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Explain Light Pen and Its working in Detail

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Light Pen and Its working in Detail

Hey Readers, Hope you are doing well! again I am here with one more new article about Light Pen and Its working in Detail. So let’s begin.

Light Pen :

A light pen is a pointing device. It is used to select a displayed menu option on the Cathode Ray Tube (CRT). It is a photosensitive pen-like device. It is capable of sensing a position on the CRT screen when its tip touches the screen. When its tip is moved. over the screen surface, its photocell sensing element detects the light coming from the screen and the corresponding signals are sent to the processor.

A light pen can also be used for graphics work. A user can draw directly on the CRT screen with the light pen if the computer system is provided with Computer Aided Design (CAD) package.

Working of Light Pen :

The light pen, with its interface and software, makes a time measurement that is translated into X-Y coordinates representative of a position on the monitor. The light pens contain a lens and a photodetector located at its tip. When the electron beam that sweeps the monitor strikes the phosphor within the light pen’s field of view, the light emitted by the phosphor is focused through the lens and onto the photodetector.

The position of the beam is tracked by the horizontal and vertical counted, which relay this information to a register. This cycle is repeated for every frame produced by the electron beam. By noting when a scan goes by the measuring the interval between scan lines or entire screen refreshes an accurate position of the photodetector on the screen is determined. The light pen software generates X-Y vectors corresponding to a point on the screen, which may be used to make a selection by activating a switch on the light pen.

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