??? 05/04/09 05:55 Read: times |
#165030 - The man who rejected video uses video as his example... Responding to: ???'s previous message |
Richard said:
The spinning mirror does the horizontal axis, so to speak, and the one moveable mirror axis is rotated over a narrow field, to produce the vertical deflection. That demands far less precision that two moveable axes. No, no difference in precision requirements. Note that the Circuit Cellar solution shows one line of text, which corresponds with with my previous post "A rotating mirror or prisma (normally found in laser printers) is fun if all you are going to do is write text, simulating a dot matrix printer. Full XY-control is generally way more useful/fun. You can for example draw lissajous curves with what looks like infinite resolution." DIY projects have the problem that max optical output you should be able to buy is 5mW, and the raster display will waste most of that power on the black pixels. If the Circuit Cellar project would display (192 pixels / 12 pixel high = 16 lines) you will not be able to just buy a 16x stronger laser. Richard said:
No question about it, those are not common DIY lasers, but the article does show that that (rasterized display) is how folks are doing it. How folks are doing it? Don't you 1) mean "some folks"? and 2) Doing what? Building laser projectors in general or building laser projectors for video output? You are mixing your arguments. You are saying "something Chico cand made with what he has" and "with limited requirements of precision". And "why video or MPEG" and "this is a 805x forum". Then you argue about a projector that: 1) Uses lasers you are not allowed to sell/buy. The legal limit is normally < 5mW optical output, even if there exists laser diodes or solid-state lasers with several W of output. 2) Requires extreme mechanical precision (people who do build thinngs of this type use to have a 5-10mm thick metal base for stability, given the need for controlling angles in fraction of mrad). 3) Uses a Bragg cell (ACM) which isn't normally available in surplus equipment. If you are going to make examples about a rasterized projector, you should instead talk about the companies who are working on small raster projectors for integration in PDA and mobile phones, allowing you to project your SMS on your hand or the table instead of having to read tiny characters from a small 40mm low-contrast LCD. We should within a very near future (if not already released) see tiny mirror modules less than 10x10x10 mm. I have seen small orange-red projectors that will give at least 10" projections of clearly readable text in indoors light, but I haven't seen anyone starting to sell them. That is way more relevant than talking about Jean Michel Jarre type of designs containing components you are not allowed to sell/buy or that may represent a full years salary. I have also seen one company claiming a small RGB projector with high resolution and low cost, but not seen how they will manage to have an out price lower than the cost of just the blue laser, so it may be a marketing ploy to get investors while waiting for prices to come down. Captured by a video camera, the display seemed very strong for only being generated from 1.4W electrical power. But clearly useful indoors. One thing to note about the 5mW limitation for optical output of handheld equipment. At least in EU, the requirement is that even in failure situations must the manufacturer guarantee that the equipment don't gets past the 5mW limit. At least green lasers varies in intensity with the temperature, so the manufacturer would either have to release a design intended for less than 3mW, or epoxy together a solution complete with electronics that measures the optical output and adjusts the driving current depending on how well the frequency of the light matches the crystal. This means that DVD, BD or HD drives are just about the only way a DIY project can get access to strong lasers. On the other hand, it should be questioned if DIY people who need to read this thread should use an laser diodes that are magnitudes stronger than what it takes to damage the eyes. A raster display will require a stronger laser to match the intensity of a XY display, increasing the interest in utilizing high-output lasers. In the end, I see five different market segments for laser projectors as displays. Listed from easy to hard: 1) XY projector. Currently very easy to build. Maximizes the use of the light from the lasers. Limited amount of data to output, but can draw in air. And yes, they really are easy to build, while allowing tricks you can't do with a raster projector. A number of people on this forum can produce one from surplus components within a weekend with time to spare. 2) Monochrome (red or possibly green) small projected displays similar to alarm clocks that had a lens to project time on the wall, but without the lens and with way more contrast). Not so simple to build as you think, and not so small for DIY. Should be possible to buy any day now, if not already released. Limited resolution and/or limited intensity. Commerciaal releases may have more than the 5mW optical power that is the legal limit to trade, allowing larger projections with reasonable intensity. 