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Thread: Open Source/Freeware Budget USB DAC

  1. #21
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    Quote Originally Posted by carmangary View Post
    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.
    Hi CarmanGary,

    Once I have been able to put a prototype together and do some testing, I will relook at the power supply section as I will have an idea of the current requirements, I know there is a limit to the amount of current that can be drawn from a USB port. It would be a plus to have it completely self contained.

    Cheers
    Paul

  2. #22
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    The killer for this revision, disallowing USB power was the line drivers (which are highly accurate and good differential drivers for this design) draw up to 7mA of standby current each. Powered by a 30V differential, that amounts to 210 mW each, too much to safely pull from the USB. (not even counting the digital parts or dc-dc conversion inefficiency)

    The power supply option 2 can be powered from a common 12V or 15V wall-wart.

    Another rev. could use rail-rail op-amps as the drivers with a +/- 5V supply from the USB (using the inverting circuit from option 2) and it could probably run from USB.

  3. #23
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    Hey, things are looking good. The only thing I would like to see is another dmx. It would be nice to have a dmx in ( from lighting console) and a dmx out (to laser head accessories like, shutters, beam steering, lumia, gratings.)

    You could get rid of one of the led lines for another dmx.

    Chad


    When the going gets weird, the weird turn pro.


  4. #24
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    Quote Originally Posted by chad View Post
    Hey, things are looking good. The only thing I would like to see is another dmx. It would be nice to have a dmx in ( from lighting console) and a dmx out (to laser head accessories like, shutters, beam steering, lumia, gratings.)

    You could get rid of one of the led lines for another dmx.

    Chad
    Hi Chad,

    Pin 26 as per the 18F4550 Data sheet. Both the hardware SPI SDO and the hardware USART RX are on this pin. I want to use the built in hardware peripheral's as much as possible so as to maximize speed.

    I will keep this request on the back burner and try and implement it once the core functions in the embedded firmware are running stable. I will also experiment with running the SPI bus by bit banging the data out, if this is stable this will free up Pin 26 so it could be configured for DMX in.

    Thanks for the feed back so far guys.... I am starting to put the hardware together today...

    Cheers
    Paul

  5. #25
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    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    Default schematic review.

    I'd bring dac B of IC4 out just because a trace and pad to do it is gonna be all of maybe 5 US cents, add another 5 cents for a 1K series limiting resistor since adding another driver chip would be lunacy. You never know when you need another output. Call it AUXOUT1 like the quadmod32 does :-) Or take the sum of the R,G,B signals in software, div by 3 and call it lumanance.....

    Steve Roberts

  6. #26
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    Default Usbdac

    Hi,

    My SSM2142 line driver samples are arriving tomorrow, so I can finish the hardware construction of the USBDAC. I will hopefully start putting the embedded code framework together this weekend.

    I'm going to be in a bit of a situation once I have the prototype up and running as I don't have decent scanner amps or galvo's to test with and optimize timings, also the cheap 80mW Red I have does not have a blanking input (only a 5V cable).

    So I need to know which Scanners should I start out with. Also which emitter is the best to start with... Remember I live in darkest Africa where the exchange rate does not like me (Well at the moment its a little better than it was last week)...

    Cheers
    Paul

  7. #27
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    Default USBDAC Pictures

    Hi,

    Here are a couple of photos of the prototype base board I have been putting together. It consists of the Main.pdf schematic and part of Power Option 1.pdf. I have finally recieved a SD Card socket so I am putting a piggy back board together that will consist of the SD Card, Ram (1Mbit) and the E2Prom for the test pattern.

    The embedded code frame work has been started and I will add to it in stages.

    1) Get all the DAC working and synced
    2) Ram Access
    3) SD Card Access
    4) DMX512 Output
    5) DMX512 Input (If possible)

    I am also planning to put a simple GUI together just to test the USB comms.

    Well here they are......
    Attached Thumbnails Attached Thumbnails USBDAC1.jpg  

    USBDAC2.jpg  


  8. #28
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    Default USBDAC photos

    Here are another two photos.....
    Attached Thumbnails Attached Thumbnails USBDAC3.jpg  

    USBDAC4.jpg  


  9. #29
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    Wow this is coming along really nicely.

    Can't wait to see how this pans out and can build one.

    Well done Paul.

  10. #30
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    Thanks... I have only had a few hours every other night to work on it... so far this is just the base board - the main parts of the DAC... there will be a piggy back board that will go on top of this board with all the extras on - RAM, SD Card, digital outputs, DMX driver, E2Prom (Test Pattern) and 8 x digital outputs to driver anything from a relay to a logic input....

    drlava has offered to layout a decent PCB once I have proven the schemtic with this proto-type board... as building this circuit using this method will take forever.... I work with this method everyday so it only took me about 2 hours to do....

    I am excited to get the SD Card facility working as I have not played with this technology yet... I have found an open source FAT32 library for the PIC and I am itching to try it out....

    Wouldn't it be great to just copy our ILDA shows to a SD Card then plug it into this DAC, power up and away you go....

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