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Thread: Why USB?

  1. #1
    Join Date
    May 2008
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    Sweden
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    26

    Default Why USB?

    Hi! I'm just wondering about a few things. Why is everyone using USB DAC's? Hooking up two DAC0832's to the printer port is very simple and works fine. I know that it may be hard to have full color and such features but for me and some others using single color simple systems it would be easier and cheaper. There seems to be no open source USB DAC's either... I'm still waiting for "Spaghetti" to support DAC0832 as promised. I may be waiting in vain since it seems that the trend amongst most software programmers is to skip the DAC0832 support in new versions of their software. I'm just a cheap hobbyist and I don't want to spend a lot of money on a DAC that I could make myself. I'm seriously thinking of skipping the PC and run all my shows from a SD card...

    Don't say that the old printer port is to slow now.
    30kpps @8bits => 30k * 2 * 8 = 480kbit/s
    The ECP specifies 2.5Mbit/s transfer speed and this shouldn't be a problem even for an older PC...

    I'm using Norms software at the moment but that is so full of bugs that its barely usable... It also nearly freezes my old p3 1000. Seems to run smoth on my core2 machine but it really shouldn't need all this processing power to run...

    Just felt like whining a bit

  2. #2
    Join Date
    May 2006
    Location
    Native Floridian
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    3,108

    Default

    I think one of the problems we've seen at the laser meets, is that parallel port DAC's have sample jitter problems. Perhaps the problem could be rectified with a well designed parallel port DAC, but another problem, is that alot of laptop's these days don't even have a parallel port! So a DAC on the USB port seems to work well and just about every computer now has a USB port. Of course the best bet is to have a QM2K with a .NET board.

  3. #3
    Join Date
    Jul 2007
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    west sussex uk
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    2,279

    Default dacs

    yep been there too ,printer port just take up to much proccesor time and gives priority to sending data to ecp and not enough time to the program trying to supply data to it and causes lot of system crashes so you need somthing over 2ghz or core duo so one core can run the printer port and the other the software,so everyone switched to less cpu intensive usb but i still like the old alphalite dac compared to my fb3

  4. #4
    Join Date
    Nov 2007
    Location
    Cairns, Australia
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    Default

    I was told to stay away from printer port DAC's , not because of the speed, but simply because the printer port is low priority on computers. So if your CPU starts working on something during a show, you could end up with a static beam!

  5. #5
    Join Date
    Jun 2008
    Location
    Boston, MA
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    58

    Default

    i dont have a printer port

  6. #6
    Join Date
    Dec 2007
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    93

    Default

    I would rather see ethernet dacs in stead of usb... cablelength is not limited to 5m like usb, works on all operating systems... no driver needed. etc...

  7. #7
    Join Date
    Nov 2007
    Location
    Cairns, Australia
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    1,896

    Default

    Neither do I. It was a pain when I was out buying a DMX controller. There were alot of easy printer port ones, but the USB one was $256AU. I ended up going with the USB, and I dont regret it, its a damn well build little controller! Ive dropped it on the floor once ( Accidental of course.. ) and the thing still worked afterwards! Eventually no computers will have a printer port, as more and more printers are becoming USB aswell there is really no need for them anymore

  8. #8
    Join Date
    Jan 2006
    Location
    Frankfurt am Main, Germany
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    29

    Default

    Quote Originally Posted by Danny View Post
    There seems to be no open source USB DAC's either...
    Take a look at bILDA http://www.linux-laser.org

    Greetings,
    afrob

  9. #9
    Join Date
    Dec 2006
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    Pflugerville, TX, USA
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    Default

    Jitter is a good reason not to use the DAC0832 DAC but that is not what Spaghetti doesn't already support it. The reason that Spaghetti doesn't support the DAC0832 parallel DAC is because of the timing issues. It's pretty easy to send a set of points and a point rate to a USB DAC. The USB DAC takes care of making sure that points are at 30000pps or whatever is specified. The LPT DAC won't do that, though. It's up to the computer to send each point to it at the correct rate. 1/30000 = .033msec. The resolution of a Windows timer or Sleep command only goes down to around 1 to 20 msec! So, in order to time things correctly, the system clock ticks have to be counted and the only way to do that is to do a tight loop that does nothing but count ticks. When you do that, CPU usage goes through the roof and leaves much less processing power for doing things like playing music or computing the next frame. It just isn't a good situation and will be evident when you try to open a file while playing a laser show and everything goes to crap.

    Now that LaserBoy and DrLava have teamed up to create a soundcard mod kit and driver, it's just as cheap and easier to build a modified "LaserBoy" sound card DAC as it is to build a DAC0832 DAC now and it will work a lot better. For that reason, I really don't have much motivation to add support for the DAC0832 DAC. I will be happier not supporting it and I am sure anyone would be happier with the Sound Card DAC.

    But honestly, the best thing to do is just to save up a little money and buy yourself a real DAC. In the end, they are a lot less headache and may offer other features. I have been playing around with my new Riya DAC and it's nice. It supports up to 2GB of SD card ram so I can put a lot of shows on it and let it run on it's own. Perfect for my Halloween show on the side of my house. You'll never be able to do that with a soundcard or a DAC0832 DAC.

    That said, I may still add support for the DAC0832 someday but don't hold your breath waiting for it. Actually, I have already written a driver but it needs updating to work with my new code. But, I blew up my test DAC by hooking up voltage backwards and need to fix it before I can test anything. haha.

  10. #10
    Join Date
    Dec 2006
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    Default

    Quote Originally Posted by highvolt View Post
    I would rather see ethernet dacs in stead of usb... cablelength is not limited to 5m like usb, works on all operating systems... no driver needed. etc...
    My new RIYA DAC supports ethernet. I haven't tried it out, yet, though. I need to do that and add support for it in Spaghetti. But, you are wrong about no driver required. There will always have to be some sort of driver that formats the data into the right format before sending it across the wire.

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