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Technology

Building Cheap 100 Inch TVs 364

Posted by CmdrTaco from the its-time-for-the-hack dept.
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. "
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Building Cheap 100 Inch TVs More

Building Cheap 100 Inch TVs

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  • WOW! (Score:5, Funny)

    by clinko ( 232501 ) on Tuesday October 16, 2001 @12:30PM (#2436543) Journal
    This is great!

    I can get a diploma, make $20,000 in just 2 weeks, and now I can have a 100 inch tv for little cost at all!

    I'm gonna start reading my hotmail bulk-mail folder more often!
  • So, once people can buy tiny TV's and make them project perfectly well onto large screens, does this mean that the consumer electronics industry will have to readjust itself? Or does anyone think that there will be lawsuits from industry groups and lobbyists to try to block this kind of thing?
    • Yes, but the "Big Woody" projector unit isn't the chrome-shiny-genuine-woodtoned-plastic that all the sheeple out there seem to think is required for entertaiment electronics. . .



      Imagine the consumer response. . .


      But it's. . .PLYWOOD. . . .and where do we take it for service ???

    • Re:what does this mean? (Score:5, Insightful)

      by silicon_synapse ( 145470 ) on Tuesday October 16, 2001 @12:42PM (#2436625)
      I would imagine that the resulting quality would depend partly on the quality of parts you use. A 3.5" portable tv certainly won't project a 100" image of the quality a 32" tv would. You still get what you pay for. But I wouldn't be too concerned with the average joe tearing apart tvs (or putting them back together) just yet. Speaking of which, don't tvs contain very large capacitors that hold deadly amounts of power for a long time? Whatch those fingers.

      • Re:what does this mean? (Score:2, Funny)

        by Anonymous Coward
        Yeah, you don't want to mess with the flyback if you don't have the right equipment. And "right equipment" does not mean a pair of rubber gloves dipped in the rubber stuff you put on tool handles, and a railroad spike. Trust me, I know.

        So much for trying to be McGuyver *shrug*

  • 100-inch TV's (Score:2, Troll)

    by yatest5 ( 455123 )
    Is this a misprint?

    The biggest TV I've ever had was 12-inches and he said he'd never seen one bigger. Great tits as well.

  • Stewpid (Score:4, Insightful)

    by Anonymous Coward on Tuesday October 16, 2001 @12:33PM (#2436561)
    I can't believe this is on Slashdot... so disappointing.

    This is as stupid as blowing up a 150x150 pixel image to 1600x1200 in photoshop and expecting a good result.

    You'll end up with a dark, low contrast, blurry mess, but go for it.

    • Re:Stewpid (Score:2, Informative)

      by Mr. Eradicator ( 470089 )
      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.

      • Re:Stewpid (Score:5, Informative)

        by Zathrus ( 232140 ) on Tuesday October 16, 2001 @01:32PM (#2436881) Homepage
        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.

    • Link to plans (Score:2, Informative)

      by sacherjj ( 7595 )
      I was curious and found a link to plans [greenspun.com]. Assume it is the same type of design. I'll stick with my projector.

  • Nastar gets even (Score:5, Funny)

    by fobbman ( 131816 ) on Tuesday October 16, 2001 @12:33PM (#2436563) Homepage
    The guy who posted this story is probably someone who was selling the plans either on eBay or on the `net for $10 a pop and figured "If you can't beat them, /. them".

    Well, it worked.

  • While the idea of turning a 17" monitor into a 100" one that would take up a good portion of my wall sounds intriguing, it sounds incredibly doubtful to me. Think about how ugly low resolution is.. especially on a large monitor. I haven't looked at the site yet, but I would imagine they simply magnify the image someway, if that's the case then you're just blowing it up.. nothing special. But doing that would uglify everything. 1/2" pixels don't sound particularly appealing to me.
    • I remember doing something like what I can only guess is on the site (seeing as its slashdotted now) when I was like 14. Just get a big magnifying glass lens, the type you can pick up at American Science and Surplus for really cheap, get a decent mirror, put your TV on its back, setup the mirror in a box at a 45 degree angle, cut a hole in the side of the box for the lens, put the whole contraption on the TV, point it at a sheet, turn off the lights and viola, really big, crappy resolution TV. It was a bunch of fun as a kid, playing crappy resolution NES games on it though, and an application of physics if you're into that sort of thing (or teaching your kids that sort of thing or whatever)
  • 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 [b0x.com] 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.
  • Damn... and to think, all this time I thought my 21" monitor was the bomb. I didn't see that my RedHat config supported a 100x100 bazillion pixel resolution, but maybe in the 7.2 release.
    • I didn't see that my RedHat config supported a 100x100 bazillion pixel resolution

      No, but debian supports a 200x200 gajillion resolution.

