By: Prayag nao
Touch-screen monitors have become more and more commonplace as their price has steadily dropped over the past decade. There are three basic systems that are used to recognize a person's touch:
The 4-wire Resistive Touch Screen consists of a conductive bottom layer of either glass or film and a conductive top film layer, separated by extremely small, transparent spacer dots. A voltage is applied across the conductive surface. Any type of probe, including fingers, gloved fingers, credit cards, pens, etc., that can be used to apply pressure against the top film will activate the screen. When ample touch pressure is applied to the top layer, the film flexes inward and makes contact with the bottom layer resulting in a voltage drop. This change in voltage is detected by the controller. By alternating the voltage signal between the top and bottom layer, the X and Y coordinates of the user’s touch are computed. In a Film on Glass (FG) construction, the bottom layer is an ITO coated glass. In a Polyester Laminated (PL) or film-film-glass construction the bottom conductive layer is polyester. An additional layer of Optically Clear Adhesive (OCA) bonds the bottom polyester layer to a backer typically made of glass or poly material.
In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch-screen driver software.
Another area in which the systems differ is in which stimuli will register as a touch event.
A resistive system registers a touch as long as the two layers make contact, which means that it doesn't matter if you touch it with your finger or a rubber ball. A capacitive system, on the other hand, must have a conductive input, usually your finger, in order to register a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object -- except hard and small objects like a pen tip.
As far as price, the resistive system is the cheapest; its clarity is the lowest of the three, and its layers can be damaged by sharp objects. The surface acoustic wave setup is usually the most expensive.
Touch-screen monitors have become more and more commonplace as their price has steadily dropped over the past decade. There are three basic systems that are used to recognize a person's touch:
- Resistive
- Capacitive
- Surface acoustic wave
The 4-wire Resistive Touch Screen consists of a conductive bottom layer of either glass or film and a conductive top film layer, separated by extremely small, transparent spacer dots. A voltage is applied across the conductive surface. Any type of probe, including fingers, gloved fingers, credit cards, pens, etc., that can be used to apply pressure against the top film will activate the screen. When ample touch pressure is applied to the top layer, the film flexes inward and makes contact with the bottom layer resulting in a voltage drop. This change in voltage is detected by the controller. By alternating the voltage signal between the top and bottom layer, the X and Y coordinates of the user’s touch are computed. In a Film on Glass (FG) construction, the bottom layer is an ITO coated glass. In a Polyester Laminated (PL) or film-film-glass construction the bottom conductive layer is polyester. An additional layer of Optically Clear Adhesive (OCA) bonds the bottom polyester layer to a backer typically made of glass or poly material.
COMPONENTS OF A TOUCH SCREEN
The touch screen is an input device that allows users to operate a device simply by touching the display screen. A basic touch screen has three main components: touch screen sensor, controller and software driver.| Touch Screen Sensor Typically a glass panel with a touch-responsive surface. | Controller A printed circuit board (PCB) that is the interface between the sensor and the display. The controller takes information from the touch screen and translates it into information a computer can understand, such as cursor control, right and left clicks, etc. | Software Driver A computer program that allows the computer operating system and the controller to communicate and helps the controller recognize input |
In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch-screen driver software.
One advantage that the capacitive system has over the resistive system is that it transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits about 75 percent. This gives the capacitive system a much clearer picture than the resistive system.
On the monitor of a surface acoustic wave system, two transducers (one receiving and one sending) are placed along the x and y axes of the monitor's glass plate. Also placed on the glass are reflectors -- they reflect an electrical signal sent from one transducer to the other. The receiving transducer is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics (both other systems have significant degradation in clarity).Another area in which the systems differ is in which stimuli will register as a touch event.
A resistive system registers a touch as long as the two layers make contact, which means that it doesn't matter if you touch it with your finger or a rubber ball. A capacitive system, on the other hand, must have a conductive input, usually your finger, in order to register a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object -- except hard and small objects like a pen tip.
As far as price, the resistive system is the cheapest; its clarity is the lowest of the three, and its layers can be damaged by sharp objects. The surface acoustic wave setup is usually the most expensive.
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