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TSC2005I Datasheet(PDF) 11 Page - Burr-Brown (TI) |
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TSC2005I Datasheet(HTML) 11 Page - Burr-Brown (TI) |
11 / 42 page www.ti.com TOUCH SCREEN OPERATION 4-WIRE TOUCH SCREEN COORDINATE PAIR MEASUREMENT ConductiveBar InsulatingMaterial(Glass) Silver Ink TransparentConductor(ITO) BottomSide Transparent Conductor(ITO) TopSide X+ X- Y+ Y- ITO=IndiumTinOxide R TOUCH + RX−plate @ X Postition 4096 Z 2 Z 1 * 1 (1) R TOUCH + R X−plate @ XPostition 4096 4096 Z 1 *1 *RY−plate @ 1* Y Position 4096 (1) TSC2005 SBAS379 – DECEMBER 2006 OVERVIEW (continued) A resistive touch screen operates by applying a voltage across a resistor network and measuring the change in resistance at a given point on the matrix where the screen is touched by an input (stylus, pen, or finger). The change in the resistance ratio marks the location on the touch screen. The TSC2005 supports the resistive 4-wire configurations, as shown in Figure 20. The circuit determines location in two coordinate pair dimensions, although a third dimension can be added for measuring pressure. A 4-wire touch screen is typically constructed as shown in Figure 20. It consists of two transparent resistive layers separated by insulating spacers. Figure 20. 4-Wire Touch Screen Construction The 4-wire touch screen panel works by applying a voltage across the vertical or horizontal resistive network. The A/D converter converts the voltage measured at the point where the panel is touched. A measurement of the Y position of the pointing device is made by connecting the X+ input to a data converter chip, turning on the Y+ and 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 because of the high input impedance of the A/D converter. Voltage is then applied to the other axis, and the A/D converter converts the voltage representing the X position on the screen. This process provides the X and Y coordinates to the associated processor. Measuring touch pressure (Z) can also be done with the TSC2005. To determine pen or finger touch, the pressure of the touch must be determined. Generally, it is not necessary to have very high performance for this test; therefore, 10-bit resolution mode is recommended (however, data sheet calculations will be shown with the 12-bit resolution mode). There are several different ways of performing this measurement. The TSC2005 supports two methods. The first method requires knowing the X-plate resistance, the measurement of the X-Position, and two additional cross panel measurements (Z2 and Z1) of the touch screen (see Figure 21). Equation 1 calculates the touch resistance: The second method requires knowing both the X-plate and Y-plate resistance, measurement of X-Position and Y-Position, and Z1. Equation 2 also calculates the touch resistance: 11 Submit Documentation Feedback |
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