Introduction: LED Projector Lamp V.1.0
My first video projector. Ever.
Last year I came across a cheap Toshiba TLP T70M projector on some e-bay wanna-be site over here in Romania. It had no lamp at all but other than that it was operating properly (or so the salesman told me). I traded it for a Shuttle computer I had in my closet and in a few days the projector was delivered. I was surprised that it was in a good condition, I was expecting cracks and scratches, it had none. I turned it on and - predictably - the “lamp missing” LED came on in about two minutes. At this point the projector shuts down automatically. During those two minutes I was able to see the startup screen by looking thru the lenses while holding a small flashlight where the bulb was supposed to be. So yes, it was operating.
I started google-ing all I could find about this projector. I came across the complete Toshiba TLP T70M user manual (it had none when I received it) and that’s about all. At this point I wasn’t really decided what to do, I was tempted to buy a light bulb for this model and use it as anyone should. On the other hand being horrified by the huge price that projector bulb had it was clear I had to find an alternative light source. Me being a LED addict I started thinking about that. It was the obvious choice but the problem will be the light output. The projector’s lamp had 2000 lumens and in “eco-mode” had 1000 lumens. I was aiming for his lower figure as I won’t be using the projector in daylight anyway. So my goal is 1000 lumens of LED light.
Insert a few weeks of random ideas and pointless calculations here. Lazyness, to be more precise.
Step 1: Parts Used
I decided I will buy the most powerful LED I can get my hands on and try to use it as a light source in my projector. All this without being distructive or making irreversible changes to the projector. Google that and it turned out my only choice in power LEDs (over here, in Romania) was a Cree MC-E M, Star, White, 752 lumens output, 4 chips, 110 degree (light beam). I was hoping for a OSRAM OSTAR rated 1000 lumens but the reseller couldn’t provided it.
The original projector lamp had 2000 lumens and 1000 lumens in eco mode. I figured if I get close to that eco-mode it might be usable in my tiny apartment. This LED is rated for 50.000 hours of operation and is considered equivalent with a 75W incandescent bulb. I also ordered a 700mA constant current power supply to power it. This one is rated up to 30V DC output @ 700mA and is powered by grid power (220V AC here). I plan to hide it inside the projector once the project is successful. But enough daydreaming.
Step 2: Electronics Involved
The first step was to fool the electronics into thinking the lamp is present so that the projector will start operating properly and get rid of that automatic shutdown. A few Google days later I came across a French site on the very same subject. It turned out all I had to do was to find a logic signal that was up (5V) during the first two minutes and down (GND) just before the LED missing indicator turned on. I found it eventually, using my multimeter. By pulling this signal up (a simple wire jumper connected to a 5V source I found on the board) it started normally thinking the lamp was present and on. I connected a laptop to it and checked that the movie was playing by looking into the lens while holding the same flashlight inside the projector. Yes! I was glad I did this, I’m not that experienced in electronics and I feared I may end up stuck at this stage.
Step 3: Construction
I ordered the LED and used a heat sink I had around from an old Pentium I. As space is an issue, I had to make sure the LED bulb will fit. This heat sink was the only choice. The LED came mounted on a small star heat sink so I drilled two holes for the screws in the Pentium heat sink to attach it firmly in place. Arctic Silver 5 thermal compound was used in between those parts. After wiring the LED (the four chips had to be connected in series first) I scavenged a flashlight for the light reflector. Inside that I put a 45 degrees matte lens I also ordered in order to make the light more focused and uniform as the four chips are not a single light source but four, close to each other. I also used two PCB boards I cut to make the bottom and the top of the light bulb. This was needed to make sure the bulb wouldn’t move inside so I cut them to the exact shape of the existing space.
Step 4: Testing the Bulb
The bulb was powered using a 700mA constant current power supply. As each chip needs 3.5V@700mA the measured output was 14V@700mA. That’s 9.8 Watts... my mind instantly told me it’s not going to be enough. But we’ll see. Anyway, it’s well below the max 30V this power supply puts out. I was a little worried about the amount of heat but as it turned out the heat sink barely gets warm, thanks to the built-in fan this projector already had for cooling the bulb.
In this picture you can see the bulb, the flash light made its light beam look weak but trust me, it’s strong and blinding if looking directly to it. It’s not recommended either, actually.
I mounted the bulb inside and proved to fit perfectly. I used the original bulb mounting holes. First tests, as you can see were indeed, disappointing. This projector being a LCD-type (unlike the better DLP ones) proved to eat up about half of the LED light output when displaying anything. This I wasn’t expected. Lack of experience and knowledge, I guess. I was quite disappointed finding this.
Step 5: Conclusion
In a completely dark room I was able to watch “Avatar” but the dark scenes were too dark. As you can see, the scenes that were full of light were almost viewable but that’s about it. It’s clear that I need AT LEAST a double amount of light. 750 lumens is nowhere near enough. Besides, not having a luxmeter I suspect that only half of that reaches the screen. It was fun nevertheless to play with a projector for the first time. I like it and I’m determined to use it. Time to get back to the drawing board. I need more power, more light, all within the same confined space.
Step 6: To Be Continued
Months passed and I still look for a better LED. I decided to try a second version of this light bulb. This one will use an array of 9 x NS6W183T Nichia LEDs. Rated at least 225 lumens each, I should have in excess of 2000 lumens of light. If 1000 lumens of those do reach my projection screen I will be happy, that’s the “eco mode” I was hoping for. The main issue with this attempt is that I have to keep the light source as small as possible while focusing it on that Fresnel lens inside the projector that’s 3x3 cm small. Oh, and the entire LED bulb has to fit a 5x5x9 cm space. Small space for serious power and an estimated 35 watts of dissipated heat. But I won’t give up. Look out for my next instructable on V2.0 once the 9 LEDs array is ready. Right now we’re about to have a baby so it’s standby for everything else. J
Thank you for reading this. Feel free to ask any questions, I’ll try to answer them.Edit: our baby was born today! I'm the proud daddy of a very cute little boy!