Light Pens :)

Introduction:

Light pen is a computer input device in the form of a light- sensitive wand used in conjunction with a computer’s CRT TV set or monitor. The light pen was used when we don’t have touch screen so for that we need a pen to select the things in the screen. The light pen is used to draw and write  something on a screen.

                         

First Light Pen: The first light pen was created in 1952 and it was a part of the Whirlwind Project at MIT. This light Pen was used in CRT screens in the U.S. air defense system. Also This first light pen was used for first time for Lincoln TX-0 in MIT.

History 🙂 The light pens was designed in 1979 by the founders of Fairlight, Peter Vogel and Kim Ryrie. The light pen became very popular during the early 1980s, because for the notable use in the Fairlight CMI and the BBC Micro.   Peter Vogel and Kim Ryrie

Something more about light pens :

The light pen had a photo sensor at the top that responds to the peak illumination that occurs when the CRT scanning spot passes its point of focus.( in the screen). the first Video game that use the light pen was the Joystick created by Will Crowther at BBN, and Don Woods

A light pen can´t work with LCD screens . the light pen was created to draw images or to write something in a screen

Circuit inside the light pen

Here is a typical basic circuit inside light pens:

     +5v
      |
      |
   resistor
      |
      +----->schmitt------->to display controller
      |      trigger
      |
  photodiode
      |
      |
    ground

HOW IS THE LIGHT PEN:

 Well as you can see in the above information the light pens is like a mouse at this moments it makes the same function, but in those years that mouse was like a pen and in the top it had a button to select the things in the screen. So well in the next video you can observe how works a light pen.

Difference between LCD and CRT screens:

In the above information I tell you that the light pens works in CRT monitor and don’t works in LCD, so i’m going to explain what is the difference between those monitors. As you can see in the image, the difference between these screens is the shape. At the same time the light pen don’t works in the LCD screens because those screens are so small so they need a big screen that is the CRT monitor.

How does it works:

When the photocell senses the beam scanning across the face of the screen, a signal is sent to the CRT controller  which causes it to record the current X,Y position of the video signal that it is generating. Depending on sophistication desired, the software can capture the limits of this region  and then determine the center of that region.

Conclusion:

So well my conclusion is that the light pen is a very important experiment because it gives us more information to created more things. The light pen in this moment is the mouse. It advanced, so is because this that we have a mouse to select the things in a computer ( screen). Interactive Light Pen Systems work with your existing mouse as an alternate selection tool.