Based on mini2440 resistive touch screen (I): Working Principle of resistive touch screen

Reference: http://blog.chinaunix.net/uid-22174347-id-1786941.html

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Development Environment

Compilation System: fedora9

Compiler: arm-linux-4.4.3

Master chip: S3C2440

Development Board: mini2440

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I. Working Principle of resistive touch screen
Ii. S3C2440 resistive touch screen interface and internal ADC Structure
3. inputsubsystem)
Iv. mini2440 touch screen Driver Analysis

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I. Working Principle of resistive touch screen

1. resistive touch screen

The touch screen is attached to the display surface and used together with the display. If you can measure the Coordinate Position of the touch point on the screen, then, you can learn the intention of the touch Based on the display content or illustrations of the corresponding coordinate points on the display. The touch screen can be divided into five categories based on its technical principles: vector pressure sensing, resistance, Capacitive, infrared, and surface acoustic. The resistive touch screen is used in many embedded systems.

To prevent confusion between the touch screen and the LCD, let's look at a physical figure. This is what we need to know about the 4-wire touch screen. At first glance, it is a piece of glass. Next we will analyze it, how it works

2. resistive touch screen structure

As shown in, the resistive touch screen is a 4-layer transparent composite film screen. The touch screen consists of two layers of plastic film. Each layer is coated with a conductive metal (usually tin oxide ), the air gap in the middle separates the two. As shown in, two layers of white outside, I Soft Film above, the white below is the glass substrate, the middle two layers are x, y two transparent electrode layers. It can be seen that the touch screen on the top of the screen is soft, so it is also calledSoft Screen(Compared with the capacitive touch screenHard Screen)

2. How to obtain coordinate points for a resistive touch screen

The following is more clear: if a bit is pressed, x + is VDD, X-Is Gnd, Y + is AD conversion, and y-is high-impedance. In this way, the Active Value of the X axis of the contact can be measured, and the Active Value of the Y axis can also be measured.

If you do not understand the above, let's make it easier to understand. The equivalent circuit is as follows. The core of the resistive touch screen is:When a fixed voltage is applied to an electrode in the direction of X and the electrode in the direction of Y is not pressed, In the Parallel Voltage Field of X, the voltage value at the contact can be reflected on the Y + (or Y-) electrode. The X coordinate value of the contact can be known by measuring the voltage of the Y + electrode to the ground. Similarly, when voltage is added to the Y electrode pair, and the X electrode is not pressed, the Y coordinate of the contact can be known by measuring the voltage of the X + electrode. Get (x, y) to get the coordinate value of a point.

Through the above, we learned how the resistive touch screen works and how the coordinates are obtained. Next we will analyze the interface for turning off the resistive touch screen at S3C2440.