There are several touch screen technologies available on the market. Each technology has its pros and cons and the choice depends on customer needs and application.
A touch screen is an touchscreen technology input device layered on the top of an electronic visual display of an information processing system. A user can input or control the information processing system through simple or multi-touch gestures by touching the screen with a special stylus or one or more fingers. The touchscreen enables the user to interact directly with what is displayed, rather than using a mouse, touchpad, or other such smartphones tablets (other than a user interface stylus, which is optional for most modern touchscreens).
When the screen is touched, a portion of the wave traveling across it is absorbed. The received signal is compared to the stored digital map, recognizes changes, and calculates a coordinate. This process happens independently for both the X and Y axes. By measuring the amount of the signal that is absorbed, a Z-axis is also determined. The digitized coordinates are transmitted to the computer to be processed.
IntelliTouch is a surface-wave touch technology that consists of a glass overlay with transmitting and receiving piezoelectric transducers for both the X and Y axes. The touchscreen controller sends a five-megahertz electrical signal to the transmitting transducer, converting the signal into ultrasonic waves within the glass. These waves are directed across the front surface of the touchscreen by an array of reflectors. Reflectors on the opposite sides gather and direct the waves to the receiving transducer, which reconverts them into an electrical signal—a digital map of the touchscreen surface.
The IntelliTouch surface wave is the optical standard of touch. It has a pure glass construction that provides superior optical performance and makes it the most scratch-resistant technology available. It is nearly impossible to physically "wear out" this touchscreen. IntelliTouch is widely used in kiosks, office automation applications and is available for both flat panel and CRT solutions.
When you touch the screen, you absorb a portion of the wave traveling across it. The received signal is then compared to the stored digital map, the change recognized, and a coordinate calculated. This process happens independently for both the X and Y axes. By measuring the amount of the signal that is absorbed, a Z-axis is also determined. The digitized coordinates are transmitted to the computer for processing.
Both SecureTouch is a surface-wave touch technology. It has a glass overlay with transmitting and receiving piezoelectric transducers for both the X and Y axes. The touchscreen controller sends a five-megahertz electrical signal to the transmitting transducer, which converts the signal into ultrasonic waves within the glass. These waves are directed across the front surface of the touchscreen by an array of reflectors. Reflectors on the opposite side gather and direct the waves to the receiving transducer, which reconverts them into an electrical signal—a digital map of the touchscreen surface.
Flat-screen SecureTouch products are made of extra-tough glass substrates that resist vandalism. These touchscreens incorporate the solid-glass and coating-free construction of Elo's proven IntelliTouch products.
The Controller sequentially pulses the LEDs to create a grid of IR beams. A touch obstructs one or more of the beams which identify the X and Y coordinates.
The CarrollTouchinfrared(IR) technology uses a small frame around the display with LEDs and photoreceptors on opposite sides, hidden behind an IR-transparent bezel.
CarrollTouch infrared technology is the survivor of harsh applications. It is the only technology that does not rely on an overlay or substrate to register a touch, so it's impossible to physically "wear out" the touchscreen. CarrollTouch technology combines superior optical performance with excellent gasket-sealing capabilities, so it's an excellent choice for harsh industrial and outdoor kiosk applications. Touched with a finger, gloved hand, fingernail, or stylus, it delivers a fast, accurate response every time. CarrollTouch infrared technology is available for flat panel solutions.
When the screen is touched, the conductive coating makes electrical contact with the coating on the glass. The voltages produced are the analog representation of the position touched. The controller digitizes these voltages and transmits them to the computer for processing. AccuTouch five-wire technology utilizes the bottom substrate for both X and Y-axis measurements. The flexible coversheet acts only as a voltage-measuring probe. This means the touchscreen will continue working properly even with non-uniformity in the cover sheet's conductive coating. The result is an accurate, durable, and reliable touchscreen that offers drift-free operation. AccuTouch screens are sealed against contamination and moisture. The cover sheet is sealed to the glass substrate with an industrial-grade caulk. This prevents the wicking of fluid between the coversheet and glass. Also, AccuTouch screens are not air vented, thereby preventing fluid ingress through an air vent.
The AccuTouch five-wire resistive touchscreens use a glass panel with a uniform resistive coating. A thick polyester coversheet is tightly suspended over the top of the glass, separated by small, transparent insulating dots. The coversheet has a hard, durable coating on the outer side and a conductive coating on the inner side.
Surface capacitive technology consists of a uniform conductive coating on a glass panel. During operation, electrodes around the panel's edge distribute low voltage uniformly across the conductive layer creating a uniform electric field. A finger touch draws current from each corner of the electric field. The controller calculates touch location coordinates by measuring the current and transmits it to the computer for processing.
The surface capacitive touchscreens provide a solution for customers seeking an alternative to the currently available capacitive options. The transparent protective coating makes the sensor resistant to scratches and abrasions. Touch performance is unaffected by everyday abuse and mishaps such as dirt, dust, condensation, liquid spills, contaminants, or cleaning solutions. And the Elo-designed controller responds to quick, light touches, and operates drift-free even in areas of poor grounding.
Resistive touchscreens are popular than any other touch technology, used in PDAs, point-of-sale, industrial, medical, office automation, and consumer electronics. All variations of resistive touchscreens have some things in common.
