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Building Cheap 100 Inch TVs
Nastar writes "If you visit eBay and such places there are guys selling 'kits' so that you can easily build your own 100 inch projection screen. There are websites such as 100InchTV selling the instructions for around $10 a pop. They say "this is the only product of this kind on the web" and "it is now possible to convert any type of television or computer monitor into a 100 inch video system that's truly amazing!". I don't like the idea of these people selling this information, especially when you can get it free from the good people at BSTV BSTV. Ihaven't built mine yet, but the reports of quality differ from so-so to fantastic! I suppose it depends on perfecting the technique involved. "
Yeah, the instruction costs $10. It doesn't tell you the equipments you have to buy.
For me, constructing 100 inch or even more display is "easy". Just buy a projector (that costs $4000) and then project it to a screen or wall. Simple. The farther the distance, the bigger is the resulting image. You can then adjust the focus. Voila. Fragging big time! :-)
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I've heard that the quality is only good for either animated movies, or real movies. I can't remember which it was, but at the time I was researching this stuff, I saw mostly images of one type, which I think was animated.
As you can see from the image at BSTV, actual footage comes out as you would expect, only so-so. It makes sense that this would only work well for animations, as those usually have large areas of solid colors, and would appear less pixelated when blown up as such.
XML is like violence. If it doesn't solve the problem, use more.
Oh, and nevermind the fact that with today's technology and a greater emphasis than ever on DVD and digital picture we're willing to throw away $10 at whatever snake oil peddler comes along. "Just project it on your bed sheets!"
For shame this made it as a Slashdot topic.
Schnapple
http://members.tripod.com/schnapple99/
Schnapple
http://www.google.com/search?q=cache:1pInHo8PDFk:w ww.webone.com.au/~caoz/bsinstructions.htm+%22free+ 100+inch+TV+projector%22&hl=en
Google cache right here
w ww.webone.com.au/~caoz/bsinstructions.htm+BSTV+100 +inch+plans&hl=en
http://www.google.com/search?q=cache:1pInHo8PDFk:
There are other sites with the instructions that haven't been slashdotted. See: http://www.greenspun.com/bboard/q-and-a-fetch-msg. tcl?msg_id=0038A5
If that doesn't survive, get it from the google cache.
ARP
Exactly.
Standard TV has 480 interlaced lines at best. There's a reason people don't make NTSC TVs larger than about 60".
If you truly want to go for 100" of quality, get an HD projector with a nice silk screen.
After a few weeks with my 65" HDTV I think I'd puke if I watched TV on a 100" STV.
That's Mr. Eradicator to you.
trance-port
Yet, 100 inches is not the height, but the diagonal measurement. (assuming a 4x3 ratio) :)
(4x)^2 + (3x)^2 = 10000 in^2
16x^2 + 9x^2 = 10000 in^2
x^2 = 10000/25 in^2
x^2 = 400 in^2
x = 20 in
3x = 60 in
60 inches = 5 feet.
So, technically up to five feet, not eight.
(I feel like I am back in middle school...
I would think it would be very blurred, very hard to see (they don't give off THAT much light), and the colours would wash out.
I'd be curious to hear of anyone's actual experiences in building one of these.
I built a setup like this as a kid using a fresnel lens and a bed sheet. I even rigged a translation stage for the lens for precise focusing.
Problems were as follows, in order of severity:
Because nothing really acts like an ideal lens, the image focused on to a curved surface. I was using a flat sheet as my screen. This meant that either the center was in focus, or a ring around it was in focus, but not both.
You can reduce this by using a longer focal length, an aperture, or both, but this is trickier and loses light.
I was using one lens. This turned the image upside-down. This meant I had to turn the TV upside-down to get a usable picture. This made the TV image turn funny colours. I have no idea if this happens to most TVs or not. A well-made TV *shouldn't* have this problem - it _should_ only be gravity-sensitive if some of the focusing coils are loose inside it. The electron beam certainly doesn't care about gravity. YMMV.
You can get around this by using two lenses instead of one, or by turning the image upside-down with two mirrors before projecting it. This adds complexity and takes up space.
An alternate solution - that I used the first year I did this - is to put the TV flat on the floor and project on to a sheet on the cieling.
You get some colour spreading, but not that much. The main problem is that the image will be at least a little blurry no matter what you do. Especially if your lens is like mine and is scratched up from handling.
Projecting through a sheet degrades resolution, because the sheet scatters light within itself. You can either look at the image from the back (either getting a mirror-image or needing a mirror to flip the image), or use a very thin sheet and view it from the front.
