The Projector Project
Build your own digital movie projector
PHOTOS: James Turner
The heart of the digital movie projector is an LCD panel , which first needs to be stripped from its casing . A triplet lens is mounted at one end of what will be the projector’s wooden case . The LCD panel is mounted in the middle. Note the lens and bulb positions marked [4, 5]. Here is the projector’s interior, seen from the side, front, and rear [6, 7, 8]. When completed, the rear will house the bulb, ballast, and a thermostat for the fan , while the center will have the two Fresnel lenses, the LCD panel and control circuitry, and a heat shield . At last! Lights, projector, action !
A good high-definition LCD projector can still set you back US $2000, but if your wiring and woodworking skills are up to speed, you can put one together for around $600.
It’s not like you have to build it from scratch. At least two companies, DIY for Life and DIY Projector Kits, sell kits and supplies that make this something any engineer could do in a weekend.
The key items are an LCD panel and a pair of Fresnel lenses. A Fresnel lens is thin and light, made out of a piece of plastic into which concentric grooves have been cut, giving it a large aperture and short focal length. (The first Fresnel lenses were invented for lighthouses.) It doesn’t do a good job of projecting light, though, so you also need a different kind of compound lens, known as a triplet lens.
Here, the first Fresnel lens beams light from a source through the liquid-crystal display, which I’d stripped from an LCD panel. On the other side a second Fresnel focuses the image to a point on the third lens, which projects the image out onto a plane about 3 meters away.
That’s the heart of the project; the rest is just the casing. The bulb gets quite hot, so a Lexan or tempered glass heat shield is placed right before the innermost lens. A fan at the back pulls cooling air down over the LCD panel from a slit in the cover.
I bought nearly everything from DIY Projector Kits: the lenses, heat shield, high-intensity light and ballast, a thermostat to run the fan, some hardware to mount the bulb, and a set of measured plans for a generic 15-inch display-based enclosure. The entire package, including shipping, ran just under $450.
I picked up a refurbished Samsung 15-inch LCD monitor for $124 on eBay. The Samsung had been rated by DIYers as very easy to strip, and sure enough, it took me less than 30 minutes to do it. I overbought on wood, probably using about $50 worth of high-quality 2-centimeter plywood.
The trickiest part was getting the light-path measurements right so that everything lined up. Then there was the adjustable focus ring. The instructions in the kit suggest starting with a 5-cm shower drain. Perhaps drains differ from region to region, but after a lot of carving with a Dremel hand tool and some plastic fumes inhaled, I finally did have a pretty nice adjustable focus.
I mounted the lens with a 1.25-cm vertical offset, to provide ventilation, and attached the bottom and right-side panels. Next I cut rear holes for the fan and plug/power-switch module and mounted them. Then I attached the rear panel, cutting grooves into two pieces of wood to space the middle lenses, the LCD panel, and the heat shield the correct distance from the front lens. Finally, I wired the electronics and the power to the LCD panel.
I tested the optics before adding the right panel, with more grooves to hold the tops of the lenses and the LCD. While I was installing the LCD panel, I twisted one of the mounts, cracking the display. It still functioned well enough for testing.
Finally, I put the top on, temporarily without a ventilation slit or hinges. I attached my MacBook to the LCD panel input and fired up the lamp. It worked perfectly the first time!
A few words of advice: Experience with optics isn’t required but would be helpful. And besides the electronics, which involves little more than basic wiring, you’ll need to be comfortable working with wood. Nothing was particularly difficult, but the measured plans leave a lot for you to figure out.
You should also be aware that at the end of the day you’ll end up with a large, heavy appliance--a piece of furniture, in fact. The version I built measures 76 by 43 by 28 cm and weighs around 10 kilograms. Also, unless the LCD panel can handle video input, you’ll have to drive the display from a computer. There’s also no zoom--you control display size by moving the unit.
The project took me about 25 hours over the course of two weeks. I still have to hinge the cover, put in the ventilation slit, and seal all the light leaks. And, of course, I’ll need to replace the cracked LCD panel.
During testing, the projector threw a very nice wall-filling image from my MacBook’s Digital Visual Interface port. I don’t have the equipment to measure the output, but 1500 to 1700 lumens is commonly reported for DIY projectors of this type. By contrast, a high-definition projector from Best Buy will put out around 1200 lm. It will also cost hundreds of dollars the first time you have to replace a bulb, which you’ll have to do every 2000 to 4000 hours. The one I used should last around 10 000 hours, and it cost $50. Now if I only had a wall in my house big enough to use it with! An ideal projection area would be around 2.5 meters, measured diagonally. James Turner
About the Author
Author James Turner says there’s more to a doâ¿¿it-yourself project than just building it. His new LCD digital video projector is sitting idle in his laundry room until he can clear enough wall space to display its capacious images. Turner is a contributing editor for O’Reilly Media and a correspondent for the Christian Science Monitor .