Structure and Detection Mechanism of
4wire Resistive Touch Screen
4wire resistive touch screen is a two-layer structure, two materials (film or glass) with ITO are attached with a gap between them so that the ITO layers are facing each other.
Touch input will be made as the top layer is pressed down and the two ITO layers contact.
There are insulators called spacing dots between the top and bottom ITO layers. These spacing dots prevent unintended contacts (inputs) of the ITO layers when not pressed.
As described above, a touch input will be made when the two transparent conductive layers contact. One of the two conductive layers constructs the X-coordinate circuit while the other layer constructs the Y-coordinate circuit.
As indicated below, the X-electrodes form the top layer while the Y-electrodes form the bottom layer.
- X(+) will be Vcc(5V) while X(-) will be Ground(0V).
- Voltage is applied between the X(+) and X(-) electrodes.
- When the touch screen is touched (pressed), the voltage of the X-coordinate on the top layer will be detected at the Y- electrode (A_in) on the bottom layer.
Example: If the point A is pressed, an X-coordinate voltage of 2.5V will be detected at A_in on the bottom layer.
Another example: If the point B is pressed, an X-coordinate voltage of 4V will be detected at A_in on the bottom layer.
- The detected voltage will be converted into digital data (A/D conversion), and the coordinate position of the X-direction will be recognized.
- When Voltage is applied between the electrodes Y(+) and Y(-). The touched point of the Y-direction will be recognized in the same manner as the X-direction; the voltage of Y-coordinate will be detected on the top layer.
- The detection processes of the X & Y-coordinates as described above is repeated alternately in order to detect the input point.