Touch screen interfaces are a highly effective medium of operating personal devices (like smartphones, tablets, etc.) or public informational devices (ATMs and ticket vending machines, for example) because of their highly interactive and user-friendly nature. Touch screen switch panels are also gaining popularity and can be seen in the control panel of cars, smart washing machines, and many other appliances. A variety of touch screen light switch is being used today in different types of applications, each having their own advantages and drawbacks. The two main types of touch screens used today are the resistive touch screens and the capacitive touch screens.
The resistive touch screen senses a touch when the pressure applied by the touch leads to contact between the two conductive layers of the screen. A capacitive touch screen, on the other hand, detects a touch when static charge from the screen is transferred to the human skin or stylus. Due to low prices, the resistive touch screens are preferred over other touch screens in areas where image quality can be compromised for low prices.
When a touch screen is touched at a given point on the touch screen, it creates an analog signal that containing some noise, which needs to be filtered and converted into digital signals, which is known as Data Acquisition. Also, when a touch screen is pressed, it leads to vibrations in the conductive layers and inductive and capacitive effects due to the drivers. The reading can be taken only when the voltage has settled. The time elapsed until this happens is called the settling-time. This settling-time also needs to be taken into account while taking the readings. Be
cause of such challenges, sensing and interpreting the touch signals requires a very advanced and sophisticated system which is generally called Touch Screen Controllers. These systems are available in the form of small chips (ICs).
As soon as the screen is touched, a series of processes are triggered inside the touch screen controllers. First of all, a few readings for the X-coordinate of the touched region are taken. After this, several readings are taken for the Y-coordinates as well. Similar happens for Z-values (if the system supports three-dimensional analysis). After this is done, the values of X, Y, and Z readings are averaged to reduce the noise in the signal. Then, the touch screen controller checks if the variation between different readings doesn’t fall outside a particular range or else, the readings are discarded and the whole process is repeated from the beginning.
The whole process involved in determining the position of the touch is carried out by the intelligent touch screen controller and no involvement is required from the CPU but the CPU just receives the final result and then processes it.
