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Thread: Open Source/Freeware Budget USB DAC

  1. #11
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    I like the idea of an automatic test frame but I really wouldn't want to power up my galvos and have them start moving by themselves until I plugged in the USB cable. That's asking for trouble because if I turned it on and forgot about it the galvos would be running forever! I'd rather have some little button that could be pressed or have it only enabled by software. This feels like a feature that would be nice to have but maybe not worth the trouble it brings.

    Number crunching for effects would basically be looping through each point one or more times and applying some sort of mathematical equation. I suppose since this would all be done in firmware so its one of those things that could be experimented with afterwards. The only hardware requirement that I can think of is that it would need memory to copy the new frames to but it sounds like you have that covered. Also, besides effects, this type of functionality could be used for automatic blanking optimization.

  2. #12
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    Default Usb Dac

    A button to enable a test frame is not a problem..(This would actually assist in debugging embedded firmware).. as for the effect facility.... Would it only apply to beam shows? eg: rotating a frame on a vertical and/or horizontal axis??

  3. #13
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    On second thought, I am not sure if on board effects processing is such a great idea. The coolest rotation effect is when the frame contains Z axis data. But that would mean that Z axis coordinates would also need to be sent to the DAC. That just requires more memory and makes it take longer to transfer frames across USB. Since modern computers have plenty of power and have no problem doing the preprocessing of effects I think my idea just doesn't make sense from a practical standpoint.

  4. #14
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    Rather than using a PIC, I really think a much better - faster way, would be to use a 16bit(at least) micro. If im not mistaken PIC's are 8 bit...

    I like sonaluma's choice of a ARM processor
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  5. #15
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    Hi Paul, do you have a timeframe of when you might have something ready to show? I'm just curious and not trying to rush you.

  6. #16
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    Quote Originally Posted by carmangary View Post
    Hi Paul, do you have a timeframe of when you might have something ready to show? I'm just curious and not trying to rush you.

    Hi Gary,

    I am still awaiting my samples of the MCP4822 to arrive, the MicroChip chaps are visiting my work on Wednesday and they will give them to me then, so I hoping to have something ready by the lastest Saturday evening.

    I am still looking at the embedded code (Bootloader work around) and trying to source some cheap SRAM. The initial plan is to get the DAC's running without any buffering, then I will concerntrate on the SRAM implementation then continue expanding the other facility's of the DAC with the help of DrLava.

    I am hoping to have a complete DAC with most of the specs I laid out by the end of November.

    I need to know if Cost is a major player in this design, if it is then I am going to implement a R-2R ladder for a 16 bit X and Y output. I put an 8 bit output together earlier and it seems to be running fine. The only thing it involves a lot of resistors which are a lot cheaper than 16 bit DAC's.

    My main objective with the X,Y,R,G and B outputs is that they must all update at the same time!

    Cheers for now... Paul

  7. #17
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    If you feel you must do R2R, PM me, I'll donate you a few dac chips if we can get them through SA customs. Maxim and AD send me free samples because I work at a university, AD has limits but Maxim doesnt seem to care if they have it in stock. 16 bit resistor dacs get noisey fast from thermal noise . If you feel you must build a dac, I have better ways then simple r2r ladders. You really want to use small cheap current sources made from diodes and npns if you must build your own over 8 bits. I can scan in schematics if you MUST go that way.

    Mixedgas

  8. #18
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    Quote Originally Posted by mixedgas View Post
    If you feel you must do R2R, PM me, I'll donate you a few dac chips if we can get them through SA customs. Maxim and AD send me free samples because I work at a university, AD has limits but Maxim doesnt seem to care if they have it in stock. 16 bit resistor dacs get noisey fast from thermal noise . If you feel you must build a dac, I have better ways then simple r2r ladders. You really want to use small cheap current sources made from diodes and npns if you must build your own over 8 bits. I can scan in schematics if you MUST go that way.

    Mixedgas
    Thanks mixedgas... I will keep your offer in mind if these 12 bit MCP4822 DAC's are no good... I finally have them in hand...WOOHOO...

    I have started the schematic layout and hopefully I will post the first revision soon...

    Cheers
    Paul

  9. #19
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    Default Usbdac

    Hi,

    Between drlava and I, We have put together the first revision of the USBDAC schematic's. Now the buffer SRAM, TTL output and SD Card Facility's have not been laid out yet.

    You can access the files at the following url:

    http://hacylon.case.edu/usbdac/

    Thanks to drlava for all his input and adjustments to the design so far..

    Let us have your comments please....

    Cheers Paul_B

  10. #20
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    I noticed you had a couple of power options. Is it not possible to just power it from the USB port? My Moncha DAC is powered from the USB power and that is really nice in terms of portability.

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