Output Voltage on Colour Signals

Discussion in 'QM2000 series of products' started by Peter, Nov 25, 2003.

  1. Peter

    Peter Member

    Hi i am having problem with the output voltage of my QM2000. Each channel is only giving out around 3.75v when projecting white. This is causing me problems as a lot of power is being lost in the crystal.

    Does anyone know of why this is happening, or know of an amplifier circuit that i could build to correct it, or even how you re-route colour channels to DMX.

    Cheers,

    Peter
     
  2. Martin Kapp

    Martin Kapp Active Member

    Hi Peter,

    I think that if you look at the colour output on an oscilloscope, you'll see that it is in fact blanking, even with an open white abstract. So that 3.75v you see is the average voltage.

    I could be wrong, as I've never tried it. But I have noticed that if you output an abstract un blanked, you get bright spots where the output is being refreshed - therefore, at the time of refresh, the beam is being switched off.

    Over to Pangolin I think.....
     
  3. Pangolin

    Pangolin Staff Member

    Thanks for the comments Martin. Here are a few things that I will mention in general.

    First, it is NEVER a good idea to measure color signals with a meter. Only an oscilloscope will give you an accurate picture.

    Second, you must follow the recommendations in our help file for best results with any projector. This includes the strong recommendation from Pangolin that you ground (tie to pin 25) the negative outputs of the color signals. In most cases, you will do this. It is only in some specialized cases that you do not ground the negative outputs.

    Third, the output voltage will depend on the loading. If you load the color outputs with a very heavy load -- say 100 ohms or less, you will get only dimminished output. Pangolin recommends an input impedance of 1K or greater.

    Bill
     
  4. spacerockets

    spacerockets Member

    Hi,

    I've checked the help file but i don't find where is indicated to ground the negative outputs, but to connect qm2000 -pin color to negative of laser modulation driver, and +pin to positive, it's right ?
    I've some trouble with a RBG projector, all modules are connect as mentioned above. For example green module, analog modulated, have +pin to 6 and -pin to 19. But output beam have like a ripple, with a pulsed noise on draw. Analog output and blank work fine.
    The -pin of modulation input is not grounded in the driver, so what i have to do ? Is this the situation where to connect to ground the negative output signal, as you mentioned (to do not) for xyz signal ?

    Thanks for help

    Andrew
     
  5. Pangolin

    Pangolin Staff Member

    If you are only seeing this on the green, or if you are seeing this in the green and the blue (worst in the blue), then what you have is called "jelly-beaning". This is where, instead of the laser producing a continuous wave output, it produces a pseudo-randomly pulsed output that, while projecting graphics, it might resemble an image constructed of a bunch of jelly beans placed end-to-end.

    There is nothing that you can do with connections, or with the software, to solve this problem. It is notoriously noticable in low-quality, low-cost lasers. And it will even vary from laser to laser of the same brand and model. If it is too bad, you should return that particular laser for a different one, and you might luck-out and get another one that doesn't do it as bad. Or return that laser and purchase a different brand.

    Best regards,

    William Benner
     
  6. spacerockets

    spacerockets Member

    Hi William and thanks for your reply.

    No, this is not the problem. The laser is a 2W absolutely not cheap and, if connect a fixed voltage as a 5Vcc from a external power supply instead of the qm2000 signal, no "beans" are displayed on screen.
    I've tried, just for a second, to ground the shield of modulator plug and that's solve the problem. But doing this, -color pin of qm2000 is grounded too. So my question is : it's acceptable or dangerous ? Or i have to disconnect the -color pin (in this case, without the girator, i'll have just 2.5 peak voltage ?) using just ground and +color pin to drive the laser ?

    Andrew
     
  7. Pangolin

    Pangolin Staff Member

    Hi Andrew,

    Well, I am glad that this will solve your problems, but I want to point out a few things.

    1. Connecting the negative color outputs to ground will not hurt anything. In fact, we recommend it. We do NOT recommend connecting the negative X, Y or Z outputs to ground, but the color outputs are OK.

    2. Connecting a laser input to +5V will, in most cases, NOT show "jelly beaning", because you will not be exciting the phenomenon which causes "jelly beaning" to begin with. "Jelly beaning" is caused by modulation, and specifically, by "thermal modulation" that results from you modulating the power of the laser. So if you connect your laser to DC 5V, you have "no modulation", so you have "no thermal modulation" and thus, will have "no jelly beaning".

    Also, "cheap" is in the eye of the beholder. Certain types of lasers will never exhibit "jelly beaning". For example, the Thin Disk lasers from Jen Optik will not jelly bean, and neither will OPSL from Coherent. But most of the more conventional DPSS lasers will, especially inexpensive ones, or ones from manufacturers who have not yet figured out one of the two solutions for that problem.

    Best regards,

    William Benner
     

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