Technologies of Touch Screen

Analog 4-wire Resistive

Analog 4-wire resistive is the most basic sensing method of resistive technology.

Top and bottom transparent conductive sheets that have uniform resistance value, are facing each other with a gap. When the top sheet is touched, the touched point of the top sheet yields, and contact the bottom sheet. The contacted point is conducted, and its location is sensed. Are you following me so far?

Yes, I learned it in the structure section.

Very well. As feature of analog 4-ire resistive technology, one sheet has electrodes for the vertical direction while the other sheet has electrodes for the horizontal direction. Voltage of a touched point is measured by the other sheet. In this way, the touched point in X and Y directions is detected. The sensing process is as below.

The sensing process

  1. Voltage is imposed between the electrode X1 and X2 on the top sheet. Then, there will be formed on the top sheet an equipotential distribution that is parallel to the X1 and X2.
  2. Assuming that the electrode X1 is 0V (Ground), then impose 5V to the electrode X2. If the central point between the right and left electrodes is touched, 2.5V would be measured by the bottom sheet. If a point 1/5 away from X1 (4/5 away from X2) is touched, 1V would be measured by the bottom sheet. The X coordinate point is detected in this way.
  3. After detecting the coordinate point in X direction, Voltage is imposed between the electrode Y1 and Y2 on the bottom sheet. The point between Y1 and Y2 (Y coordinate) would be measured by the top sheet, just in the same manner as X coordinate in the step 1-2.
  4. As the set of step 1 ? 3 is repeated, the X and Y coordinate points of touched locations keeps being detected.

I see. The top and bottom sheets measure each others' voltages and the sensor knows the touched point from the measured voltages. For instance, if 2.5V is detected from the top and bottom sheets, the sensor will recognize that the center point of the panel is touched.

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