Capacitive touch

Common forms of capacitor screens:

(1) Capacitive Touch (SCT,Surface)

When the finger touches the metal layer, due to the electric field of the human body, the user's touch screen surface forms a coupling capacitance. For high-frequency current, the capacitance is a direct problem, so the finger draws a small current from the contact point. This current flows out of the four electrodes of the touch screen, and the current flowing through these electrodes is proportional to the distance from the finger to the four corners. The controller calculates the precise proportion of these four currents to get the position of the touch point.

(2) PCT, Capacitive Touch

Basic principle of self-Capacitive touch

In touch detection, the self-capacitor screen detects the horizontal and vertical electrode arrays in turn. According to the capacitance changes before and after touch, the horizontal and vertical coordinates are determined respectively, and then the planar touch coordinates are combined. Self-capacitor scanning is equivalent to projecting touch points on the touch screen to the X-axis and Y-axis respectively, then calculating the coordinates on the X-axis and Y-axis respectively, and finally combining them into the coordinates of touch points.

Basic principle of mutual capacitive touch

The cross capacitor screen also USES ITO to make transverse electrodes and longitudinal electrodes on the glass surface. The difference between it and the self capacitor screen is that capacitance will be formed where two sets of electrodes cross, that is, these two sets of electrodes constitute the two poles of the capacitor respectively. When the finger touches the capacitive screen, it affects the coupling between the two electrodes near the touch point, thus changing the capacitance between the two electrodes. When the mutual capacitance is large, the horizontal electrodes send out excitation signals in turn, and all the longitudinal electrodes receive signals at the same time. In this way, the capacitance values of the intersection points of all the horizontal and longitudinal electrodes can be obtained, that is, the capacitance of the two-dimensional plane of the whole touch screen.