Compare All Resistive Touch Technologies
(5-, 6-, 7-, and 8-Wire Explained)
Compare All Elo Touch Technologies
Component Integration Considerations for Elo TouchSystems Touch Technologies
Resistive touchscreens are used in more applications than any
other touch technology–for example, PDAs, point-of-sale, industrial,
medical, and office automation, as well as consumer electronics.
All variations of resistive touchscreens have some things in common:
 They are all constructed similarly in layers-a back layer such as glass with a uniform resistive coating plus a polyester coversheet, with the layers separated by tiny insulating dots. 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 which are then 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.
- Both the touchscreen and its electronics are simple to integrate into imbedded systems, thereby providing one of the most practical and cost-effective touchscreen solutions.
Eight-Wire Variation
Eight-wire systems are usually seen in sizes of 10.4" or larger where the drift can be significant.
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 extra sensing points helps 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.
Five-Wire Resistive
 As we have seen, 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-linearities. The simple buss 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 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 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 eight-wire designs.
Six- and Seven-Wire Variations
There are some manufacturers who 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. It is not needed for improved performance, and in some cases is not even connected to the companion controller.
The seven-wire variation adds two sense lines, like with the eight-wire design, to decrease drift due to environmental changes. The proprietary Elo AccuTouch "Z border" electrode pattern is a better solution to prevent drift.
General Information on AccuTouch
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