RESISTIVE TOUCH SCREEN

TOUCH SCREEN

A touch screen is an electronic visual display that can detect the presence and location of a touch within the display area.

ADVANTAGES WITH TOUCH SCREENS

•      Eliminates the need of keyboard input.

•      Device becomes cheaper and lighter.

Quicker to navigate/ speed of correct selection is increased.

    

TYPES OF TOUCH SCREENS

•      There are several types of touch screen such as   resistive, capacitive, surface acoustic wave, optical imaging, strain gauge and so on.

•      The most commonly used types are the resistive and capacitive.

RESISTIVE TOUCH SCREEN

Resistive touch screen basically have two layer i.e. X-layer and Y- layer with both having resistances connected in perpendicular fashion to each other. As a result of this resistance pattern there exists a specific value of output voltage at specific points on the touch screen. These are read as the values of x and y respectively. Now these x and y values makes a sort of matrix and thus can be used to define n number of switches.

RESISTIVE TOUCH SCREEN PRINCIPLE

•      This layer has resistance network from right to left.

Now if we supply voltage across right and left sides of this layer then there will be specific value of voltage for each row, which can be taken across any of the two remaining sides and ground.

4-Wire Resistive Touch Screen

These are the least expensive and most commonly used types of resistive touch screens. Conductive bus bars with silver ink are implanted at the opposite edges of a screen layer.

The principle of operation is such that, as shown in Figure if one side of a layer is connected to +V and the other side to ground, a potential gradient results on the screen layer, and the voltage at any point on this layer becomes directly proportional to the distance from the +V side.

In a 4-wire touch screen two measurements are made one after the other one to determine the X and Y co-ordinates of the point touched by the user. Figure shows how the X co-ordinate can be determined. Here, the right and left hand sides of the top layer can be connected to +V

and ground respectively. The bottom layer can then be used to sense and measure the voltage at the point touched by the user. An A/D converter is used to convert this analogue voltage to digital and then determine the X co-ordinate.

Similarly, Figure shows how the Y co-ordinate can be determined. Here, the upper and lower sides of the bottom layer can be connected to +V and ground respectively. The top layer can then be used to sense and measure the voltage at the point touched by the user. Again, an A/D is used to convert the voltage to digital and then to determine the Y coordinate.