need help with dac/scanner build

carmangary · May 27, 2010

spanqee said:
doesnt ttl blanking give up artifax more readily when using 20kpps + scanners, isnt it difficult to get a decent color blend for true color or even 256 color palletts on anything but a static beam? so i would wanna go with analog for projecting more complicated colors of animations at higher speeds, right?

TTL doesn't cause more artifacts but it does make it harder to get the blends correct since you don't have any control via software. TTL modulation is a thing of the past. I am not sure why anyone would go that route unless they are limited to certain hardware.

ElektroFreak · May 27, 2010

TTL is a thing of the past as far as full-color projectors are concerned, but only to a certain extent. One of the most respected professional interfaces, Full-Auto, is TTL only, but it has been used by some of the biggest truly pro laser show companies for years.

With single-color systems TTL is just fine.. Analog has it's added perks like the ability to fade the laser in and out, but with the VAST majority of very high-powered pro green systems (usually surgical lasers repurposed to do light shows) TTL is all you get, analog isn't even an option.

Benm · May 27, 2010

I suppose analog modulation is most useful for full-color systems, not so much for RGV scanners as the bluray prevents many colors from being blended at reasonable brightness levels.

Also, many ilda frames are TTL so it's hard to make good use of color blending options.

carmangary · May 28, 2010

I don't agree with that. Analog control allows balancing your levels so that you obtain the correct levels to obtain white. It also allows fading for effects fade-in effects or for reducing power levels for save audience scanning.

For blu-ray systems, fading allows adding a touch of green to the blu-ray so that your blue looks blue instead of purple.

Most all laser software has color effects for fading, morphing colors, etc. That isn't possible if all you have is TTL lasers.

Let's face it. Lasers displays are all about color. Anything you can do to increase the amount of colors you have only make sense. Saying that TTL is good enough is like saying black and white TV is good enough, or like saying HD TV isn't really necessary.

Benm · May 28, 2010

I suppose it depends on what you want to do really. If its just about giving a very nice beamshow, TTL will likely suffice. If you want to get a color-reliable projection, analog is a must.

carmangary · May 28, 2010

Even with beam shows it would be lacking in some important features. Watching a funnel pulse the music is really cool. With TTL it would just flash on and off. Still cool but definitely not as much so. Also, you would not be able to attenuate the beams for audience scanning, which is kind of important with beams shows, with just TTL.

I agree that you can get by with TTL and if that is what you are used to you will be happy. But, why limit yourself when were only talking around $20 for an analog driver, or whatever they cost. If it cost a couple hundred more for analog I would agree with you. But, it is far cheaper than that.

Benm · May 28, 2010

I suppose you're right on the cost argument, its doenst cost very much extra to have analog modulation if you build the drivers yourself. That might be different if you buy a complete laser unit, in which case you are stuck with what the manufacturer chose. I'm not sure about the price difference between those options however.

Do you have any ilda frames that use analog modulation? I could test it for a bit to see how easy or hard it would be to implement in a DIY driver design, but i have never found a ilda frame that just produces some intensity bars (like a tv test screen) to actually test it.

carmangary · May 29, 2010

You can create frames with shades of colors with many applications. With Spaghetti, you could just apply a rainbow effect to a frame to get all colors of the spectrum. I am sure other programs offer similar features.

Benm · May 29, 2010

It would be helpful if you could post some ilda frames that actually have analog modulation in them. I'm working on a tutorial to build a scanner, and including a bit about analog modulation would be useful, but i'd need to have some stuff for people to test it on.

Solonar · May 29, 2010

Try this. Not really a test pattern, but will show analog modulation.

carmangary · May 29, 2010

Actually, almost all frames use analog modulation. The ILDA format has always supported at least 255 colors in a frame. The default palette is usually 64 colors. If you analyze most frames you will find that the values for R, G, and B are not just 255 or 0 but values in between. So, even though a frame may appear to use only 3 or 4 different colors, it is very possible that those colors are not simply bright red, bright green, or bright blue ( or some combination of the three). For example, you might run across some frames where only one color is used but the specified color might be light blue. It is impossible to create light blue using TTL modulation.

In short, to show analog modulation, all you have to do is to create a frame that has a light blue circle. Then display it on an analog modulated system and then a TTL modulated system. The difference will be apparent.

Good luck with your tutorial. I hope to be able to see it when you are done.

Benm · May 30, 2010

I'm putting things together using TTL red and green at the moment, but the actual LD drivers are compatible with analog modulation, they just max out at 5 volts input so they take ttl too. I suppose upgrading to analog would just be a change in the compensation amp which is easy enough to make.

I still need some good patterns to test it really, not frames that run on a couple of mixed colors, but ones that show 0-10...90-100% intensity bars/lines for each color something like that. Thats they only way i can tell if its actually working properly, and i wouldn't like to publish something i'm not certain about.

Perhaps i can make such frames myself, i'd have to investigate that.

carmangary · May 30, 2010

What exactly are you testing? It seems like the most straight forward and reliable way of knowing if your driver is working is vary the modulation input and check that output current varies linearly. You don't even need to have it connected to a laser diode for that.

Benm · May 30, 2010

Testing the driver isn't the problem, and that works fine - gives a linear current output for input voltages between 0 and 5 volts.

I want to test it with the soundcard dac and any electronics required between them - so i know the entire chain of devices works as it should.

carmangary · May 31, 2010

Right on. So just load up Spaghetti and change the power settings and it will do that. If you don't have Spaghetti then the settings are probably in whatever else you use.

spanqee · May 31, 2010

whew ,
just got back from the rocklahoma gig. it was HOT, i dont mean "africa hot" but more like "hell hot" spent most of my free time photographing the more severe cases of sunburn since im not that into 80's hair bands.
the concert site was HUGE!!! @40 min out of the local metro. you may have expected us to destroy that last set of scanners in transit before we even reached the campgrounds ... and we certainly did just that!!! but we were able to throw together a pickoff deck and got our redline beamscan unit repaired right there on our campsite. :crackup: what kind of foo goes camping with a soldering iron and computer(they even had wifi)???:crackup: that aint camping!
my spine is killing me , my feet are hurtin', im exhausted and sunburned yet i still managed ,in spite of all the problems, to have a great time. even found time to catch most of "zz top's" performance. :bowdown:that was the only band i really wanted to see out of all the groups there throughout the whole weekend.

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