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Jul 26, 2009

The Incomplete Guide to Touchscreens Technologies


With the latest rumors about the support of Windows Mobile 6.5 to capacitive screens I decided to look for some more information about the different types of touch screens.

I decided to summarize the things I found in another "incomplete guide". Hope you'll Enjoy it.


-Before you continue!

Check out our previous mobile technologies guides:

How does 'Direct Push' work-

The History of PDAs

The Incomplete Guide to D-Pads

Different Screen Resolution in Windows Mobile Devices


The Incomplete Guide to Mobile Form Factors

More guides in here.

OK, now that we covered that one... let's begin:

The Incomplete Guide to TouchScreens Technologies!


Resistive Touchscreens:

A resistive touchscreen panel is composed of several layers, the most important of which are two thin, metallic, electrically conductive layers separated by a narrow gap.

When an object, such as a finger, presses down on a point on the panel's outer surface the two metallic layers become connected at that point: the panel then behaves as a pair of voltage dividers with connected outputs. This causes a change in the electrical current which is registered as a touch event and sent to the controller for processing.


This technology is pressure sensitive so it can be used with fingers, stylus, gloved hand, Spoon or even your elbow is you know how to control it good enough...

It's a cheap technology, very accurate when using stylus, and resistant to dirt, humidity etc.

Unlike what people think, resistive touchscreens can support Multitouch.

Surface acoustic wave

SAW technology uses ultrasonic waves that pass over the touchscreen panel. When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. Surface wave touchscreen panels can be damaged by outside elements or be contaminated... spooky.


Good old iPhone style capacitive touchscreen panel is a sensor typically made of glass coated with a transparent conductor such as indium tin oxide (ITO).

This type of sensor is basically a capacitor in which the plates are the overlapping areas between the horizontal and vertical axes in a grid pattern. Since the human body also conducts electricity, a touch on the surface of the sensor will affect the electric field and create a measurable change in the capacitance of the device. Like the stylus used in the defunct CED video disc, these sensors work on proximity of the conductive medium (finger), and do not have to be directly touched to be triggered. It is a durable technology that is used in a wide range of applications including point-of-sale systems, industrial controls, and public information kiosks.


Capacitive screens have a higher clarity than Resistive screens, but they only respond to finger contact and will not work with a gloved hand or pen stylus (unless the stylus is conductive which is annoying once you lose it...) - so they usually cannot support signature capturing etc.

On the other hand, the fact that you don't need to press the screen is so nice, it makes every phone operation smooth and fun.

Multitouch is of course supported...


Cannot use capacitive screens...

(It's a joke.. sure he can... once he turns into a real kid).


PenTouch Capacitive

This one is an interesting combination of both durable Capacitive technology with a tethered pen stylus. The screen can be set to respond to finger input only, pen input only, or both. The pen stylus is a good choice for signature capture, on-screen annotations, or for applications requiring precise input.


Conventional optical-touch systems use an array of infrared (IR) light-emitting diodes (LEDs) on two adjacent bezel edges of a display, with photosensors placed on the two opposite bezel edges to analyze the system and determine a touch event. The LED and photosensor pairs create a grid of light beams across the display. An object (such as a finger or pen) that touches the screen interrupts the light beams, causing a measured decrease in light at the corresponding photosensors. The measured photosensor outputs can be used to locate a touch-point coordinate.


Infrared touchscreens did not become popular as the other technologies because of their higher price, and because there is an issue with performance in bright ambient light. Oh, and multitouch is not supported...

Expensive and without multitouch...

Strain gauge

In a strain gauge configuration, also called force panel technology, the screen is spring-mounted on the four corners and strain gauges are used to determine deflection when the screen is touched.

This technology has been around since the 1960s but new advances by Vissumo and F-Origin have made the solution commercially viable.It can also measure the Z-axis and the force of a person's touch. Typically used in exposed public systems such as ticket machines due to their resistance to vandalism.

Optical imaging

A relatively-modern development in touchscreen technology, two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared backlights are placed in the camera's field of view on the other sides of the screen. A touch shows up as a shadow and each pair of cameras can then be triangulated to locate the touch or even measure the size of the touching object.

This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units.


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There are more touchscreens technologies: Acoustic pulse recognition, Dispersive signal and more, you can find more details in here.

Also, there are combinations of technologies, for instance, the Storm's touchscreen is a capacitive screen but it also includes a clickable surface. You can read more about it in here.

Here's a nice comparison between different touchscreens: 


Haptic/tactile touchscreens:

Some touchscreens include haptic feedback to ease the user experience when working on a flat surface with no real buttons.

One of the researches showed that when using haptic feedback users managed to reduce input errors (20%), increase input speed (20%), and lower their cognitive load (40%).

Interesting don't you think? Maybe this is why I liked the Omnia so much...

BTW, in some mobile devices, haptic feedback is built in,in others, it can be done using software only (a software that controls the vibration of the phone). Here's an example of such applications.


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