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Thread: Laser Projector (Red, Green, Purple) "Laser 3D Party Light" from Spencer's

  1. #21
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    swamidog is online now Jr. Woodchuckington Janitor III, Esq.
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    one of the forum member (zoof) wrote an awesome asteroids clone called "laseroids". check it out. it's really really excellent.

    Quote Originally Posted by opcom View Post
    good ol asteroids is monochrome. If there was a way to have the game with its analog outputs that would be great but the only way I know of to make it work is to have the board. Some research for me to do.

    Anyone recall space duel? a great color XY game.

    This cheap system called these things to mind. I wonder what can be done to get the waviness out of the lines in the test pattern.
    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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    Quote Originally Posted by opcom View Post
    This cheap system called these things to mind. I wonder what can be done to get the waviness out of the lines in the test pattern.
    Could possibly be the cheap PSU or a dirty signal going to the amp. I wonder if it is 60hz noise that a good ground might clean up because that test pattern doesn't look too bad otherwise. The lack of a solid baseplate easily accounts for the alignment being off.
    If you're the smartest person in the room, then you're in the wrong room.

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    Quote Originally Posted by james View Post
    Huh? The Correction Amp is way simpler than that! Each channel takes just one single stage op-amp. I like the TLO72 duals.
    I was talking about the XY Board in the projector that I have... i.e.:
    Attachment 34596

    I was just surprised how simple it is, basically being driven by an audio amplifier.

    Quote Originally Posted by opcom View Post
    Anyone recall space duel? a great color XY game.

    This cheap system called these things to mind. I wonder what can be done to get the waviness out of the lines in the test pattern.
    Yep... Space Duel is a lot of fun... got one in my basement.

    I was also wondering about the waviness, especially in the vertical lines. Grounds and noise from the power supply are good guesses, I'll look into them.

    DogP

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    Dog, you might be shocked at whats really in the galvo feedback loop. Its a bit more then a audio amplifier, as it has to go down to DC. Usually at least one means of current sensing as well as the position sensor. The amp has to nail any ringing or overshoot in about 3 cycles of shaft resonance. A really good galvo has a first resonance around 2500 Hz.

    CRT vector rates are 100x faster then the Galvos. So it takes a considerable amount of code to go from the fast vector to the slow lasershow vectors. Ie point reduction/adding, adding blanking, anchor, and guide points. Laser/Lazy Mame does this. As does Pangolin's Asteroids program and so does Zoof's vector game programs.

    As far as hurting the galvos, no PWM, no short, sharp, full field square waves at very high rates. Do not bang into whatever limits the rotation in the galvo. Known as "hitting the stops" this will damage them very fast.

    No one here has ever torn down a very low cost clone, nor reverse engineered its tuning. This is a first.

    The ILDA test pattern PPS is changed by changing the point output rate, not by changing the pattern. PPS is D to A converter updates per second.

    PPS divided by the number of points in a given frame = refresh rate.

    So you increase the PPS in software on a well tuned pair until the circle is uniform and just falls inside the square. That point in your speed is your "PPS". Since you do not have a display or user interface to tell you the point rate, your up the proverbial creek without a paddle. If you have a GOOD oscilloscope, you might be able to measure the total frame for the ILDA pattern, divide by the number of points in the pattern, take the inverse, and gain a rough idea of your pps. I'm guessing around 8 to 12 K PPS for a less then 100$ set of galvos.

    The circle in the square shows a 3 dB down point for the galvo response. The actual pattern was devised by artists and engineers in the 90's, and little has ever been published in terms of its engineering rationale. But it is the standard and it does work well for setting up galvos for image transfer. There are other test patterns used for linearity, making the X and Y speeds match, color response, overshoot, etc. ILDA pattern is a OVERALL test, but you can tune on it.

    Looking at the board, I'm GUESSING P,I,D and Sensor offset pots. I see no current source for the position sensor LEDs, so guessing they just run the leds off a resistor to save costs. So any lack of "Stiffness" in the galvo psus is going to cause droop in the power supplies and show up in your images. I do not see much in the way of filter caps in the projector. A good galvo draws 4-6 amps peak as it slams the brakes on a long jump. So a "Stiff" psu is important for good image quality, as is a lack of 60 Hz feedthrough.

    The easiest way to determine the pots is to disconnect the controller, and look at the processed feedback signal with a scope. You inject a 30 hz square wave, and work out what each pot does to the waveform, and thus the system tuning. One pot will be one not to be messed with, it will do the scaling or offset. As slow as that design is, unless you can tune the board to oscillate, I don't think you'll hurt them with small changes to the pots. A person whom has tuned galvos before can tell you what does what, except for pots that adjust sensor/offset parameters just by looking at the laser image.

    DOG-P, Where are you located? We can often pair folks up who live within a hour of you.

    Lets get you the other test patterns, that would be a big help. I'm at work, so I do not have the files with me.

    http://www.pangolin.com/ILDAtest.html



    Steve
    Last edited by mixedgas; 08-30-2012 at 08:20.

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    Interesting... thanks for the info!

    I guess my question is about generating a lower PPS ILDA test .ild file. In my case, I downloaded a 12KPPS .ild test file, and can adjust the speed using a parameter in the .prg file. The speed parameter seems to change the playback speed (change the time between the points)... so speeding it up makes the image quality worse, but less flickery. I think I'd like a test file that looks undistorted at some "full speed" to know what it's performance specifications are. I imagine a 12KPPS file would be something like 500 points, and played at a 24 Hz "refresh rate". So, I think I'd need something like a 250 point file played at 24 Hz to do 6KPPS. Does such a .ild file exist, or is there software out there to generate it?

