Oh man. I spent all this time preparing a post and I just needed to to use an s at the end of LED (tried LED bulb, light emitting diode, LED array, LED board) and change the search function to all forums (not the one I was in) to find information regarding viability of LEDs as a light source. Sorry, feel like such a dopey noob now. I tried to delete my post but don't see the option to. Sorry all.

This is probably one of the more comprehensive LED threads. Take a look.

Thanks for the reply. While the use of LEDs looks entertaining, I think I will just stick with a single point light source for my first PJ. I am normally on late at night EDT, just moved from CA to CT (took a red-eye and got no sleep) so I am having a hard time adjusting to the time change... that's my excuse heh.

Anyhow, I found some 10mm LEDs with color temp of 5500-6500K @ 125k mcd 13deg ang . They aren't cheap by any means 300 for $103 USD shipped, but an array of about 700 could cover an area (with overlap if my measurements are correct)of a 15.4 monitor using approx 35x20, but that would be about $240 just for the LEDs then you have to solder them all (talk about tedious) and then make/find a reliable power supply(more money). I know I am beating a dead horse now, so I will drop it. Thanks again for the link.

Before you order any, try this google search:
http://www.google.fr/search?num=100&hl...rcher&meta=

Hehe laughed as soon as I saw the search. Yeah, I don't believe it either, but 33.5k is still nice. I will have to do a lot of research before I consider using LEDs and it certainly won't be on a screen over 9". Awesome info BTW.

Since I am in process of building a LED projector, I guess this thread is appropriate. My design so far uses a 17" LCD Panel with a 10mm LED array 27x34 (maybe 1+ row per each edge if the edges become darker).

I already have with me 1000 10mm LEDs (they say 110,000mcd but I highly doubt it), as the poster above me noted their probably the ones true to 35,000mcd (but that would still work wonderfully for this). I guess it all comes down the technique one uses to measure. But a small prototype array I made using 4x4 LEDs I had at 20mA, the brightness was more than enough when I pointed it toward the projection screen. I also just got a 17" Samsung 712N (which is already gutted out and laying bare). The projection lens I will be using is a 550mm quadruplet projection lens (it's quite big... I it works with my calculations but I might get another one since it's so big).

I chose to do the LED for a couple of things. Mainly to see if it's really possible, since so many people say it can't be done and the most I hear it, the more I want to do it and test it out. The other factors are lower power consumption (I plan on having this on all the time), very low heat output from LEDs (meaning no need for fan, in term meaning no sound). The size of the projector would also be shorter since the space before the LCD panel would be at max 4 inches, unlike a point light source which needs much more room to spread evenly and be in focus with the Fresnel. Also this does not the first Fresnel lens since all the light is parallel. Another advantage is this will have no dark corners since the light is generated equally among the whole LED surface.

In sort: Less power, low heat, zero noise, smaller, no dark corners.

I am taking a big gamble, already invested quite a bit of money into it. The last part I am looking for is a perf-board the size of 27cm by 34cm or larger (but I have been unsuccessful so far). If I can't find one by this weekend, I will by 6 smaller ones and do the array that way (this would also make it easier for me to repair a potential problem if I have any with the LEDs). Any ideas on where I should check out?

Thats all the info I got for now, I hope this project will turn out the way it is on paper and my head. I will start a project log as soon as I start physical constructing of the projector.

Feel free to criticize as much as you want, I this is the time to point out if I do have any faults in my design before I start actually building. Thanks.

Do you realise that maybe only 6% of light shone on the back of the LCD will actually make it out the front?

Well actually I didn't know it was that low (I was expecting more like 80% light loss through all the optics including the LCD (so 20% of source light on the screen). Since I will be using one fresnel compared to two, I will won't be losing as much ligh as with using two.

So since I used 16 LEDs, that test was only with 1.7% of the total output of the original array (16//918). If it doesn't, all I need to do to make it a conventional DIY projector is replace the LED array with a point light source. Hoping the light will be enough.

Very cool, can't wait for you to start.

I'm not clear on what your total LED count is. 918?

918 x 20ma = 18360ma / 1000 = 18.36 amps. Yes?

Either way you probably should blink each row, thus the circuit will only see the amperage for one row.
You can use a $3 Parallax SX chip to blink the rows so fast that you would not notice the blinking.
A side effect would be brightness control.

On a side note be very careful of the power a LED sees. Overpowering a LED will not due much for brightness but will reduce its life by a factor of ten or more.

Oh, and good luck.

If you carefully read my statement you will see that I am just referring to the LCD on its own! Fresnel lenses and triplets will reduce it even more.

Well that would be if I did a whole bunch of LEDs in parallel with each one having a resistor. I am instead going to use a 48V (or higher if I can find one) DC power supply. Then arrange the LEDs in a series-parallel method.

Each series will have 13 LEDs (13*3.4V = 44.2V total drop) leaving 3.8V to be dropped on the resistor (180ohm + potentiometer, which I will explain why later) which will limit each series 20mA. So having a whole bunch of these strings in parallel would give me a current divider.

So I would have 71 Series of LEDs, each series needing 20mA, which equals 1.42A total. I would add the 190ohm + potentiometer so I can vary the resistance by 180+-20ohms more, since not all LEDs work alike in real life, and I can fine tune it using a DMM to test the exact current going through and get it to 20mA.

I was actually suprised the other day when testing out a prototype of of the LED array on how big a difference 17mA was compared to giving it 20mA.

I just wanted to inform people in case you are following this topic that el Jefe passed away in his sleep last Wednesday Aug 30th. He was my brother-in-law and was really enthused about building his PJ for their new house. He was 28 years old. He leaves his wife and 3 young children.

Jim Madsen

That really sucks. Condolences to your sister and her children. and at 28 too, shame.

Jim

My sincere condolences.

Good Lord, 28. such a loss.
The hard part is for the living.

So sorry.