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Thread: What exactly is the "correction amp" for??

  1. #1
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    Default What exactly is the "correction amp" for??

    Well, recently I have been playing around with my projector, running it from the USB sound card (Using the signal BEFORE the coupling caps and all), WITHOUT using any kind of amp, and the output image size is reasonable up full volume, but why are the patterns so distorted? As far as I know, the "correction amp" just amplifies the signal. The output size is fine, but how does the correction amp fix the distortion?


    Cheers

  2. #2
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    It not only amplifies it but offsets it. The center of the signal is not at 0V coming from the sound card. It is at 2v or something like that. You should be able to use the signals from the soundcard as they are but your image will be smaller and shifted to one side than it ideally should.

    Not sure why the patterns would be distorted. What are you using to display the signals?

  3. #3
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    hey carmangary, I am using Spaghetti to display the signals. For example, is the sphere pattern supposed to look something like this?



    The test pattern is also quite distorted. Some patterns are just totally horrible, and some are OK. I am not sure as to why its distorted either ...

    BTW, I have built the correction amp, and it appears to be doing what you described, but I cant understand why everything is messed up :/

    hmm

  4. #4
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    Let me give you an example of what it looks like.

    OK, so I set the speed in Spaghetti to 20000pps. Now in the laserboy folder, there is the main laserboy ILDA file. There is a pattern in there, of a gear. Now instead of having large, bits sticking out of it as gears do, its actually more rounded than it is gear shaped.

    When I try to display the laserboy logo thingy, it comes out as total crap, and theres a few others in there that do it. WOuld this be the case of an inverting sound card/interference or something?? its really crazy.

    EDIT: Also, just so you know, I have tried also completely removing the filter cap from the X and Y channels.
    Last edited by Things; 09-18-2008 at 06:19.

  5. #5
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    what happens when you display a more simple frame like the big circle?
    (frame 9 in the default ilda file.)
    -Josh

  6. #6
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    Yea, the sphere pattern is supposed to look something like that. I am not sure why it is called "Sphere" because it isn't a sphere at all. I need to replace that pattern with something better.

    When displaying the ILDA test patten make sure that the blanking optimization is NOT enabled. If it is enabled the ILDA test pattern will look like a mess. The other patterns should look relatively OK with or without blanking optimization enabled. I haven't tried displaying the LaserBoy logo. It could be that you need to adjust the blanking optimization settings or that your galvos aren't tuned correctly or are too slow. But, without knowing exactly what you have or what you are seeing I can't say for sure. If you could take a picture that would help, I think.

  7. #7
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    OK well, the big circle (Frame 10), has a few dodgy edges. The blue blimp ones shows up OK, along with frame 29. frame 36 shows up as kind of a squarish shaped circle. The green Christmas tree ends up more rectangle than triangle, and the edges down the bottom are rounded.

    Is that enough info?

    EDIT: Yeah I have tried to get a pic with my webcam, but due to the speed its hard to capture. I'll try again with my better cam soon

  8. #8
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    can you take a picture of your op amp setup?
    -Josh

  9. #9
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    Try lowering your scan speed and decreasing the projected image size. See if that helps. If it does, it just means you are driving your galvos too hard. If it doesn't then it is something else. But lets rule out that out first.

  10. #10
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    Make sure that your sound card isn't modifying the signal with any effects or equalizers

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