Component classification of resistive touch screen

Component Classification

4-wire touch screen

The four wire touch screen contains two resistive layers. One layer has a vertical bus at the left and right edges of the screen, and the other layer has a horizontal bus at the bottom and top of the screen. To measure in the X-axis direction, offset the left bus to 0V and the right bus to VREF. Connect the top or bottom bus to ADC, and make a measurement when the top layer and bottom layer contact.

To measure in the Y-axis direction, offset the top bus to VREF and the bottom bus to 0V. The ADC input is terminated to the left bus or the right bus, and the voltage can be measured when the top layer contacts the bottom layer. Figure 2 shows a simplified model of a four wire touch screen when two layers are in contact. For the four wire touch screen, the most ideal connection method is to connect the bus offset to VREF to the positive reference input terminal of ADC, and connect the bus set to 0V to the negative reference input terminal of ADC.

Five wire touch screen

The five wire touch screen uses a resistive layer and a conductive layer. The conductive layer has a contact, usually at the edge of one side. Each of the four corners of the resistive layer has a contact. To measure in the X-axis direction, offset the upper left corner and lower left corner to VREF, and ground the upper right corner and lower right corner. Since the left and right corners are of the same voltage, the effect is similar to that of the bus connecting the left and right sides, similar to the method used in the four wire touch screen. To measure along the Y axis, offset the upper left corner and upper right corner to VREF, and the lower left corner and lower right corner to 0V. Since the upper and lower corners are of the same voltage, the effect is roughly the same as that of the bus connecting the top and bottom edges, similar to the method used in the four wire touch screen. The advantage of this measurement algorithm is that it keeps the voltage in the upper left corner and lower right corner unchanged; However, if grid coordinates are used, the X and Y axes need to be reversed. For the five wire touch screen, the best connection method is to connect the upper left corner (offset as VREF) to the positive reference input terminal of ADC and the lower left corner (offset as 0V) to the negative reference input terminal of ADC.

Seven wire touch screen

The implementation method of the seven wire touch screen is the same as that of the five wire touch screen, except that one line is added to the upper left corner and one line is added to the lower right corner. When performing screen measurement, connect one line in the upper left corner to VREF and the other line to the positive reference end of SAR ADC. At the same time, one line at the lower right corner is connected to 0V, and the other line is connected to the negative reference terminal of SAR ADC. The conductive layer is still used to measure the voltage of the voltage divider.

8-wire touch screen

In addition to adding one line on each bus, the implementation method of eight wire touch screen is the same as that of four wire touch screen. For VREF bus, one line is used to connect VREF, and the other line is used as the positive reference input of SAR ADC digital to analog converter. For 0V bus, one line is used to connect 0V, and the other line is used as the negative reference input of SAR ADC digital to analog converter. Any of the four wires on the unbiased layer can be used to measure the voltage of the voltage divider.