Teaching and Learning Forum 95 [ Contents ]
Projecting the power of your computer
School of Management Information
Edith Cowan University
In lectures and presentations, students and trainees these days have high expectation. They expect slick computer graphics, multimedia, demonstrations of software, and even live excursions on the Information Super highway. All of this can be achieved by linking the computer to a range of devices that allow images to be projected on to large or small screens. However, the technology is not yet being widely used for everyday teaching activities, because lecturers and trainers - particularly those who do not have a technical background - perceive these devices to be too complex, too bulky, too difficult to set up, and too temperamental to use on a regular basis. This paper discusses a comprehensive range of projection devices suitable for use with either small or large audiences, listing their advantages, disadvantages, and of course costs, which are falling rapidly.
Educators are now increasingly making use of desktop presentation software, such as Microsoft PowerPoint, Harvard Graphics, and Aldus Persuasion, to create professional looking colour slides. There are growing opportunities to make use of multimedia and other computer based and CD-ROM based material to enhance lectures and presentations, requiring the direct projection of computer screen images in to the teaching room. In areas involving the extensive use of computers as either a teaching or learning aid, it is often essential that the presenter can give "live" demonstrations of computer based material. The emergence of the Information Superhighway also means that educators will increasingly want to be able to project "live" computer images. Despite these advances in technology, the most widely used visual aid is still the overhead projector (OHP), in conjunction with basic black and white acetates. The OHP is perceived by lecturers to be simple and straightforward to use, and it is generally readily available in every teaching room. However, a wide range of devices now exist that enable computer screen images to be projected directly on to a wall or screen. In this paper I will discuss the types and range of devices available giving examples of specific devices and discussing their pros and cons.
Probably the most widely used projection device is the Liquid Crystal Display (LCD) panel sitting on top of an OHP. The LCD panel is connected to a computer and the images on the computer's monitor can be projected via the panel and the projector. This is a fairly cumbersome way of making a presentation, and the equipment can be difficult to transport and set up.
The biggest problem with LCD panels is the quality of the projected image. Most OHPs are fitted with a standard 250 Watt globe, whereas the LCD panel works best with a 300 Watt or greater quartz halogen globe. This means that in addition to the LCD panel a special OHP unit is also required, and this will cost typically in excess of $2,000. One solution is to have a trolley set up with a powerful projector, LCD panel and laptop or desktop computer. The trolley can then be moved from room to room, however in practice, this becomes very inconvenient when the equipment has to be moved between buildings or between floors.
The technology of LCD panels is not new, however it is changing rapidly in terms of number of colours, increasing panel size, ability to show video and animation. Costs are also falling steadily. A range of panels are manufactured by companies such as Sanyo, Proxima, ViewFrame, and Electroboard. The typical price of an LCD panel is $7,000-$9,000 for one that will project in colour from both PC and Macintosh. Many panel displays are too slow for video and animated graphics, but the newer active matrix panels can handle full motion video. The number of panels available is too large to allow each to be discussed in detail here, however, I am able to highlight the key items to consider when purchasing an LCD projection panel.
As with an OHP and acetates, the greater the distance between the OHP and the screen, the larger the image, and the less the brightness. An LCD panel provides a viewing window that is considerably smaller than the that of the OHP. As you might expect, the larger the window, the higher the price tag. When purchasing an LCD panel, each of these variables has to be considered in terms of the size(s) of the room(s) in which the panel will be used, and in terms of whether or not you have, or are willing to buy, a brighter OHP. Generally speaking the distance of the audience from the screen should be no more than six times the width of the projected image.
The Proxima Ovation is a typical active matrix LCD panel capable of displaying 226,981 colours. Its resolution is 640 by 480 pixels with a pixel response time of about 30 milliseconds and a contrast ratio of 200:1. The display window is 213 by 158 mm.
- LCD technology in panels, projectors, or in a laptop computer, can be either passive matrix or active matrix. In a passive matrix LCD the pixels are turned on and off using brief pulses of electric charge. They suffer from a relatively slow response time of typically hundreds of milliseconds, and so suffer from a certain amount of blurring when the image changes rapidly. In an active matrix LCD the response time is typically below 50 milliseconds, there is less blurring of rapidly changing images, and still images are considerable sharper. Needless to say an active matrix LCD device will cost more than a passive matrix device.
- The contrast ratio is the intensity difference between pixels that are "on" and those that are "off". In a passive matrix LCD this is typically in the range of 5:1 to 10:1. In an active matrix device it is typically 200:1 and greater, giving more vivid and contrasted colours.
- Ease of Use. How easy is it to set up the panel and use it? On some panels the cabling can be very fiddly, especially when connecting an additional monitor. Some have very poorly designed controls for adjusting, colour, contrast, brightness and so on. Finally, does the panel have an infrared remote control? Does it control the computer and the panel, or just the panel?
LCD projectors are based on exactly the same technology as LCD panels, the only difference is that the LCD projectors contain their own light source. As with the LCD panels, several companies manufacture a range of devices. The integrated light source is the projector's main advantage. The light sources are of the required brightness, and the whole unit is potentially far more portable than a panel and separate OHP. On the whole the image quality from LCD projectors seems to be superior to that of the panels, and most projectors have built in stereo audio speakers. Unfortunately these devices are not cheap, but prices are falling steadily. Most of the points already discussed with respect to LCD panels also apply to the projectors. In addition, however, the buyer, must be careful to check both the cost and life expectancy of the light source. Replacement lamp units typically cost in excess of $350 dollars, and last for about 1000 hours (not so bad if you think in terms of 35 cents an hour).
