DLP HDTV

This is the place to discuss DLP projectors, UV Lasers, Galvanometers, LCD screens and similar display devices. Also discussed are optics in general.
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fly_boy_bc
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DLP HDTV

Postby fly_boy_bc » Tue Jun 30, 2015 7:19 pm

In the last few weeks I have seen no fewer than SIX DLP HDTV's on Craigslist for under $100! One was only $25.00 (1080i 50 inch Samsung rear projection HDTV) and the owner swears it's in perfect condition! I completely understand why these DLP's are becoming available cheap what with all the LCD, Plasma and LCD screens out there.

Obviously I would want to look up the specs. on any projector to make sure the lumens and resolution are reasonable for use as a beamer but is there any reason to not consider using the engine out of one of these machines?

Can the "beamer" be easily separated from the rest of the box? Or would I be tearing my hair out trying to get the thing to run outside of the TV box itself?

Anybody ever try one?
Gary (flyboy)

khbaur330162
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Re: DLP HDTV

Postby khbaur330162 » Fri Jul 03, 2015 3:11 am

I'm also highly interested in this prospect. Sadly, I can't help very much.

1920x1080 DLP HDTV's can be found for pretty cheap locally. Not only that, but given the increased size of their light engines, I speculate it'd be easier to swap the lamp for a UV LED (no idea if there's any truth to that).

I'm highly interested in looking into this right now. I've contacted someone via craigslist and may or may not be picking up a cheap DLP TV for gutting soon. The only reason I didn't spring for a DLP engine off eBay was because many only come with the optics, DMD chip, and DMD driver board. I don't want to have to deal with scrapping together power supplies and analog I/O boards to power/feed the DMD with a video signal. I'd rather just have a complete unit I can tear apart and piece back together inside a more adequate DIY case for my printer, which after everything's said and done can be plugged into the wall for power and my computer's HDMI out for video signal.

khbaur330162
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Re: DLP HDTV

Postby khbaur330162 » Wed Jul 08, 2015 8:25 pm

Got a 1080p DLP HDTV the other day off craigslist for cheap ($100, 7 month old lamp, ~35mi away to pick it up). I also saw a 1080p DLP HDTV on craigslist which the owner left on their curb (fully functional), but was a day late in nabbing it. If you're patient I'm sure there are even better deals to be had than what I found.

Anyway, so I opened her up and it looks promising. Haven't taken the DLP engine or any of the boards out yet so I'm not entirely sure what all this stuff weighs, but the TV itself is pretty heavy (Samsung says it weight 75lb's, although I'm not sure I believe it, or maybe that's just 75, very awkward, pounds :oops: ). Would definitely make for a bulky printer, although it might not be too bad with creative mounting of all the boards and ballast and what have you.

Shorting out the optocoupler should be as easy as any theater projector hack you've seen, although I'll need to take a closer look at the ballast when time allows. I still stand firm in believing a ~60W UVA LED or car headlight mod should be relatively cheap and straight forward when the bulb inevitably burns out.

The projector lens has a fixed focal length. I believe the rear mirror is to a DLP TV as a wall or projector screen is to a theater projector. Due to this I'm imagining I'll have to play with diopter strength and projector distance to get an image that focuses with my desired build dimensions. The lens itself is relatively large (didn't measure it, I forgot to before closing it all back up), but there's a Vivitar diopter lens sent with 86mm diameter for ~$18 shipped on eBay. I'm imagining that's large enough for what I'm doing. The projector lens is also aimed at a ~20 degree angle or so onto the rear mirror (also at an angle). I'll have to figure out if the image is projected as a trapezoid onto the mirror, or if it's rectangular. This will determine whether or not I have to match/offset the lens angle exactly when I mount the engine (in order to attain a perfectly vertical projected beam), or if I have to figure out the mirror's angle and compensate for it when mounting the engine.

