Optical pencil

Photo of the Hypertext Editing System (HES) console at Brown University, near October 1969. The photo shows HES at an IBM 2250 Mod 4 exhibition station, and you can see the lightpen and the scheduled function keyboard, the channel coupled to the central unit of Brown's IBM 360.

The stylus pen is an input peripheral for computers, in the form of a photosensitive wand, which can be used to point at objects displayed on a CRT television or monitor, in a similar manner to a touch screen but with greater positional accuracy. This peripheral is commonly used to replace the mouse or, with less success, the digitizing tablet. It is connected to an electrical cable and requires special software for its operation. By having the stylus touch the monitor, the user can choose program commands (the equivalent of a mouse click), either by pressing a button on the side of the stylus or by pressing the stylus against the screen surface.

Operation

It was long believed that this peripheral could work with any CRT-based display, but not with liquid crystal displays, projectors, or other display devices. However, in 2011, Fairlight Instruments released its Fairlight CMI-30A, which uses a 17-inch LCD monitor, controllable with stylus pens.

The pen contains light sensors and sends a signal to the computer whenever it registers light, such as when you touch the screen when non-black pixels under the pen tip are refreshed by the electron beam from the pen. screen. The computer screen is not fully illuminated at the same time, but the beam of electrons that illuminates the pixels goes through them line by line, all in the space of 1/50 of a second. By detecting when the electron beam passes under the tip of the stylus, the computer can determine the position of the stylus on the screen. The stylus does not require a special screen or coating as can be the case with a touch screen, but it has the disadvantage that holding the stylus against the screen for long periods of time becomes tiring for the user.

Modern stylus pens offer a bluetooth connection to the device, which improves the usability of the pen.

History

The stylus was created in 1952 as part of the Whirlwind Computer, developed by the Massachusetts Institute of Technology. In the early 1970s, highly specialized and high-budget machines like the CMX 600 incorporated it to give the commands required. It became quite popular during the 1980s, when it was used on the Fairlight CMI and the BBC Micro. The stylus was also compatible with various IBM PC graphics cards, including the Color Graphics Adapter (CGA), the Hercules Graphics Card (HGC), and the Enhanced Graphics Adapter (EGA). Since 1984, contestants on the television game show Jeopardy! have used stylus pens to write their bets.

Since light pens operate by sensing light emitted by the phosphors on the screen, there must be a certain non-zero intensity level at the coordinate position to be selected; otherwise the pen will not activate.