Analog is gone, long live digital! Not only have video and audio moved into the world of bits and bytes — the connectors associated with them have, too! Not only that; digital connections have gotten smarter and are now true “plug and play” interfaces. Just connect your video player, computer, digital camera, and projector, and the connection does the rest.
In this installment of Your Guide To Classroom Projection, we’ll examine each of the digital connections you’re likely to find on a classroom projector in more detail — how they work, what they can and can’t do, and what they’re likely to look like in the future. We’ll also touch on some new digital connectors that you may see coming to market in the near future.
We’ve been dealing with a bucketful of different analog video, audio, computer, and control signal standards for years now. Composite, S-video, component, RCA, mini, RS232, VGA, SCART — no two of these plugs looked or worked the same.
The result was usually a rat’s nest of wiring and a color-coding nightmare. Didn’t have the right video or computer connection for your projector? Too bad, because that often meant a long search for the right adapter — a search that didn’t always end happily.
Sometimes it was a breakout cable to connect component video through a VGA jack. Other times, it was a VGA-to-BNC adapter. If the projector manufacturer opted for a proprietary, non-standard connection, you were stuck forking over lots of money for the required video and audio adapters. Grrr!
With digital interfaces, it’s a different ball game. Manufacturers have standardized on a few connector types, some of which are actually related to each other! This has greatly simplified projector wiring and has also cleaned up the rat’s nest.
That doesn’t mean that analog interfaces have gone away just yet. You’ll still find the time-tested 15-pin VGA jack on most classroom projectors, although there is a digital replacement waiting in the wings. And the familiar yellow composite video jack is still hanging around, as is the ubiquitous S-video DIN jack (even though practically no one uses S-video connections these days).
Now, let’s take a closer look at each of those digital interfaces, and talk about where you are likely to find them.
DVI connectors have been around for over a decade. They were originally developed to replace 15-pin VGA jacks on desktop computers and monitors, establishing a “smart” connection between the two and optimizing the picture size and sync automatically. This is accomplished with a connection known as Extended Display Identification Data, or EDID, and includes the display’s brand name, model number, serial number, screen size, supported resolutions, and native display resolution.
DVI connectors exist in two forms. The first, known as DVI-D, is an all-digital interface and uses either 12 or 24 pins in a locking connector to carry video signals from computer to projector. The second, DVI-I, is actually a hybrid digital/analog interface. Four additional pins carry analog red, green, blue, and sync information. DVI-I allowed monitor manufacturers to support both older computer graphics cards and the newest DVI-equipped cards.
There are two operating modes for DVI, and they’re known as single link and dual link. In single link mode, the maximum bandwidth of a DVI connector is 165 MHz. That’s sufficient to show a 1920x1080-pixel image refreshing at 60 Hz, or a 1280x1024-pixel image refreshing at 85 Hz. Only 12 of the connector’s 24 pins are used in single-link mode.
In dual link mode, all 24 pins are used, increasing bandwidth to 330 MHz. That’s enough to show images with a maximum resolution of 2048x1536 pixels and a refresh rate of 60 Hz. In practice, single-link DVI is the most common connection, and you’ll be most likely to find it on larger desktop and installation classroom projectors.
One thing to remember about DVI is that it only carries video and computer signals — no audio. DVI can also carry a copy-protection data channel, ensuring the connection between media player and projector remains secure.
At one time, DVI was a common connector on DVD players and set-top boxes, but the lack of audio connectivity pushed it out of favor. Instead, a newer, smaller digital interface, HDMI, stepped up to replace DVI on these devices…and is fast becoming a ubiquitous audiovisual interface on a wide range of products.
HDMI came into existence in 2002 and was originally developed as a digital AV connection for consumer electronics devices. Functionally, HDMI is identical to DVI when it comes to moving video signals. But HDMI also adds a layer of digital audio — up to eight different channels. It retains the copy protection function originally developed for DVI, which goes by the name High-bandwidth Digital Copy Protection (HDCP).
HDMI connectors look very different than DVI connectors. The connector shell is much smaller and flatter, and there are no screws to fasten an HMDI plug to its jack. HDMI uses fewer pins — 19, instead of 24.
HDMI v1.1 offered the same bandwidth as single-link DVI-D (165 MHz, or 5 gigabits of data per second). The standard has been updated several times, with the most significant changes coming in 2007. HDMI v1.3 saw the single-link bandwidth increased to 340 MHz, allowing a maximum data rate of 10.2 gigabits per second. That was essential to connect higher-resolution displays and video sources.