      --
      Evan "Dances with SuSE" E.

  • 100InchTV (Score:5, Funny)

    by matt_wilts ( 249194 ) <matt_wilts@@@hotmail...com> on Tuesday October 16, 2001 @12:37PM (#2436592)
    Why on earth would I want a 3-foot tall transvestite?

    Matt

  • Comment removed (Score:3, Interesting)

    by account_deleted ( 4530225 ) on Tuesday October 16, 2001 @12:37PM (#2436594)
    Comment removed based on user account deletion

    • Experience building these. (Score:5, Informative)

      by Christopher Thomas ( 11717 ) on Tuesday October 16, 2001 @01:12PM (#2436797)
      I can't get to the linked site right now (I'm presuming it was slashdotted allready), but the way it worked was to basically use a magnifing glass. The screen emmits through a box of a certain size (the screen size), If you put a lense over that, in theory, you could magnify that light, so that it would be large enough to fill a "100 inch" screen, but it would look horrible!

      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:
      • Your focal plane isn't a plane.

        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.

      • My TV distorts colour when turned upside-down.

        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.

      • Fresnel lenses are crappy.

        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.

      • The sheet has to be very thin, or you have to be looking at the TV-side of it.

        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.

      • The projection is very dim.

        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.

      • Re:Experience building these. (Score:4, Interesting)

        by taniwha ( 70410 ) on Tuesday October 16, 2001 @01:31PM (#2436880) Homepage Journal
        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.



        No - but it does care about the angle of the earth's magnetic field .... which is in effect reversed when you turn it upside down. Degausing the tube will help - but really you need either a helmholtz cage or a TV designed for the southern hemisphere (where of course they mostly use PAL so I guess you're SOL :-).



        Back when I worked for a company in the computer monitors biz I learned that monitors for the northern hemisphere are alligned in Japan all facing in the same direction, those for the southern hemisphere are aligned in special cages (virtually facing the same way I guess) - we learned this the hard way after selling some monitors down south and having some really pissed customers

        • It is related to gravity.. The picture tube has a shadow mask. It is thin. It sags slightly (affected by gravity). It is true the beam is affected by the earth's magnetic field, but distortions to the shadow mask are a bigger influence. Try this at home... turn a large TV around and notice the color shift. This color shift is due to reversing the earth's magnetic field 180 degrees. Now lay the set on it's side or upside down. This color shift is due to both gravity and magnetic field. Notice how much greater this shift is. Only a small portion of the shift is due to the earth's magnetic field. The magnetic field was most noticable on large computer monitors that has a fine dot pitch as the small shift could more easly misallign the beam to the phosphor. Most TV's have large pitch so the magnetic field has a smaller effect on color purity.
      • This turned the image upside-down. This meant I had to turn the TV upside-down to get a usable picture.

        Why don't you just turn the lens around?

        yes, that was a joke.
        How much distortion do you get using a second lens?
        • How much distortion do you get using a second lens?

          I never did get around to doing this. I had a glass lens from an old slide projector, but grew tired of the project.

          The way I'd do it would be to use the Fresnel lens to focus the tv picture down to a very _small_ image, and use a second lens to blow that up on to the screen (image size much smaller than the lens's focal length means a closer approximation to an ideal lens). OTOH, I'd still have curved-surface distortion focusing down the TV image.

          If you try it, please let me know how well it works :).

      • Re:Reason for lack of brightness (Score:5, Interesting)

        by Technician ( 215283 ) on Tuesday October 16, 2001 @07:51PM (#2439050)
        For anybody who wants to know why they are so dim..

        A CRT projector of the 3 tube variety uses this setup for several reasons related to brightness. Number one on the list is no slot mask! Each tube is one color. You are not blocking 80% of the electron beam to the phosphor with a matrix shadow mask inside the CRT.

