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'[EE]: Build you own LCD projector?'
2002\04\11@130241 by Colin Constant

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I would really like a smallish LCD projector.  Since LCD projectors cost
thousands of dollars I thought it might be worthwile to build one.

At first glance this might seem like a rehash of the "Build your own PC" thread
but I think it might be a rather different situation.  I'm thinking that the
price of projectors is partly dictated by low volumes.  Maybe there's a lot of
labour involved.

On the other hand the parts are probably expensive.  IIRC even replacement
lamps can run to hundreds.  And, of course, the optics.

Any thoughts?

Colin

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2002\04\11@131311 by Douglas Butler

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I think the hardest part will the the LCD itself.  It will have to be
fan cooled, probably using Infra Red filters too.  I see it as a thermal
management project.

Sherpa Doug

> {Original Message removed}

2002\04\11@133154 by Simon-Thijs=20de=20Feber?=

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Hello,

Someone at http://www.diyaudio.com is doing/planning the
same.

grtz

Simon



--- Colin Constant <.....Colin_Constant-NRKILLspamspam@spam@RAYTHEON.COM>
wrote: > I would really like a smallish LCD projector.
Since
{Quote hidden}

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2002\04\11@133859 by Colin Constant

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Does the LCD need cooling in itself, or is it the heat of the lamp that causes
the problems?  I don't get the part about the Infra Red filters  at all.  No,
wait :-)  Are you saying that you need to filter the IR from the lamp before it
gets to the LCD?

Thanks,
Colin




I think the hardest part will the the LCD itself.  It will have to be
fan cooled, probably using Infra Red filters too.  I see it as a thermal
management project.

Sherpa Doug

> {Original Message removed}

2002\04\11@135456 by Douglas Butler
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The LCD will be heated by the lamp.  LCDs are known for being heat
sensitive.  If it is an incandescent lamp a lot of its output is in the
infra red.  Some projectors use tiny arc lamps which produce less IR but
still a lot.  If you use a "cold mirror" type IR filter you can separate
most of the IR before it gets to the LCD.  Also look at "hot mirrors".

Sherpa Doug

> {Original Message removed}

2002\04\11@172333 by M. Adam Davis

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The hardest part is getting the right LCD.  Unless you want to use very
large optics, or lose a lot of light from the lamp you need a small
transmissive LCD that works at high temperatures.

I've seen these in spec sheets from lcd manufacturers - different from a
regular lcd, and they don't include integrated electronics.

What do you mean a smallish LCD projector, anyway?  You want a projector
that's physically small, or one which makes a small image (ie, not as
nice as expensive projectors).

What do you want to use it for?  Computer monitor, TV projection or both?

What is your target resolution and brightness (ie, good in dim rooms,
good in dark rooms, good in lit rooms, etc)

Let us know how your search goes!  This is different from a modern
computer in that the signals are not difficult to manage, but it may be
difficult to source the parts you need one at a time at a reasonable price.

-Adam

Colin Constant wrote:

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2002\04\12@034207 by Alan B. Pearce

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I believe most of these projectors now use a micro mirror display unit made
by Texas Instruments. This gives much better resolution and better colours
and registration than the old LCD units.

Go to http://www.dlp.com/dlp/resources/tech_dlpmems.asp and scroll down the
page looking for "DMD" for an explanation of how these work.

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2002\04\12@043042 by Peter L. Peres

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Maybe buy an inexpensive pocket LCD TV and add projection optics. The
resolution will be very poor.

Peter

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2002\04\12@043102 by Peter L. Peres

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>Does the LCD need cooling in itself, or is it the heat of the lamp that
>causes the problems?  I don't get the part about the Infra Red filters
>at all.  No, wait :-)  Are you saying that you need to filter the IR
>from the lamp before it gets to the LCD?

Yes on all accounts. The LCD produces heat (the shift registers on it do),
the lamp produces heat, and the LCD contrast point is very sensitive to
heat, plus it is easily damaged by heat. So you need to aim at running the
LCD at constant (low) temperature. An IR filter on the lamp is mandatory,
better use a lamp with little IR emission (arc lamp).

Peter

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2002\04\12@091613 by M. Adam Davis

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The more expensive projectors use texas instruments DLP, and they
advertise that fact since they are brighter and often more responsive.

But the DLP chip and driver is probably more expensive than the lcd - it
is only a few years old.
http://www.dlp.com/dlp/home.asp

-Adam

Alan B. Pearce wrote:

{Quote hidden}

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2002\04\12@092103 by Jeff DeMaagd

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DLP systems have their own problems due to the inherent design of
single-chip systems where colors are produced by flashing red, green and
blue in a high speed sequence, it can give people headaches.

Older DLPs were worse than equivalent LCDs from the time.  Only starting
last year did have get better color, mostly from a darker black or better
contrast ratio.  Right now, the one chip design also currently wastes
considerably more light energy and have a shorter bulb life, often 1000
hours for DLP vs 2000 or more for a lot of LCDs.

Either way, I suggest leaving this up to pros to design and build, to do
better than them would cost more.

You can get relatively newer used SVGA units for $1000.  You can also get a
new Panasonic AE-100 - a 850x480 resolution widescreen projector from Japan
for about $1500 from pricejapan.com.  Its bulb is rated for 5000 hours in
economode.  Read the projector forums at AVScience.com for more details.

Jeff

{Original Message removed}

2002\04\12@100720 by Jim

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 "where colors are produced by flashing red,
  green and blue in a high speed sequence,
  it can give people headaches."

How does this compare with the frame rates from,
say, a standard 'movie projector' - or how about
a TV or computer CRT monitors with their varying
scan rates?

