor plates. When a user rotates the phone, the proof mass gets displaced in the X,  Y, and Z directions by Coriolis forces (the Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating reference frame).

The ASIC processor then senses the proof mass’ displacement through capacitor plates located underneath the proof mass, as well as finger capacitors at the edges of the package. The V654A type ASIC die converts the tiny capacitive signals from the GK10A MEMS die into a digital signal which is fed into the iPhone Hardware interface. This data is used accordingly for iPhone applications such as to turn the steering wheel of a car or to aim a gun in games.
In terms of mechanics, the sensitivity of MEMS gyroscopes is usually in mV/dps (or degrees per second), so the output of the oscillator (in mV) divided by the sensitivity (mV/dps) provides the angular rate applied to the package, in degrees per second.

Some pictures of MEMS Micro-Structures

Complete Article at iFixit


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