DLP Projector Discoveries

© Beverly Howard, Austin, Tx, 2004

As one can imagine, since we "killed our TV" almost four years ago, watching rented movies on VHS and DVD has become a primary entertainment source.  After looking at the mouthwatering, but "out of our price range" plasma displays since their introduction, I was finally very close to opening the bank account and taking the plunge anyway.

A couple of accidental events suddenly removed the possibility of paying $6,000 for a mid range plasma display.  The first was a visit to a "Home Theater" store in Austin.  As it happened, during the hour that I was there, almost all of the displays were showing a water racing event that involved huge rooster tails of water spray behind each vehicle... and those tails told the unmistakable tale that the displays were not fast enough to keep up with the screen updates as the few CRT based sets in the store were able to do.

I ended up at a friend's house for supper about a week later.  He works for Dell and had brought home a Dell digital DLP projector to use the following morning for a presentation that he was giving.  "Just for grins" we hooked the tiny projector to his DVD player with an SVideo cable, popped Shrek into the player and pointed it at the sheet rock wall.

After we figured out the configuration and remote control, I was stunned... the quality of the picture on painted sheet rock far exceeded anything that I had seen on any plasma display, including the $15,000 units.  The movie we watched with leisure that evening was four times as large as the largest plasma screen on the home market.  Both of us agreed that the only downside of the temporary setup we had just thrown together was that the projector was unacceptably loud and that it would be necessary to build a soundproof housing to make home movies totally acceptable.

The DLP concept is mind boggling. Over a million movable mirrors on a computer chip allow the generation of a bright, crisp and accurate image that approaches the image quality that you will encounter in the theater itself.  An additional benefit is that the technolgy is immune to "pixel burnout" something that I had also been able to observe on the plasma displays the previous week.

About a week later the tiny (3.5 lbs, 9.4 x 7.4 x 2.9 inches) Dell 3200MP DLP Projector arrived and, to our delight, the projector noise problem had been addressed to the point that the fan noise was not noticeable during a movie.  It's price was below $2,000, less than a third of what I had finally been ready to pay for a plasma screen. Although this unit's life here was destined to be short lived, it provided a good introduction to DLP projectors.

Screen Interference 

After the great "sheet rock" viewing experience, I had been looking forward to seeing projection on a truly reflective screen and put up our slide projector screen for the first viewings... but there was a problem, specifically "pattern interference"  This screen was made up of a grid small rectangular reflective "cells"  Since the image is also made up of a rectangular grid of "pixels" the result displays halo patterns across the screen... the simple blank wall was a better match.

Since there appeared to be no reasonably priced screens in Austin, the next stop of Lowes for a sheet of gloss white masonite.  It was to be temporary, but is still reflecting pixels after eight months of use.  It was actually too reflective... and, as you can see from the picture, the board is flush with the wall at the bottom but leans outward about 4" at the top.  This deflects the reflection of the bulb light through the lens to the floor.

Also discovered during the screen and mounting process was the fact that locating the mount point was critical to the inch.  The Dell had a zoom lens but it was also quickly discovered that the full zoom only provided about a foot of difference in placement the projector to fully cover the screen.

Because of the relative close distance between the projector and screen, "keystone" issues are exaggerated.  The projector setup "default" assumes that the projector will be about even with the bottom edge of the screen, or in the case of mounting it upside down on the ceiling, with the top edge.  In the image above, you can see that the projector is mounted around 3 feet above the top edge of the screen when the screen angle is considered.

This results in a trapezoidal image with the bottom edge becoming about 8 inches wider than the top image... and the ability to adjust difference is built into the projector's configuration.  The configuration also has the ability to adjust for the same type of distortion horizontally in the case that the projector is left or right of the center of the screen.

However.... if both horizontal and vertical are off, you can adjust each, but the corrections are not perfect as the distortions in each plane compounds the other plane's distortion.  In fact, in the example shown, positioning the projector more than an inch left or right of the exact center of the screen becomes unacceptable.  (As a result, there are now four holes in our ceiling ;-)

Ceiling Mounts

Looking at the available commercial ceiling mounts left me cold.  The ones that I saw were far larger than necessary for the tiny DLP projectors not to mention the fact that they were very expensive in view of the construction and design, so I fabricated my own and it went through a several step evolution.