I won't have complete control over the dimensions of my build area, a lens set only gets me so far before having to mess with shims and focal length which I don't really want to get into atm (time will tell). But for what I paid? In theater projector talk that money typically gets you 1280×720, maybe less. I'd say as of now this looks like a good budget-minded option for people who don't mind fussing with stuff as behemoth as old DLP TV guts. I'd like to stick with it and see how far I can take it.

khbaur330162
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Re: DLP HDTV

Postby khbaur330162 » Fri Jul 10, 2015 5:27 pm

Optic engine (includes lamp ballast) weighs ~11.5lb's. The main and video boards combined weigh ~7.5lb's. They're not nearly as heavy as I imagined, the screen and mirror make up the bulk of the weight.

The main lens is ~85mm so the 86mm Vivitar close up lens set should work well.
Image


The ballast: I see three optocouplers smack dab on top, one of which is mounted upside down.
Image
Image
Image



The projected image is rectangular so mounting should be as easy as measuring the lens angle and propping the whole engine under base up that degree to offset it.

Btw, I've got a huge mirror out of this and not much use for it. If anyone's interested in me cutting a chunk of it off per their desired dimensions feel free to PM me (I'm based in the continental U.S.). I realize can be found for very reasonable prices, but if you need a larger size? Not really sure, just thought I'd throw the offer out there before chucking it in the recycling.

khbaur330162
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Re: DLP HDTV

Postby khbaur330162 » Fri Jul 17, 2015 10:08 pm

Slight update:

Image

Totally missed this. :oops: That focus wheel has gobs of play. The only thing I'm worried about is the ridiculously short throw of this engine. In order to get the build area most of us want the vat would basically have to sit on top of the lens. So, while I may still need that 86mm close up lens I'll at least have full control over the build area.

khbaur330162
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Re: DLP HDTV

Postby khbaur330162 » Mon Jul 20, 2015 7:44 am

Another slight update:

Image

That's roughly 192mm in the x direction and as you can see there's severe stretching at the image's extremities, worst at the corners. The wide angle lens combination used isn't good for really short projection distances such as this. So, that rules out DLP TV's as a drop in solution. :|

The whole lens assembly comes off in a single piece and is fairly easy to work with. I'm going to see what I can do with a home theater projector lens and try to get a square image at <9" diagonal.

fly_boy_bc
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Re: DLP HDTV

Postby fly_boy_bc » Mon Feb 29, 2016 2:45 pm

Khbaur,

I am really impressed with the experimentation you have done! Thank you for sharing it. You conclude that the DLP rear projection engine is not a "drop in solution" due to the edge distortion at 9" but your results actually looked very promising to me. At least the image is projected squarely and does not require tilted elements to normalize it. Do you suppose that the edge distortion might be mitigated by a different lens set or by just going with a larger build area and dealing with the subsequent longer exposure times? Is the light intensity sufficient? How big do you estimate the build area would have to be in order to reduce the distortion to an acceptable level?

My personal "dream" SLA would have a larger build area than average anyway. I would try the salt water method of resin conservation.

Gary.

fly_boy_bc
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Re: DLP HDTV

Postby fly_boy_bc » Mon Feb 29, 2016 2:56 pm

Oh, I forgot to ask if you concluded that the build itself would be any more difficult than with a projector. Would it be easy enough to remove the engine and get it set up? Can the color wheel be removed completely or does it have to stay plugged in? The focus wheel had a lot of play but were you able to adjust it with precision?

If the only issue is the edge distortion you demonstrated I am more than willing to grab one and see what my 25 years of optical lens manufacturing experience can do for the problem. 8-)

aggiehavoc
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Re: DLP HDTV

Postby aggiehavoc » Thu Jun 16, 2016 3:00 pm

Any update on this? I have an old DLP TV lying around that I'd like to take apart and convert into an SLA printer.

fly_boy_bc
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Re: DLP HDTV

Postby fly_boy_bc » Sun Jul 10, 2016 12:37 pm

Any further experimentation here? If an old rear projector can be adapted to SLA use it would open up a whole new world of cheap beamers!


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