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Thread: Rendering oscilloscope trace, light intensity

  1. #1
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    Default Rendering oscilloscope trace, light intensity

    Hello,

    I am doing lissajous music using basic analog signal on a X+Y+Z axis basis, Z being the signal intensity.
    Until now, I was using analog CRT-based oscilloscope to render the signal.
    In order project to a wider audience, I need to record the screen of the oscilloscope to be able to project it on a standard beamer.
    The result is not good as the signal intensity (the shade of the light), as well as the signal dynamic are poorly rendered.

    I am therefore considering using laser to be able to render the trace as close as possible as an oscilloscope CRT would do.
    I am not familiar with it and I would like to purchase a test device for my experiments.

    Few questions:
    a) I see ILDA standard has analog inputs for each color at 0-+10V, including intensity at 0-+5V(my Z axis). It seems that for my purpose, software is not needed. Can i directly feed the ILDA input of the laser with my analog signal without using/buying any software ?
    b) I cant find good example of similar usage with a good light intensity control. Can you advise power/laser type that would best fit my purpose ? it is a key aspect as this provide a huge part of "feeling".
    c) Is the laser scanning the signal as an oscilloscope does ?

    Thank you in advance to the community,

    Xavier

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    If you are interested in producing video to be shown later rather than in real time. You can import your vector data into LaserBoy and render it as a directory of numbered bitmap files. Then use ffmpeg to compile them into a video. You get the benefit of rgb color and it doesn't matter at all how much vector data there is per frame. There is no concept of points per second when you render to bitmaps.

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    The ILDA 30K specification for a laser projector scan speed equates to an approximate maximum frequency (ie Small signal bandwidth) of about 2400 Hz for very small angle steps. If you have a larger budget you can email Scannermax and get something a bit faster. So DC to roughly 3 Khz at 8 degrees wide optical angle for each axis may be assumed. The laser diode drivers usually have a bandwidth of around 10 to 30 Khz for a high quality analog unit.. Now, if your doing many large angle jumps, out to 30 to 60 degrees optical, things slow down as expected with a mechanical system.

    Stock projectors of known value come from X-Laser USA, Kvant, Goldenstar and many more. Keep in mind with lasers you have an eye-safety issue, so the laser projector and screen must be three meters up and two meters horizontal from any audience member. Japan allows laser projection but does not allow the laser to land or touch the audience directly. Adding a fence so the audience cannot reach the laser light suffices for this requirement, in case you are in a room with low ceilings.

    Unlike a CRT, overdriving in terms of frequency or amplitude on a scan pair in a laser projector may have adverse consequences. We have had a few music synthesizer operators have to learn that the hard way. Especially if you dial in on a system mechanical resonance "because that looks so cool" or exceed the XY driver PID loop bandwidth deliberately.

    If the galvos do more then make a faint audible hum or some soft clicks, you'll hear it and see it in the image just before they start to overheat.

    Generally a good analog laser diode driver will have a 20000:1 or better contrast ratio, far exceeding that of even a CRT. Used properly you'll also have perhaps 30% area on the CIE curve , meaning color mixes no CRT can create. Especially more then a NTSC CRT or an Analog Gaming console CRT.

    Edit, missed a power of ten on the contrast ratio..


    Steve
    Last edited by mixedgas; 07-18-2020 at 16:01.
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    Thank you Steve and James.
    I am puzzled about light intensity. I can't find any relevant example where light intensity can be rendered properly.
    I understand the light balance is much higher with lazer but I can only find example where "objects" are rendered with different intensity.

    A light intensity on a CRT makes a thicker line. For a CRT, it becomes more like an object and not anymore a vector.
    On a lazer, it makes exactly the same line at lower power, which is very different and less sensible for the eyes.

    Please have a look at what I want to render.
    It will be self explanatory.

    https://youtu.be/UFvzq_bCHeE?t=135

    PS: I got your point when the galvos start smoking then I should stop the experiment ;-)


    XP
    Last edited by Cyranoo; 07-30-2020 at 05:39. Reason: Typo, replaced lzr with CRT

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    most of this will not be a problem at all to render in laser.

    Quote Originally Posted by Cyranoo View Post
    Thank you Steve and James.
    I am puzzled about light intensity. I can't find any relevant example where light intensity can be rendered properly.
    I understand the light balance is much higher with lazer but I can only find example where "objects" are rendered with different intensity.

    A light intensity on a CRT makes a thicker line. For a lzer, it becomes more like an object and not anymore a vector.
    On a lazer, it makes exactly the same line at lower power, which is very different and less sensible for the eyes.

    Please have a look at what I want to render.
    It will be self explanatory.

    https://youtu.be/UFvzq_bCHeE?t=135

    PS: I got your point when the galvos start smoking then I should stop the experiment ;-)


    XP
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

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    From what I understand, some scopes have a beam intensity input, but the required signal is not standard. LaserBoy can put a few different signals into the 6th channel of a wave file. One of them is intended to be an O-scope intensity. It is zero volts for full brightness to maximum voltage for fully dimmed. It is analog. You can make the voltage swing whatever you want with an opamp gain circuit.

    Also, I should note that the kaleidoscopic effects in the video you posted are actually done with mirrors around the screen of the scope. The trace on the scope is quite simple.

    There is a Facebook group called Vector Synthesis that is totally dedicated to exactly this artform. There are quite a few very talented people there.
    Last edited by james; 07-30-2020 at 07:03.
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    Ah, the phosphor decay time. That can be simulated in software, or by scanning on a fluorescent phosphor screen using a UV laser. We have folks here that use a long or medium persistence P1 or P2 Zinc Sulfide Phosphor (ZnS:Ag or ZnS:cu) and make phenomenal images. That will give you "objects".

    Cool thing, you could even simulate P7 with a RGB laser by varying the signal and adding a tiny integrator or low pass time constants on the RGB inputs. You can also simulate an older oscilloscope CRT with intensity inputs by adding a simple op-amp and transistor log generator and or inverter.
    All you have to do is remember Vdne (Do not exceed) is -0.3 negitive and +say 5.6V positive when accessing the zero to five volt intensity control inputs.


    Steve
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    Quote Originally Posted by swamidog View Post
    most of this will not be a problem at all to render in laser.
    I don't think you can easily render this kind of line.
    It becomes an object due to the thickness.
    Note the tails...
    Attached Thumbnails Attached Thumbnails vlcsnap-2020-07-15-12h40m00s247.png  


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    yes, exactly ! this is what I was looking for :-) New doors opening.

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    In fact one of my favorite tricks is to go back and "quench" the phosphor with near IR laser light, depleting the stored energy and putting a halt to the glow.

    So you can turn it off, as well as turn it on, if you have the right phosphor.

    It is not too hard to find a low cost rgb projector using a 440 nm diode as the blue, which while not ideal, will drive the more common phosphors just fine.

    So an email and then a short phone call with Jeri resulted in this video on Quenching. My then employer insisted that his employees have no tech videos on Youtube, so after watching Jeri's video on phosphors, I thought she should know about the dark side, one of the ways of making IR detection phosphors for lasers.


    Enjoy

    https://youtu.be/jPg3dU4YWVc

    Now you know what the O. in O. Steven is...

    Steve
    Last edited by mixedgas; 07-30-2020 at 23:22.
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