DIY Projector Guide - Part 1 - The Parts
From Lumenlab
Contents |
Introduction
Yes you can build a high quality lcd video projector for a fraction of the cost of a consumer video projector. As a matter of fact you can build a high quality XGA projector for the cost of a light bulb for a consumer projector! (A light bulb for a consumer projector costs between $250-$600!) This project is fun and relatively simple. It can be completed in a few days if you have obtained your parts. In the following example the total cost was $400, using all new components. You can save even more money by sourcing used components from Ebay...it’s up to you. You can take your projector all the way to HDTV by using a high quality lcd panel. There are many advantages to building it yourself! You learn in the process and get to make it exactly the way you want. Your friends and family will be impressed to say the least, and you will have many years of enjoyment from your creation. The best part is when you need a new bulb years from now, it will only cost you $15! This project can be fun for the whole family and would make an excellent science fair exhibit. This guide should contain the basics you need to get you on your way, but even more information is provided in the Lumenlab Forums. I hope you enjoy building your projector as much as I did!
Lenses
For an in-depth look at lenses see Lenses What lenses do and a bit of how they do it.
Projection Lens
The projection lens is simply a magnifying lens in that it takes the projected image and magnifies it onto the projection screen. This can be accomplished with what is called a singlet lens (single lens). Problems occur when using a singlet lens, namely chromatic and spherical aberration, which is the tendency of a single lens to shift or distort the color information and the image information. To correct these aberrations, other lenses can be used to compensate for the singlet lens’ problems. The most common lenses used in projectors today are triplet lenses. The triplet lens contains 3 lenses in total; a magnifying lens and two additional lenses that correct for aberrations in the magnifying lens. Fortunately, high quality triplet lens assemblies are widely used in overhead projectors and readily available.
The FocalLength of your projection lens is important to the construction of the projector, and should be matched to your collector FresnelLens. The FocalLength of our projection lens for this project is 320mm.
Important Considerations: Our DIY projectors un-like most commercial projectors use a fixed projection lens rather than a zooming lens. This means that the only way you can control the picture size is to move the projector closer or farther away from the screen. A zoom lens is a complicated and expensive component. As of this writing there is no acceptable zoom lens for our projectors. As it stands you’ll need to carefully consider where your projector will be located. You can use the Lumenlab.com focal length calculator to determine throw distances and picture size. You could use a longer focal length projection lens to make the picture smaller but you would have to find a matching fresnel lens. Your enclosure size would also be increased. It is a market reality that quality fresnel lenses other than those used for overhead projectors are quite expensive. You can however make your picture smaller using your computer software or your lcd monitor’s controls, this does however decrease the resolution.
Where to Buy:
- S15 Projection Lens - 15" Projectors
- Pro Projection Lens - 17-19" Projectors
Fresnel Lenses
A thin optical lens consisting of concentric rings of segmental lenses and having a short focal length, used primarily in spotlights, overhead projectors, and the headlights of motor vehicles.
The fresnel lens is simply a flat sheet of optical acrylic (plastic) or glass that has been embossed, molded or cut to have a series of concentric beveled circles (or beveled horizontal lines for a different type of fresnel) on its surface. When a light ray strikes the beveled edge it is bent at an angle to the bevel. The greater the angular degree of the bevel, the more the light ray is bent. All of these beveled circles acting together form a lens. Anyone who has seen a flat page magnifier has seen a fresnel lens.
Due to the fact that fresnels are a series of lines or circles, they do not make good optics for projecting real images. Some of the image information would be missing because a fresnel only imitates a spherical lens surface. The fresnel lens is however a nearly perfect lens for bending raw light; it is cheap and it is large, a comparable spherical glass lens would cost a fortune.
The Fresnel lens is divided into annular zones, each of which duplicates the contour of the corresponding zone of a regular lens. With the exception of the outermost zone, each zone of a Fresnel lens is thinner than in a regular lens. The steps between the zones do reduce the Fresnel lens' optical quality, but for some applications the much reduced weight makes this a worthwhile tradeoff.
Where to Buy
- S15 220mm Fresnel Lens - 15" Projector
- S15 317mm Fresnel Lens - 15" Projector
- Pro 220mm Fresnel Lens - 17-19" Projectors
- Pro 650mm Fresnel Lens - 17-19" Projectors
LCD Panels
The heart of the 15” projector is the TFT LCD panel. The LCD panel is translucent, which is how we can shine a light through it and project the image created on the panel. If you’re interested in how a LCD panel works I would suggest reading:
http://computer.howstuffworks.com/lcd.htm
3a. A common lcd computer monitor
3b. A ‘stripped’ LCD monitor
‘Raw’ panels are available, but we will be using a LCD panel from a common computer monitor. While it would seem easier to buy a bare panel rather than strip a computer monitor, it isn’t. The primary reason is expense. To buy a bare panel with the same specs you would have to spend several times the amount for which you can get a common computer LCD monitor. Strange isn’t it? Thanks to market forces the assembled computer monitor is ubiquitous and cheap comparatively. New computer LCD monitors can be found for as little as $125, but there are some issues you should be aware of before buying one. The first consideration is quality; that is, how good do you want your projection to be?
