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Thread: Blanking delay

  1. #1
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    Default Blanking delay

    Hi! I'm just a happy hobbyist building a laser projector for fun. I'm an unemployed electronics engineer and I need too be a little creative I made everything from scratch including my own closed loop (optical PD) galvos and drivers. I have one question about blanking delay. My (homemade) laser driver has TTL modulation and I control blanking delay through the microcontroller that is a part of my DAC. But how is this achieved when you are using analog modulation? Then blanking delay would be more like a phase delay from the XY-signal..? Can blanking delay be configured in the settings of commercial software or is this controlled by the projector?

  2. #2
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    In LaserBoy it is done by reading and rewriting all of the data in the multiple tracks of its own generated wave file. The X and Y information usually stays where it is and the color channels are shifted 5 to 7 samples behind (at 48KHz). A chunk of information, stored in the header of the wave records the sample offset numbers so that it can be undone and redone again.

    Another possibility for making a stand alone outboard analog time delay is to use chips called serial analog delays. They are the core of most time related audio effects, like flanging, phase shifting, chorus, echo, etc. They are a strange combination of ideas. They are clocked, but they are truly analog.

    James.

  3. #3
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    Many software packages add extra points to begininning and ends of segments to allow the galvos and lasers to settle. This works most of the time. Side effects include longer times needed to draw the frames (since more points are added) and sometimes there are hot spots if too many points are added and the galvos momentarily stop (or slow down a lot).

  4. #4
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    Cool

    Quote Originally Posted by Danny View Post
    My (homemade) laser driver has TTL modulation and I control blanking delay through the microcontroller that is a part of my DAC. But how is this achieved when you are using analog modulation?
    Basically the same way; it's controlled by the software, which modifies the signal timing coming out of the DAC. The controller that maintains the timing between the X and Y scan signal outputs also controls the timing of the blanking outputs. Usually there is a setting in the software that allows you to adjust the speed of the blanking (often measured in points of offset).

    The extra points added to corners and so fourth have more to do with settling the galvo in position than with color. Color timing offset is a constant setting that is normally never changed once it's been adjusted correctly.

    Adam

  5. #5
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    Quote Originally Posted by buffo View Post
    Color timing offset is a constant setting that is normally never changed once it's been adjusted correctly.
    This would require a constant scan rate, right? I'm still trying to increase maximum scan rate so I have to make the delay adjustable (just a few lines of C code and 2 buttons). Need better cooling of the galvos... Did a really bad design on my galvos when totally neglecting heat losses. Soooo stupid of me. I really should now better. I'm limited to 500mA (rms) drive current and that gives me about 12kpps @ 20 degrees. My next galvo version (if ever built) will handle a lot more current... =)

  6. #6
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    If your time delay and your sample clock are totally unrelated, then time delay is constant.

    If not, then changing your sample rate will obviously change your time delay.

    Can you share any of your efforts with us in pictures or more description?

    I see you like C !!!

    Delightful!

    What are you up to?

    James.

  7. #7
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    Sorry for blabbering on about my project and not posting any photos. I dug up some for you to look at. The projector is going to be fully portable and runs of a 9-18VDC source (12V lead-acid battery will be built in soon). Will also do some more C-programming to make it read images and animations of a SD memory card. I did not have any photo of the ILDA test image, sorry. The photos show projections before I had any blanking delay. Need to do some more tuning but I think the image quality is better than I expected to get from my homemade galvos. The laser is an 20mW Uniphase uGreen 533nm DPSS running at low intesity for safe testing.
    Attached Thumbnails Attached Thumbnails projector2.jpg  

    projector.jpg  

    question.jpg  

    box.jpg  

    Snowflake.jpg  


  8. #8
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    WOW.

    I'm impressed!

    James.

  9. #9
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    Quote Originally Posted by Danny View Post
    I'm limited to 500mA (rms) drive current and that gives me about 12kpps @ 20 degrees.
    Very nice value. My current 7K-8K homemade galvos with their drivers reqiure about 3A X 22V (bipolar).

  10. #10
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    That is a AWESOME home build job! I read the guide on building galvo's, and just said to myself, "I think i'll just wait till I get some money!"

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