Sunday, May 10, 2009

I love Overhead Projectors… sigh...

Even if you have no interest in building a homemade DIY projector, consider for a minute the hackable parts that comprise a given Overhead…like…optics! You can find anything from a single element, doublet, or even a high-resolution triplet lens in its head... Also, hey! Did someone say Fresnel lens?! They’re not just for lighthouses anymore! Not only are they crucial for homemade projectors, they’re also great for DIY solar ovens, death rays, or even as "concentrators" for solar panels! I’ve actually found that good quality Fresnel lenses can be both expensive and difficult to find… So even if you’re just looking for some parts, consider the Overhead projector!

My first encounter with DIY video projection occurred in November of 2004, by way of an article posted on Tom’s Hardware entitled Supersize your TV for $300 by Frank Völkel. His design reflected similar efforts by various European DIY communities at the time such as the German “DIY Beamer” scene and as well as some of the earliest designs by members of the DIYaudio forums. The fact that these early proofs of concept utilized ubiquitous parts like cast-off Overhead projectors and dismantled LCD monitors meant that they were (and still are) a highly accessible project and something that I’ve had a lot of fun with…(The difference between paying $300+ for a commercial projector replacement bulb and less than $20 for an Overhead’s is considerable!). While this is nothing new, I thought I’d make a post about it and talk about some of my experiences with DIY projectors, and hopefully offer some useful advice for someone interested in getting started themselves…

While the designs and sophistication of today’s homemade projectors have long since transcended Frank Völkel’s original offering, my own projector is still based on an old Overhead… Virtually all of the high end DIY projectors these days utilize metal halide bulbs… which are significantly brighter than the Halogen variants found in most Overheads, but which also require very special voltages and consequently, their own ballasts/electronics as well. I’ve been told that, unshielded, metal halide bulbs are capable of burning the paint off of a pop can within a few minutes… and while I can’t verify this myself… this kind of lore does suggest their power… So I think that for someone’s first endeavor into DIY projection, a bright Overhead is a great option… Also… for me, a great deal of the value of the project has always been in the re-appropriation of outdated (or worse, simply cast-off) though otherwise, perfectly functional machines… Surely you’ve seen a lonely Overhead projector in the corner of some classroom or office? It seems to me that after a lifetime of charts, and graphs, a perfect retirement for these machines would be a repurposing to a new life of 80’s horror movies, video games or even other projects (more to follow!). The results (and fun!) of even the most rudimentary setups are - I think - well worth the effort in tracking down some cast-off parts and dedicating a little table-top space…

I guess what strikes me the most about DIY Projectors is how simple and inexpensive the setups can be... In particular, LCD panel prices have dropped considerably since 2004 and there are even more commercial devices capable of being dismantled or “stripped” for use in a home projector… Furthermore, many of the old “Projection Panels” still haunting Ebay are still easily capable of producing VGA/SVGA (800x600) quality images… just fine for DVD!

I’ll try to explain some of the different approaches by way of my own experience and various setups that I’ve used, but please bear in mind that my aim is to illustrate the “salvaged parts + Overhead Projector” method predominantly… You can get caught up with all the current designs over at the Lumenlab user forums, but I wanted to write about the really accessible ways of putting together a homemade LCD projector… So that everyone can have one!

My first setup (2004): Modest Overhead Projector and LCD Projection Panel

My first Overhead utilized a singlet lens and I believe was rated at around 2000-2500 lumens output. The LCD projection panel was a Proxima Ovation 846 with a 640x480 native resolution @16.7 million colours… Really basic… but it worked! What’s that? What’s a projection panel? They’re basically LCD monitors without backlights… or well, backs of any kind… this is so that the light of an Overhead Projector can shine through… I guess they were sort of the original digital projector… In their heyday these panels were insanely pricey… It’s astounding to find their original early 90’s list prices… Oh wait! here they are!

OOF! Unreal, eh?

However, these days you can often find them for around $30-$100 on Ebay, depending on the model… There’s definitely a minimum range of specs required for decent video projection… Not all of these panels are “active matrix”, and not all are fast enough to produce a watchable moving image… While today’s LCD monitors (once dismantled) will produce a far superior image compared to projection panels, the latter remain one way that someone can still construct a home LCD video projector for very little effort and expense… (This option is also particularly well suited to those who may not be comfortable dismantling anything). If you’re interested in pursuing this method, you can reference the LCD projection panel database here which is very helpful for identifying potential panels, though I highly recommend that you take the plunge and go for a higher resolution LCD monitor to strip if you can get your hands on one… they produce a hugely superior image!