The IntelliTouch surface wave is the optical standard of touch. Its pure glass construction provides superior optical performance and makes it the most scratch-resistant technology available. It's nearly impossible to physically "wear out" this touchscreen. IntelliTouch is widely used in kiosk, gaming, and office automation applications for flat panel and CRT solutions.
They are all constructed similarly in layers- such as glass with a uniform resistive coating and a polyester cover sheet. Tiny insulating dots separate the layers. When the screen is touched, it pushes the conductive coating on the coversheet against the coating on the glass, making electrical contact. The voltages produced are the analog representation of the position touched. An electronic controller converts these voltages into digital X and Y coordinates transmitted to the host computer.
Because resistive touchscreens are force-activated, all kinds of touch input devices can activate the screen, including fingers, fingernails, styluses, gloved hands, and credit cards.
All have similar optical properties, resistance to chemicals, and abuse.
The touchscreen and its electronics are simple to integrate into embedded systems, providing one of the most practical and cost-effective touchscreen solutions.
Four-wire resistive technology is the simplest to understand and manufacture. It uses both the upper and lower layers in the touchscreen "sandwich" to determine the X and Y coordinates. Typically constructed with uniform resistive coatings of indium tin oxide (ITO on the inner sides of the layers and silver bus bars along the edges, the combination sets up lines of equal potential in both X and Y.
In the illustration below, the controller first applies 5V to the back layer. Upon touch, it probes the analog voltage with the coversheet, reading 2.5V, which represents a left-right position or X-axis.
It then flips the process, applying 5V to the cover sheet, and probes from the back layer to calculate an up-down position or Y-axis. At any time, only three of the four wires are in use (5V, ground, probe).
The primary drawback of four-wire technology is that one coordinate axis (usually the Y-axis), uses the outer layer, the flexible cover sheet, as a uniform voltage gradient. The constant flexing that occurs on the outer coversheet with use will eventually cause microscopic cracks in the ITO coating, changing its electrical characteristics (resistance), degrading the linearity and accuracy of this axis.
Unsurprisingly, four-wire touchscreens are not known for their durability. Typically, they test only to about 1 million touches with a finger-far less when activated by a pointed stylus which speeds the degradation process. Some four-wire products even specify 100,000 activations within a rather large, 20 mm x 20 mm area. In the real world of point-of-sale applications, a level of 100,000 activations with hard, pointed styluses (including fingernails, credit cards, ballpoint pens, etc.) is considered normal usage in just a few months.
Also, accuracy can drift with environmental changes. The polyester coversheet expands and contracts with temperature and humidity changes, thereby causing long-term degradation to the coatings as well as drift in the touch location.
While all of these drawbacks can be insignificant in smaller sizes, they become increasingly apparent the larger the touchscreen. Therefore, Elo normally recommends four-wire touchscreens in applications with a display size of 6.4" or smaller?
However, the relatively low cost, inherent low power consumption, and common availability of chipset controllers with support from embedded operating systems make Elo AT4 four-wire touchscreens ideal for hand-held devices such as PDAs, wearable computers, and many consumer devices.
Eight-wire resistive touchscreens are a variation of four-wire construction. The primary difference is the addition of four sensing points used to stabilize the system and reduce the drift caused by environmental changes. Eight-wire systems are usually seen in 10.4" or larger sizes, where the drift can be significant.
As in four-wire technology, the major drawback is that one coordinate axis uses the outer, flexible coversheet as a uniform voltage gradient, while the inner or bottom layer acts as the voltage probe. The constant flexing that occurs on the outer coversheet will change its resistance with usage, degrading the linearity and accuracy of this axis.
Although the added four sensing points help stabilize the system against drift, they do not improve the durability or life expectancy of the screen. Therefore, Elo does not recommend eight-wire touchscreen solutions.
As we have seen, four- and eight-wire touchscreens, while having a simple and elegant design, have a major drawback in terms of durability in that the flexing coversheet is used to determine one of the axes. Field usage proves that the other axis rarely fails. Could it be possible to construct a touchscreen where all the position sensing was on the stable glass layer? Then the coversheet would serve only as a voltage probe for X and Y. Microscopic cracks in the coversheet coating might still occur, but they would no longer cause non-linearity. The simple bus bar design is not sufficient and a more complex linearization pattern on the edges is required.
In the five-wire design, one wire goes to the coversheet (E) which serves as the voltage probe for X and Y. Four wires go to the corners of the back glass layer (A, B, C, and D). The controller first applies 5V to corners A and B and grounds C and D, causing the voltage to flow uniformly across the screen from the top to the bottom. Upon touch, it reads the Y voltage from the coversheet at E. Then the controller applies 5V to corners A and C and grounds B and D, and reads the X voltage from E again.
So, a five-wire touchscreen uses the stable bottom layer for both X- and Y-axis measurements. The flexible coversheet acts only as a voltage-measuring probe. This means the touchscreen continues working properly even with non-uniformity in the coversheet's conductive coating. The result is an accurate, durable, and more reliable touchscreen over four- and eight-wire designs.
Some manufacturers claim improved performance over five-wire resistive with additional wires.
The six-wire variation adds an extra ground layer to the back of the glass, which doesn't offer improved performance. In some cases, it is not connected to the companion controller.
The seven-wire variation adds two sense lines, like the eight-wire design, to decrease drift due to environmental changes. Elo's patented AccuTouch "Z border" electrode pattern is a better solution to prevent drift.
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