Technologies of Touch Screen

Analog 8-wire Resistive

Analog 8-wire resistive technology is similar to analog 4-wire resistive and was developed as an advanced version of it.

The structure and sensing method of 8-wire resistive technology is same as 4-wire resistive technology. Two transparent conductive sheets are facing. One sheet has electrodes on right and left sides, and the other sheet has electrodes on top and bottom sides. Voltage is imposed on the sheet with electrodes on right and left sides, then a touched point in X direction is detected as the voltage is measured by the other sheet. Then, voltage is imposed on the sheet with electrodes on top and bottom sides, then a touched point in Y direction is detected as the voltage is measured by the other sheet.

It sounds exactly same as the analog 4-wire resistive technology so far.

Yes, but there are additional wirings connected to each electrode in analog 8-wire resistive technology. Each electrode is added with one more wiring. These added wirings work as supplemental electrodes and measure voltage on each electrodes, then feedback the information to the controller.

What is good about the analog 8-wire resistive technology comparing with the analog 4-wire resistive technology?

Resistive technology requires a task called "calibration" before using it. It is the task to match the touched points on touch screen with positional data of cursor on the display.

Calibration is the task to align a touch screen's coordinate to the display behind it, isn't it?

Exactly. Analog 4-wire resistive technology required calibration not only at the beginning but regularly because touch detecting points are gradually going off the alignment due to change of resistance value on wiring and/or connector parts with the passage of time. In analog 8-wire resistive technology, supplemental electrodes measure the voltage on each electrode automatically, and feedback the measured values to the controller. The voltage detected at touching is transformed into locational information in the relative ratio with the feedback voltage. In this way, the effects of voltage change at electrodes can be cancelled, thus recalibration would not be required.

So, Is analog 8-wire resistive technology better than analog 4-wire resistive technology because it corrects the alignment automatically and saves the trouble of recalibration?

Yes, the basic idea is as you said. But, the demand for 8-wire resistive sensors is decreasing after 1990s. This is because design and materials of resistive touch screens have been improved, and the recent 4-wire resistive touch screens can be used for long enough without recalibration in many applications.

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