Required Parts and What to Look For: Minimum Specs


In terms of minimum specs…for the old-school LCD projection panels: 640x480 is your absolute minimum resolution, and I would advise at least 1.6 million colours… Also, careful with those Ebay sales, make sure it’s an active TFT not a passive or an even older greyscale panel... In my opinion, if given a choice between a 640x480 and an 800x600 panel… go for the one with the greater colour range… I’ve moved on in terms of panels, but my old Proxima Ovation 846 looks better to me in some regards than an 800x600 panel only capable of 262k colour… For newer LCD monitors, anything at or above XGA (1024x768) will be ideal… Bear the colour range in mind, but chances are your response time will be a non-issue, particularly for movies… Even older panels in the 30ms response range are often quite fine for DVD.

Overhead Projector:

In the world of the Overhead Projector, brightness is measured in “Lumen” (lm)… For projection through an LCD panel, aim for as close to 4000+ lumens as you can… and I’d say that 2500 lumens would be your absolute minimum... with that you’d probably be just fine in a completely dark room… In terms of optics, a triplet lens is ideal, but you can get away with a single or double as well just fine… On the one hand, more optics = more detail, but also more for your light to travel through, so you’ll want to make sure that if you’re using say, a triplet lens, you’ll want to have at least 3000 lumens of light to shine through it, or your image may be too dim…

Another thing to consider when selecting an Overhead projector are the dimensions of it’s “stage”, that is, the available surface area of the projector that is visible to your lens/your projected image… This has led many on a quest for panels small enough to fit within the dimensions of an Overhead stage, but with a high enough resolution for a high quality projected image. However there are some ways around some of these difficulties and I’ll explain below, but overall, the larger your “stage” the better… Oh! While I’m talking about the stage, one thing to keep an eye out for is “curved” corner stages… as opposed to clean 90 degree corners… The curved corners can crop your image in unwanted ways… while these corners can often be “dremeled,” it’s worth bearing these small details in mind as they all add up! Be sure to read the Afterthoughts and Useful Links section for some help with stage-size issues.

Putting it all Together:

If you’ve opted to use a “Projection Panel” there’s not really much left to explain… Place it on your Overhead’s stage and away you go… However, if you’re planning on stripping an LCD computer monitor, there are a few things to consider… Firstly, size and resolution: You’ll want a good resolution, but you also need it to fit well on your projector’s stage…The original guide on Tom’s Hardware recommends an XGA panel (1024x768)… This is still ideal, and anything higher is pretty much bonus… unless you’re totally intent on projecting in HD… These days most panels start well above XGA resolution, but bear in mind many of today’s panels are wide, and your typical projector stage is… well, not so much… So, in my experience a 15”-17” panel is probably going to be your maximum size, but more and more panels are turning up with much higher resolutions and in smaller physical sizes all the time (there’s a rather popular 12.1” WXGA (1280x800) kit that many people have used). The NEC panel I’m currently using is totally ideal in this capacity being SXGA (1280x1024)…square, though it is a little big for the stage… Much like “projection panels,” there are numerous user forums dedicated to which LCD monitors are most easily stripped down for use in DIY projectors…The most common issues that prevent a monitor from being suitable for the project are usually FCC cable-related… These are the extremely fragile ribbons which connect the various parts of your LCD monitor together… Sometimes they are connected across the back of the screen, which makes projecting an image through it next to impossible… Some have successfully purchased “extender” cables to remedy this in particular models, but my advice again is to just do your research and try to go with a panel that has been verified as “strippable”… of course if you manage to salvage an LCD/don’t have a choice in the matter (as most often tends to be the case) there’s only one way to find out… open it up! Once you’ve opened a few LCD monitors you’ll find that they’re all mostly the same inside... in fact, the stripping process really isn’t that bad (albeit always a little nerve-wracking)… Just remove one component at a time (don’t rush!). Always be extremely careful with the thin connectors attached to the screen… as many guides state, they are virtually beyond repair if damaged… Just take your time and before you know it you’ll have your panel down to something that looks like this…

Stripped LCD panel and accompanying hardware...

