Kunlun Tongtai touch screen - the component classification introduction of resistive touch screen

Four-wire touch screen

The four-wire touchscreen contains two resistive layers. One of the layers has a vertical bus on the left and right edges of the screen, and the other layer has a horizontal bus at the bottom and top of the screen, see Figure 1. For measurement in the X-axis direction, the left bus is offset to 0V and the right bus is offset to VREF. Connect the top or bottom bus to the ADC and take a single measurement when the top and bottom layers come into contact.

Kunlun Tongtai touch screen - the component classification introduction of resistive touch screen

Figure 1

　　For measurements in the Y-axis direction, the top bus is offset to VREF and the bottom bus is offset to 0V. The ADC input is terminated to either the left or right bus, and the voltage is measured when the top layer comes into contact with the bottom layer. Figure 2 shows a simplified model of a four-wire touchscreen when two layers come into contact. For a four-wire touchscreen, the ideal connection is to connect the bus biased as VREF to the positive reference input of the ADC and the bus set to 0V to the negative reference input of the ADC.

Figure 2

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

Seven-line touch screen

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

Eight-wire touch screen

Except for adding one wire on each bus, an eight-wire touchscreen is implemented in the same way as a four-wire touchscreen. For the VREF bus, one wire is used to connect the VREF and the other wire is used as the positive reference input to the digital-to-analog converter of the SAR ADC. For the 0V bus, one wire is used to connect to 0V and the other wire is used as a negative reference input to the digital-to-analog converter of the SAR ADC. Any of the four wires on the unbiased layer can be used to measure the voltage of the voltage divider.

Kunlun Tongtai touch screen - the component classification introduction of resistive touch screen

Sections viewed

Contact

working hours