DIY True 4K Projector | Hacker News Reader

DIY True 4K Projector

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171 pointshumbfool240 comments

Since the right people might be reading through the comments here -

I've been looking at making a hi-res ceiling projector for a living space. Perhaps not one, but a set of several projectors with an overlap, but the key point is that they need to be placed in a way so not to interfere with the normal flow of life. Nor to be easily shadowed by people walking around, etc. This (likely) mandates placing them around the room perimeter, possibly on the walls at some height. This in turn means that they will be projecting at an angle.

Do I understand correctly that it's not possible in principle to achieve proper focus on the target surface when projecting at an angle like this? That is if I am to project, say, a star field then it's not be possible to have stars close to the projector and far from it to be both in focus at the same time?

Look up "Short Throw Laser Projectors" it's somewhat possible with funky optics depending on how much distance you can afford.

Thanks. Can't seem to find how they work exactly except for "with mirrors!" remarks :)

Spherical mirrors and fisheye lenses do the trick.

Once you know something is possible, it becomes dramatically easier. :)

Current generation non-laser short throw projectors may already hit the price/performance you need, just mount them so they face the ceiling, on top of a bookshelf. (Laser projects are still quite expensive.) If they don't, then physics, specifically optics, has the equations to calculate the mirror specifications you need for your exact use-case. Custom-made mirrors aren't the cheapest, but what you're asking for sounds possible, though it's impossible to say without more information, specifically the dimensions and the brightness needed - you'll lose a lot of brightness from the mirrors.

The setup for Fishbug was two projectors facing a hemispherical mirror. https://www.youtube.com/watch?v=ThtF-FY28hM

Most projectors are throwing at some angle. For example, the bottom of the image is further away than the top is. Like my projector lens is in line with the top edge of my screen, and works just fine. Most projectors have some way of compensating for this skew.

I would think if you mounted it vertically on a wall, it would be fine. You would still want it centered horizontally though.

In principle, it is possible. A tilt-shift camera can bring any plane in focus, so running it in reverse will project the image sharply on your ceiling.

See https://en.wikipedia.org/wiki/Tilt–shift_photography for cameras. https://www.projectorcentral.com/Understanding-Lens-Offset-a... learnt me that you can buy projectors that use this method. I suspect that back-projecting televisions (https://en.wikipedia.org/wiki/Rear-projection_television) often use it, too.

Thanks, these are good leads.

My older Epson 8350 projector has a feature they call "Lens shift." When setting it up you make sure that it is perpendicular to the screen surface. Then it has two mechanical adjustments to vertically and horizontally shift the image. Page 25 of this user manual shows that it can shift the image vertically up to one image height up or down. And horizontally up to one half image width either way. It makes setup a lot more flexible. I'm not sure how common the feature is though on newer more available projectors.

https://files.support.epson.com/pdf/plhc87u/plhc87uug.pdf

As another commenter suggested, it's common for projectors to have a movable/adjustable lens (also called lens shift) to move the projected image without altering focus too much.

There are also ultra short throw projectors that can be mounted a few feet away from their target, designed for classrooms. They probably don't have the blackest black levels though.

A number of them support the unit being placed about 6in. from the wall. When you include the depth of the unit, that may be placing the mirror closer to 2ft. away, but that is still pretty darn close.

I’ve seen applications where they use redundancy with overlapping projections to avoid shadows of people walking in front. The image is still slightly interrupted, but the overlapping projections do a decent job filling it in - if done properly.

IIRC academy of science sf did this in one of the lines for an exhibit.

I can't really answer your question directly, but check out teamLab Borderless[0] (also definitely go if you have the chance, it's an amazing time). They use 500+ hi-res projectors to cover the entire place in seamless imagery. Maybe you can find some more technical information regarding the installation.

[0] https://borderless.teamlab.art/

Haven't been there, but I've been to https://www.carrieres-lumieres.com/en and the sheer scale of it is absolutely mind-boggling.

This is so awesome! Back in 2008 I built a projector from an old unsued laptop and a high powered metal halide overhead projector that I bought off ebay for 50 bucks. It was surprisingly good looking; I was very happy for the total investment. It was unwieldy and pretty power hungry, but none of that really mattered living in my college dorm at the time.

When the laptop screen eventually gave up (I think just the connector) I never ended up rebuilding it. Nowadays you can get a really awesome looking projector setup for so little, it's not really worth trying the same approach.

But from what I skimmed through, this is a build of way higher complexity, cost, and quality. I'm looking forward to watching this video tonight.

In 2006 or so I did the same, building a projector out of a laptop LCD (without the laptop, just a plain LCD module and a controller), some lenses, a fresnel lens (cut in half, one part before and one after the LCD) and a 400 watts mercury vapor lamp usually intended to be used to light up factory halls. I constructed a housing for it from wood, a cooling system using lots of PC fans to vent that 400 watts of heat, and even a microcontroller-based control system for the entire thing, with a small LCD display, which managed stuff like tracking bulb used time, monitoring internal temperature via a temp sensor IC and letting the cooling system run for some time after turning off the lamp to get the heat out.

That thing was heavy and loud as hell, and it wasn't very bright considering it used 400 watts of light power, but it was about half the price of an equivalent projector back then, which effectively allowed my poor student self back then to enter the home cinema scene, which I couldn't have afforded otherwise.

There even was an entire little scene back then of DIY projector enthusiasts (at least in Germany) with bulletin boards and even some niche online shops specialized in selling suitable lenses and LCDs and matching controller boards. It was great fun and a great learning experience, especially since you could get help from like-minded people and ideas from other people's projector projects.

