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Technology Behind Touchscreen Interface

Satya Sravan
2nd year
 Electronics & Communication Engg.

Hope many of us use a touchscreen mobile or a gadget with touch screen interface. Did you ever think what the technology behind touchscreen is? Let’s know what a touchscreen is, how it works and about the technology behind its operation.

A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area.The touch screen is one of the easiest to use and most intuitive of all computer interfaces. The touchscreen interface is being used in a wide variety of applications to improve human-computer interaction.

HOW IT WORKS ?
Basically, there are three components used in touch screen technology.

  •   Touch sensor, a panel with a touch responsive surface.

  •  Controller, the hardware that converts the voltage changes on the sensor into signals the computer or other device can receive.
  • Software, tells the electronic devices what's happening on the sensor and the information coming from the controller.
TOUCH SENSORS
Systems are built based on different types of sensors: resistive (most common), surface acoustic wave, and capacitive (most smart phones).

RESISTIVE TOUCHSCREEN TECHNOLOGY
The resistive system is comprised of five components, including the CRT (cathode ray tube) or screen base, the glass panel, the resistive coating, a separator dot, a conductive cover sheet and a durable top coating.
The two metallic layers become connected when a finger or stylus presses down on the top surface. The surface acts as a pair of voltage dividers with connected outputs. This causes a change in the electrical current. The pressure from your finger causes conductive and resistive layers of circuitry to touch each other, changing the circuits' resistance, which registers as a touch screen event that is sent to the computer controller for processing.
HOW IT LOOKS


WORKING


OPERATION

 http://www.youtube.com/watch?v=2X30LkAtHjg



CAPACITIVE TOUCHSCREEN TECHNOLOGY

The touch pad contains a two-layer grid of electrodes that are connected to a sophisticated full-custom mixed signal integrated circuit (IC) mounted on the reverse side of the pad. The upper layer contains vertical electrode strips while the lower layer is composed of horizontal electrode strips.

A human finger near the intersection of two electrodes modifies the mutual capacitance between them, since a finger has very different dielectric properties than air. When a user touches the screen, some of the charge is transferred to the user, and makes the potential difference on the screen. After the panel controller recognizes that, the controller will send the X-Y axis information to the PC port.

Capacitive technology includes technology based on the surface capacitance, projected capacitance, mutual and self-capacitance.

The advantage is that capacitive technology transmits almost 90% percent of the light from the screen.
HOW IT LOOKS


 WORKING

OPERATION

 http://www.youtube.com/watch?v=2C-fxPF564A



SURFACE ACOUSTIC WAVE (SAW) TECHNOLOGY

It is one of the most advanced touch screen types.The technology is based on two transducers (transmitting and receiving) placed for the both of X and Y axis on the touch panel. The other important element of SAW is placed on the glass, called reflector.

The controller sends electrical signal to the transmitting transducer, and transducer converts the signal into ultrasonic waves and emits to reflectors that are lined up along the edge of the panel. After reflectors refract waves to the receiving transducers, the receiving transducer converts the waves into an electrical signal and sends back to the controller. When a finger touches the screen, the waves are absorbed, causing a touch event to be detected at that point.

WORKING

OPERATION

http://www.youtube.com/watch?v=hwjMWhpxWqo




INFRARED TOUCHSCREEN TECHNOLOGY

The Infrared Touch Screen is a frame which is integrated with a printed circuit board that contains a line of IR-LEDs and photo transistors hidden behind the bezel of the touch frame. Each IR-LEDs and phone transistors are hidden behind the invisible infrared light. The bezel covers the parts from the operation environment while allowing the IR beams to pass through.



The controller sequentially pulses LEDs to create a grid of IR light beams. When a user touches, the screen enters the grid by a stylus which can interrupt the IR light beams. The photo transistors from X and Y axes coordinates to the host.

Other technologies include optical imaging, dispersive signal technology, strain-gauge touch screen technology and acoustic pulse recognition. 



