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How to build a replacement bulb for my projector.
March 9, 2009 11:52 AM   Subscribe

I'm looking to buy a projector off a classifieds site but the only issue is it requires a new bulb upon purchase. Besides the obvious problems that could come of this like having no way to proove that it works. I was wondering how difficult it would be to replace the lamp with some High powered LED's.

Things I have come up with that could pose issues:

Will the led's have a similar disbursal pattern as the bulb, since this is probably true how much could it effect it.

I'm considering some Cree XR-E Q5's from deal extreme (since they're cheap). I dont want to have to modify things on a massive scale i just want to come up with a different kind of bulb On the cheap.

Since these leds are only about 220 or so lumens AFAIK I will probably have to build a small array and use small mirrors to focus the light?

The site that i buy from, unless theres a better suggestion, will be here. They say that one of these leds produce 1000mA: 214 ~ 228lm (Lumens).

I need to make a total lumen "quota" of 1200 lumen (approx 6 leds), while still dissipating heat properly and not having to rebuild the whole projector...

NOTE: The projector that im looking at is a used well kept Hitachi pjtx-200

Any advice suggestions will be greatly appreciated.
posted by Chamunks to Technology (14 answers total) 1 user marked this as a favorite
 
You cant just stick bulbs in there. Usually the bulb is encased in a little chassis with a custom connector. You would first need to get that chassis before you can start modifying anything.

Why not just look at the connection and plug a multi-meter into it. If there's power then it probably works.

Or you can buy the bulb now, bring it, test it, and if it doesnt work then return it. You'll have to buy the bulb someplace with a generous return policy. I imagine bulb returns happen all the time as people order the wrong part.
posted by damn dirty ape at 12:02 PM on March 9, 2009


Update I'm looking for suppliers other than dealextreme as well preferably that use paypal.
I haven't looked into these guys much but this page looks very promising.
posted by Chamunks at 12:03 PM on March 9, 2009


Thanks I almost forgot my multimeter I don't think the sellers going to appreciate me field stripping his projector but for the price I think I just may.
posted by Chamunks at 12:05 PM on March 9, 2009


I know that the guy who builds Work Printers replaces the bulbs with LEDs. Maybe he can give you some tips.
posted by trinity8-director at 12:25 PM on March 9, 2009


Either get a projector with a new bulb, and forget the LEDs, or get one with a used bulb and try the LEDs, but it seems like a simple waste of money to insist on an unused bulb if you plan to not use it.

Additional issues with LEDs:

- Color spectrum of white LEDs is not balanced. Reds will be dim, blues will be over-bright.

- Your system of combining and focusing their light to match the lamp is going to lose a lot of light, and the projector system itself will lose more light. So an array of six 220 lumen LEDs is not going to result in a 1200 lumen projector output. I really have no idea how much light is going to be lost, but I'd think you'd be lucky to get half that.

- The high-power LEDs you're looking at have lens accessories which hopefully could give them usable, if not similar, light dispersal to the bulb, but an LED array is a problem as I expect the bulb enclosure is designed to produce something akin to a point-source, which would involve additional optics to try to achieve from an array.

- If you want to try the LED route, get DLP instead of LCD, and there is less light lost. DLP uses a spinning color wheel. For a really nice hack, you'd use high-power R, G, and B LEDs, instead of white, then modify the colour wheel so that the filters are removed and it drives a switch system instead that operates each LED colour at the correct time.
This would also enable you to use fewer LEDs, as they can no be shone full brightness directly onto the mirrors, instead of losing light through the fliters.
Furthermore, it allows you to correctly color-balance your projection, as you will have individual R, G, and B control.

- The projector will have circuitry to check that the bulb assembly is in place and working. You will need to circumvent this circuitry to take out the bulb without the projector refusing to run.


I think retrofitting a projector for LED is going to be a difficult project. You may be better off building one from scratch using an old laptop screen. It would be bulkier, but much less likely to fail. There are a lot of DIY projector projects online. Check them out - they will give you an idea of what is involved and what difficulties you will face, as well as some established routes that work, which will more easily allow you to experiment with an LED array.

