Hardware Concepts: Input Devices(Continue i)

Hardware Concepts:  Input Devices(Continue i)

1.      Touch panel

The touch panel allows the users to point at the screen directly with a finger to move the cursor around the screen, or to select the icons. Following are the mostly used touch panels.

a.      Optical touch panel

It uses a series of infra-red light emitting diodes (LED) along one vertical edge and along one horizontal edge of the panel. The opposite vertical and horizontal edges contain photo-detectors to form a grid of invisible infrared light beams over the display area. Touching the screen breaks one or two vertical and horizontal light beams, thereby indicating the finger's position. The cursor is then moved to this position, or the icon at this position is selected. It two parallel beams are broken, the finger is presumed to be centered between them; if one is broken, the finger is presumed to be on the beam. There is a low-resolution panel, which offers 10 to 50 positions in each direction.

b.      Sonic panel:

Bursts of high-frequency sound waves traveling alternately horizontally and vertically are generated at the edge of the panel. Touching the screen causes part of each wave to be reflected back to its source. The screen position at the point of contact is then calculated using the time elapsed between when the wave is emitted and when it arrives back at the source. This is a high-resolution touch panel having about 500 positions in each direction.

c.       Electrical touch panel:

It consists of slightly separated two transparent plates one coated with a thin layer of conducting material and the other with resistive material. When the panel is touched with a finger, the two plates are forced to touch at the point of contact thereby creating the touched position. The resolution of this touch panel is similar to that of sonic touch panel.

2. Light pen

It is a pencil-shaped device to determine the coordinates of a point on the screen where it is activated such as pressing the button. In raster display, Y is set at Y_max and X changes from 0 to X_max for the first scanning line. For second line, Y decreases by one and X again changes from 0 to X_max, and so on. When the activated light pen "sees" a burst of light at certain position as the electron beam hits the phosphor coating at that position, it generates a electric pulse, which is used to save the video controller's X and Y registers and interrupt the computer. By reading the saved values, the graphics package can determine the coordinates of the position seen by the light pen. Because of the following drawbacks the light pens are not popular now a days.

·         Light pen obscures the screen image as it is pointed to the required spot

·         Prolong use of it can cause arm fatigue

·         It can not report the coordinates of a point that is completely black. As a remedy one can display a dark blue field in place of the regular image for a single frame time

·         It gives sometimes false reading due to background lighting in a room