    I'm pretty sure I can determine the number of PPS that corresponds to the "speed" parameter... in the case of the 12KPPS .ild file, a speed of 5 refreshed the entire screen ~2.6 times/sec (from a simple stopwatch test). So, if the 12KPPS file is 500 points, then speed 5 would be about 1.3KPPS. I could check another speed to verify linearity, but I imagine the speed could be interpolated. I do also have several high speed oscilloscopes and logic analyzers.

    I'm probably not being clear on what I'm saying, due to lack of experience and (probably) wrong terminology. And I'm in Northern VA, just west of DC.

    Thanks,
    DogP

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    AT 1.3 Kpps, you'd flicker horribly. You need at least 22 hz refresh rate to avoid flicker.

    A stopwatch is not going to give you much data unless you know everything about a whole animation. You need a scope.

    PM me with a email, and I'll send you some files in the morning. We have to figure out which ILDA format version (There are about 3 formats used) your card supports.

    I'll make you a 250 or 500 point frame with a distinctive waveshape. Once you have that, its scope time.

    Steve

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    Points per second is such a weird way to look at this.

    It's really radians per second.

    I has to do with how fast the scanner shaft can accelerate from a stop and decelerate back to a stop.

    There are different kinds of galvos. The ones you have are free rotating. They have no torsion spring to return them to the center of their rotation. There is a rotational position sensor on the other end of the shaft. The magnets are on the shaft. The coils are in the stator. The coils are only energized when the there is a difference between the actual position of the shaft and the voltage being applied to the galvo amp that would put the shaft in that position. If the shaft in under rotated, the coils are energized with the polarity to move it toward its target. If it's over rotated the coils are energized in the in the opposite phase. to move it back. Actually, the motion of the shaft is first started with the coils and before the shaft gets to its correct position, the coils are reversed to slow it down and stop it. That's what makes the scanner amp so interesting.

    James.
    Last edited by james; 08-30-2012 at 11:17.
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  8. #28
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    It would be easy to quantify in radians per second if the galvo was in smooth repetitive motion. Rads/sec is not a good approximation on a macro time scale such as laser display. As Laser display uses the ballistic region of the galvo, things are a little more complex.

    Right now let's find out what he has. He could easily measure a small signal jump or 3 dB falloff on his scope. He could also find the un-damped resonance(s) if he killed the feedback. It would tell us little about what he actually can do with those scanners, because you would have to do it at EACH jump angle size combination and frequency. That is a nearly infinite set of data. Great data at sinusoid for loud speakers, lousy data for a galvo. Humans do not read complex 3D data sets very well. That is why the existing test patterns exist. Test patterns are a compromise, but they sure simplfy things and allow for file transfer.



    Steve
    Last edited by mixedgas; 08-30-2012 at 09:38.

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    Quote Originally Posted by mixedgas View Post
    AT 1.3 Kpps, you'd flicker horribly. You need at least 22 hz refresh rate to avoid flicker.

    A stopwatch is not going to give you much data unless you know everything about a whole animation. You need a scope.
    Yeah, it was flickering horribly, but it was so slow that I could actually count the number of times the text "12K/30K" was being drawn. I assumed that it's drawn once per frame, so if I know how many points there are in a frame, then I figured that'd let me compute PPS. Maybe that's not a valid assumption.

    Quote Originally Posted by james View Post
    There are different kinds of galvos. The ones you have are free rotating. They have no torsion spring to return them to the center of their rotation. There is a rotational position sensor on the other end of the shaft. The magnets are on the shaft. The coils are in the stator. The coils are only energized when the there is a difference between the actual position of the shaft and the voltage being applied to the galvo amp that would put the shaft in that position. If the shaft in under rotated, the coils are energized with the polarity to move it toward its target. If it's over rotated the coils are energized in the in the opposite phase. to move it back. Actually, the motion of the shaft is first started with the coils and before the shaft gets to its correct position, the coils are reversed to slow it down and stop it. That's what makes the scanner amp so interesting.
    Oh... cool, I assumed that the galvo vibrated back and forth, not just constantly spinning. I haven't looked at it closely yet though, so I'm sure there's a lot of stuff I'm gonna learn.

    DogP

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    The only reason "points per second" is ever used as a measure of scanner speed is because scanners are most often driven by pseudo-analog signals from clocked DACs.

    Scanners are pure analog devices and they don't know or care about points!

    They can just as easily be driven by pure analog signal sources like Moog Synthesizers.

    No points there!

    The factors that make one scanner better than another are mass of the moving parts, friction and jitter in the bearings, force produced by the coils, power of the magnets on the shaft, accuracy of the rotational position sensor and possibly the most important, the quality and precision of the scanner amp.

    It's also interesting to note that scanners are not instantaneous. It takes time to translate the input voltage to an actual position in the scanner. Modulation of the lasers, however is instantaneous. So a laser controller must employ some delay between the color control signals and the scanner signals. In a multi channel wave this is done by shifting samples back in time between the channels.

    Oh and BTW what you have there is a violet laser; not purple. Violet is a region of the spectrum. Purple is a human perception of red and blue.

    http://en.wikipedia.org/wiki/Line_of_purples

    James.
    Last edited by james; 08-30-2012 at 13:27.
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