first laser project - soundcard DAC trouble?

[daderaide]

Hello everyone! Fist let me introduce myself by saying that I love your forum and i hope to meet some of you that might be in the pacific northwest at a meet and greet someday. What a wealth of knowledge you have here.

The search function has really gotten me far with my project but i am getting some very strange (to me) results that I'm hoping someone here might recognize. I'm working on building a modified sound card dac to go with spaghetti. The sound card is one of the c-media cheapos. After fiddling around with the driver for a bit, i finally got the channels sorted out (I think) and i'm on to adjusting the correction amp (I'm using the laserboy schematic and BOM) I'm using an ILDA big white circle that I downloaded. The problem is that the image is very distorted. I get the white circle but it's very small and way off to the bottom right corner of the scan area (see image)


The galvos are 20K from ebay. I tried adjusting the pots on the driver boards but none of them made any real difference to this particular affliction. anyone have an idea what might be wrong with my set-up? Thanks!!!

[Grix]

Hm, have you set the rate of the sound card correctly in the sound card control panel? It should match whatever is in the ezauddac ini file. For example 48000 Hz or 44100 Hz . If this is set wrong, the card might play through the allocated data too quickly and end up displaying some gibberish data from an unused portion of the ram for the rest of the frame, causing the laser to jump to the corner like that. Not sure if that's something the ezauddac driver would do, just a thought.

If not maybe there is a loose connection in the circuit somewhere causing the signal to be disconnected for some microseconds at a time randomly. If you try to shake or rustle the correction amp or sound card while it is playing and the output reacts, that is probably it.

The projector works fine using any other playback method? How about different ILDA files?

[JohnYayas]

Spaghetti doesn't use the ezauddac driver so there shouldn't be any reason to mess with that unless you are using other programs that do use it.

To help narrow things down, I'd recommend starting with some laserboy created wav file that display a vert line, a horiz line, and a single point. That will help determine where the noise is coming from. Most of the time the problem has to do with how Windows will mix the channels all together in order to simulate surround sound on 2 channel systems which will appear portions of the color signals in your XY channels. Try a circle that is just R, G, or B and see if the image shifts.

[mojo]

check if your soundcard output is set to either 5.1 or 7.1.

[daderaide]

Changing the circle color does shift the image around. It doesn't appear to do much with the big lines but definitely having a big impact. This must be a big clue that windows is mixing in the color info. Any suggestions on how to go about making it stop that lol? In the process of working on the driver, I created a cm106.ini file that I copied from from a post on laserboy forum and put it in the drivers folder. At least I think it was the right folder. All of the info I could find on that subject was several years old and for windows XP, so I'm not sure if it applies to windows 7.

[absolom7691]

The galvos are 20K from ebay. I tried adjusting the pots on the driver boards but none of them made any real difference to this particular affliction. anyone have an idea what might be wrong with my set-up? Thanks!!!

Do you have access to an o-scope with XY function? Also, it is highly advisable not to touch the pots on your scanner amps. It may have been possible that the amps are out of tune but I wouldn't even go that route until you are 100% certain that it is not your sound card DAC/drivers/software. Once a set of scanners are out of tune, getting them back to perfect tuning is an EXTREMELY daunting task, especially if you've never tuned scanners before.

[daderaide]

I do have a 2 channel scope that can plot both channels in relation to each other if that's what you mean by xy function. Hopefully I didn't mess up those pots too bad I only turned them side to side and right back to where they were, so hopefully it's ok. I'm not sure what I would be looking for on the scope that I wouldn't already see from the laser output. It seems pretty clear that it's a windows issue, right?

[absolom7691]

I do have a 2 channel scope that can plot both channels in relation to each other if that's what you mean by xy function. Hopefully I didn't mess up those pots too bad I only turned them side to side and right back to where they were, so hopefully it's ok. I'm not sure what I would be looking for on the scope that I wouldn't already see from the laser output. It seems pretty clear that it's a windows issue, right?

They are 25 turn pots so, I doubt you mis-adjusted anything on them. Along with that, you probably wouldn't have seen any difference just turning them side to side, less than one turn.

As far as XY, I meant vectoring. You should be able to hook both XY channels from your DAC to your scope (in vector mode) and it should yield what you're trying to project. I only recommend this because if it is something with your DAC or windows setup, you don't want to fry your galvos from weird oscillations. On the Laserboy website, here is a pic of what I mean: http://laserboy.org/p_laserboy_41.html

Also, you might want to try send James a PM, he knows a great deal about these sound card DACs and correction boards. Here's his profile: http://www.photonlexicon.com/forums/...php/6005-james

[NobleGas]

Does the mod to the sound card include making it DC coupled and correcting the offset?

[absolom7691]

Does the mod to the sound card include making it DC coupled and correcting the offset?

I was just thinking about asking him that too. Based on the image, it looks as if there is no offset correction. Hard to tell about the DC coupling.