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A light pen is fairly simple to implement. The light pen works by sensing the sudden small change in brightness of a point on the screen when the Electron Gun refreshes that spot. By noting exactly where the scanning has reached at that moment resolves the X,Y position of the pen. This is usually achieved by making the light pen cause an Interrupt , at which point the scan position can be read off from a special register, or computed from a counter or timer. The pen position is updated on every refresh of the screen. The light pen became moderately popular during the early 1980s . It was notable for its use in the Fairlight CMI , and the BBC Micro . However, due to the fact that the user was required to hold his or her arm in front of the screen for long periods of time, the light pen fell out of use as a general purpose input device. The first light pen was used around 1957 on the Lincoln TX-0 computer at the MIT Lincoln Laboratory . Contestants on the Game Show '' Jeopardy! '' use a light pen to write down their wagers and answers for the ''Final Jeopardy!'' round. Light pens are used country-wide in Belgium for voting. SEE ALSO |
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