Finally, if the purpose of the LED project is that projectors are awfully expensive and you hate the idea of having to buy a $$$ new bulb after a while, then you can rest easy. The lifetime of these bulbs is thousands of hours, which in real-world use usually translates to "by the time you need a new bulb, you're going to be working in a different job, probably promoted to a higher salary, and your decision won't be whether you can afford a new bulb, it will be whether you should get a new bulb or just buy a new and better projector"
posted by -harlequin- at 12:47 PM on March 9, 2009


For a really nice hack, you'd use high-power R, G, and B LEDs, instead of white, then modify the color wheel so that the filters are removed and it drives a switch system instead that operates each LED color at the correct time.

-harlequin-, nice idea, but led's, whatever color they might be, work by exciting luminescent materials. They have a relatively slow ramp up and cool off, so even if you could get it synced electrically, the illumination would lag way behind.

If the purpose of your project is to gain a life lesson, go ahead with the led replacement.
posted by StickyCarpet at 2:52 PM on March 9, 2009


I'm with StickyCarpet -- you need to think about the goal here. If you want to learn (a lot) about electronics and frustration, this is a good project. But even with the very high cost of a replacement bulb you can't possibly make the time/money equation work out. This is one of those projects that is doable but which you could sidestep by, for example, signing up to pour coffee, at minimum wage, for one tenth the time you'll spend getting the electronics to work.

On the other hand, if there are intangible benefits (learning, electronic machismo, etc.) then those might factor more into the project's value.
posted by range at 3:11 PM on March 9, 2009


I've been using a projector for a TV for the past few years now. To my thinking, once a bulb burns out, it's actually cheaper to go buy a new projector, since you will invariably get better stuff for only a small increase in investment. Were I you, I wouldn't buy a used projector unless it was REALLY cheap or a REALLY REALLY high end projector being offered really cheap.

Times this would make sense:

-XGA projector being offered for > $100
-1080p projector being offered for > $700 with some sort of money back guarantee if it doesn't work
-1080p projector being offered for > $300 with no guarantees.
-720p projector being offered for > $300 with some sort of money back guarantee if it doesn't work
-720p projector being offered for > $150 with no guarantees.

Anything else doesn't really make sense to me. You can get a decent new projector for about the same cost as a lot of replacement bulbs, which is what I've done. My upgrade path has been:

Purchase SVGA projector, use for a couple of years. Lamp life gets into the ~1800 hour range of recommended 2000 hour replacement window. Options: Replacement bulb is $400, XGA projector (higher res) with a better lamp life and 1.6x the lumens is $520. My actions: Sold SVGA projector for $150 on Craigslist, and bought new XGA projector with 3000 hour bulb for $520 on sale from Staples. When my bulb life gets to 2600 hours, I should be able to snag a 720p widescreen projector for under $600, and will sell this one for $150-$175.

So yeah, buying a bulb for a used projector you can't test is risky, and building your own LED replacement light source will be very difficult/not worth the effort. An example of an inexpensive projector that isn't a whole lot more than most replacement bulbs is this one.
posted by barc0001 at 4:58 PM on March 9, 2009


-range-, Well once its done the first time doing it again cant be that difficult.

-harlequin-, I believe that they do provide more warm whites aswell as the blue whites as well.

My guess is that LED bulbs have far longer life spans than most other bulbs making them preferable. They probably produce far less heat though I'm told they still produce significant heat.


I wonder if building an led array as such, one Red Blue and Green Led with potentiometers to adjust colour balance and three or more white leds, or would you think that just simply using some warm leds with pure white to possibly fix the reds balance and such?
posted by Chamunks at 5:01 PM on March 9, 2009


Also, just to give you a little more of an apples-to-apples comparison to what you're looking to buy, here are the Hitachi PJ-TX200's specs, and here's the specs of a comparable BenQ 720p which you should be able to find for about $800 USD street brand new. If the deal you're getting on the Hitachi makes it quite a bit cheaper, it may be a good deal to try, but if not, you might just want to see if you can buy a new projector for a similar investment after bulb replacement. Plus you'd have a warranty.
posted by barc0001 at 5:46 PM on March 9, 2009


If you're really looking to do this more as an electronics project instead of purely going after the goal of having a projector, you might want to look into building your array of LEDs and mounting it behind a salvaged LCD monitor instead. Or an overhead LCD panel which can be snagged cheap on Ebay and others. That way you would have a lot of space to work with when building the LED array.