        Number 2 on the list is F stop. A large CRT giving off light with a lens far away gets very little light to and thru the lens. Most (about 80% or more) of the light hits the inside of the box instead of the lens. A projector set uses a small set of CRT's so the lens is very close to the CRT getting most of the light thru the lens. The smaller CRT's can easly have flat faces taking care of the focal plane problem also.

        Raw Power.. The small CRT's in a projection set are not limited in beam current as there is no shadow mask to worry about overheating. The face of the CRT is gel or liquid coupled to the lense to reduce interelement reflections and aid in cooling. They can put out brightnesses on the face of the CRT's that can be painful to look at unlike a conventional tube.

        The last item is when the distance to a projection surface doubles, the brightness goes down with the square of the distance. Doubling the distance to double the size decreases the brightness 4 fold. This is true for both a real projector and the home made variety, but the home made doesn't have the brightness to sacrifice on the larger immage.

        With all these factors working for a 3 tube projector and against a single tube, the diffrence in projected brightness is typicaly more than 200X brighter. Translation.. a room with a couple candles in it will typicaly wash out the image on the home made projectors.

  • Scam? (Score:5, Informative)

    by Schnapple ( 262314 ) <tomkiddNO@SPAMgmail.com> on Tuesday October 16, 2001 @12:38PM (#2436598) Homepage
    Isn't this the same thing they've been "selling" for decades now? It consists of a large sheet, your television and a Fresnel lens (where the $10 comes in, BTW). You basically throw a sheet in front of your TV and place the Fresnel lens between them and viola. Of course, this is a flimsy arrangement, so blueprints to construct a wooden monstrosity to hold the whole thing are included. Oh, and of course this will produce an upside down picture (since we have basic telescope theory at work here) so you have to turn your TV upside down (which may have been less of a big deal back in the 1950's when TV's were basically boxes and they came up with this idea).

    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/ [tripod.com]

    • OT: Viola? (Score:5, Funny)

      by WSSA ( 27914 ) on Tuesday October 16, 2001 @01:18PM (#2436815)
      Why do I keep seeing all these instructions for building stringed musical instruments? "Do thing A, do thing B and viola!"

      Or perhaps you mean "voila!" ;)
    • you have to turn your TV upside down

      I haven't ever turned a TV upside down, but I have turned computer monitors upside down. Try it yourself and you'll see that the colors distort (and that the distortion can be corrected with the degauss button, if available).

      I've always been curious about the cause of this (hint, hint, Slashdot readers); I assume it's related to the effect of the earth's magnatic field on the stream of electrons painting the scren.

      Since I've never seen a TV with a degauss button, and since I presume a TV would suffer discoloration just like a monitor, this would seem to be another reason not to bother with this kludgy setup.


      • Different monitors act in different ways, as I learned from turning monitors sideways for playing games with MAME. Some have little distortion, some have a ton of it.


        I'm not sure about weather or not magnification/low resolution would be a problem. I've noticed that sending a real player file that's encoded at around 2 megs/minute to my older 25" set noticeably reduces the artifacts that are viewable, and smoothes out the image (at least with anime, maybe I should try a "real" movie someday), but divx/avi still have noticeable artifacts occasionally, due to (I'm assuming) real media compressing large areas of the same color better. The lower resolution of the TV also helps some games, especially emulated consoles, the game looks more "real", while on the computer screen, the high resolution actually hurts some emulated console games. Now if the lens is exact, then there will be pixilization problems, however, if there is a certain amount of imperfection (blurryness), I'm guessing a lot of games would be playable, and vids would be okay.


        Just my $.02

  • Comment removed (Score:5, Funny)

    by account_deleted ( 4530225 ) on Tuesday October 16, 2001 @12:39PM (#2436608)
    Comment removed based on user account deletion

    • Re:Legality (Score:5, Funny)

      by unformed ( 225214 ) on Tuesday October 16, 2001 @12:45PM (#2436653)
      Exactly...by adding a magnifying glass or projector to the screen, you are depriving the copyright owners by reproducing the image on an unlicensed object, such as a wall...

      You will be undoubtedly sued under the DMCA...blah blah blah yipetty yay
      • That was damn funny, thanks for making my day!

        But seriously, I wonder if there is a legal defense here, or at least a convincing argument against treating intermediate formats as copies instead of simply a means to an end.

        IANAL, IANA physicist... that said...

        What the hell am I talking about?

