Touch Screens are not only display but also imput devices. Electronic visual devices which are sensitive to pressure and hence detect the presence and location of touch within the display region. A user interacts with the computer by touching the pictures or words on screen, as the screens are sensitive to pressure. The term “touch” refers to contact or touch to the display of the device by finger or hand. It refers to a situation of “direct manipulation”. Doctor Samhurst developed the first touch sensor in 1971 and it was patented by the University of Kentucky Research Foundation. Now-a-days smart phones, portable game consoles, PDAs etc are driving the demand for touch screens. With time, display manufacturers & chip manufacturers acknowledged this trend of acceptance and began integrating touch screen functionality in to the fundamental design of their products.
Touch screens advantages over normal/conventional devices are as follows :-
- Easy to use :- It provides a rich user interface experience as it is just facilitated by touch.
- Saves Space :- Intelligent utilization of space is of great importance. This touch screens facilitates this by saving space of keyboard.
- Speed & Reliability :- Navigation with other devices is comparatively is slow as compared to touch screens as just by touch the navigation becomes extremely faster and reliable.
Basic Components of a Touch Screen :-
Touch screen have basically 3 components and as it is I/O device, so it should be combined with a display and a PC to make a complete touch input system.
- Touch Sensor :- A clear glass panel with a touch responsive surface. The Touch panel is placed over the display screen in such a manner that the responsive area of the panel covers the viewable area. Various touch sensor technologies are available in market which uses a different method to detect the touch. In general sensor has an electric current going through it and as soon as somebody touches the screen that causes a voltage change which in turn helps to locate the presence of touch on the screen.
- Controller :- A samll PC card that connects between the touch sensor & the PC. Controller takes information from touch sensor and translates it into such a language that a PC can understand. Its usually installed inside the monitor. It determines the type of connection we need on PC.
- Software Driver :- Its a software update for the PC system that allows the touch screen and computer to work together. Operating system gets intruction on how to interpret the touch event information that is sent from the controller.
Types of Touch Screen technology :-
Various technologies are available. Few of them are described here :-
Resistive Touch Screen Technology :- A resistive touch screen panel is consists of several layers but the important layers are two thin, metallic, electrically conductive layers separated by narrow gap.
As shown in the figure as soon as an object such as finger presses down on a point on the panel, the two metallic layers become connected at that point and act as a pair of voltage dividers with connected outputs. Hence it causes a change in electric current which is recoreded as touch event and sent to controller for processing.
Few points regarding Resistive Touch screen :-
- Low activation pressure required.
- Transmissivity is < 82% which means distortion to graphics due to coatings.
- It requires periodic recalibration due to wearing of coatings
- Display size 19″
- Integrated in component only and any pointing device can be used
- Polyester top sheets affects the optics and is susceptible to damage
SAW (Surface Acoustic Wave) Technology :- It make use of ultra sonic waves that pass over the touch screen panel.
As soon as the panel is touched a part of wave is absorbed. This change in ultrasonic waves record the position of the touch event which is being sent to controller for processing. The touch screen panel can be damaged by outside elements. It can also interfere with the functionality of the touch screen.
Few points regarding SAW Technology :-
Low activation pressure required.
Transmissivity > 92%
- Requires periodic recalibration
- Adversely affected by moisture
- Display size 10.4″- 30″
- Integrated in component only and touch method is finger
- Surface contamination causes dead zones which requires recalibration.
Surface Capacitance/ Capacitive Technology :- In this one side of the insulator is coated with a conductive layer.
A small voltage is applied to the layer which results in a uniform electric field. When a conductor such as human finger touches the uncoated surface, a capacitor is formed dynamically. Sensor controller determines the location from the change in capacitance as measured from the four corners of the panel.
Few points about Surface Capacitance :-
- Activation pressure is low.
- Very good transmissivity > 92%
- Resistant to moisture & other surface contaminants.
- Display 8.4″- 21″
- Requires human touch , scratches in coatings causes dead zones.
- Field replacement difficult due to calibration
Optical Imaging :- One of the modern touch screen technology. It uses optical sensors to detect the touch.
Two or more image sensors are placed in the camera’s feild of view. A touch shows up as a shadow & each pair of cameras can then be pin pointed to locate the touch, it can also measure the size of touching object.
Few points about Optical Imaging :-
Zero activation Force required.
- High Resolution and no calibration required
- Can discern two distinct points
- HID Compliant, no driver required
- Display 12″-120″
Recently multi-touch has made its way into consumer market. The generation is moving towards multi- touch. Touch screen is considered as the future on which all new gadgets shall bank on. We are already in the era that has seen many ground breaking technologies emerge and touch screen is one of them which has changed the way users interact with their gadgets to a whole new level. Its not right to say that the further improvement in this technology is inevitable and this can change the way we think what input-output devices are. Our world today has already started to see the emergence of visual screen that are flexible, can be worn on wrist like a wrist watch ,gadgets with gait recognition all thanks to ground breaking technology of touch screens that set the ball rolling.There is more to touch screen technology and people are waiting with bated breath for the next surprise
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