The first fabrication was for the Dell which provided a 1/4" camera mount threaded socket on the bottom of the projector.  A washer was welded to a 2.5" piece of 3/4" steel conduit.  A piece of aluminum angle was secured to the Dell mount through a piece of sheet rubber to both avoid damage to the case as well as prevent movement over time.  The 2.5" length of the mount tube was eventually reduced to 1.5"

The projectors are mounted to the ceiling upside down and the configuration on all digital projectors should allow you to invert the image back to upright.  The inverted mount gives the additional advantage of being able to easily reach the control and power buttons on the projector from below.

The analog to digital component on the Dell went south shortly after the projector was moved to the ceiling... the projector still worked fine when attached to a VGA output but any analogue input resulted in hash on the screen, so it was Dell tech support time... <sigh>

Suffice it to say that this support experience resulted in the decision to return the unit for refund even though I feel that it is an excellent piece of hardware.  IMHO, if a piece of equipment that is more expensive than any computer that I had bought in the five previous years condemned me to that level of support, the ability for it to provide a useful viewing experience for the next several years was in serious question.

Enter the Viewsonic

The Dell's replacement was a Viewsonic PJ250 using the same DLP technology.  With a lower price and smarter shopping, it ended up costing over $350 less than the Dell 3200MP and was even smaller.

The most obvious difference was the lack of zoom lens, a decision made with the experience learned from the Dell.  The Viewsonic offered less lumens (1000 vs 1300) but higher contrast (2000 vs 1800) which, in our case, we felt was a wash.  Both of the units were native XGA (1024x768 pixels) and far, far superior to the lower cost SVGA (800x600) resolution projectors.

The Viewsonic cabling approach was also more standard... the Dell took all analogue input through the digital interface... which means you have to use expensive adapter cords if you need a second cable or a replacement.  The Viewsonic has a smaller digital connector and uses a separate 1/8" audio connector (available at Radio Shack) to input analogue composite, SVideo and Component I signals.

The Viewsonic also didn't have a tripod mount, but offers three small (3mm) threaded points on the bottom of the projector so that a triangular piece of aluminum plate can be mounted on short standoffs and the plate drilled to provide a solid mount.

After purchase, I found two significant negatives (which were still not worth returning the projector) that would, however, have been significant pre purchase factors.

First, the cooling fans do not turn off when the projector is shut down... if the power cord remains attached, the fans continue to run at a very low speed, quiet, but noticeable in a quiet room.  My solution was to add a switch to the power connection.

Second, some configuration settings, notably the "keystone" settings are not retained when the power cable is disconnected, both probably on the assumption that the unit will be constantly moved from one location to another.


Both projectors were actually very quiet when run on a table or camera tripod, but the ceiling mount transmitted these minimal vibrations to the ceiling sheet rock which did an admirable job of amplifying the sound several times... enough to be distracting during a movie and very noticeable in the dead of night with the Viewsonic in it's "off" state.

Back to the ceiling mount drawing board.  I removed the ceiling mount and cut a 1/4 inch section out of the 1.5 inch length of 3/4" conduit.  After rounding the edges of the cut ends (and with difficulty ;-) I inserted the two pieces into a section of automotive heater hose leaving about a 1/4" gap between the cuts and secured the hose with two pop rivets at each end.  To my relief, this "shock mount" removed all of the noise that had been previously transmitted to the ceiling.

Couple of final notes... as the final image shows, the mount is adjustable in two planes... horizontally leveling the projector requires bending the aluminum angle.  For a size reference, the nuts are standard 1/4" size... smaller than the image would suggest.

You might have noticed from the images that the ceiling mount location changed between the Dell and the Viewsonic.  The discovery there was that the screen location will drive the furniture layout of the room (doh!)  The screen was originally mounted on the fireplace which forced the furniture into an unworkable layout when we were not watching videos, so make that part of your planning, plus you might want to set things up temporarily for a couple of weeks before you start drilling holes.

The flat conduit on the ceiling in the pictures is available from hardware sources.  This minimal conduit runs both the power and the triple lead analogue video input.  While I have tried all of the input options, in the end, settled on using composite input.  My eyes cannot tell a difference and it provides the ability to easily switch between the DVD and VHS players which only provide composite output.

Further, it allows the use of many tuner/amp consoles which provide the ability to control both the audio and video feeds from both players using a single tuner control.  The "One for All" controller makes a huge difference because one remote controls three devices for each movie, four devices in all when the different players are considered.  In our case, the remote we have is pre-programmed for all of the devices except the projector which was addressable by capturing the projectors on, off, keystone and aspect buttons to programmable buttons on the remote.