        Basically, you are creating an intermediate "copy" of the television program or movie via the Freznel lens. It's a copy because of the properties defining how light travels through the lens.*

        If you could demonstrate this to the Courts, your Congresscritters, etc., then perhaps you could convince them that an intermediate format of a copyrighted work stored in RAM does not count as a copy of a work and therefore is not subject to copyright restrictions or regulation. Not that you couldn't be sued for using the intermediate format to make thousands of copies of the work and selling them for $5 a pop... it would just a priori prevent Congress from regulating it directly.
        * I am not a physicist, but IIRC from high school physics, copies of the original photons are generated from the lens.
        Cheers,
        -l

      • by adding a magnifying glass or projector to the screen, you are depriving the copyright owners by reproducing the image on an unlicensed object, such as a wall

        Not as far-fetched as it may seem as first. By modifying your television to have a larger display size, you potentially convert it into a tool for public performance, and even without the Digital Millennium Copyright Act and foreign counterparts, the copyright laws of the United States and most other jurisdictions reserve the right of public performance to the copyright holder.

  • Old plans... (Score:2, Interesting)

    by Rob Parkhill ( 1444 )
    I have an oollllddd (1980??) copy of Popular Electronics kicking around somewhere that shows you how to do this too. Maybe when big screen TVs were hard to come by and insanely expensive, this was a good idea...

  • Alternative link to Google Cache of similar page (Score:2, Informative)

    by Anonymous Coward
    http://www.google.com/search?q=cache:1pInHo8PDFk:w ww.webone.com.au/~caoz/bsinstructions.htm+%22free+ 100+inch+TV+projector%22&hl=en
  • Many years ago I participated in a "buy something/subscribe to something (I dont' remember what it was but it was something I wanted at the time) and get a free big screen TV". What I got was a large fresnel lens in a plastic frame that you put in front of a regular TV to project its image on a wall, just like on the website. I never tried it out for its intended use but I did have a good time using it as a death ray^h^h^h solar concentrator to set leaves and stuff on fire.

  • you know what 640x480 on a 21" monitor looks like? (Score:4, Interesting)

    by carlcmc ( 322350 ) on Tuesday October 16, 2001 @12:40PM (#2436615)
    Now take that and multiply it times your worst possible dream to get pixels the size of green peas across the wall in your 100" display.
  • Turning a normal monitor or TV into a projector is nice idea, if it works. I'm fairly concerned about the quality. I strongly suspect the picture will end up grainy and will perhaps be distorted.


    Still, it would be cool for gaming. Can you imagine playing Quake III with this? And it would be more suited to gaming than an LCD projector, because the refresh rate is going to be whatever your monitor uses, rather than the dismal LCD refresh rate. All in all, a pretty cool idea.

  • Karma Whore, where are you? (Score:2, Informative)

    by Anonymous Coward
    Google cache right here [google.com]

    http://www.google.com/search?q=cache:1pInHo8PDFk:w ww.webone.com.au/~caoz/bsinstructions.htm+BSTV+100 +inch+plans&hl=en

  • more links (Score:2, Informative)

    by pruss ( 246395 )
    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
  • Like my eye sight isn't bad enough already!

  • I sell a similar product (Score:3, Funny)

    by billmaly ( 212308 ) <bill,maly&mcleodusa,net> on Tuesday October 16, 2001 @12:45PM (#2436658)
    Maybe you've heard of Amway...No??? Well sit down, let's chat. HEY!!! Where you going???

    Darn....guess it's back to "Lose weight now, Ask me how!!"

    Anyone sending money to this guy is a foole.

  • Did this years ago (Score:5, Interesting)

    by Scutter ( 18425 ) on Tuesday October 16, 2001 @12:52PM (#2436701) Journal
    My dad had a setup years ago that was basically a wooden box with a lens. Inside the box, he put a 13" TV with the picture reversed and upside down (I have no idea ho he managed that). He projected it on the wall. It looked fantastic. The most expensive part was the lens.

    The only real downside was that you could really only see it well if the lights were turned down (or off).

    • It's actually very easy to reverse the picture, all you need to do is to swap the deflector yoke connections, so that when the TV diverts the beam to the top left of the picture, it diverts to the bottom right of the tube.

      The alternative, of installing the tube upside down is not possible in most systems, as the tube & the casing are not symetrical.

  • It's always fun to go into the junk-mail folder and look at some of the crap that _somehow_ must seem believable to some people.

