كيف يتم توصيل ال Touch Screen واين تباع فى مصر ؟

A touch panel is a thin, self-adhesive transparent panel placed over the screen of a graphic LCD. It is very sensitive to pressure so that even a soft touch causes some changes on output signal. There are a few types of touch panel. The simplest one is the resistive touch panel.

It consists of two transparent rigid foils, forming a 'sandwich' structure, that have resistive layers on their inner sides. The resistance of these layers usually does not exceed 1K. The opposite sides of the foils have contacts available for use through a flat cable.

The process of determining coordinates of the point in which the touch panel is pressed can be broken up into two steps. The first one is the determination of the X coordinate and the second one is the determination of the Y coordinate of the point.

In order to determine the X coordinate, it is necessary to connect the left contact on the surface A to ground and the right contact to the power supply. This enables a voltage divider to be obtained by pressing the touch panel. The value of the divider is read on the bottom contact of the surface B. Voltage can be in the range of 0V to the power supply and depends on the X coordinate. If the point is closer to the left contact of the surface A, the voltage will be closer to 0V.

In order to determine the Y coordinate, it is necessary to connect the bottom contact on the surface B to ground, and the upper contact to power supply. In this case, the voltage is read on the left contact of the surface A.

In order to connect a touch panel to the microcontroller it is necessary to create a circuit for touch panel control. By means of this circuit, the microcontroller connects appropriate contacts of the touch panel to ground and the power supply (as described above) in order to determine the X and Y coordinates. The bottom contact of the surface B and left contact of the surface A are connected to the microcontroller's A/D converter. The X and Y coordinates are determined by measuring voltage on these contacts, respectively. The software consists of writing a menu on graphic LCD, turning the circuit for touch panel control on/off (driving touch panel) and reading the values of A/D converter which actually represent the X and Y coordinates of the point.

Once the coordinates are determined, it is possible to decide what we want the microcontroller to do. In this example, microcontroller turns on/off two digital pins, connected to LED diodes A and B.

This example use functions belonging to the Glcd and ADC library.

Considering that the touch panel surface is slightly larger than the surface of the graphic LCD, in case you want greater accuracy when determining the coordinates, it is necessary to perform the software calibration of the touch panel.

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