I solved this by hosting my video parties in the basement and covering the windows. YMMV. Real projection TVs have CRTs designed to operate more brightly than normal TV screens.
These aren't insurmountable problems; just very annoying ones to solve.
I was curious and found a link to plans. Assume it is the same type of design. I'll stick with my projector.
There's a reason that people who are actually INTO projection only use line doubled (or better) images. It takes a lot of the ugliness out of the NTSC standard. Most HDTV sets are sold with built in line doublers now, of varying degrees of competence.
There's no way in hell you could put one on this kind of thing though. The electronics can't handle the increased scan rate that would be required.
It's not an issue of resolution - you're going to get the same resolution no matter what - it's an issue of quality. The real projection manufacturers work to control things like bloom, distortion, convergence, etc. on this scale. The requirements for a 32" TV are far less. And the vast majority of consumer TVs do a piss poor job even at their designed size. You have colors that don't even vaguely approximate reality because sets with more red sell better on a showroom floor. The contrast and brightness (aka white balance) are way off the scale because of the same reason.
And brightness on these suckers is gonna suck. CRT projectors have low brightness anyway, and they're designed to be projected up to large sizes. Digital projectors (LCD, DLP, DILA) have 2-5x the brightness of a CRT and are still made for darkened rooms.
Will some people be happy with it? Sure. Same people that download 100MB VCD's of some 2 hour movie and think it looks and sounds great, or listens to lowest quality MP3's (or hell, FM radio) and thinks they've never heard anything better.
The only thing that makes me hope that the average consumer can indeed choose VASTLY improved quality over price is the success of DVD.
IANAEE, I got tired three credits short, but...
Consider a hypothetical tv show which displayed a solid, bright, red background. Your red LED would need to put out enough light to illuminate your screen bright red. Now, take your Photon microlight out of your pocket. (Surely all slashot readers have at least one of those by now. Ultra bright LED on a keychain.) Sit in a lit room and shine the microlight on a white surface, adjust the distance from the surface until your red (or white, or whatever color your microlight is) spot is about as bright as you would like the TV to be. Compute the area of the spot on the white surface. Mine is four square inches with a white microlight in a dim room. Maybe calibrate your idea of brightness by looking at your TV up close and then comparing to your illuminated spot.
Using the `no free lunch' rule of physics, you need to admit that a single LED is only going to provide enough light to adequatly illuminate 4 square inches. Hence, a 100" tv (4800sq in) is going to take 1200 LEDs. The way bright LEDs are something like $3 each in huge quantity, thats $3600 before you add optics, mechnical oscillators, and electronics.
I found another site with the instructions for free. This one hasn't been /.ed yet so have fun:
http://www.ductape.net/~bradya/100inchtv/
Dozings.com -- Its kinda funny... If you're as crazy as me.
Has anyone ever taken apart (or seen the inside) of a big screen TV? Do any of you youngins remember the old big screens from the 70's and early 80's?
The picture display tubes used in typical big screen TV's are in reality nothing more than liquid cooled versions of the tube used in a typical TV. These tubes are liquid cooled (on the front - it is a passive cooling - think of using water as a heat sink, with no pump) because they are driven to insane brightness levels (way brighter than maximum brightness on a normal TV set), to get the picture as clear as possible in the final result. Furthermore, most big screen systems use three tubes, one red, one blue, and one green (they are black and white tubes with filters - not unlike stage gels), each aimed and focused separately to get the highest resolution picture possible (this seperate aiming, etc is one reason why you should have your big-screen adjusted after moving it - even if it is across the room). HDTV sets merely use ultra high-res SVGA tube systems to get the resolution needed.
After that step, it is simple optics - most of the time no more than one or two largish glass lenses (with anti-chomatic aberation built in) and a mirror or two to flip and reverse the image - sometimes the image is projected inverted and reversed and bounced off of one mirror to get the final image. The idea is to get the projection as near parallel with the screen as possible. Where that isn't possible (due to the size of the cabinet), special lenses are added (or it is done electronically) to "keystone" the image in the proper direction so that it comes out "square" in the end.
That is all - amazing, isn't it, that one would pay almost 2000 bucks for a few TV sets, some wood , and some optics? Well, you do get a better quality system, and the optics are top notch, too - plus, the TV sets are anything but normal...