HDMI v1.3 also added support for wide color spaces, like xvYCC, as well as multichannel digital surround-sound formats. In addition to carrying eight channels of digital audio, HDMI can also handle control signals for operation of AV equipment. All that, in a single cable that can run 15 feet or more!
A new update to HDMI has been announced. HDMI v1.4 can handle even higher image resolutions (4K x 2K) and incorporates a two-way Ethernet channel that offers speeds up to 100 megabits per second. HDMI will also support two independent channels of high-definition video for 3D displays.
Not all of these features are important on projectors, and most of them will wind up on consumer HDTV sets, set-top boxes, and media players. But it’s possible that HDMI may eventually replace the DVI connectors found on larger projectors — that is, if a more secure HDMI connection is developed, one that locks into place and can’t slip out easily.
Although it’s not yet in widespread use, the DisplayPort connector should start to appear on classroom projectors within the next five years. DisplayPort was developed by the Video Electronics Display Association (VESA) to replace the VGA connector, once and for all. But it’s a more sophisticated approach than DVI.
DisplayPort connectors look a lot like HDMI connectors. They’re much smaller than DVI plugs and also slide into place with no locking screws. Unlike HDMI, DisplayPort is considered to be an “open” interface standard — not proprietary.
DisplayPort uses 20 pins for signal communication, differing from DVI and HDMI connectors by its use of high-bandwidth “lanes” to move all display data in sequence, not in separate channels. Up to four lanes are available in one direction to move “micropackets” of data that contain RGB signal levels and clock information. A smaller, return lane is used to transmit EDID and HDCP information between the computer and projector at a maximum rate of 1 megabit per second.
At present, DisplayPort can carry up to 10.7 gigabits of data per second. That’s enough to display images with 2550x1536 pixels of resolution! It can also carry multiple channels of high bite audio, like HDMI, and supports 8-bit, 10-bit, 12-bit, and 16-bit color information.
The scalable architecture of DisplayPort is intended to handle even higher resolutions and refresh rates. Compression of the data packets makes this possible — higher compression allows more packets to pass at maximum bandwidth. Error correction is built-in to the system to accommodate dropped packets.
More importantly, DisplayPort can directly drive a comparably equipped digital display with cable lengths up to 15 meters (50 feet). The minimum specification for direct drive is 1920x1080 resolution with progressive scan at 50/60 Hz refresh rates and 24-bit color. The current version of DisplayPort, 1.1, also includes a design for a 26-pin connector to be used in embedded applications.
Although it’s not a display interface, many people still mistake the USB connector on a projector for that purpose. USB was designed as a fast way to move data from peripheral devices to computers, and the current version (2.0) was standardized in 2001. Keyboards, mice, printers, scanners — all of these depend on USB connections.
USB can move data at speeds up to 40 Mb/s. That data can include everything from video and still photographs to audio files, spreadsheets, and documents. It can even include Internet connections! Flash memory “thumb drives” use the USB interface exclusively and have enabled easy connections to projectors for applications such as displaying photos.
There are also companies that have actually demonstrated computer display hookups to projectors using USB ports, instead of the usual DVI and HDMI connections. Because it is just a high-speed serial data interface, USB has no copy-protection issues, like HDMI.
USB technology isn’t sitting still. A new specification (3.0) was released last year and will provide data transfer rates ten times faster than USB 2.0. Ultimately, this will allow direct playback of high-definition video files directly through projectors without a separate, external media player.
Sanyo’s new PLC-WTC500L is a high-brightness LCD projector that delivers WXGA (1280x800) resolution with 500 lumens of brightness. It’s ideal for large classroom and auditorium installations.
Sanyo designed a brand-new optical engine with organic LCD panels for the PLC-WTC500L. It also includes SANYO's Lamp Selection System, which automatically cycles between two separate projection lamps, resulting in as many as 6000 hours of operation before lamp replacement.
Two lamp operation modes are available. “Alternating Mode” uses a rotation cycle that alternates between the two lamps at regular intervals, while “Relay Mode” uses one lamp continuously and switches to the other lamp when the first lamp reaches the end of its useful life.
The PLC-WTC500L also features Picture-in-Picture and Picture-by-Picture modes, which enables the simultaneous projection of two images from separate sources. The Picture-in-Picture Mode displays a sub-screen over the main screen.
The projector is also equipped with SANYO's exclusive Active Maintenance Filter (AMF) system, which detects air blocks or clogs and automatically scrolls the filter reel to the next clean filter. There are ten filters included in every cartridge, dramatically lowering maintenance and the time required to check and change filters.
Power vertical/horizontal lens shift plus 360-degree vertical tilt allow the projector to be installed almost anywhere, including the ceiling or the floor. The PLC-WTC500L is available now and has a suggested retail price of $6,995.