Some Discussions On Resistive Touch Screen Technology

- Sep 20, 2019-

ouch screen technology is beginning to penetrate the medical, industrial and automotive markets outside the consumer market for reasons such as aesthetics, maintenance, cost and hygiene. With the advent of touch screens, a number of touch technologies have emerged, such as capacitors, resistors, inductors, surface acoustic waves, and infrared touch technology. Each design technique has its own advantages and disadvantages. Capacitive touch screens are based on the electrode design on the printed circuit board. They are popular among users due to touch keys, sliders and scrolling. The easy touch function adds a lot of color to the user experience. Surface acoustic wave touch technology is based on sound waves and exists in design that requires a transparent display, such as an amusement park and a large indoor environment. Infrared touch technology is based on the light discontinuity method and is mainly used for low resolution large screens. Inductive touch screen technology is primarily used for panels in plastic, aluminum or stainless steel, or panels that are exposed to liquids. Among them, resistive touch screen technology is the most cost-competitive and easy to integrate into embedded designs. This technology is mainly used to design touch screens with panel sizes up to 19 inches. Support for finger touch detection and stylus detection expands the range of applications of resistive touch technology in consumer electronics



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More and more wide. In order to choose the best touch screen technology, application designers must consider the application requirements. Resistive touch screen technology requires only a simple printed circuit board design, unlike capacitive and inductive touch screen technology, which requires electrode or coil etch on the printed circuit board. Because the touch screen is directly overlaid on the display, the printed circuit board space required for mechanical switches or capacitive touch key electrodes can be saved. Resistive touch screens are not recommended for use in harsh environments, such as mines or work sites that are often exploding or dusty. Little damage on resistive touch screens can affect touch accuracy and linearity.


Resistive touch screen works


1. A resistive touch screen is a transparent glass plate with a surface covered with a touch-responsive film.


2. The resistive touch screen panel consists of two resistive layers (indium tin oxide) with a thin layer of separation in between.


3. The two thin film layers of the resistive touch screen form a resistor network that acts as a voltage divider for the touch position detection function.


4. The touch screen causes a voltage change on the voltage divider formed by the resistor network. This voltage is used to determine the contact position of the touch screen.


5. The touch screen controller (TSC) converts the captured analog voltage signal into a digital touch coordinate signal. A built-in analog-to-digital conversion channel acts as a voltmeter for measuring analog voltage.


6. After touching the screen, the touch controller functioning as a voltmeter first applies a voltage gradient VDD at the X+ point and a ground voltage GND at the X-point. Then, the analog voltage on the Y-axis resistance is detected, and the analog voltage is converted into a value, and the X-coordinate is calculated using an analog-to-digital converter (Fig. 2). In this case, the Y-axis becomes a sensing line. Similarly, the Y coordinate can be measured by applying a voltage gradient at the Y+ and Y-points.


7. Some touch controllers also support touch pressure measurement, or Z-axis measurement. When measuring the Z-axis coordinates, a voltage gradient is applied to the Y+ axis and the X-axis.


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here are two main forms of resistive touch: software tactile solutions and dedicated touch screen controller chips.


In software tactile solutions, the microcontroller is responsible for all touch detection and coordinate calculation tasks. The microcontroller-based software algorithm uses an internal microcontroller to perform touch position voltage measurements, performing touch detection functions and coordinate processing functions.


Within the dedicated touch screen controller, the controller initiates an interrupt request to the system host (microcontroller) to detect a touch event and output digital data representative of the touch coordinates. The main processor (MCU) then reads the digital data and executes the operational commands that the client expects.


The design method based on the MCU calculation parameters requires the main processor to be very fast, in order to manage frequent touch operations. This is not a very reliable design for fast touch detection applications. Because there is no data averaging and touch detection delay function, the detection accuracy of this type of design is relatively low. A dedicated touch screen controller chip with data sampling, averaging of measurement values, touch detection delay configuration and digital touch coordinate calculation is the real touch screen controller. These chips are easy to integrate into product designs for higher performance.