Home made projector project (using LED lighting)

During the research into LCD updating on the T6x IBM’s, I learned a few new things.

One of those was that I had some of the parts lying around the office necessary to make a projector.
As my office desk typically looks like a mad scientist uses it, I thought I may as well add some more goodies to fill the missing bits.

First up was an LED light off taobao. As the 100 watt ones are still a little pricey, I’m going with a 50w one for testing purposes.
Visitors to the office who still have LED driven holes burned into their retina’s agree that yes, it is quite bright.

Probably not bright enough for our purposes, but good enough for testing.

Some photos of that here –

The hokey CPU fan cooler hooked up to the back adds to the effect.

The LED comes in a variety of color temperatures, ranging from yellow white, pure white, through to blue white, we chose pure white, as thats closest to what they normally use in projectors.

Projector and fan came to about 400rmb including shipping. Seller was quite nice to deal with too, and advised us which would be best for the purpose.

Now that our lighting requirements were minimally in place, we looked at the next requirement.

LCD screens.

As the 2 or 3 people that read this blog are aware, I just bought some rather nice QXGA LCD’s. These would be quite nice to use for a projector, but, unfortunately, getting hold of controllers for them is a little bit harder than I thought it would be.
I did manage to find some, but the prices are a little high, so I put that on the back burner for now. I will be looking into that again in the near future though.

First, a little detour onto the subject of LCD’s.

Essentially LCD’s are mass produced these days by a small handful of manufacturers, and the controllers for LCD’s are also mass produced.
Controllers pretty much come in a few different capacities, but essentially they’re all the same featurewise.
You buy a controller based on the maximum resolution it can handle, then program it for the LCD you have.

Controllers are dirt cheap – most can be found for 20rmb low end eg SVGA, through to 120rmb for medium end – eg 1920×1200 /DVI+VGA.
This means that most laptop screens can easily be reused as desktop screens for reasonably cheap prices.

TV’s are also essentially exactly the same as screens now, so the hardware is exactly the same.
Controllers for TV are usually a little more expensive, but not overly so. I bought a multi-input (HDMI, VGA, Tuner etc) with USB for 200rmb.
Different chipsets do better jobs at HD, but its very very generic stuff these days.

You need an invertor board for the lighting (if its not an LED based LCD) – those go for 10-20rmb.
You need a controller card to drive the LCD. (Most sellers will make you a cable for your specific LCD, and program the controller for a minimal charge)
You need a power supply (typically 12v 3amps+-).
Lastly you need a case.

We gave this a test run with a salvaged a 14″ LCD from a hosed laptop.
We bought a controller board (20rmb), power supply + empty screen casing (130rmb) off taobao. While it wasn’t necessarily worth it to do that, we did learn that its fairly easy.

Programming controllers is also pretty straightforward, but I’ll probably expand on that in another post.

As I wanted an HD capable projector I looked at what the smallest size HD screen (WUXGA) available on the market today is – that happens to be the Samsung LTN154U1
I got mine for about 500rmb.

Most people will be wondering right now at this point how an LCD screen is going to be used in a projector.

Essentially LCD’s are transparent – an LCD screen typically comes sold ready to use. This means its shipped with lighting built in, plus a reflective back surface.
We’re going to need to denude the LCD off all that – I’m going to have to disassemble the LCD display, and take out all the non-essentials. What I’ll end up with will be transparent, and fairly delicate.
Hopefully I won’t break anything when I take the LCD out of the casing, and remove the lighting, backing etc. Breaking it will be costly!

Next we’ll need a way to shine our light source through the LCD.
While we have a strong light – it won’t be very useful as is, as the light will mostly be concentrated in the center of wherever its pointed at.
So, we need a way to disperse the light in a directed way.

Typically this is done with a Fresnel. Fresnels are rather cool lens typically made out of plastic. They magnify or reduce anything passed through them.
We’ll be using a fresnel in front of the LED light to disperse the light evenly through the LCD.
Once its through the LCD, we’ll be using another Fresnel to concentrate the light back into a smaller focal area, so that we can throw it through a lens, and see something on a screen.

For a 15.4″ screen, we need a 400×320 sized 330mm Fresnel, and a 500mm Fresnel.
The 330mm (aka our collimator) will be placed in front of the light source, the LCD will be placed 10-15mm in front of that, then finally the 500mm (aka our collector) to concentrate the light + display output into a nice ready to use focal area for our rather expensive triplet lens.
We’re using a 500mm triplet as the lens, mostly as all the projector websites are using those for 15.4″ screens.

Fresnels were fairly cheap – 80rmb each or so.

The lens was rather more expensive. Ours was close to 600rmb with shipping!
When it arrived, we saw why. It definitely feels like its worth the money.. Unfortunately ours arrived with a crack from shipping, so we had to send it back. The replacement should arrive in a day or three.

While I haven’t setup the fresnels yet in action, I did test out the controller board, and LCD.

Photo’s below of everything.

While I haven’t built any casing yet, I’m fairly confident we should be able to knock something up quickly to house all the parts.
Hopefully ours will be sturdier than this professional build I saw online –