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DIY Full HD Projector, need advice

K

kindler

n00b
Joined
Apr 5, 2013
Messages
10
I am looking to build a 1080p projector from a stripped down LCD monitor, an overhead projector, and a light source. I need help with choosing the light source. I would like no more than 3000 lumens, and could probably do well with just 1500. It would be awesome if it was dimmable as well, so that it could be easy on the eyes and also to conserve electricity.

Should I get halogen or LED lights? I realize that LED may be more efficient, but would they run hotter than the halogen? Would the quality of the picture be different? Are there other alternatives, like metal halide bulbs or others? Also, I already have the monitor, and my budget for the rest shouldn't exceed $150. Thanks for your advice.
 
I did this a lot years ago.
I'll pass on what I recall.

You need to find a fresnel lense that is as large or larger than the size of the display panel.
Fresnel lenses come in different forms, some are single lense which are not good enough (unless you can make a uniform LED array light source).
What you are looking for are dual lenses or a single lense that can be split apart.
Place the LCD panel between the 2 lenses.

These lenses are used to take the light radiating from the light source and make it travel vertically upward into the the LCD.
The vertical light out from the LCD hits the second fresnel and is angled toward a focal lense (or lense system) which feeds to the screen.
There are different angle fresnel lenses, choose one appropriate to the distance your bulb is away from the lower fresnel lense and the distance your LCDs upper fresnel is away from the focal lense.
Or adjust your setup to match the needs of the fresnel lense.


There are a lot of losses with an LCD screen.
The basic loss just due to the LCD colour cells leave you with only 33% of the initial light power.
There are further losses, you will probably end up with nearer 15 to 20% of the starting light output.
Any glass that the light passes through adds loss, including lenses.


The light source must be a single point light source.
This rules out LED because there is no way you can buy a lamp that will concentrate enough light power into a point source.
Unless... you can provide a uniform light source that covers the whole LCD and is powerful enough, then you would dispense with the lower half of the the fresnel lense and accept the vertical radiating component of the light source into the LCD.

Halogen light is entirely pointless.
They run very hot because they are very inefficient, the bulbs dont last long, cost a lot and the colour spectrum is very limited and lacking blue content, making the image look yellow and blues look a bit black.

The only real option is metal halide lighting unless you can get a powerful enough even spread LED light source that covers the whole screen.
I got away with a ceramic 150W metal halide on a 1024x758 res screen @ about 60" but compared to todays projector power output and large screen sizes, its not going to cut it.
So you need at least 250W, probably more.
Choose a lamp that blocks UV otherwise it will destroy the LCD panel.

A strong light source brings problems with heat so you will need good active cooling, even with a 150W bulb.
I blew fans across the LCD and across the light.


The colour quality of the bulb is determined by its CRI (Colour Rendering Index).
You want an absolute minimum of 85 CRI otherwise colours will look wrong.
90 is pretty good, 95 even better. 100 is the max.

Theres more, cant remember it all.

oh yeah, you need a spherical reflector behind the lamp to prevent huge losses in light power.
The quality of this will affect the colour and brightness of the light sent to the LCD.
 
Last edited:
Wow, thank you for the advice! I am wondering, though, do I need to buy extra fresnel lenses if I am using an overhead projector? For example, I am also trying to follow what these people did:

http://www.tomshardware.com/reviews/supersize-tv,918-7.html

They mounted the LCD screen onto an overhead projector, and it seemed to work sort of OK. Well, except for the obstruction near the corners of the picture.

Also, do you know if anyone sells completely quiet metal halide ballasts? I tried once to build an indoor metal halide fixture, and the reason that I didn't was the annoying buzz the power supply created.

Thanks again.
 
The above was written assuming the LCD would be level with the floor projecting upwards, lamp below with a mirror + lense setup above to direct the light toward a screen.
The LCD can of course face the screen with the light behind it, no mirror is needed then.

When I said you can split a single fresnel lense, some fresnel lenses come as a pair of lenses attached to each other.
These can often be split apart to give the 2 required lenses.

