Been eyeballing those sweet new high definition projectors? So have we. We're not going to feel guilty for it either, we know what we like. But if your wallet is a little light from your last Engadget inspired shopping session you might dig our how-to latest project. In Today's how-to, we'll start taking a look at building your own HD projector... from an LCD Monitor. This isn't one to be missed.

Building your own projector isn't a new idea. Disassemble a desktop LCD display, put a really, really bright light behind it and add some optics and voila! you've got a projector. The real question: is it worth it? Since you might be a little leery of dropping several hundred dollars on parts and gutting a nice display because people you don't know on an online forum said so, we're going to do it for you.

If you're hell-bent on doing all the research yourself, there are couple of places to check out. Lumenlab recently made access to their forums free. Alternatively, The DIYaudio forum users have some interesting ideas.

Lumenlab has put together a nice document describing the details. We'll give you our short version here. The design is really quite simple. The light source is reflected towards the LCD. A Fresnel lens behind the LCD straightens the light so the maximum amount will pass through the polarized LCD. Another Fresnel focuses the light towards the projection lens.

The LCD is key to the project. The latest crop of LCDs is cheaper and better than ever. Notably, the contrast ratio has been increasing. It's important to choose a display that can be disassembled easily and won't have any inconvenient electronics in the way. Size does matter. LCD size will affect the lenses required and obviously the size of the completed enclosure. For our build, we chose the Samsung 940MW-SV Silver 19-inch 8ms Wide-screen LCD Monitor with built in TV Tuner. This beauty has a contrast ratio of 700:1 and a .294mm pixel pitch. The 16:10 screen has a 1440x900 native resolution, so it will display 720p natively. The built in scaler supports 1080 input as well.

We have to give props to the guys that are using the WXGA screen that's usually only found in laptops to achieve native 1080 resolution. There was enough interest for these that they actually had a custom controller built to support it.

More importantly, our LCD accepts almost any input. It sports DVI (With HDCP support), VGA, Component, S-Video input and even coax for the built-in TV tuner. We should be able to hook up just about any HD gear we want to this display. We run standard definition video through our video scaler, but there's just not a good way to push a HD signal into the PC from an external tuner like our HD Tivo.

To maximize the light aimed at the screen, we'll add a reflector just behind the bulb. Some use Ikea napkin holders, but we opted for this reflector from Lumenlab. It's coated with a dichroic material that reflects visible light, but allows infrared heat to pass through.

The light source is a 400 Watt Metal Halide bulb. You can score these at the hardware store, but for the best color we want one that puts out light that's a similar to daylight as possible. That means a bulb with a color temperature of 6500 Kelvin (and hopefully an even spectral output).

The Mogul base of our MH bulb is quite a bit bigger than the average light bulb.

To ignite a Metal Halide bulb, some interesting voltages are needed. To produce them we'll need a ballast. These things come in a few flavors. The coil type are cheap, but produce a humming noise that might interfere with your viewing pleasure. Electronic ballasts are preferred because they'll protect the bulb better and don't produce annoying noise. Our 400 Watt MH electronic ballast cost $100+shipping from HID hut. (They shipped it five minutes after we ordered!) We didn't expect it, but our ballast came with a ceramic Mogul base.



Back to our diagram we see that the LCD is sandwiched between a pair of Fresnel lenses. The lenses need to be at least the size of the LCD, if not bigger. The only source we could find with big enough Fresnel lenses is Lumenlab. The Projection lens needs to be matched to the Fresnel lens on the same side of the LCD.

Since we required their large lenses anyway, we ordered a set of matched Pro lenses. The 'Pro' lens kit includes both Fresnel lenses and the projection lens.

Now that you've got the general idea of what we're doing, it's a good time to start crunching numbers to get a rough idea of what we're looking at. Lumenlab has a couple of calculators built just for figuring things out. Focalcalc runs under windows. Remember that if you're entering the width of the LCD diagonally, then the screen width is a diagonal as well. If you prefer other OSs, there's a php version that runs under most web browsers.

Lumenlab took about a week to ship out their backorder, once they did, our stuff got here in record time. The star of the order was this 'pro' lens. It costs about four times as much as its little brother, but it's the way to go if you're using a large LCD like we are.

We compared the picture quality from the HDMI and component outputs from our HR10-250. There was simply no question that the digital signal produced a much cleaner picture. Unsurprisingly, 720p output from the TiVo produced the most pleasing results.

We picked up a pair of new cables to get our video signals to the new photon gun. A 25 foot HDMI to DVI-D cable for our TiVo and a new 25 foot SVGA cable for the HTPC. No, the HDMI-DVI cable wasn't that expensive.

Before we add up all our parts, keep in mind that this is an Engadget build. There are plenty of ways to save money on this project, but we're feeling sassy. (And we're hoping to build something worthy of replacing a venerable Sony VPH-1272Q CRT projector.)

Let's recap all the parts we bought so far:
  • Samsung 940MW-SV $330 from NewEgg (We spotted them at Sam's Club too)
  • Pro Lens Kit (2x Fresnels and projection lens) $199 from Lumenlab
  • Pro Reflector $15 from Lumenlab
  • Ceramic Mogul Base $10 from Lumenlab (We scored an extra with our ballast)
  • 400Watt 6500K Metal Halide bulb - $50 from Lumenlab
  • 400Watt MH Electronic Ballast $99 from HID Hut
  • 25 foot HDMI to DVI cable $37 from Monoprice [For our HR10-250 HD Tivo]
  • 25 foot VGA cable $8 from Monoprice [For our HTPC]
Total parts cost far: $748 (This thing better work...)
Left to buy: Enclosure, cooling fan and a few finishing touches.

Given the cost, why build your own? Replacement lamps for commercial projectors cost around $300 each and only last a few thousand hours at most. The lamp in our projector should last about 10,000 hours and costs $50 to replace. You can build your own projector for far less than we're spending. LCDs with bad backlights are cheap, and the lenses needed for the smaller LCDs are only $60 for a matched set. You can scrounge them up from surplus shops, but you'll spend some time hunting them down and getting things right.

We've geeked out, ordered a load of parts and scared our editors with the hardware tab. Next time we'll gut our sweet new LCD and give you all the details on doing it yourself. Then we'll move on to designing, testing and building our enclosure. When it's all done, we'll give it a thorough review.