    Here's what the site itself says:

    "For entertainment purposes only. This is a FUN site. We make no claim that anyone will be completely satisfied with our product"

  • is that if you magnify a TV's screen by a factor of 2, you reduce the brightness by a factor of 4. Magnification factors of the sort mentioned makes the TV too dark to comfortably watch.

  • All those pixels (Score:5, Funny)

    by ejaytee ( 186527 ) on Tuesday October 16, 2001 @01:02PM (#2436750)

    This would be great. Right now, I can barely see my pixels. If I could blow them up really huge, I might take the time to get to know each one. Soothe them when they're red, give 'em a hug and a smile when they're blue. Sometimes, just drop by to talk.

  • Forget lenses, what about scanning LED projectors? (Score:5, Interesting)

    by dschuetz ( 10924 ) <.gro.tensad. .ta. .divad.> on Tuesday October 16, 2001 @01:10PM (#2436785)
    I experimented with a similar lens arrangement like 15 years ago with a fresnel lens from an overhead projector. Neat idea, but, well, it sucked.

    I've been wondering for years, and have wondered aloud here before but gotten no response, about the possibility for building a scanning projection TV out of LEDs and mirrors.

    Basically, rather than projecting an entire image at once, like an LCD projector does (and, thus, limiting your resolution to how big your LCD or DLP array is), this would take the output of red, green, and blue LEDs and bounce them off a mirror vibrating in two directions (horizontally and vertically) to provide a raster scan. With today's high brightness LEDs (ever notice how blindingly bright the new LED traffic lights are?), I'd think this could, with the right focusing system, give you a quality image on a decent screen.

    All that remains is to decode the video signal for processing by the projector. In a simple mode, you might even be able to simply take the HSYNC and VSYNC signals and, essentially, use them to mark the edges of your scanning motion, then simply vibrate the mirror back and forth within that time frame. (this is hard to describe, but hopefully it'll make sense to some of you).

    For something like this, the most expensive bit would be the lens at the front. You'd have a bunch of $2 LEDs (running cool and quiet, too, unlike the bulbs in DLP/LCD projectors), a simple electro-magnetic mirror mount (speaker coil for a prototype, maybe?), and maybe $50 worth of electronics.

    Any EEs out there who think this makes sense? Or should I just keep waiting for HDTV projectors to come down to a kilobuck?

    • Something like that, for it's digital movie projectors. Costs an arm and both legs for the projector.

    • ...empirical data says no (Score:4, Informative)

      by victim ( 30647 ) on Tuesday October 16, 2001 @01:49PM (#2436951)
      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.
      • IANAEE, I got tired three credits short, but...
        (me, neither, but I gave up after I noticed I only did computer-related homework for two semesters. :) )

        Using the `no free lunch' rule of physics

        Heh. You probably don't believe in perpetual motion, either. Heathen.

        you need to admit that a single LED is only going to provide enough light to adequatly illuminate 4 square inches.

        Good point, and I agree heartily. However, I'm not suggesting you use a single LED to illuminate an entire image -- you SCAN the image, and rely on human image retention in the eyeball to make it look like a solid image. That'd be one key question -- whether you can scan fast enough to do this. You might even need to double-scan images (twice per visual field) or somesuch.

        Also, you could (and probably would) use a 3x3, 6x6, or 9x9 array of LEDs per "pixel" to get the brightness up a bit, too...
        • Um, no. If you wave the LED around, then its brightness goes down. Think of it this way: it's only turned "on" for the amount of time that it is actually at the spot you're looking at. The rest of the time it's busy pointing somewhere else. Persistence of vision isn't some magical cure for this. The apparent brightness of a scanning LED will be a tiny fraction of the brightness of the
          steady LED.
        • Scanning the spot across a large surface wouldn't make the large surface appear to all be as brightly lit as the spot - it would make the whole large surface appear to be dimly lit. For retention to work the image must form on your eye first, but if the image is only in one position for a fraction of a second, it won't get formed in the first place.

          Why do TVs work then, you ask? Well, the phosphors on your TV are individually much much brighter than an LED shined on a surface from some distance away. Also, the phosphors continue to glow for some time after the electron beam has already passed.

        • Good point, and I agree heartily. However, I'm not suggesting you use a single LED to illuminate an entire image -- you SCAN the image, and rely on human image retention in the eyeball to make it look like a solid image. That'd be one key question -- whether you can scan fast enough to do this. You might even need to double-scan images (twice per visual field) or somesuch.
          So you are going to use the LED to illuminate one pixel at a time. For a 640x480 screen there are more than 300,000 pixels. At 30 frames/sec, each pixel is going to be illuminated for around 0.11 microseconds.

          The problem is the eye has an integration time of about 1/30th of a second, but the pixel is only illuminated for 0.11 microseconds. This is equivalent to integrating the same illumination level for the 0.11 micro second time. But when you are just shining the LED on the wall you are integrating to the full 1/30th of a second. The let's assume the illumination level is 1. So the integral for the Photon on the wall is 1 integrated for 1/30 of a sec or .033. For your scanning LED the integral is 1 integrated for 0.11 microsencond or .00000011. For a given pixel size, this means you need to make the light 300,000 brighter if you scan it than if you don't if the eye is going to see the same amount of light.

          Your TV solves this problem by having a phosphorous surface on the back of the screen. A powerful electron beam excites the phosphorous and then moves on. The phosphorous holds the image while the electron beam is elsewhere.
      • 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.

        That's for a single-color TV, yes? You'd need RGB LEDs, to be able to cover the necessary brightness across the spectrum. Provided your other math is right, we're talking $10,800 at this point, no?

    • Suppose you used a middling-sized laser rather than an LED: could this be bright enough? (Monitor burn-in is an issue, though. :)

      Alternately, instead of a pixel-mapped display, you could use this scheme for a vector display (anybody remember those?). Trickier to drive, but potentially a lot easier to get enough brightness.

      • Re:Laser? (Score:5, Funny)

        by FFFish ( 7567 ) on Tuesday October 16, 2001 @02:56PM (#2437363) Homepage
        Lasers? Good god, man, you'd get wall burn-in! Imagine how embarassed you're gonna be when you freeze-frame the money-shot, and end up with it etched in your wall just a few hours before your mom comes over for Thanksgiving dinner!

        God forbid the cat get in the way. Poof!
      • You mean this:
        http://www.mitsi.com/Projects/alp.htm

        I heard a story (I have no idea how true it is) that a bunch of engineers for a TV mfg. company built a giant laser projection TV to demonstrate at the company picnic one year. Supposedly it worked great at first, but after watching it for a few minutes it would give people headaches. They didn't know why, so they never made one again.
    • I have been involved in the CATV broadcast business (as an engineer) for 10 years and believe that I can provide some information that will help your proposed development.



      A TV scans across (the horizontal refresh rate) the picture tube at 15.7 KHz. The mirror would have to match this rate to reproduce a picture from a convention broadcast facility, so it would have to vibrate across the chosen field of view 15,700 times per second. I don't know the physics involved behind making a mirror move that fast, but it sure would sound awful, since its vibration would cause compression waves in the air at a very high pitch.



      The TV scans from the top of the screen to the bottom (the vertical trace and retrace) 60 times per second. The mirror would therefore also have to deflect up and down 60 times a second. In my opinion, that makes the mirror movement pretty complicated.



      Don't despair, all is not lost! I remember seeing an early head mounted display that used a column of pixels and a mirror that vibrated left and right 60 times per second. I think that a pretty good image could be created by making a row of 640 clusters of LEDs (each cluster being 3 LEDs - a red, green and blue) and scanning the mirror up and down 30 times per second (Only 30 instead of 60 because you can paint both the odd and even frames at the same time). There would be some electronics involved, since the horizontal picture image must be captured and store in the LEDs. This also has the advantage of providing way more light than 3 LEDs, so you'd have a brighter image.



      Good luck

    • Thanks to the entire slashdot community for dashing my dreams. Now I just have to figure out how to get LEDs for, lessee, a 1920x1080 array, and...umm...HOW MUCH would that cost?

      Seriously, I'm glad I finally got a good rundown on some of the issues here, especially the feasibility of image retention for such a fast scan (doesn't work) and the problem of precision hardware. Someone else mentioned lasers, but even the little laser pointers scare the bejeesus out of me, and I certainly wouldn't advocate making a TV out of 'em.

      *sigh*

      Now, about that array of microscopic thermocouples to use as an air conditioner / power source....

      d.

      (anyone ever think it might be useful to have a "crazy ideas" website to discuss, well, crazy ideas?)
    • All that remains is to decode the video signal for processing by the projector. In a simple mode, you might even be able to simply take the HSYNC and VSYNC signals and, essentially, use them to mark the edges of your scanning motion, then simply vibrate the mirror back and forth within that time frame. (this is hard to describe, but hopefully it'll make sense to some of you).

      An easier way to do this is to use two spinning mirrors to do your scanning. The problem with this is that you'd need to buffer and re-send the image data, because your "blanking intervals" will be much larger than your display time under this scheme. If you don't mind hacking CRTC settings and are using a computer instead of a TV, you might be able to get your video card to drive its monitor port with this kind of signal instead (had a lot of fun making video cards do things they were never intended to a couple of years back).

      You'll also need to have the spinning mirrors fairly far from your projection screen or wall to avoid distortion (you're scanning at constant angular frequency, not constant linear speed on the wall). This makes sych problems worse (blanking interval is that much larger, because you're using that much narrower a wedge of the circle the beam is scanned through).

      Electronics to synch the mirror rotation to the synch pulses is easy to build. Use a classical control system with extra damping. $2 worth of electronics to clean up the input signals and $1 worth of electronics to control the speed of the mirror-spinning motors.

      Now, the big problem (as others have pointed out) is that you must deliver enough power to your LEDs to brightly illuminate a large patch of wall (or screen, if you prefer). This means shelling out tens of thousands of dollars for a high-power krypton laser (so you get R/G/B from one laser), some decent optics (gratings to separate out the colours, mirrors, etc), and "three accousto-optic modulators" (devices that modulate a signal on to a laser beam). This will probably be cheaper than your laser, but that's only because the laser is bloody expensive.

      Still a very fun project; just not a cheap one :).
    • Not enough millicandella (or candela) output, I'd suggest R G and B lasers to do it, but that would be cost prohibitive... but REALLY bright and nice color balancing.

  • What's so wrong with selling information ? (Score:4, Insightful)

    by tmark ( 230091 ) on Tuesday October 16, 2001 @01:12PM (#2436795)
    I don't like the idea of these people selling this information, especially when you can get it free


    How is this any different than (say) O'Reilly selling books on Perl/Oracle/Linux, when people can get all that information for free on the web as well ? Someone has gone to the trouble of packaging the information, and sending it to people who may not even have web access, or may want printed instructions, so I say all the more power to them.
  • God forbid the light catch this thing just right. Probably burn a hole through your wall... or your cat.
  • I looked at this a year or so ago. I have an unresolved question which is slightly interesting. How well would a vector monitor (aka "Asteroids" or "Tempest") fair when projected? The lines are bright, but skinny. Will they be lost in the magnificant?

  • Sad But True (Score:5, Funny)

    by John_Booty ( 149925 ) <johnbooty@booty p r o j e c t . o rg> on Tuesday October 16, 2001 @01:21PM (#2436830) Homepage

    On a similar note... last year, I wanted a bigger TV set, but didn't have the money. So I just moved my couch closer to the TV... yes, I know it's sad. But it has nearly the same effect as getting a bigger set. :)

  • What about LCD? (Score:2, Interesting)

    by andylaurence ( 233927 )
    Whilst ripping apart an old lapop a couple of weeks ago, it struck me that the heart of an LCD screen is just a glass panel. After thinking about having moving pictures on the wall, I came up with a possible idea.

    Take one OHP (Overhead Projector), and one LCD screen. Remove all packaging on the LCD screen until you can see through it. Place the LCD screen on the OHP and hold down with some masking tape. Turn on OHP and LCD (make sure it's connected to something!).

    Any comments as to why this won't work? I work out costs at around £400ukp new (£300 for LCD screen, £100 for projector).
    • I've seen these, but can't find them anywhere for sale. Basically, it's just exactly what you're describing... An LCD monitor with a clear screen and no blacklighting behind it. It sits directly on top of the overhead projector of your choice with no special adapters or fitting. A college math professor was using one to graph equations. It was 94, so it was monochrome. Surely these still exist. Anyone know for sure?

      Also, there were several popular graphing calculators that came in a 'regular' version and a 'clear' version for use on an overhead projector.