What these 100 inch plans and systems try to do is do all of that on the cheap - a light tight box is built around the TV set, a fresnel lens is added (it is a cheap lens), and you turn the TV set upside down and add a mirror to reverse the image. Typically, you might also crank the brightness up to get a slightly better image for the larger 100 inch displays.
What does this get you? Actually, if you do everything perfectly (and watch out turning that set upside down - sometime the magnetic field of the earth screws things up, and you need to degauss the set to recover in the upside down mode), have it all aligned, use a good fresnel lens, a good lighttight, square, painted black inside box with a nice mirror, and you use a larger set (15-19"), and a good projection surface (not a sheet - not enough reflection - ideally, you want a silver beaded projection screen, for maximum gain - but since it would be stupid to spend $150 on a screen for a $10 big screen, there are alternatives, more on that later) - you can get a reasonable image. You will have to turn out the lights, and let your eyes adjust - but you will get a watchable image. It isn't a scam. The edges will tend to be fuzzy, though, because a fresnel lens isn't a perfect lens, and has focus issues at the edges. Put a black border around your projection surface to mask these off, and things don't look too bad. Also, don't try to go for a 100" display - try a 40" display first, and adject until you are happy with pixel size and clarity. It is possible to make it look damn good, good enough for most entertainment uses.
Now, want to know how to make a better projection TV system (though this time, it will cost a bit - more than $10, but less than $500)?
LCD projection systems are really systems designed to rip the gullible off. At least with CRT projection, the manufacturers have an out with the special CRTs and optics they use. LCD projectors, though, are the simplest of them all (note, DLP projectors are not LCD projectors, so I can forgive their cost) - it is crazy that they sell these ultra expensive projectors that are nothing more that glorified slide projectors...
That's right! Slide projectors! The optics and light system are the same (nearly equal) as to what is in an "old-time" slide projector - the slide now is an LCD panel! This panel is typically rather small for it's resolution - but this doesn't excuse the cost, because LCD production quality is supposed to go up as the size goes down, and the price is supposed to go down as well, right? Well, it hasn't - at least I don't know where I can get a $150.00 800x600 LCD projector yet, which typically uses a smaller LCD display (less than 2" diagonal). Anyhow - all one has to do to build their own LCD projector is to get an LCD about the size of a slide, and drop it in place of the slide in a slide projector (which can be bought cheap off of Ebay). This kind of projector system was first described by Robin Cook in his book "The Virtual Reality Homebrewer's Handbook". One thing he recommended was to use a fan to cool the LCD, because the projection lamp could overheat the LCD, causing it to shut down or burn out. What is used for the LCD? Why, an LCD TV, of course - you take one apart, remove the backlight (because the projection bulb will be your backlight), and put the screen in place of the slide in an old slide projector. You also need to re-route the electronics and cabling, but it can be done. Also, try to use a TV with a TFT display for clearest moving images. It is also possible to scale this up by using larger LCD displays (various electronics surplus dealers sell $99.00 4 inch LCD displays for use in in-car video systems), and a custom lens/projection system. A larger LCD will give a clearer image.
Now, what will be the quality of such a system? All I can compare it to is a device I have, that works the same way, and is how I got my "Big Screen" experience cheap. I own a Fujix P401 LCD projector - cost me $250.00 a few years ago, and gives me an "OK" picture. I can comfortably display X on it if I use a 640x480 setting - some things are readable - but mostly I watch VCDs on it (using mtvp - anyone know of an equal Free replacement to mtvp?). Higher res images can be displayed, but they are fuzzy, at best. I would imagine a homebrew system to be comparable to this, possibly better.
Now, would it be possible to reproduce a three tube CRT system? Of course! You could build three of the 100" systems, but use black and white sets with colored pieces of plexiglas (or stage gels) in front of them. It would be a little bulky, though. I could imagine gutting some small (9" or smaller) portables to do this, and building a custom cabinet. Another possibility is to get (through various electronics surplus retailers on the net) surplus big-screen optics (which shouldn't cost more than $25.00/ea), and put them in front of the CRTs you are using. This would result in a more compact system (especially if you removed the casing of the TVs - be careful of the high-voltage inside, though - one hand in pocket when poking around inside those sets!!!).
