7" LCD Projector w/ Keystone, Remote, Compact Design


2005-08-13 5:08 am
7" LCD Projector w/ Keystone, Remote, Compact Design

Hello everyone. This is my first attempt at a homemade projector. I wanted to build a somewhat “portable” unit that I could carry around and setup wherever. My intentions for this projector are to be able to set it up outside and project on to the side of a house or a hang down screen. I decide to go with a 7” LCD to keep the unit a reasonable size. I realize that you can get much better quality out of a 15” but I just didn`t want a projector that big. The LCD I chose was a Lilliput 7” monitor. It was claimed to be XGA, but the resolution is only 768x480. Better than most 7” screens but not what I would consider XGA. I went with a 250W Metal Halide light setup from HQI mainly because it is so much smaller than the 400W setup. I figured for a 7” screen and a not-so-giant projected image, it would be sufficient.

I had some features that I wanted to include on the projector:
-- Keystone adjustment with a easy to use “roller” interface
-- Full remote control of power for the LCD and Light source (ie relay to control the light)
-- Easy focusing (Varifocal triplet)
-- Rugged and good looking enclosure

I liked the design of the Pico projector but I thoughe the unit could be even smaller by rearranging the components a little. The design I ended up using folds the incoming light once and leaves a compartment on the side of the enclosure to house the ballast and LCD circuitry. Below is a layout of the components of the projector.


And here are some images of the finished projector:



The LCD panel had audio inputs and a small speaker. I incorporated the audio inputs into the projector as well as the speaker. In reality the projector will probably be used with a amp so I included audio outputs which are the black RCA's next to the inputs. Thinking about the way cables work, this made a lot of sense



The enclosure was construced entirely from lexan painted black on the inside and is bolt together with aluminum angle. I like the look that it produced. Looks very industrial

Here is the projector along with my Xbox and a small 60W audio amp I built for size copmparison



Here are some images of the projector with the cover off and the components exposed.


The light is mounted directly to the wall of the enclosure. Aluminum flashing was used to act as a heat shield for the area around the light and also as a light barrier to keep the light from shining through the painted lexan. The piece of flashing that is hanging down to the right folds over the lighted area to prevent light from shing throgh the cover. There is some light leakage through the case at corners and such but it is not bad.


In the above picture you can see the two fans. The main fan is a 80mm with a thermocouple that adjusts the speed of the fan accordingly. The max speed is supposedly 4000RPM. The internal fan is a 50mm fan. It pulls air from the circuitry compartment and blows it over the bulb. There is a pretty steady flow of cool air over the bulb and out of the enclosure.. Behind the mirror is all the power circuitry, mainly the switches and 12V supply.

I used strips of balsa to frame the collimating fresnel and the LCD. The lens and the LCD are not glued in and can be pulled out for whatever reason.


The above image is looking from the rear forward. I somehow mirrored this image when I was editting it so everything is on the wrong side. You can see how the mirror is fastedned in this shot. I made two brackets out of aluminum and epoxied the mirror to them and bolted it to the walls. It is very rigid.


Above is a better shot of the compartment behind the mirror. Two toggles control the 12V supply and the light. The black box to the right is the relay that controls the light for the remote control operation. The relay is 12V operation. I found a point on the LCD board that has 12V when on and 0V when off. I ran a lead off that poin on the board to the input of the relay. When you turn on the LCD panel either with the button or the remoate the light turns on as well. It works very well and is quite handy.


Above is a deatail shot of the light. The main fan is directly beside the lamp holder. I was worried about the fan getting too hot but it doesn`t seem to. The thermocouple for the fan is taped just above the light. I figured this would be the hottest location in the enclosure.


Above is a detail of the keyston adjustmant mechanism. The field fresnel was cut from a full size lens and I left little pivot shafts on the lens so that it cold pviot for keystoning. You can see where the lens pviots near the center of the image. To adjust the lens angle I used a long screw. The bolt isfixed from rotating by the square piece of lexan. I embedded a nut in the black roller and as you turn the roller it slowly and precisely moves the lens. the springs put tension on the sysem to take up any play. When the cover is on the roller jsut protrudes through the top. It is very easy to run your thumb over it a few times to adjust the keystone.

I don`t have any good pictures of the projected image yet. I`ll post em as soon as I take some good ones. The maximum size it will get due to the limits of the focusing projection lens is about 90". At that size the room needs to be pretty much completely dark to get a bright image. I have been projecting about 70" images and they look very bright. You can tell that the panel is not the best resolution but the image is most definitely watchable.

I had fun building this projector and will probably build a larger unit with a 15" high res panel. The final product turned out better than I initially expected. I was able to achieve all the features that I wanted to include
very good design!

I like how the air is pulled over the LCD surface before it goes past the lamp & out of the box. Is that DIYprojectorCompany IR glass? Have you made any temperature measurements to see how well it filters the IR?