  • Found another free one (Score:4, Informative)

    by dozing ( 111230 ) on Tuesday October 16, 2001 @01:55PM (#2436977) Homepage
    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/ [ductape.net]

  • What this is, how it works, and doesn't... (Score:5, Informative)

    by cr0sh ( 43134 ) on Tuesday October 16, 2001 @01:58PM (#2436997) Homepage
    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 [aver.com] 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!
    • 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 [geocities.com] 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...
      • Something I just thought of:

        Maybe the edges are blurry because most TVs and monitors have curved glass fronts (especially cheap TVs) - perhaps using a WEGA or some other flat tube might help things? I know that the actual image may be "flat" - but there is a lot of glass it still has to pass through, thus possibly distorting it when you magnify it?

  • Point: technically TV's have no pixels (Score:3, Informative)

    by Anonymous Coward on Tuesday October 16, 2001 @01:59PM (#2437011)
    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.
    • Actually, TV's _do_ have pixels (except they aren't called pixels, but instead "dots", hence, "dot-pitch ratio", which gives the distance between adjacent dots).

      Each dot is formed by a thin piece of material called the "electron gun shadow mask", which is basically a very fancy method of saying "a piece of thin metal with lots of precisely placed holes in it". This mask is swept on the back by the electron stream from the "electron gun" in the back (actually, three different "guns" are used, one for each color R, G and B). As the beam passes over the hole, it lights up a corresponding dot of red, green, or blue phospor, which glows in the proper color. This beam is varied in intensity, to change the color level of each dot, to give the wide variety of colors (interesting point - most TVs aren't balanced to pure white, but rather to the blue end of the spectrum, adding blue to a display makes it look brighter to our eyes, but purists have issues with it - also note the same is used in laundry detergent). These dots are very small, and close together, but they exist nonetheless. If this mask wasn't used, extreme smearing would result (now, your statement is correct prior to the mask, but not after it). One other thing, some picture tubes use a grid of vertical wires as a mask - not sure how it works, but I would imagine it is similar, but with less interfereing, and no holes to create pinhole camera electron beam distortion effects, there exists less blurring (ie, the beam doesn't stray from its phospor dot onto adjacent dots). I am sure there is a good FAQ on this out there.

      If you want to "see" these dots, up close, take a magnafying glass and look at your monitor or TV, or, alternatively, get some beads of water on your TV, and you can see them (badly, of course).

  • Screw television. A 100 inch Freznel = Anarchy! (Score:3, Funny)

    by Fantastic Lad ( 198284 ) on Tuesday October 16, 2001 @02:33PM (#2437231)
    Screw television.

    Here's what I think would be fun:

    For about $100, you can buy a 48"x36" freznel lense. I want to mount it in a giant magnifying glass frame with a long handle, (kind of like one of those leaf scoopers used to clean the crud from the surface of suburban swimming pools.).

    Then. . . Oh boy the damage you could cause!

    We're talking about being able to set on fire, with a dowel and a sheet of plastic, the upholstery inside parked cars, punishing stupid owners who leave their automobile anti-theft devices blaring unattended. --Without even having to touch the vehicle! --Or you can set office buildings on fire by shining sunlight through the windows just by walking down the side walk with the magnifier over your shoulder. Any number of bizarre fire-crimes become feasible.

    Yeah, yeah, I know you could get the same net effect with a can of gasoline and lighter, but this is FAR cooler! (What!? I'm just walking here with my sheet of plastic! I don't care about optics! Get your filthy law enforcing paws off me!) And if you somehow managed not to get caught, the authorities wouldn't know what the heck to make of it. --You might even be able to popularize the term, 'spontaneous office furniture combustion,' or something equally weird.

    Of course, in this day and age of too many cameras and rampant terrorist paranoia, you'd probably have your eight foot magnifying glass and turban confiscated.

    Bummer.

    Fantastic Lad --What's a little pyromania among friends?
  • Some great infos and links on howstuffworks.com

    http://howstuffworks.lycos.com/question244.htm

  • AcidWarp [noah.org] and The Warper [noah.org]

    I am not really sure if this is the earliest incarnation - somehow, I doubt it. But it has to be an early one (1992)...
  • I built soemthign like this in college out of a big old black and white set and a lense from a Xerox machine.

    The problem was brightness, it was basicly unviewable except in pitch black. You can up the brightenss by putting a tube transformer in the set but it reduces your picture tube life. (You can also up the brightness by getting a scotchlite screen, but they are serious bucks.)

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