Alternatively, you can just use the combined lense close to the lamp side of the LCD, but...
The light coming from the combined fresnel is angled toward the front projection lense and you can lose some of the screen estate due to the smaller area it will cover by the time the light hits the LCD.
I also found that passing light through the LCD panel at this slight angle reduced the light transmitted through the LCD.
So its better to use a split fresnel with the LCD between the lenses.


I tried hard to design a 1080p projector but found that fresnel lenses were not large enough to cope with the larger size of the LCD panels.
I was previously using a 15" 1024x768 panel on a modifed Overhead Projector (OHP).
The smallest 1080p LCD I could find (that wasnt drastically colour limited) was 17".
There were some larger fresnel lenses but the cost was silly.
This situation may have improved, I havent checked.


Instead I waited a few years and bought the Optoma HD131x 1080p projector. Its brilliant + very cheap (and does excellent 3D).
The bulbs last 3500hrs on full power, 6000hrs on eco mode and cost not much over £100.
It is a stunning piece of kit for very little money and is out of the way on my ceiling.
(note you need 4m throw distance for this pj and it must sit at the top or the bottom of the screen, unless you dont mind using keystone correction - which tbh doesnt look bad)
There are newer versions of this pj now, some with higher power lamps.
But I'm finding that even halfway through this lamps life, its easily bright enough.

This is the better route to take by far, buy a cheap pj like the above, there are a few to choose from.
I paid £650 new, 1.5 years ago, they are cheaper now and can be found second hand.

Good luck :)
 
kindler said:
Wow, thank you for the advice! I am wondering, though, do I need to buy extra fresnel lenses if I am using an overhead projector? For example, I am also trying to follow what these people did:

http://www.tomshardware.com/reviews/supersize-tv,918-7.html

They mounted the LCD screen onto an overhead projector, and it seemed to work sort of OK. Well, except for the obstruction near the corners of the picture.

Also, do you know if anyone sells completely quiet metal halide ballasts? I tried once to build an indoor metal halide fixture, and the reason that I didn't was the annoying buzz the power supply created.

Thanks again.
Click to expand...

You can follow my project here.
http://www.aoaforums.com/forum/grap...er-peripherals/28248-home-made-projector.html
I was very unwell at the time so had plenty of time to do it but almost no cash!
Hence the gung ho approach, but it should answer almost any questions you have if you really want to go ahead.
I didnt know much at the start, it was a long learning curve, so some statements early on get revised later.
I tried to correct some things with edits, buts it a gargantuan thread.
I dont mind assisting if you go ahead.
 
There are lots of places to buy metal halide lamps, the ballast and starter from.
If you get that far, I'll help you choose.
Dont forget the circular rear reflector. The quality of this will affect the reflected light colour and brightness.
 
Oh wow, thanks again. Your further suggestions have made me reconsider a bit, but I have to do some more reading before making a decision. Would it be easy to replace the cooling fan in case a projector like the Optoma happens to make too much noise? In truth, I am considering some miniature projectors that might be more within my budget, but nothing definite yet. I'll update as I find out more useful info.
 
Theres no need on the projector I have, its very quiet.
But you dont want to open up a retail projector, you may need the warranty some day.

Case in point:
The projector I bought before this was an Epson TW3500 (UK version).
This was rated at 4000hr bulb life on eco yet the bulb didnt last more than 750 hrs before it started deteriorating badly and then exploded.
Epson replaced the bulb but it happened again.
Owners of this projector and the US version were up in arms because they had the same problem.
Epson claimed it was certain bulbs but the problem didnt ever get fixed, not even years later.
Epson refused to allow the shop to accept returns so I had to threaten the shop with legal action.
Luckily they complied, I gave them a little back for the use I got out of it.
I will never buy another Epson.

If there was no warranty, I wouldnt have been able to get a replacement bulb or return it.
Dont mess with a shop bought pj :)
 
Thanks again, your insights have been very helpful. I will take your advice and try to snag a used optoma or something similar from ebay in the coming days. Things really seem to have come down in price (including the bulbs) over the last few years. I will post the deal if and when I get it, so that others can see what might be possible with a bit of bidding. Speaking of which, now I will get to learn how to bid well. :)
 
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