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07-17-2010, 11:16 PM #1
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Solonar
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Modulation frequency for Green

Whats a good modulation frequency for a green with analog modulation.

I've looked(here and PL) and can't seem to find a reasonably concrete answer.

My current green is modulated by the FlexMod( set to the minimum ~50khz), but the module im looking at is TEC cooled, so I would need to use the supplied driver.

Is 10khz a reasonable speed for a 30k projector, or should I look for a higher speed

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07-18-2010, 03:29 AM #2
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LSRFAQ
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Re: Modulation frequency for Green

Very few laser graphics will EVER change color on a point by point basis.

30K = 1/30,000 seconds per point = .000033 second per point, lets go for 4 points between color changes for the color rate (extremely fast color) so 4 x .000033 = .000132 seconds , 1/.000132 = 7.5 khz (Nyquist's rule does not apply) so 10 Khz is Decent , and as you climb above 10Khz, life gets MUCH better. So 15-20 Khz would be my target, unless I'm doing graphics professionally at a trade show or planetarium, and in that case I would be using a AOM for green control anyways. Since the upper lasing state storage time for Nd:YAG and ND:YVO4 is 800 microseconds, going very, very fast with direct modulation is a moot point, as most DPSS GREEN could not track faster then the storage time.

Steve

Last edited by LSRFAQ; 07-18-2010 at 02:06 PM.

07-18-2010, 04:40 AM #3
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Solonar
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Re: Modulation frequency for Green

Thanks!

07-18-2010, 02:19 PM #4
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Benm
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Re: Modulation frequency for Green

Quote:
 Originally Posted by LSRFAQ Since the upper lasing state storage time for Nd:YAG and ND:YVO4 is 800 microseconds, going very, very fast with direct modulation is a moot point, as most DPSS GREEN could not track faster then the storage time.
Using that as a basis anything faster than 1250 Hz would be pointless.

The effect is quite noticeable though, but it can be compensated for in software - just just turn the laser off 0.5 to 1 ms before it actually needs to be off.

One problem i found with that (using LFI) is that it doesnt support different blanking delays for each colors. Obviously directly used diodes (like red) don't have this delay, while dpss greens do have a delay - both in turning on and turning off. The turn-on delay can be lowered by running the diode idle at the treshold of emitting green (the pump diode will already be lasing at that point).

As far as the actual drivers are concerned: it is no problem to make them fast enough to blank on a point-by-point basis, 30 kHz is well within what simple opamp based drivers can reliably handle.

You won't be doing that much in practice though, but i've done it in PWM testing. Up to 10 kHz everything is totally fine, and it even worked as fast as 200 kHz. At that point the diode becomes the problem though: current into a dummy load looks fine, but you can capacitive and inductive problems with the laser diode and even the wiring if its rather long.

07-19-2010, 11:30 PM #5
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LSRFAQ
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Re: Modulation frequency for Green

One problem i found with that (using LFI) is that it doesnt support different blanking delays for each colors. Obviously directly used diodes (like red) don't have this delay, while dpss greens do have a delay - both in turning on and turning off. The turn-on delay can be lowered by running the diode idle at the treshold of emitting green (the pump diode will already be lasing at that point).

end quote.

Even Pangolin Pro does not have color by color delay. I Wish it did.
As far as I know, no software has internal color delay correction, which is why DZlaser sells a color correction delay board. Now they do have global delay settings, to make up for the difference between AO and mechanical blanking (one leads, one lags the XY) but NOTHING has individual color channel delay adjustments.

Steve

07-20-2010, 02:04 AM #6
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Solonar
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Re: Modulation frequency for Green

I had looked in to getting DZ's correction board, but he closed the store.

I plan on upgrading to Stanwax's ILDA interface board, and getting his correction daughterboard when available.

My projector works reasonably well given the time and money put into it, but there are still improvements to be made(getting a green that can keep up with the other lasers power wise, replacing the particle board base with aluminum, and changing my optical design).

07-21-2010, 12:44 AM #7
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Benm
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Re: Modulation frequency for Green

I think this should just be implemented in software - set blankings for each color channel. It would be a relatively easy to do in software.

Obviously its possible to delay the red (and 445) signals by hardware, but thats doing things at the wrong point. I wonder why this rather simple feature was omitted in software - a combination of diode and dpss sources is not -that- uncommon in laser projectors.

To use mechanical blanking is a step even beyond... at least when you do it just to compensate for delays. It's too bad to see that development on LFI has seized - the latest version is well over a year old.

I would love to implement a feature like that, but windows software development is not one of my strong points

07-21-2010, 03:21 PM #8
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Solonar
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Re: Modulation frequency for Green

I asked gary if it could be included in *********, and got a no go.

07-21-2010, 03:49 PM #9
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mickatcol
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Re: Modulation frequency for Green

You can set blanking delays in Laserboy.
LaserBoy ~ Linux Laser Project by James Lehman ~ Extra Stimulus Inc.
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07-21-2010, 04:31 PM #10
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LSRFAQ
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Re: Modulation frequency for Green

Quote:
 Originally Posted by mickatcol You can set blanking delays in Laserboy. LaserBoy ~ Linux Laser Project by James Lehman ~ Extra Stimulus Inc.
But its not a controller, and pre-adjusting the whole animation defeats the point of owning a controller or using ILDA files for transfering art. Create the art, pass the file back to laserboy, adjust it, save it, pass it back, via the dos window, to the controller, adds a bunch of extra steps. It SHOULD be in the show controller, not the artistic phase. Now when you go to use it on another machine or with another projector, your not ready to go, and need to repeat the process.

As for LFI Player,
BTW, if you contact Mike, the author of LFI player, and ask him for a mod, he tends to deliver. He would be thrilled to know someone is still using his software. Its a Gem, a little known Diamond. It has some quirks, but once you learn them..... It rocks.

Steve

07-21-2010, 05:40 PM #11
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ElektroFreak
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Re: Modulation frequency for Green

Quote:
 Originally Posted by LSRFAQ As for LFI Player, BTW, if you contact Mike, the author of LFI player, and ask him for a mod, he tends to deliver. He would be thrilled to know someone is still using his software. Its a Gem, a little known Diamond. It has some quirks, but once you learn them..... It rocks. Steve

I second that!! LFI is my favorite free laser control software.. works GREAT with the soundcard DAC.
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07-22-2010, 01:27 AM #12
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Re: Modulation frequency for Green

I agree on that - LFI is easy to use software to display ilda files or text.. apart from getting some basic settings right, anyone could work with it. I don't think that per-color blanking adjustment would be that hard to add either, after all, global blanking delay is already included.

And it would be a good addition too - when displaying ilda test frames its obvious that you can get blanking spot on for a red, but if you activate green instead of read, it requires readjustment... and it lacks a way of getting both right for now.

07-22-2010, 01:27 AM #13
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carmangary
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Re: Modulation frequency for Green

There are DACs that allow you to set color delays. RIYA does and I think Lumax does as well. Actually, the Lumax DAC lets you set all kinds of things to correct color problems. It's pretty cool.

One day I might experiment and potentially add something like that to ********* but I have more exciting things planned before that.

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