Light pens

In the ancient times" the 1950s), data were transferred to computers by using punched cards. But already in 1959 Ascher Opier from Dow Chemical Company reported the use of a light pen for graphical entiy of chemical structures into a computer. Light pens were also used in the Chemical Abstracts Service in the 1970s. 

Any program developed in-house must be easy to use, or user-friendly. If the program has various options for input, analysis, computation, and output, then it must provide the user with a fast way to select them. To meet this need, the system is likely to be menu-driven. The peripheral interactive devices such as mice, joysticks, light pens, graphic tablets, and templates are helpful and often used to expedite the selection process. 

A tablet is a device for placing selectable menus or modules on a separate, peripheral plate. It is helpful for a user of CAD software to have all the modules available displayed on the screen for selection. The only drawback in such an arrangement is that it takes away a portion of the screen space and therefore less space is available for the actual CAD activities. Selection of an item from a tablet can be made with a mouse or light pen (Fig. 4). 

Fig. 4. Selection from a tablet with a light pen. Courtesy of CalComp Inc.

Aiming Peg board Placing a dot, the beam of a light pen, etc. into circles or squares arranged in various patterns Inserting pegs into rows of holes in a board A few minutes... 

Processing the data file to remove the artificial absorption signal is relatively easy in the event that the spectrum is not too densely populated with lines and 0% absorptance levels may be found across the range of the recorded spectrum. We find that a simple point-to-point base-line subtraction method is simplest and gives the best results. This requires some accurate method to display and measure data values in the file. In our case, we use a graphic display with light pen to acquire a base-line subtraction data set. Other, less direct methods should work also. Sensitivity tests are not difficult to design and execute. 

After Fourier transformation, the effects on the spectrum of data manipulations, such as phase adjustments, can be controlled on a display before giving final calculating commands. Communication with the computer is generally via keyboard and graphic display. Light pen control via oscilloscope is also possible. 

The display hardware requires a high resolution unit (512 x 512 can be acceptable for some use, others may require 1024 x 1024) capable of at least 16 gray shades or colors (the human eye can distinguish 64 shades of gray). Some form of hardcopy is needed. The most appropriate is a photographic device (Dunn Instruments or Matrix - about 10,000). A "pick" device - a light pen, cursor, or tablet - is sometimes desirable to indicate special regions of interest. 

The term "light pen" is a misnomer, rather than writing with light, the device - a long narrow tube -detects light. The way a light pen functions is... 

Like the light pen, the joystick is a two-dimensional pick device. The Gamma-11 system used a joystick to indicate regions of interest for medical images. 

No longer are PEEKs, POKEs, or ML necessary to read the game controllers. The function JOY returns the status of either joystick. POT returns the position of one of the four paddles, and PEN is used to read the X,Y coordinates of the light pen. 

One additional type of peripheral—the light pen—can also be connected to this port. (On those models with more than one joystick port, the light pen can be connected only to port 1.) The pen contains a phototransistor that switches when it detects the electron beam of the video display sweeping past. A line is connected from the phototransistor through the port to the chip that generates the video signal (the VIC chip in the VIC, the VIC-H chip in the 64 and 128, and the TED chip in the Plus/4 and 16). 

When the video chip receives the signal from the pen, it latches (stores) the current position of the raster (electron beam) in a set of registers (memory locations within the chip). The stored value can then be read, and the position where the pen is touching the screen can be calculated. In 128 mode, the 128 s BASIC 7.0 provides the functions PEN(O) and PEN(l), which return the x- and y-coordinates, respectively, of the light pen s position on the screen. 

The usual input device is a keyboard which may contain 90 or more keys. For the novice computer user, simply finding the correct key can be a daunting task, so alternative input devices have been developed. These include touch-sensitive screens, tracker balls, light pens and so on. Perhaps the most common alternative to the keyboard is the mouse. This is simply a small box with one or more buttons on the top and a tracker ball on its underside. The mouse is connected to the computer via a single cable. As the mouse is moved over a flat surface, sensors detect the movement of the ball and the computer can calculate the position of the mouse. An arrow or similar symbol is usually displayed on the screen and this symbol moves in synchrony with the mouse. The mouse can be used to move the symbol to indicate choices on the screen and these can then be selected by pressing one of the buttons on the mouse. While experienced computer-users sometimes complain that mouse-based... 

P-41 (Zn,Mg)F2 Mn-t- Ca2MgSi207 Ce orange- yellow long (100 msec) light pens, etc... 

Radar display =16 Fl dng spot scanner = 8 Storage monitor = 1 Light pen on display = 1... 

This process of elimination left two 8088-based systems in the running One of these was the, then, recently introduced IBM PC However, the graphics capability then available on the IBM PC was limited to 640 horizontal by 200 vertical pixels Furthermore, the two general types of graphics input devices for the IBM PC were inadequate light pens were severely limited as to resolution... 

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