Water will increase the capacitance, which will affect the capacitive touch screen to judge the signal, and even water droplets on the tablet touch screen, even after wiping the water droplets, and that piece of the touch has problems, or not working, or occasionally appear false touch signals. On a good day, a finger touch can be detected after a while. In most cases, it is difficult to regain the original touch sensitivity. We know that a qualified product does not allow such a situation to occur, let alone rely on good luck. Therefore, how to solve the problem of finger touch failure and false trigger caused by water is a challenge in the design of multi-point capacitive touch screen. When water falls on the touch screen, because water conducts electricity, it changes the electric field coupling between the two sensing modules. For a water drop the size of a finger in diameter, the change in the signal generated by it will certainly be smaller than the change in the signal generated by a finger touch. It is usually 1/4 the size of the finger touch signal, but it is in the opposite direction of the finger touch signal.
Because finger touch decreases mutual capacitance, water drops increase it. This makes it easy for designers to create the illusion that water dripping on the mutual capacitance screen is not mistaken for finger touch, which means that the product is not triggered by mistake. When the offset of the basic present value due to water approaches or exceeds the set hand value threshold, the false trigger occurs at the moment the water is wiped off. In many cases, this false trigger cannot be easily restored to normal because the offset base line value cannot be easily updated back to the normal base line value. False trigger will last a long time, even need to reset the touch screen system.
How to eliminate the false trigger caused by the wiping of water droplets is a challenge for the waterproof design of the mutual capacitor screen.
To solve this problem, it is important to know when the droplets start to arrive on the capacitor plate. There are several possible reasons why the base line value is skewed in the opposite direction of the AD conversion value when the finger touches it. For example, changes in ambient temperature (high and low temperature test), humidity; Static interference; When the touch screen system is started, the finger is just pressed on the touch screen, and the finger is removed after starting, etc.
How to distinguish the basic line value change caused by water droplets on the mutual capacitance screen and the basic line value caused by other circumstances is the key to know that there are water droplets on the mutual capacitance screen.
The main feature of the capacitive touch screen is the different behavior caused by the influence of water on the self-capacitive and mutual capacitive screens. Taking full advantage of this feature and using alternate scanning makes it possible to design a waterproof intercapacitive touch screen.
It requires touch screens to be capable of both mutual capacitance scanning and self-capacitance scanning. By alternating the scans, the signals produced by the droplets are detected in the signal changes caused by various factors. Once the signal produced by the drop is detected, the base line value will remain unchanged until it knows who has been wiped off and the base line value will be updated in good faith according to the previous rules.