A few years later it all quickly went down the drain when the first Full-HD projectors with acceptable quality dropped into price ranges that were affordable for the general public. It simply wasn't possible to compete with that anymore, neither in terms of quality nor in terms of price. I myself replaced my hunk of a self-made projector after about 4 years of use or so, with one of these entry-level full HD home cinema projectors (which I'm even still using today, so that was a really good investment in my book). But that self-made device was worth every cent and every hour of work, and I still have fond memories of building it and tweaking it for maximum quality and then watching movies with it, all the while thinking "man, I built that thing basically from scratch".

DIY Perks is a fantastic channel. So much good stuff, so little time to try everything :D

I agree! I particularly liked the one using a two-way plastic mirror and webcam, so that you can maintain eye contact when you're video calling someone. Similar principal to a teleprompter.

https://www.youtube.com/watch?v=2AecAXinars

For fun, keep count of how many times Matt does something that you wouldn't have thought to do on your own, which would torpedo the whole project or be way too hard to self-diagnose.

I hit about 20 before I said "this project is way beyond my skill level." But I still got a vicarious sense of pride from watching his success!

He created an amazing 'desk PC' with computer components housed in a slim, completely silent enclosure and placed under a fold-down desk.

https://www.youtube.com/watch?v=QaoFh1DH51U

I know, right. My MacBook Air from 2015 went bust. I was looking for ideas to reuse some of the stuff when I encountered his "making a dual screen laptop video" [0]. There's ton of fun stuff he does with broken LCD screen, the camera module etc. I remember binge watching the entirety of his channel.

[0]: https://youtu.be/9aLzfjZu1DY

When you buy an expensive projector you are paying almost entirely for brightness, so this result isn't too surprising.

And HDMI 2.x, HDMI 2.x, power levels, & color settings.

Still, it looks like a fun project. I ended up watching the entire video.

You pay for brightness (My 4K projector has a xenon arc light source) and for black level (LCOS, etc.)

The super low-cost version of this is a magnifying glass and a shoebox - it works surprisingly well if you're only throwing a few feet in a dark room.

I never even knew Sony had released a 4k phone. What a clever way to kill two birds with one stone: Get an android system with a 4k screen but for 1/5th the price.

This guy is a true hacker.

A bit disingenuous for the presenter to completely ignore the obvious vignetting of his dim projected image, the results seemed pretty mediocre from where I'm sitting.

I built a similar LCD projector when I was in high school! Same basic principal as is used here, shine light through a bare LCD panel (mine was from a broken laptop), add some fresnel lenses and a focusing lens and throw it all in a box.

Pretty cool, but just buy a damn projector. Do not approach this as something practical that's going to be useful, because it's not. It's huge, probably loud, you'll get dust and stuff stuck in all sorts of places messing with the image and it lacks advanced focusing like keystone transform https://en.wikipedia.org/wiki/Keystone_effect

Yeah, we did something similar in our apartment in the early 2000's. It was one of those old overhead projector/fresnel lens/repurposed monitor LCD panel deals that were all over the internet at the time.

It was a cool project and when it was just me and a friend sharing an apartment, we didn't care that it was janky (especially since any large format screen was way too expensive for us at the time). But now you can get better performance from a cheapo projector and for a bit more, you can even find decent short-throw models these days.

My current project (that is collecting dust) is a big dual-lamp auditorium sized Epson that I snagged when it was getting tossed out at work. Sadly, while it was working when I picked it up, somewhere along the way from the office and through a couple of moves the auto-iris got stuck/damaged.

It's the most frustrating thing because the projector works fine but when it powers on, there's an error message stating that the auto iris has an error and it won't let you proceed. I don't even care about the auto iris and while I've dismantled it quite a bit and blown out/lubed everything I could find, I still get the error. Apparently they all had this problem but it's way out of warranty and I don't see much point in paying to have a free projector repaired.

This is marvelous.

Now imagine, with no right to repair, manufacturers locking all components making these things impossible.

He mentions that adding a reflector to the LED will reflect too much heat onto the LCD. Could this be solved with a pane of glass between the LED and the LCD to absorb the IR light?

The audio seems to be a let down though: plug something into the (disassembled) phone's audio jack.

I wonder if phones can deal with USB audio cards (that have surround options), or if there are any Bluetooth audio solutions that offer surround sound.

Or I guess you can replace the phone with a PC/laptop, and have the display connected to an LVDS driver..

On an android, I assume you're not using any video sources that exceed the capabilities of a stereo jack. It's not like it's HDMI pass-through from a home cinema.

Wait. It's a phone. That means, it does have bluetooth. Or you can buy one of those dongles that are basically like a wireless aux cable (I forget the technical term for it)

Edit: Something of this sort: https://crossbeats.com/collections/all-products/products/con... (No affiliation to the company or the product)

Android devices most certainly can handle USB audio devices. I've used Logitech G930 and G933 USB headsets with a variety of phones and they all worked as expected.

No idea if it handles surround sound properly though, but considering phones are offered with HDMI outputs and there's the whole Android TV lineup I'd imagine there's some kind of support in there.

Interesting. I’ve been thinking of trying to find a decent projector that operates off 12V for hurricane season. Something cheap because we’d not use it too often. DIY might be an option. I don’t have access to any way to make the metal panels like this one has though.

You can cut and drill them with simple power tools and a good desk, it's pretty hard, but doable. The lens and display would be more of a problem for me haha

Does hurricane season mean your family is camping out in the basement?

Florida doesn’t do basements.

Get one of these 12->230VAC boost converters. Had a 1 kW one in my VW van a decade ago, that thing could run anything except flourescent tubes.

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