TSC2102 datasheet(13/54 Pages) TI

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TSC2102

SLAS379A− APRIL 2003 − REVISED JUNE 2004

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OPERATION—TOUCH SCREEN

A resistive touch screen works by applying a voltage across a resistor network and measuring the change in resistance

at a given point on the matrix where a screen is touched by an input stylus, pen, or finger. The change in the resistance

ratio marks the location on the touch screen.

The TSC2102 supports the resistive 4-wire configurations (see Figure 9). The circuit determines location in two coordinate

pair dimensions, although a third dimension can be added for measuring pressure.

The 4-Wire Touch Screen Coordinate Pair Measurement

A 4-wire touch screen is constructed as shown in Figure 10. It consists of two transparent resistive layers separated by

insulating spacers.

Conductive Bar

Transparent Conductor (ITO)

Bottom Side

X+

X−

Y+

Y−

Transparent Conductor (ITO)

Top Side

Insulating Material (Glass)

ITO= Indium Tin Oxide

Silver Ink

Figure 10. 4-Wire Touch Screen Construction

The 4-wire touch screen panel works by applying a voltage across the vertical or horizontal resistive network. The ADC

converts the voltage measured at the point the panel is touched. A measurement of the Y position of the pointing device

is made by connecting the X+ input to an ADC, turning on the Y drivers, and digitizing the voltage seen at the X+ input.

The voltage measured is determined by the voltage divider developed at the point of touch. For this measurement, the

horizontal panel resistance in the X+ lead does not affect the conversion due to the high input impedance of the A/D

converter.

Voltage is then applied to the other axis, and the A/D converts the voltage representing the X position on the screen. This

provides the X and Y coordinates to the associated processor.

Measuring touch pressure (Z) can also be done with the TSC2102. To determine pen or finger touch, the pressure of the

touch needs to be determined. Generally, it is not necessary to have very high performance for this test; therefore, the 8-bit

resolution mode is recommended (however, calculations are shown with the 12-bit resolution mode). There are several

different ways of performing this measurement. The TSC2102 supports two methods. The first method requires knowing

the X-plate resistance, measurement of the X-Position, and two additional cross panel measurements (Z2 and Z1) of the

touch screen (see Figure 11). Using equation 1 calculates the touch resistance:

TOUCH +

X–plate

X–position

4096

–1

The second method requires knowing both the X-plate and Y-plate resistance, measurement of X-Position and Y-Position,

and Z1. Using equation 2 also calculates the touch resistance:

TOUCH +

X−plate

X−position

4096

* 1

* R

Y−plate

Y−position

4096

(1)

(2)

TSC2102 Datasheet(PDF) 13 Page - Texas Instruments

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