Touchscreen Technology - II

It has two coatings as well.

Conductive lower coating (Indium-Tin-Oxide)

No top coating, only rigid protective cover

Finger serves as second conducting layer

 

Ohm’s Law relates current to voltage in DC circuit in the form of V = iR

Capacitive touch screen uses Alternating Current (AC).

The current is continuous across the ITO surface, remember Sinusoidal waves from lab.

    

Impedance is equivalent to resistor in AC circuit implies, V = iZ; where Z = (1/JwC)

And, J = sqrt(-1) w= 2pF where F = Freq.

C = Capacitance = (erA)/d

Human body achieves capacitance and conducts current.

Touch Event implies, Voltage drop at the point of touching.

Thus affecting the strength of current, across the ITO surface.

Also, Voltage gradient across surface.

Conductive ITO surface allows for continuous current across the surface.

Electronic circuits located underneath ITO surface measure the resulting distortion in the sine waves produced by voltage drop as a result of the touch event.

Based upon emission and absorption of sound waves

Materials used are:

Transducers

One glass screen

Reflectors

Sensors

Two transducers are placed along the X and Y axes and generate sound waves.

The waves propagate across the glass and are reflected back to the sensors.

When screen touched, a portion of the wave is reflected back to the sensors immediately.

The sensor is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly.

                             

How do the sensors tell?

Waves travel at the speed of sound, Speed of Sound = 343 m/s

Based on the time it takes for the wave to return to the source, the sensor can tell if it was disturbed or not.

If it was, based on the time it takes to get back to the source, the sensor can calculate the distance.

These calculations will generate (X,Y) coordinates

100% clarity because of the lack of metallic layers in the screen

Able to interact with the use of multiple mediums like Stylus, finger, glove etc

Screen can become contaminated and cease to operate correctly.

An infrared touchscreen uses an array of X-Y infrared LED and photodetector pairs around the edges of the screen to detect a disruption in the pattern of LED beams. These LED beams cross each other in vertical and horizontal patterns. This helps the sensors pick up the exact location of the touch. A major benefit of such a system is that it can detect essentially any input including a finger, gloved finger, stylus or pen. Unlike capacitive touchscreens, infrared touchscreens do not require any patterning on the glass which increases durability and optical clarity of the overall system. Infrared touchscreens are sensitive to dirt/dust that can interfere with the IR beams, and suffer from parallax in curved surfaces and accidental press when the user hovers his/her finger over the screen while searching for the item to be selected.

This is a relatively modern development in touchscreen technology, in which two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared back lights are placed in the camera's field of view on the other side of the screen. A touch shows up as a shadow and each pair of cameras can then be pinpointed to locate the touch or even measure the size of the touching object (see visual hull). This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units.

Introduced in 2002 by 3M, this system uses sensors to detect the piezoelectricity in the glass that occurs due to a touch. Complex algorithms then interpret this information and provide the actual location of the touch. The technology claims to be unaffected by dust and other outside elements, including scratches. Since there is no need for additional elements on screen, it also claims to provide excellent optical clarity. Also, since mechanical vibrations are used to detect a touch event, any object can be used to generate these events, including fingers and stylus. A downside is that after the initial touch the system cannot detect a motionless finger.

In this system, introduced by Tyco International's Elo division in 2006, the key to the invention is that a touch at each position on the glass generates a unique sound. Four tiny transducers attached to the edges of the touchscreen glass pick up the sound of the touch. The sound is then digitized by the controller and compared to a list of prerecorded sounds for every position on the glass. The cursor position is instantly updated to the touch location. APR is designed to ignore extraneous and ambient sounds, since they do not match a stored sound profile. APR differs from other attempts to recognize the position of touch with transducers or microphones, in using a simple table lookup method rather than requiring powerful and expensive signal processing hardware to attempt to calculate the touch location without any references. The touchscreen itself is made of ordinary glass, giving it good durability and optical clarity. It is usually able to function with scratches and dust on the screen with good accuracy. The technology is also well suited to displays that are physically larger. Similar to the dispersive signal technology system, after the initial touch, a motionless finger cannot be detected. However, for the same reason, the touch recognition is not disrupted by any resting objects.

Kiosks: ATMs, Self Checkout Counters, Airport Check-in, etc.

PDAs

Tablet PCs

Mobile Phones or rather Smart-Phones

Handheld Gaming Consoles

  

Different Methods of determining X-Y position of the finger.

           

A person working on Smartphone.







Boy playing Jigsaw Puzzles on HP touch-smart.

Here's a video of a Surface acoustic Wave technology.