As a human-computer interaction interface, the touch screen has largely replaced the previous human-computer communication methods such as keyboard and mouse. Resistive touch screens have become one of the main touch screens for their low price and stable nature. In daily applications, it is often necessary to operate multiple points at the same time. However, the touch points of the touch screen will affect each other, resulting in wrong touch point coordinates. This paper optimizes the judgment algorithm of two-point touch, and realizes the correct recognition and positioning processing of multi-touch. Experiments show that it can realize the functions of zooming in, zooming out, and rotating the image.
Multi-touch refers to the technology that can correctly recognize and locate two or more touch operations at the same time, can independently determine the operation meaning of each touch point, and realize the corresponding function. This is a simple and convenient human-computer interaction operation mode that gets rid of traditional input devices. There are currently two types of multi-touch technology 1: multi-touch gesture recognition and multi-touch position recognition.
At present, the most common method on the market is multi-touch gesture recognition. When a finger touches multiple points on the screen at the same time, it can recognize the direction of each finger's movement, and can perform operations such as rotation, zooming, and translation, but it is not yet possible to determine the specific position of each finger. However, in the case of two-point touch or even multi-point touch, multiple maximum values will be generated on the X and Y axes, and the system cannot determine the exact position of the touch point at this time. The points that are not really touched are usually called "ghost points".
Multi-touch location recognition is the true multi-touch technology, which can identify the specific location of the touch point without the phenomenon of "ghost points". This touch technology is based on the mutual capacitance detection method, which judges the touch point by the change of the coupling capacitance Cm at the intersection of the rows and columns. When the finger touches the mutual capacitance between the rows and columns, it can be judged that the touch point exists, and the position of each touch point can be accurately judged.
1 Resistive touch screen multi-touch technology
To achieve two-point touch, each work unit must be independent of each other, and the touch points can only be in the same work unit. The method of multi-touch with resistive touch screen is given: apply voltage to the X1 electrode, and read the X coordinates detected by the A, B, and C touch units by the Y1, Y2, and Y3 electrodes; in each subsequent cycle Read the coordinates of X2 and X3 in sequence. After obtaining the X coordinates of all touch units, voltage is applied to the Y electrodes in turn to obtain the Y coordinates of each touch unit, so as to achieve two-point touch.
2 Two-point touch judgment algorithm implementation
cut unless touch point
When there is a touch point on the surface of the touch screen, the upper ITO conductive layer dents downwards, deforms, and contacts the lower ITO. There is a resistance between the two ITO conductive layers of the contact point. The smaller the resistance value between. By calculating the corresponding resistance value, the touch position can be obtained, but if you want to correctly identify the position of the two-point touch, you must first eliminate the non-touch point. The so-called non-touch point refers to the point of contact that has no intention. These touch points are random and are not valid touches. For example, when the touch force is light, the resistance of the ITO conductive layer of the touch screen is at the critical point of being connected and not connected, and touch points like this are non-touch points. The contact points produced without the control of will are meaningless for the whole test, so they must be eliminated.
Considering the randomness of non-touch points, the method of two measurements can eliminate them. If the result of the first measurement is a valid value, but the result of the second measurement exceeds the range specified by the resistance of the entire touch screen and is a large value, then it is regarded as an invalid value, and the point is non-contact Point, it must be eliminated. Conversely, if the result of the second measurement is within the range specified by the resistance value of the entire touch screen, it will be regarded as a valid value and a valid touch point.
improvement of contact resistance
The pressure of the touch screen is different, and the resistance value of the ITO conductive layer is also different. That is to say, the resistance generated by lightly touching or re-touching the touch screen is different. The control chip can test the resistance value of the contact resistance, but it cannot distinguish whether it is a light touch or a heavy touch. This will only affect the accuracy of judging the touch point, which will affect the reliability of the entire touch screen.
