AR1011-ISLASHML datasheet(7/61 Pages) MICROCHIP

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DS40001393C-page 7

AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER

2.4

8-Wire Sensor

An 8-wire resistive touch sensor consists of a stable

and flex layer, electrically separated by spacer dots.

The layers are assembled perpendicular to each other.

The touch position is determined by first applying a

voltage gradient across the flex layer and using the

stable layer to measure the flex layer’s touch position

voltage. The second step is applying a voltage gradient

across the stable layer and using the flex layer to

measure the stable layer’s touch position voltage.

The measured voltage at any position across a driven

axis is predictable. A touch moving in the direction of

the driven axis will yield a linearly changing voltage. A

touch moving perpendicular to the driven axis will yield

a relatively unchanging voltage.

The basic decoding of an 8-wire sensor is similar to a

4-wire. The difference is that an 8-wire sensor has four

additional interconnects used to reference sensor

voltage back to the controller.

A touch system may experience voltage losses due to

resistance changes in the bus bars and connection

between the controller and sensor. The losses can vary

with product use, temperature, and humidity. In a

4-wire sensor, variations in the losses manifest

themselves as error or drift in the reported touch

location. The four additional sense lines found on

8-wire sensors are added to dynamically reference the

voltage to correct for this fluctuation during use (See

Figure 2-2).

FIGURE 2-2:

8-WIRE DECODING

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