Also, bear in mind the amount of space you will have in that Hitachi is about 1/3 the volume of an average male adult's fist. If you truly believe you can cost effectively build an array of LEDs that will take advantage of the projector's power feed that will give decent light, not to mention will play nice with any onboard diagnostics that the projector has to determine bulb health (some just won't start if it detects the bulb is gorked), by all means, and please post an update since this would be of interest to at least myself as well.
posted by barc0001 at 5:59 PM on March 9, 2009


stickycarpet:
"-harlequin-, nice idea, but led's, whatever color they might be, work by exciting luminescent materials. They have a relatively slow ramp up and cool off, so even if you could get it synced electrically, the illumination would lag way behind."

This is entirely wrong. LED switching speed is so fast that the cheapest of the cheap can optically send data at bitrates that make projector colour wheels look like a snail next to a speeding bullet. LEDs were doing square-wave switching at rates of 5 Mb/s back in the 80's.

I was guessing you may be thinking of white LEDs, which are a trick whereby a white phosphor is excited/powered by a blue LED, but even so, was with any other LED they have switching speeds far far in excess of projector colour wheels, so I think you might be thinking of some other technology altogether.

(LEDs don't work by exciting luminescent materials. They are semi-conductors that put electrons into lower-energy holes, forcing a loss of energy, which the electron emits as a photon. This means that LEDs also work backwards - shine a light on the junction and you can get electricity out the wires. Not many people realise that, but they're sometimes used as cheap photo-transistors because of this. Whereas light sources that excite luminescent materials don't work in reverse.)
posted by -harlequin- at 1:02 AM on March 10, 2009


I wonder if building an led array as such, one Red Blue and Green Led with potentiometers to adjust colour balance and three or more white leds, or would you think that just simply using some warm leds with pure white to possibly fix the reds balance and such?

R, G, B LEDs will give you more control, and more brightness per energy/heat than white. If you're doing RGB, then I suspect that mixing in white LEDs may be pointless - it seems likely to just increase the complexity and may reduce your results. But maybe some experimenting is called for?

If you look at the spectra of warm LEDs here or here, you'll see it's fairly hopeless to expect to get very useable colour from using them in an RGB projector (which both DLP and LCD are). Furthermore, you're throwing away a lot of your brightness by illuminating the entire spectrum instead of just the wavelengths that matter. Incandescent bulbs can get around this by throwing out more light, but you're going to be working hard just to get enough light, so I'd suggest going RGB.
posted by -harlequin- at 1:22 AM on March 10, 2009


Wow after the response from my question I almost feel obligated to work on this project and intimidated by it at the same time. If I do come up with something for this I promise to make an instructable for it and mail all who responded to this question.


I think that I may try the RGB route but since Cree is apparently the current leader in high intensity led's and they dont currently produce an all in one led I will have to find a way to combine the three colours into one focused light beam.

I have some diamond cutting bits for my dremmel and walmart has uber cheap glass mirrors I think that i may have to dabble in creating some sort of mirror system to converge the beam from each of these led's to appear as a single ultrabright ultra effecient bulb. I can sortof picture what I would do in my head but as some of you pointed out I will have issues with the whole reverse engineering part for the safeguards they put in place for the lamps.

This hitachi projector is going for 450$ CAD about 400 USD?(estimate) There really is no real rush I can wait for the next best deal to come up as they do. I may in the mean time want to buy a full projector and work on creating a bulb replacement as I eat away at my 2000 hours.
posted by Chamunks at 5:04 AM on March 10, 2009


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