I never recall getting a headache from watching/viewing
movies from a projector (and I once dissassembled a Bell
and Howell 16 mm projector and removed one blade from
the optical 'chopper' that doubles the 'blink' rate to
make a slightly better film chain for a small institutional
studio operation) -

- nor do I recall any problems from that (almost) bygone
era.


Jim




{Original Message removed}

2002\04\12@115411 by Jeff DeMaagd

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----- Original Message -----
From: Jim <@spam@jvpollKILLspamspamDALLAS.NET>


>   "where colors are produced by flashing red,
>    green and blue in a high speed sequence,
>    it can give people headaches."
>
> How does this compare with the frame rates from,
> say, a standard 'movie projector' - or how about
> a TV or computer CRT monitors with their varying
> scan rates?

The two don't seem to correlate well.  Some people aren't bothered yet
demand high refresh CRTs, others are bothered but aren't as fussy with
refresh.  This is different from film projection as each primary color is
flashed on the screen in sequence at a very high speed on one chip DLP / DMD
projectors, but with film, all colors are flashed from the film frame at the
same time.  I really don't know how many people are bothered by it, I would
guess somewhere between one to ten percent of the people that watched one
for a while.

For those seriously looking into such a system, I suggest finding some way
to test one out for the length of an entire movie.

Jeff

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2002\04\12@124441 by M. Adam Davis

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There are links from the site http://www.dlp.com/ to theaters that have
DLP projectors.  Many computer animated films are shown on them, and
star wars episode II will certianly be shown on them coming up.

Of course, these projectors are much more expensive than consumer or
business level projectors, and are likely higher quality - you won't be
bothered by them.

As a side note, LCD pixels are turned on and off in a very similar
manner to produce the color variations.  Since the LC material presents
itself like a capacitor, though, it doesn't turn fully off (or on), and
smooths out the flicker.  Same way greyscale is achieved on smaller
graphics LCDs, which can have a frame rate of 200Hz.

The DLP, IIRC, can be run faster, but I suspect there's a tradeoff
between longevity and speed of use as it is a mechanical device.  But
the contrast blows just about everything else away.

-Adam

Jeff DeMaagd wrote:

>{Original Message removed}

2002\04\12@130444 by Jim

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I had a chance to see a demo of DLP at a TI DLP open-house
a couple of years back - could not detect flicker
or any other effects - the unit was set up at their
Spring Creek/Plano, TX facility in a small theater built
for just that purpose of demo-ing to other vendors
and manufacurers ... the resolution was awesome, too.
We had a choice of 'program' sources including off-air
HDTV, standard TV, satellite as well as some of the
highest resolution source that was meant to show just
what DLP technology could do given hi-res media/material.

Many internal details via cutaway units and displays filled
the hallway of this small demo facility - giving one an
opportunity to see the history and development of the eventual
hardware that is used to 'pull off' this DLP trick - and since
this was actually a job fair - many other technical-types
were there as well a number of hiring managers looking for
talent ...

Not half a mile away up US-75 on the same side of the highway
is a theater which uses DLP ... coincidence?

Jim

PS. What is the upper limit/frequency response of the human eye
to 'impulse' or on/off cycled light sources?



{Original Message removed}

2002\04\12@131742 by Spehro Pefhany

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At 12:40 PM 4/12/02 -0400, you wrote:
>There are links from the site http://www.dlp.com/ to theaters that have
>DLP projectors.  Many computer animated films are shown on them, and
>star wars episode II will certianly be shown on them coming up.

I'd like to see Laser CRT technology in the flesh. Anyone here ever
seen one? (I believe they were developed for military displays in the FSU).

The color gamut is larger than conventional phosphor CRTs, for one thing.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
KILLspamspeffKILLspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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2002\04\12@141352 by M. Adam Davis

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Jim wrote:

>
>PS. What is the upper limit/frequency response of the human eye
>to 'impulse' or on/off cycled light sources?
>
The eye will blend light that is faster than ~30Hz, but depending on the
pulse width and the device emitting light you can detect flicker (given
no other aid or light source) up to ~45Hz (determined
experimentally/informally/non-scientifically) when the source is an LED
and the signal is a square wave of 50% duty cycle.

The flickering is also detectable when there are other light sources
which flicker - they beat against each other and produce another slower
more easily detectable beat.  This is one of the reasons viewing a CRT
under flourescents at a low refresh rate is so annoying.  You may see
the flicker out of the corner of your eye (where there are fewer color
receptors, and more rods).

There is a lot of information about this out there, though, and you'll
find some disagreement among different studies.

-Adam

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2002\04\12@154207 by Jeff DeMaagd

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----- Original Message -----
From: M. Adam Davis <RemoveMEadampicTakeThisOuTspamUBASICS.COM>


> There are links from the site http://www.dlp.com/ to theaters that have
> DLP projectors.  Many computer animated films are shown on them, and
> star wars episode II will certianly be shown on them coming up.
>
> Of course, these projectors are much more expensive than consumer or
> business level projectors, and are likely higher quality - you won't be
> bothered by them.

There are three chip DLPs that are for theatrical use - they do not have the
flicker I wrote about.  Each DMD chip gets its own primary color, rather
than using a rotating color wheel to "time share" a single panel between
different primary colors.  They run well over $10,000, to even many times
that.  The systems that use only one chip do have a benefit of a simpler
light path and allows fewer optical pieces to be used - so it is in that
case easier to get better contrast.

I don't pretend to be an expert, I just did enough looking around and
weighing the tradeoffs before settling on an NEC brand LCD projector.

Jeff

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2002\04\13@055936 by Peter L. Peres

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