Now, what to use for the projection screen - well, since you are doing this on the cheap, you can't very well buy a nice screen - they can be expensive. However, sometimes you can get a used silver projection screen fairly cheap (under $50.00 sometimes on Ebay, less at garage sales) - but make sure it is good quality. Most of these are tripod style, and don't have a ratchet mechanism to allow a "pull-down-from-ceiling" setup, that is much more enjoyable. To solve this, use what I used: A pure-white blackout shade. These can be found at Home Depot, and they can be had for ultra-cheap prices (less than $30.00 for the largest size). You can build mounts by using some bolts and a couple of bookshelf brackets, with careful setup, a pull down system is easy (I had mine together in an hour). These shades are smooth, have a high reflectivity, and are very inexpensive. Another alternative is high reflectivity white paint on a board. You can also use a white vinyl shower curtain, stretched tight. There are numerous options. Just look around and imagine.
Finally, I want to tell you what I used to display X under Linux on a TV (or projection system with composite input, like these homebrew projectors use). There is a device called the Averkey iMicro that is a true plug-and-play system. Pop it into your VGA port, load up X, and it will recognize the settings - no need to mess around with your XF86config settings (unless you need a certain res) - high-res, low-res - don't matter - it can recognise it. And it gives a great image, and it is cheap (around $100). I highly recommend this product.
OK - now you know the scoop. I hope this long, long comment will help someone. Realize that you won't get the be-all and end-all of projection images with these systems. However, I don't think they are a scam - in reality, they are selling the lens and some plans, and true, as good or better plans could be found on-line. But people are lazy, so I tend to think that they are selling a lens, some plans, and the cost of research - for $10.00 or less in many cases, that isn't a bad deal. I tend to wonder if I compiled all the info I had onto a CD, and sold that with a lens, if I could make some cash - but I am lazy, so if someone else wants to take a stab at it, go for it!!!
Have fun, my friends!
Reason is the Path to God - Anon
Alot of people have remarked that the pixels would be huge. I just wanted to point out that television and television CRT's are innately analog and have no pixels. The scan line is drawn in one continuous swipe horizontally across the screen. I'm not arguing that the image would be great, I'm sure it wouldn't be, but I don't think it would be as grainy as alot of you suppose.
I would imagine that the issues here would be with brightness more than grainyness. Large screen televisions are limited to the same basic resolution as small screen televisions are, the source data, a.k.a. the video signal, is sent at the same resolution to all TV's. Televisions have 525 vertical scan lines, but horizontal resolution is difficult to describe in terms of pixels as they are different for the chroma and luma components. The luma ( brightness, i.e. black and white ) horizontal resolution is 442, the chroma ( color ) horizontal resolution is 377. This was done for a number of reasons, including bandwidth limitations, backwards compatibility with black and white televisions, etc... If you take this overlap of color and black and white signal, then add the fact that the vertical scanlines are interlaced ( vert refresh is 60 Hz, i.e. 30 frames per second ), you will see that standard television is not at all similar to computer monitors. Televisions are very low definition devices ( thus the need for HDTV ) and that low definition means that a magnified image might benefit from the shortcomings of the human eye.
Please note that all my numbers were for NTSC, most PAL implementations run at 50Hz vertical refresh, 625 vertical scan lines ( chroma and luma horizontal resolutions vary amongst the PAL standards ). SECAM is 50Hz, 625 lines as well.
Also note that this is for standard TV, HDTV used MPEG-2 just like DVD video and thus is obviously a digital format.
Image Inversion:
It is possible to flip the wires around on the deflection coil in your TV or monitor. It is also possible to rotate the deflection coil assembly on some monitors/TVs. Here is a webpage detailing flipping wires.
BE VERY CAREFUL IF YOU ARE WORKING ON THE INSIDE OF A TV OR MONITOR - THERE ARE LETHAL VOLTAGES PRESENT, EVEN IF THE TV OR MONITOR IS OFF!!! DISCHARGE THE PICTURE TUBE AND ALL CAPACITORS!!! EVEN THEN, BE ULTRA-EXTRA CAREFUL - YOU CAN KILL YOURSELF IF YOU ARE NOT CAREFUL!!! IF YOU HAVE _ANY_ DOUBTS, DON'T FUCK WITH IT!!! I CANNOT STRESS THIS ENOUGH!!! (maybe I should add more exclamation points?)
I am amazed that the kid (at the link I gave) didn't kill himself.
Correcting Fuziness:
Two options - bend the screen horizontally (like the Torus screens in theaters), possibly vertically as well, to bring the edges in focus. Might be difficult to do. Option B (probably more difficult) would be to bend the fresnel lens slightly...
Reason is the Path to God - Anon
This one even has diagrams and all.
http://broch.subnet.dk/projector/start.htm