Lcd Controller

Lcd Controller

Resistive Touch Screen Lcd Monitor And The Lcd Display

Resistive Touch Screen LCD Monitor and the LCD display is difficult to fully and accurately all the points with, so addition to calibration of precision mechanical assembly technology, the use of software must also be calibrated before. This article describes the calibration method first determine the source of error, and then export the three selected points, touch-screen calibration matrix, and use the software method to implement the corresponding relation between points of calibration. To master this technique for reducing the cost of embedded systems is essential.
Figure 1 shows a resistive touch-screen cross-section, its structure is very simple, from top to bottom the relative placement of two pieces of glass composition, the inner surface of glass coated with a thin layer of conductive material, and used some small glass beads across the surface of the conductive open. When the finger or stylus press the glass surface, the upper contact with the lower glass bending glass. The structure of glass beads determines the distance between the touch screen sensitivity. The more glass beads placed near each other, the sensitivity the smaller the greater the pressure necessary to make reliable contact with two layers of glass.

Touch screen calibration method – mxpopstar – The Frozen Throne
Figure 2 shows the equivalent circuit of touch-screen. Through a touch screen controller (AD converter) to the power of the positive and negative added to a conductive layer of the glass at both ends, and the other a piece of glass on the conductive layer is to play the role of a potentiometer cursor. On glass of different touch points, conducting the situation is different, digital converter will be recorded in the different test voltage value, then controller will be recorded in the voltage value converted into a two-dimensional coordinates: X-axis coordinates and Y coordinates of .
These controllers can be 200 times per second or more of the sample. Sampling rate usually associated with background noise and controls relating to the quality. Intelligent controller also has other features such as touch is detected when the interrupt CPU, it detects a continuous sample rate of touch created before the sample. Do not touch, the controller is in standby mode.
Since resistive touch screen, simple structure, operation easy to understand, there are multiple vendors of hardware and software required to choose from, it can be used for cost-sensitive designs. However, due to its 7 Inch Touch Screen LCD display behind the (LCD or otherwise) between the corresponding points is difficult to fully cope with, so almost all with resistive touch screen equipment in the factory prior to go through a certain degree of calibration. Otherwise, the touch screen by clicking on a button or select a feature, the built-in software will not be able to make the right response to this click.

Touch screen calibration method – mxpopstar – The Frozen Throne
This article describes the calibration method requires three target points / or test points, and then in turn touch the test to determine the screen-specific calibration factor. Final adoption of these calibration factors to the corresponding point of touch-screen display and the actual corresponding points correspond exactly to them.

Source of error
There are several error sources affect the touch screen controller, make it impossible to generate the correct corresponding points X and Y coordinates. The main error source is the electrical noise, mechanical error and the amplification factor. In addition, the operator’s misoperation will have an impact, such as finger or stylus press time is not long enough or pressure is not big enough. All of the above errors would generate useless data, it must be corrected in order to compensate for touch-screen work.
In a variety of electrical systems, from the thermal effects or electromagnetic effects as well as system design flaws caused by electrical noise is everywhere. In the touch screen, because the AD converter front-end circuit with high input impedance, it is particularly vulnerable to electrical noise. In addition to touch screen controller with a careful layout of the circuit, we usually increase the AD converter input low-pass filter to solve this problem. In addition, the software can also choose to approach, abandoning AD conversion of the smallest one, two, and use the algorithm allow the error falls outside the scope of some data points removed from the sample stream. The software algorithms can also be eliminating user-generated error.

8 Inch Touch screen calibration method – mxpopstar – The Frozen Throne
Calibration methods described in this paper can be used to solve due to mechanical error and the amplification factors of the error. The circles in Figure 3 under the LCD touch-screen display graphics, oval indicates when the user along the circle, when the image LCD display, touch screen corresponding to the set of points, but somewhat exaggerated. The redevelopment of the graph is clear through a series of rotation, shift and zoom, but also the parameters of transformation in each direction is different. Focus calibration malpractices displayed on the touch-screen graphics through the transformation of this reconstruction, conversion out of the graphics and the LCD display consistent set of corresponding points.

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LPC2478 LCD Controller