The only thing missing is something I need to add to mine: A dust filter on the air intake. I run my PJ in a fairly dusty room (courtesy of my avatar, his sister, and mother!) and I have to take it all apart every couple of months to clean the dust out. If you run your PJ outside, you need a dust filter to keep bugs out of it, too! Although it is rather entertaining to watch a fly walking around on the LCD surface. Like "Invasion of the Giant Insects". :D


2005-08-13 5:08 am
The IR glass was the last thing I put in. It was kind of an afterhought. I took all the pictures before I did it, thats why its not in the photos. The collimating fresnel is a 330mm so the lamp is pretty far away from the LCD so the LCD doesn`t get too hot. The piece of glass is a scrap my father had that is supposed to be IR filtering. I had it so I stuck it in there for extra protection. I haven`t taken any temp measurements of the LCD but I am thinking about installing a digital thermometer that I took out of an old computer case to read the LCD temp. If I do that I`ll take some reading with and without the glass and post them

Thats a good point about the filter. I hadn`t thought of that. The slot for air to come in is about a quarter inchwide and 4 inches long, definitely big enough to ingest some crap. We have 3 cats so I sympathise with you on the rampid pet hair. I`ll probably try and figure out a good (not ugly) to way to filter the intake. Any ideas?


2005-04-24 3:18 am
Someone might suggest nylon stockings or some fabric filter for the air intake,but I've never tried that.The ballast gets really hot if it doesn't get enough air and cooling(at least mine does,its an icecap 250w hqi elec.)and I didn't see if there was any metal between it and the lexan it is mounted on.If there isn't I would recommend putting something there,along with a fan of some form,maybe a squirrel cage fan so you dont have to make it wider.
I ran mine in open air without a fan,and it got hot enough to cook on after about an hour or two.I added a squirrel cage fan,and its room temperature no matter how long its on.


2005-08-13 5:08 am
Here are some raelly crappy screenshots. This was the best I could do with my camera.

The projected image is 88" diagonal





That actual iamge is a little brighter than it seems in the pictures . I had to do some fancy finagling of the camera settings to get them as good as they are.


2005-08-13 5:08 am
vmos said:
Someone might suggest nylon stockings or some fabric filter for the air intake,but I've never tried that.The ballast gets really hot if it doesn't get enough air and cooling(at least mine does,its an icecap 250w hqi elec.)and I didn't see if there was any metal between it and the lexan it is mounted on.If there isn't I would recommend putting something there,along with a fan of some form,maybe a squirrel cage fan so you dont have to make it wider.
I ran mine in open air without a fan,and it got hot enough to cook on after about an hour or two.I added a squirrel cage fan,and its room temperature no matter how long its on.

I haven`t noticed the ballast getting exceptionally hot. It barely seems to get warm. I have an Ice cap 250W as well. I did not put and heat sinking material under the ballast. It is bolted directly to the lexan. I`ll keep an eye out on the ballast temp to see if it gets too hot. It would be easy enough to add another fan across the ballast.


2004-11-17 4:59 am
Just passing through on the forum, haven't checked for a while and noticed this projector. Great build!
Have you tested out the keystoning? I am going to build a pico projector to play around with keystoning correctly. In my theater setup I have the screen tilted to make up for the lack of major keystoning from my projector.
I like the use of Lexan to build the projector, I might have to try that .


2005-08-13 5:08 am
I am very happy with how the keystone adjustment worked out. The adjustment is very crisp and precise...no play. It provides compensation for about 10 degrees of projector angle in either direction. I hung my projector from the ceiling to project in the house but I take it outside a lot and set it up on the ground. It is really nice to be able to easily and quickly adjust the keystone.

Good eye. Right now the VGA input is the little black S-video looking cable taped to the top of the ballast. I am waiting on a female connector to install for a more permanant solution. The VGA cable taht came with the panel plugs into that connector. Also tossing around just mounting the existing connector into the wall of the projector and using the proprietary cable. Kinda awkward right now with the cable just hanging out of the top.

I thinking about installing a condensor lense to increase brightness but I have a few questions. When using a condensor where does the condensing fresnel focus? Right now I have a 330mm fresnel focusing on the center of the bulb. If I were to install a condensor would I have to reposition the components. Where is the focus of light with a condensor in place? Do you think I could switch to a 220mm fresnel and install a condensor in the appropriate location?

I`ll try and get some better results pictures up as son as I figure out how to take better ones.
pre-condensor lens

With a 330 mm fl condensor fresnel feeding a 7" LCD, you are losing A LOT of light! It would be much brighter with the right pre-condensor lens.

The most important concept for selecting a lens, is that the condensor fresnel has to "see" the light as if it was coming from its focal distance. When you add a pre-condensor lens, it magnifies the lamp arc which makes it appear to be closer. So the total lamp to fresnel distance has to get a bit shorter.

If you draw a full scale picture of the light going from your lamp arc to your condensor fresnel, then you can see where a particular pre-condensor lens diameter would intersect that cone. (ie. A 4" diameter lens would have to be closer to the fresnel than a 3" lens.) Once you have decided where to put your lens, then the distance to the lamp arc depends on the lens focal length. The easiest way to get it right, is to put the lens in the light path and then move the lamp arc back and forth until it lights the entire LCD evenly. If you pick a lens with an optimal focal length, then it will be close enough to your lamp arc to capture a lot more light than your fresnel would alone.

Changing from a 330 mm fl fresnel to something shorter would make your projector shorter (but so would adding a pre-condensor lens). But it would also make your image dimmer at the corners. (Inverse square law at work there.)

You might want to check out this post for more info: