Light pen

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Using a light pen on a computer terminal , 1969

A light pen , also Lightpen or Light Pen called, is a computer pointing device to work directly on a CRT monitor . It was developed in 1955 at the Lincoln Laboratory ( Massachusetts Institute of Technology ); the first CAD application Sketchpad with light pen was presented in 1963.

If you keep the narrow one, with a photo transistorIf the end of the rod-shaped device is provided on the screen, the “flash of light” generated when the electron beam hits the luminescent layer (which the human eye can perceive as permanent light) is converted into an electrical signal. If, on the other hand, the electron beam hits a different position than that of the light pen, the phototransistor remains inactive. On the basis of the time of the signal triggered by the phototransistor, the start time and the speed of the electron beam guided over the screen, the position of the light pen can finally be calculated by the computer; the position is therefore determined indirectly. The light pen cannot work on black or very dark parts of the picture because of the missing light pulse.

Professional use experienced light pens u. a. in control rooms for air traffic control and data centers , for example , which can still be seen today in films and documentaries.

Light pen for Thomson home computers

The light pen gained a certain popularity in the early 1980s (especially through its use as a universal pointing device on Thomson home computers such as the TO7-70 and as a kit for the C-64 ), but was increased a few years later by the much more ergonomic and in the Production of cheaper computer mouse displaced.

On modern screens ( LCD , plasma , 100 Hz tube) the light pen is unusable due to the missing or no longer assignable light flash.

The lightgun (light gun) used for some computer games is based on the same principle, but has additional focusing optics in order to be able to detect the “flash of light” generated by the electron beam at a greater distance from the screen. For modern, no longer tube-based televisions, however, a different procedure is necessary.

literature

  • William Newman, Robert Sproull: Principles of Interactive Computer Graphics, pp. 180-182, 199-204. McGraw-Hill, New York 1973, ISBN 0-07-046337-9

Web links

Commons : Light pens  - collection of pictures, videos and audio files

Individual evidence

  1. Lev Manovich: The Language of New Media (PDF; 989 kB) ( Memento of the original from July 30, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.manovich.net
  2. ^ Wurster, Computers ISBN 9783822857298 p. 23