3) RGB small projected displays possible to view movies with as complement to iPod or similar. Limited amount of light and currently waiting for price drops for green and blue lasers. Probably available with reasonable price within 1-3 years. Very, very, very hard to build yourself because of the extreme need for mechanical precision. Also quite costly with the green and blue laser and the dichro mirrors. Commercial releases my have more than the 5mW optical power than is the legal limit to trade, allowing larger projections with reasonable intensity 4) RGB big projected displays as complement to DLP or LCD projectors. Definitely in need of cheaper strong lasers - stacking multiple lasers isn't so easy. May also be legal problems, because of the strength of the required lasers. The advantage with a laser projector is the high native contrast ratio, removing the need for an iris as used in high-end LCD projectors, to dim all projector output in dark film sequences. Obviously not a DIY project, given the cost of involved components - right now, the required intensities are "build-to-order" for laboratory equipment, with prices you could buy one or more cars for. 5) True tri-dimensional displays, where the image is projected in a volume instead of on a surface. Still expensive, slow and dim. Bigger/cheaper lasers needed. May also be affected by regulatory problems depending in size/intensity. Most definitely not DIY since it is currently research-level and the hardware built-to-order. Richard said:
while I've been unable to find any manufacturers of laser displays other than the ones suited for rock concerts, where they just do stuff that's "kewl" rather than useful, and, incidentally, where precision isn't critical. And may that not be because these "kewl" systems are quite "inexpensive" at $12000 to $40000 and can do things you can't do with other equipment, while there is a very minor market for video-type of projectors ("who said anything about video") that contains really expensive components when video can be displayed very cheaply by other technologies? You may currently get a $5 red laser pointer. Maybe $20 for a green. Maybe $400 for a blue. Next thing is that a pulsed laser will produce its own dots on the wall when you sweep the ray. And if you don't buy a laser module (normally very expensive) or a laser pointer (cheap and low power if legal and maybe impossible to modulate) but instead look for the laser diodes, you will need to fight with alignments of crystal to change the frequency, and the collimator to create the ray. And if you forget the IR filter, you can destroy your eyes with a ray you can't even see. Commercial video products requires a commercial market. When commercial products can be built with reasonable prices, then the volume will go up and the costs down. Then there will suddenly be ways for DIY people to get their hands on either parts from broken equipment, or now much cheaper components. Trying DIY projects before commercial companies can produce reasonably priced products, is seldom easy. Another thing: How many on this forum knows how to build the electronics to control two loudspeakers based on DAC output to produce lissajous patterns? How many on this forum can build a graphics card with 256x192 output at 30 fps? If the 8051 processor should emit every pixel, it has to emit 1.5 million pixels / second. If each pixel is one bit, and the processor just has to emit one byte for every 8 pixels, it has to emit about 190kB/s. That does not sound too easy for a 12MHz processor doing 1 MIPS (I think that was your intended processor requirement), so you would probably offload more than youst an 8-bit shift register to external logic. If I designed, I would probably offload everything to external hardware, or use a faster (but not more expensive) processor. Given how hard you had to pick up the function of a single buffered SIPO for driving a multiplexed LED display, I would think that a number of people on this forum would have a bit of a problem designing a graphics card even if they are capable of building a XY projector, so don't let your previous experiences with graphics cards color your definition of "easier". And don't be too colored by your view of what is useful. In the end, yesterdays million-dollar projector may be tomorrows 10-dollar projector. But it is important to try to focus on what is simple and cheap to do. People who have the knowledge and capital will not be limited by any text in this thread. People who do ask for help are more likely to manage a XY projector than a raster projector. And they are more likely to get the components to get good intensity with a XY projector. Richard said:
and, incidentally, where precision isn't critical. Define critical? The timing for emitting video data to a raster display is critical. On the other hand, XY systems for presentation may not have the same requirements for absolute precision as a solder machine, but depending on intended use, the repeatability precision may be required - without repeatability, you will see multiple weak and flickering images on the wall instead of a single one. If you looked at the projects I linked to, you would notice that most of the projects (even one of the loudspeaker projects) had good or very good repeatability. By the way - all this time, you have never once given any feedback why you think lack of intensity is irrelevant? Just one of all the questions you prefer to forget and hope other readers will also forget? |