As you remove the various “sheets” from behind the LCD panel, be careful to keep tabs on which sides are front/back as it can be hard to tell without an image present… Also, avoid as much unnecessary handling of the backlight material as possible, and make sure to wash your hands well after handling any or all of the insides of LCD monitors! As the Tom’s Hardware guide states, you’ll want your panel to sit about 8 to 10mm above the surface of your projector’s stage… Styrofoam is a great material to use for some small platforms... I also like to use a regular PC fan powered by an old ATX power supply for cooling… A single fan to the side of the panel is usually just fine. Some also recommend placing a UV filter and or tempered glass in between the light source and optics/ LCD panel to protect them, but I’ve found this isn’t much of a concern when dealing with an average Overhead Projector bulb… However, a metal halide driven setup would require both without exception.

When assembling your Projector, it’s usually easiest to place the panel down first and then connect it to its hardware once it’s properly in place … It also helps a great deal to mount the panel’s hardware on a small board to keep them in place (especially helpful if you plan on using multiple inputs on your Projector). All of these measures amount to how you basically want to minimize the “flex”/movement of those thin connectors as much as possible… I had one that broke on me in a real sack-over-the-head-punch-in-the-stomach sorta way … and then again, I had another panel that the kittehs knocked to the ground (a totally fragile stripped panel!) and it’s still completely fine… go figure. But it never hurts to be super careful!

My Current Setup: 3M 9700 and NEC 1712 17” LCD

I was really lucky and came across an old 3M 9700 a few years ago and I’ve been using it ever since… It’s rated at around 4000 lumens and (according to the internet) uses a 342mm triplet lens… It was love a first sight obviously… Until recently, I had been using an LCD that I had stripped from an old Samsung cell phone advertisement-kiosk-thing… It has a resolution of 800x600 but as I mentioned earlier, only 262k colour… Initially, I was hoping it would prove to be a significant step up from my old projection panel, but in retrospect, I think the colour of the Proxima panel more than made up for its modest resolution… It’s not really a fair comparison as the smaller kiosk LCD really wasn’t made for movies… Then, close to a month ago a friend of mine gave me an old no longer working 17” LCD monitor… Upon close inspection, besides a failed backlight, the panel itself was in great shape… I knew what had to be done…

Stripped 17" LCD panel...

She may not look like much, but she's got it where it counts...

Afterthoughts and Useful Links:

There are some really useful resources out there for would-be DIY projection hobbyists… Many sites have all sorts of parts for sale (you can upgrade literally every part of your projector once it’s up and running)… Additionally, some sites such as the DIY Projection Company/Lumenlab even have downloadable plans, should you want to build an enclosed design. If you’re looking for info on Overhead designs and other techniques I highly recommend reading through some of the old DIYaudio threads where some of the earliest designs emerged… Both sites have excellent user forums!

Since the parts for DIY projectors are so often salvaged, it’s not uncommon to find yourself with great components, but ones that don’t want to work together… In this capacity, perhaps the most common difficulties involve a mismatch of LCD panel size and projector stage size… Some opt for programs such as Powerstrip (or a display driver utility) to manipulate display resolutions to get a better fit… However, if your LCD is simply larger than your projector stage (most common scenario), fear not! Not too long ago I stumbled across Zort15's blog… A fellow DIY projection hobbyist in a similar situation, he wrote a really clever little program that allows you to resize your image and adjust its display position it on the fly… It’s sort of hard to appreciate how useful this app is until you find yourself needing something like it... Download link below.

Lastly, (and it often really is the last thing one has to consider) is what precisely you’ll be projecting onto… Again, there are countless options for DIY screen making, from special paint, to simple “blackout cloth” from Fabricland/ville. I’ve even heard of people getting decent results with shower curtains… Point is… You have many options! Thanks to some sweet retired teacher hookups I managed to get an old projection screen that was being tossed from a local high school… but eventually I caved and purchased a 100" 16:9/ “wide” projector screen (visible in the pictures) which I have been very happy with… Whether you intend to build an HD projector, or are just looking for something to do with an old LCD panel, DIY LCD projectors are not only a lot of fun, but one of many cool projects possible with Overheads!


The LCD Projection Panel Database
Zort15’s Projector Program
The DIY Projector Company
Lumenlab DIY Projector Forums
DIYAudio Forums

News of the summer project soon!

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posted by Marcus at 8:57 PM | 0 comments
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