To give a typical example, the Sanyo PLC-300M is an active matrix projector for IBM and Macintosh computers, and also projects images from standard video cassette recorders. It has motorised focus and zoom, built-in stereo speakers, and projects 16.7 million colours. With a weight of 13.2 kg it is easily portable. The image quality is excellent, but the price tag at about $14,000 (ex tax) is rather high. Replacement lamps cost about $385 and last about 1000 hours.
It is also possible to purchase more sophisticated LCD devices having either memory or a floppy disk drive. This means that there is no need for a computer as the presentation can be read straight from the LCD device itself.
RGB video projectors
Many teaching facilities are equipped with ceiling mounted video projection units. Relatively inexpensive interface devices can be purchased that enable computer screen images to be projected directly through the video projection units. As with most projection devices, quality is improving and prices are falling. The quality of the projected image can be very good indeed, but is governed by the quality of the video projector rather than by the interface device. The interface devices can be awkward to set up, however, they can be permanently installed so that a user has only a single wire to connect to the back of their computer. There is a catch however in that older video projectors a may require adjustments before they can be used in this way, and may not be compatible with all IBM and Macintosh computers. Newer "data" quality projectors are much more flexible in this respect. A separate audio connection is usually required.
The Inline IN2020 video Interface is compatible with most IBM and Macintosh computers. It measures only 4.75" by 3.25" by 1.12" and weighs under 0.5 kg. An IN2020 costs about $730 (ex tax), with additional cabling costing typically about $150 depending on length. A separate audio connection is required.
Stand-alone video projectors are now available with built-in computer interface capabilities. These are essentially the same as the typical ceiling mounted units but may be somewhat smaller. They are usually advertised as being portable, but in practice they are far too heavy to carry around. New projectors are appearing all the time. One of the latest is the NEC MultiSync 6PG Plus, which sells for about $27,800 (including tax). Cheaper devices are available, but prices inclusive of tax are still likely to exceed $20,000.
Output to TV
For the small room presentation the computer can be connected directly to a conventional TV set. Some of the latest machines in the Macintosh range have built-in circuitry to enable output directly to a TV monitor without the need for additional hardware or software. At the moment this facility is limited to the desktop sized Quadra and PowerPC machines. However Macintosh laptops should soon have TV compatibility built in a standard. Of the Windows compatible machines, to date only the latest (and most expensive!) of the laptops in the IBM ThinkPad 755c range allow direct output to TV. The quality of the output is not outstanding, particularly where viewers are expected to view written material, but it is adequate for small group presentations. The quality of the output is also dependent upon the quality of the TV monitor being used. While direct output to TV is currently limited to the top-of-the-range models of laptop computer, the required circuitry is not in itself particularly expensive, and should add no more than a couple of hundred dollars to the cost of a machine. It seems very likely therefore that such capabilities will increasingly be delivered as standard over the next year or so.
A range of devices exist that between them will interface between almost any computer and a TV screen.
For IBM PC users, the Video Expert PV-680 PC to TV Adaptor at about $580 (ex tax) will connect any IBM PC/XT, AT 386, 486, PS2, or compatible computer. The device is controlled under the DOS operating system, but enables images generated on both DOS and Windows to be viewed on the TV, and supports the PAL standard (Australian TV standard). The screen image can be viewed simultaneously on both the TV and the computerŐs existing monitor or LCD display. The Video Expert is easy to set up and use, however it does require additional software to be installed on the computer, which can be a nuisance where it is being used by several different people. The quality of the TV image is mediocre, but adequate for small group presentations.
The Multigen Genlock adaptor supports all of IBM PC, Apple Macintosh, Atari ST, and Archimedes computers. At about $1100 (ex tax), the Multigen is a little more expensive than the Video Expert, but has the additional advantages of supporting a wide range of computers, and of being a hardware-only device. The Multigen is very easy to set up and use, but as with all other inexpensive devices of this type, the quality of the TV image is mediocre.
Other projection technologies
Other new products on the market are the Sony LCD Data Projector and the Bell & Howell Desktop Projector. Sony's projector requires the fitting of an interface board to match particular needs (i.e. Mac or PC). This projector also offers an autofocus and zoom feature which are not available on other systems.
The Bell & Howell system projects a strong, sharp image and is relatively portable. Both the Sony and the Bell & Howell are capable of projecting both computer and video outputs.
The VideoShow Presenter is a hand-held remote control which provides a miniature screen for the presenter's use. This prevents the presenter from having to look at the overhead screen thereby turning his or her back on the audience. The VideoShow Presenter also allows the presenter to preview the next image and display speaker's notes.
Summary and conclusion
Many devices now exist to enable computer screen images to projected on to a large screen. Devices exist to suit every teaching situation from large groups in traditional lecture theatres with existing audio visual facilities, to small group situations in rooms with no specialised equipment. At the expensive end of the market, the quality of the projected images is steadily improving while prices steadily fall. For those who are willing to compromise on quality, a range of less expensive devices are available that will connect to conventional large screen TV sets.
|Please cite as: Burton, A. (1995). Projecting the power of your computer. In Summers, L. (Ed), A Focus on Learning, p29-32. Proceedings of the 4th Annual Teaching Learning Forum, Edith Cowan University, February 1995. Perth: Edith Cowan University. http://lsn.curtin.edu.au/tlf/tlf1995/burton.html|
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