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Thread: X/Y Audio Laser Control - Like an oscilloscope

  1. #1
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    Default X/Y Audio Laser Control - Like an oscilloscope

    Hello everyone,

    I'm a laser 'n00b', as we like to say here, on the internet. So I'm asking for your advice.
    I feel like this should be a very easy thing to do but I'm having great difficulty finding any info about it.

    At present I am using audio to make lissajous figures on an oscilloscope - like this: https://vimeo.com/80815024
    Left audio channel pushes the oscilloscopes dot horizontally, right pushes it vertically. Simple.

    I'd like to take the same data and use it to move a laser beam.

    Any suggestions for any kind of solution?

    Thanks very much!

  2. #2
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    get a 5.1 or 7.1 external usb sound card.
    You can get or make a correction amp to make the so called Audio DAC
    Some laser software supports it.

    However these isn't that much "good" free lasershow software out there.

  3. #3
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    Quote Originally Posted by masterpj View Post
    However these isn't that much "good" free lasershow software out there.
    Working on it (though no sound card output is planned at the moment).

    There were a few threads on PL about the subject of using audio signals to drive a laser projector. I can't find them right now. I remember an important point being a maximum frequency you shouldn't exceed to not damage the scanners.

    Do you already have a laser projector?

    Also, I really like to know how you created the effect at around 10 seconds in your video! (The lissajous pattern where a part becomes a spiral).

    I think you're going to have more luck with a commercial DAC (controller card), but it looks like you have a nice pattern generating program for audio signals. If you can get more outputs to control red, green, blue and blanking, you might just already be good to go. Some of your patterns are definately too complicated for scanners though. You'll have to be careful when testing it out.

  4. #4
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    Thanks masterpj,

    Free would be nice but not what I'm asking for: I'm willing to pay some monies (but not all of them).

    What you mention sounds promising and searching the terms led me to Laserboy.org. But I can't easily find an explanation of how this works… I'm trying to read up now but it's tuff to find a 'how to' or anything.

  5. #5
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    Hi colouredmirrorball,

    I don't have a projector, I'm afraid. I'll probably be renting.

    The effect at 10secs is not too difficult to produce but explaining is quite long-winded.. I'll PM you so I don't mess up the thread too much?

    Yeah, I know I'll have to compromise a lot of what I've been doing so I'm not overloading the scanners. I was hoping I could get hold of a system that would prevent overloading the scanners.

    At the moment, I'm only looking for X & Y control. I might want to change colour etc in future but for now the idea is to stick with green.

  6. #6
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    Even if you only want X & Y control, you'll also need a signal for the green laser. In a DIY setup, this would mean just putting 5V on the modulation input of the driver. But if you're renting, you'll need to do this through a standard Ilda connector. This is a regular DB-25 connector.

    Click image for larger version. 

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    http://www.laserfx.com/Backstage.Las.../ISP-DB25.html

  7. #7
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    Thanks mirrorball,

    See what you mean about a signal for the green - taken on board!

    But any ideas on how to send this stuff through an ILDA connector?

  8. #8
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    Quote Originally Posted by colouredmirrorball View Post
    Working on it (though no sound card output is planned at the moment).
    Also, I really like to know how you created the effect at around 10 seconds in your video! (The lissajous pattern where a part becomes a spiral).
    Actually, just thinking... if you're familiar with lissajous and how they're created, then this is easy to answer: I have produced a low-freqency 'wing' lissajous shape and then faded in a high-frequency circle shape. The circle shape is faded in and out very quickly to make it appear concentric. When it's being modulated/moved around by low frequency 'wing' it appears as a 'tube' of circles.

    Does that make sense?

  9. #9
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    You would put 5V on pin 6 (green) with respect to ground, pin 25 (normally, the negative signals - pins 18, 19 and 20 are not used for colour signals).

    For the X/Y channels, you need to start with a signal between -5 and 5 V relative to ground pin 25 (i.e. 10 V peak to peak amplitude) as described in the link I posted above. You need to send these signals through pins 1 and 2, and the inverted signals through pins 14 and 15. This is a differential signal, and is used to eliminate noise. If you're not familiar with differential signals, it works like this: say you have a cable, and something is interfering with it. Both signal wires (+ and -) get an additional noise voltage. But the system only looks at the difference between these values, so the noise is ignored. This also makes it unnecessary to use the ground level, which is mostly not connected to the XY inputs on scanner amplifiers as it can only add more noise (but this is something the designers of the laser projector have decided on so if you're renting, don't care about it).

    Be warned that I'm not an expert on this field and will probably be corrected by experts in 3... 2... 1...

    I don't know how you can get inverted signals from the original XY signals, but you're the guy with the oscilloscope :P

    I have to add that these kinds of experiments can cause damage to the projector so I'm not sure how smart it is to rent one...

    Quote Originally Posted by adoxo View Post
    Actually, just thinking... if you're familiar with lissajous and how they're created, then this is easy to answer: I have produced a low-freqency 'wing' lissajous shape and then faded in a high-frequency circle shape. The circle shape is faded in and out very quickly to make it appear concentric. When it's being modulated/moved around by low frequency 'wing' it appears as a 'tube' of circles.

    Does that make sense?
    In a way. Gotta experiment

  10. #10
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    Thanks again mirrorball,

    This is handy information but I guess I should have been more clear with what kind of answer I'm looking for: more like "what software & hardware can I buy to make this work?"

    This seems increasingly like a DIY project—and I'm quite willing to get the soldering iron out—but I'm hoping to find something that I will be able to use in clubs and music venues. If I make an amplifier and pop an ILDA connector onto it, I guess I'll be in health & safety regulation hell..

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