The secrets under the iPhone’s multi-touch screen

12 05 2010

When talking about new technology and advancement with smart phones, it is easy to see how far they have progressed over the years. They are smaller, look better, and most importantly, they function better (specifically the iPhone).  The iPhone’s touch screen is one of the reasons why the it prevails over the rest of the competition.  The iPhone features a multi-touch screen which allows the user to control the phone with more than one finger (functions such as pinching to zoom in or out, greater functionality in games, etc.).  Unlike all other smart-phones, the iPhone’s touch screen utilizes technology that monitors changes in electrical current, instead of pressure upon the screen, which allows a much more sensitive and accurate response for the user.  Putting multi-touch and electrical current monitoring in one device leads to results that leap over the competition. [1]  If you own an iPhone, then you know how smooth and responsive the screen acts, but have you ever taken the time to think about how this revolutionary screen works? Neither have I, until now.

Basic touchscreens

Most current phones that feature a touchscreen use a different, and less advanced technology than the iPhone.  Some use pressure sensitive touchscreens, which do not allow more than one touch at a time.  Others monitor changes in the reflection of waves, which could be sound waves or beams of light. [2] A few systems measure changes in vibration caused when your finger touches the screen.  Some even use cameras that monitor changes in light.  All of these systems end up less accurate compared to the iPhone’s electrical impulse reading touch screen for many reasons. [2]


The iPhone’s multi-touch screen is one of the most revolutionary user interfaces since the invention of the mouse.  It allows the user to control everything just using their fingers.  That’s easy to understand, but understanding how this technology works is a different story. Just like many other touch screen devices, the iPhone includes layers of capacitive material (it stores electrical energy).[8]  What’s different however is that the iPhone’s capacitors are arranged in a coordinate system, and the circuitry can sense changes at each point along the grid.  So each individual point on the grid generates its own signal when touched, and that information is then sent to the iPhones processor.  This allows for the phone to locate simultaneous touches in many different locations.  Because the touch screen operates using capacitors, the screen will only respond when touched with the fingertip, and will not work with a pen or other non-conductive materials.  The iPhone detects touch through mutual capacitance (Picture on the right).  This requires two layers of material.  One includes driving lines, which carry the current, and the other includes the sensing lines, which detect electrical current (touch) at the nodes. [4]

Ok, so we’ve learned what happens on the outside of the touchscreen process, but what happens internally when you touche the screen of an iPhone.

From touch, to processor

When you touch the screen, there are many steps that the impulse must undergo before you see the action take place on your phone screen.  All of these steps take place instantly.  So fast in fact, that it feels instant.  Thanks to the iPhone’s incredible processor, this is possible.  First, as explained in the previous section, a signal, or multiple signals, travel from the touchscreen to the processor as electrical impulses.  The processor then analyzes the impulse according to location on the screen, size, and shape.  The gesture-intepretation software then determines the beginning of a gesture and the end of a gesture, such as sliding your finger across the screen to unlock the phone.  It combines physical movement across the screen with whatever application you were using to determine the right instructions to relay.  The processor then sends the information to the program that is in use causing the desired action on screen.  That signal is also sent to other hardware if necessary.  If touch data doesn’t match any programmed commands or gestures, then the iPhone automatically classifies it as an invalid touch.  All of this happens every time you touch your iPhone screen, and within the blink of an eye. [6]

The practicality of multi-touch

There are many reasons why this revolutionary screen is practical for everyday phone users.  You can pinch in to zoom, which adds extreme ease of use when looking a photos or browsing the web.  You can swipe up or down to scroll through a web page or flip through your music with ease.  Looking a Google maps will never be as easy as it is with the pinch to zoom in or out.  Plus, many applications within the iPhone’s app store utilize the multi-touch function, such as games, photo apps, editing apps, music editing apps, ect (the list goes on and on).  Apple has set new standards for touch screen cell phones with the iPhone.  No other phone works as smooth and functions as well as the iPhone does, thanks to its superior technology.[7]

The future of multi-touch

Multi-touch technology is becoming one of the most practical and exciting ways to do everyday tasks.  We have seen the assortment of applications iPhone can achieve with this technology, but what is in store for us in the future of multi-touch.  Will there be multi-touch screens in the places we work.  Or maybe at restaurants as a way of ordering food or passing time by playing a game.  Will the walls in our homes no longer have wallpaper, but multi-touch screens?  The future is upon us as you read this, and these technologies will continue to advance beyond the conceivable.  All you have to do is sit back and enjoy the ride.













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