LCD monitors come in a variety of resolutions, contrast ratios, diagonal sizes, response times and dot pitches. Resolution should be as high as possible. Contrast ratio should be as great as possible. Diagonal size should be as small as possible. Dot pitch should be as small as possible...in a perfect world. Realistically excellent quality projections can be made with resolutions as low as 800x600 pixels (SVGA)...and many quality panels are available rather cheaply. For the 15” projector an excellent panel would be a 1024x768 (XGA) monitor with a 400:1 contrast ratio, 15ms response time and .28 dot pitch. The drawbacks of low cost panels meeting these specs are their size: 15” diagonal. The bigger the panel, the bigger the enclosure, optics etc. Naturally we’d want our projector to be as small as possible in most cases. Economics require us to use panels that are 7” or bigger; the cost skyrockets for high resolution sizes smaller then 7”. A 15” high quality panel is very affordable, for the XGA panel mentioned above we’d pay ~$150 new and as little as $50 used as of this writing. The 15” ["CMV 1515"] in the picture above (3a.) meets our requirements with XGA resolution, 500:1 contrast, 15ms response and .28 dot pitch. This panel may or may not be available in the United States at any given time. Most budget high quality panels are imported from China and supplies can be sporadic.
Important considerations: Depending on the monitor/panel you choose you may only have VGA (computer monitor) inputs. This basically means that you can only send signal to your projector with a computer unless you have a dvd player with a VGA output (available online for $50 and up). LCD monitors are available with VGA and composite (standard rca) inputs but they tend to cost much more for no apparent reason. Having VGA inputs only isn’t so much of a problem though. You can use your computer’s video card to ‘passthrough’ video if you have such a card. You can also obtain dvd players that have VGA outputs. Probably the best option is a ‘line doubler’ or ‘external TV box’. These are relatively cheap devices that have several types of inputs (VGA, composite, s-video, coax) and a VGA output. They may come with a TV tuner and remote as well. Your video projector is a high resolution device capable of displaying 1024x796 pixels or higher (or lower) depending on the monitor you selected. This is important to note because television resolution is a mere 320x240, and has ‘scan lines’; that is, a TV only displays every other line of information for each scan pass it makes. If you were to simply project a television signal through your projector your image would be small and you would see these scan lines, in other words it would look pretty bad. This is not a limitation of your projector but rather a consequence of the old TV broadcast technology. At any rate the line doubler fills in these scan lines and can sometimes up-scale the resolution of TV broadcasts to your projector resolution, 1024x768. While the picture won’t look as good as a digital medium like DVD, it will be acceptable. Line doublers such as KWorld’s ‘TV box’ do all of this for around $60. Needless to say video tapes will have this same problem as they are designed to be played on a television. To get good results you’ll need the line doubler or a computer video card that does the same thing.
LCD Resources
Lighting
Lamps
Although there are many lamps that can be used in your projector, extensive research and testing by Lumenlab and our members have proven the 65K T15 lamp to be the best for a 15" projector. Using this lamp has several advantages. A perfect color temperature, a high CRI and a lifespan rating of 20,000 hours. By comparison, the lamps in a consumer video projector have life spans of 1000-3000 hours and cost up to $200-$600 a piece! That’s more than you would have to spend on your entire projector!
Ballast and Base
You’ll also need a socket (base) for your lamp. The 65K T15lamp uses a mogul base. Additionally you’ll need a ballast for your lamp. Metal halide lamps use high voltage to create an arc that excites a mixture of gasses in a quartz envelope. The ballast is what transforms normal household current into the higher voltage. There are two types of ballasts you may consider, ‘electronic’ and ‘coil and core’. Electronic ballasts are solid state, compact and lightweight, efficient and run much cooler than a coil ballast.
Understand that the ballast needs to be matched with the lamp. You cannot use a ballast for a high pressure sodium lamp with a metal halide lamp! You cannot use a 250 watt ballast with a 400 watt lamp!
WARNING: Working with line voltages can be very hazardous. These instructions cannot teach you about 120 volt wiring and safety. If you do NOT understand basic 120 volt wiring STOP NOW. Metal halide bulbs can emit dangerous UV radiation if the outer glass envelope is cracked. DO NOT USE A DAMAGED BULB! These bulbs become hot and can burn you, use common sense and be very careful. Do not look at the bulb for any extended period of time, it will burn your eyes!
Lighting Resources
Where to Buy