COMPARISON TABLE
RESISTIVE
CAPACITIVE
SAW
INFRARED
Accuracy
2% of screen dimension
1% of screen dimension
1% of screen dimension
1% of screen dimension
Resolution

 16K x 16K
10K x 10K (approx.)
384x16
Light transmission
<= 82% overall
<= 88% @ 550nm
<= 92% overall
92%, Up to 100%
Operating temperature
-20C to +50C
-15C to +70C
-20C to +50C
-20C to +85C
Operation          
Finger or stylus
Finger only
Finger or soft-tipped stylus     
Finger or stylus
Positive talk
More accurate and durable, low cost
Repeatability, no moving parts, protective overcoat
Good response, reliability, easy to maintain
High resolution, clarity, durability, safety.
Negative talk
Optics are not much better, easily vandalized
Less transmission, expensive, affected by EMIR
Hard to integrate, affected by humidity & dirt
Highly sensitive



CONCLUSION

The touchscreen technology is used in ATMs, Self-Checkout Counters, Airport Check-in, PDAs, Tablet PCs, Mobile Phones, Handheld Gaming Consoles, Multi-Touch Collaboration Wall, image processing and image capture etc.

Touch screen technology will increase in significance as an I/O technique for user oriented embedded systems. The steady improvement in the use of touch sensors punctuated by innovation will continue to broaden the range of applications that touch screens can serve.





 

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Technology behind 3D television


Akash Bohare & Rishika Gaud 
Second Year
Chemical
                                                              
How 3D works..

The first of the 3d movies made its debut in 1922 using the oldest form of technology - anaglyph images - to produce stereoscopy. To understand this we need to consider how the eyes work to see in real life. Assuming no vision issues, our eyes are spaced a number of centimeters apart, so when looking at any object the eye send information to brain from two slightly different perpectives. The brain interprets this information and combines the two images to create depth perception and see one 3 dimensional image.

Stereoscopy originally involved taking a single image, and adding two additional image layers with slightly different perspectives. One layer was tinted red and the other blue. When watching a 3D movie, the audience would wear cardboard 3D glasses that had one red and one blue lens. Each lens would filter out its similarly colored image layer, thereby tricking the brain into creating a 3D image by mashing the two images together. 




Stereoscopy








Stereoscopy is most widely accepted method for capturing and delivering 3D video. It involves capturing stereo pairs in a two-view setup, with cameras mounted side by side, separated by the same distance as between a person's pupils. 

If we imagine projecting an object point in a scene along the line-of-sight (for each eye, in turn) to a flat background screen, we may describe the location of this point mathematically using simple algebra. In rectangular coordinates with the screen lying in the Y-Z plane (the Z axis upward and the Y axis to the right) and the viewer centered along the X axis, we find that the screen coordinates are simply the sum of two terms, one accounting for perspective and the other for binocular shift. Perspective modifies the Z and Y coordinates of the object point by a factor of D/(D-x), while binocular shift contributes an additional term (to the Y coordinate only) of s*x/(2*(D-x)), where D is the distance from the selected system origin to the viewer (right between the eyes), s is the eye separation (about 7 centimeters), and x is the true x coordinate of the object point. The binocular shift is positive for the left-eye-view and negative for the right-eye-view. 

For very distant object points, it is obvious that the eyes will be looking along the same line of sight. For very near objects, the eyes may become excessively "cross-eyed". However, for scenes in the greater portion of the field of view, a realistic image is readily achieved by superposition of the left and right images (using the polarization method or synchronized shutter-lens method) provided the viewer isn't too near the screen and the left and right images are correctly positioned on the screen. Digital technology has largely eliminated inaccurate superposition that was a common problem during the era of traditional stereoscopic films.

Technologies..

There was another problem with these colorful anaglyph images, though. They altered the coloring of the movies and interpreting the different images would often cause headaches after a short time. This led to the creation of the polarized 3d glasses we see in cinemas today.but the 3d technology used in movies is different than what is used in homes.

To overcome the above problem, the newest glasses innovation is a LCD shutter glasses which work on a system known as 'active technology'. These active shutter glasses work by alternately blocking the vision in each eye in conjunction with the refresh rate of the display screen. 3D TVs that use this form will display alternate images with slightly differing perspectives at a high rate, and the glasses darken each lens in time with the alternating images, causing the brain to do the classic image mash-up.


This technology works in a similar fashion as the older glasses, by blocking what image enters which eye. Shutter glasses simply take the idea to the next logical step by literally blacking out the lenses at a high rate of speed. Subsequently, shutter glasses are able to offer a much clearer three-dimensional picture than older methods





















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