Converting DLP projectors for grayscale operation, part 2.

Now that I’ve outlined some reasons for wanting a grayscale (color-wheel-free) projector, here’s how to make one. It’s simple, and the procedure is generalizable onto pretty much any DLP/DMD device.

First, turn off and unplug your projector. In this case, the projector is a Dell 5100MP.

Remove these screws. Don’t miss the studs on the DVI connector, they hold the top on. Take it off.

This is the internal layout of the projector. We’re really only interested in the color wheel right now. It is held in by two screws. Unscrew them. Remove it by gently prying at the base, and grasping the little metal clip with a needlenose pliers. Wear gloves so that you do not contaminate the optics with finger oils.

Now that the color wheel is free, inspect it. Note the dichroic coating and the clear section. The clear section is used to increase the overall luminance of the image. When you adjust “brightness” or go into “brightness mode” on your projector, you are adjusting how much light the mirror array reflects through this clear section.

The color wheel is a very simple device, built much like a hard drive platter. It is a series of optical filters mounted on a brushless DC motor (BLDC). Under the clear section, there is a piece of black tape (blanking patch) which subtends the same angle as the clear slice. An infrared detector watches this tape to signal a complete cycle. In a future article, I will examine the exact relationship between this tape strip/detector and the actual refresh rate of the projector. In combination with a NI-DAQ, it might be a good way to use commodity DLP systems for time-critical research. It might also be possible to inject a timing signal in place of the optical detector to control the refresh rate manually.

Now that your color wheel is out of the optical path, you can simply put it out of the way. I secured the color wheel assembly to the lamp box with double-sided tape and covered it with a lexan blister pack. Fire up your projector to make sure you haven’t ruined everything.

Ahh, that’s what I wanted to see. A grayscale image unperturbed by color wheel tomfoolery.

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6 Responses to Converting DLP projectors for grayscale operation, part 2.

  1. marian says:

    I need a color wheel projector Optoma EP 739H
    Please if you can help me to buy this component
    Thank you.

    Marian Petrovici
    Iasi, Romania

  2. Chuck says:

    Now that the color wheel is removed, what can you do to prevent the mirrors form dithering as if the color whee was still there? While you will still have PWM to control brightness, how do you get the PWM signal to be consistent throughout the entire rotation of the now-missing colorwheel?

    Further, if you fully remove the colorwheel (unplug it) so you can close the projector, will the system still work, even though it does not get the positional feedback from the colorwheel?


  3. danreetz says:

    Hey Chuck,
    Well, unfortunately my advisor shut this work down. I was building an HDR display with a black and white projector as an active spatially modulated backlight, but he did not want the work to continue. I never got much further with it, because later the building collapsed and I dropped out. I did re-install the color wheel in this projector for them before I left.

    However, I did some fiddling with color wheels later on, at another job of mine. You can either set the color wheel aside (mine were just taped to a plastic box on the side of the projector) and use its’ pulse to drive the DLP chip, or you can do what I did later and just make an Arduino send similar pulses. If you use an RTC you can keep the drift really low.

    Interestingly, you can freeze some DLP projectors on single frames and look at the dithering done for each color. Watch out, some projectors do not use a signal directly off the color wheel, rather they have a photodiode down the optical path that reads to a sensor mounted directly on the mainboard.

    But for a solution you can use now… IIRC the TI DLP development kits have grayscale capability and they have come way down in price. Check out the DLP commander series. Though more expensive than commercially available projectors, they save a hell of a lot of development time. I can’t say much about what I did with them, but they’re good to work with and a lot more fun than fooling around with commercial stuff and all the attendant problems.

    Feel free to contact me if you need more info. I’d love to know your application.

  4. jessica miranda says:

    Hello good evening
    I want that they quote a color whell of a projector dell shape 2400mp with number of series 35CS0D1
    TEL.01(55) 53747017

    hola buenas tardes

    quiero que me coticen un color whell de un proyector dell modelo 2400mp con numero de serie 35CS0D1


  5. Chris Munz says:

    Curiously, depending on the type of color wheel used what do you think the relative brightness difference would be for full white with and w/o wheel?


  6. Sanjay.H.Musruck says:

    Hi i have a Barco Projector Model(CLMR10+)if i removed the color wheel completely what would be the results of the image.As the color wheel is hard to find and costly too,please help how to solved this issue and i will need also a DMD chip for the above model .I think get a quick reply soon,thanks in advance.


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