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Thread: Open Laser Show DAC (USB)

  1. #1
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    Default Open Laser Show DAC (USB)

    Hi everyone.

    I am posting some specs and a link to a relatively new USB DAC on the block. The Open Laser Show DAC (or OLSD for short).

    It is based on a Arduino microcontroller shield format and sports some basic but very useful specifications:

    * Scan Rates: 1 kpps to 30 kpps
    * XY Resolution: 12 Bits
    * Color Resolution: 3 bits (for a total of 512 colors - 8 shades of gray)
    * Colors: Red, Green, Blue outputs
    * TTL Shutter Output
    * Built in test patterns accessible by button.

    These are the specs for version 3. Version 4 sports 32k colors (32 shades of gray) and a reduced IO count. It is totally open source. Here is a link the main web page:

    http://www.fab-favreau.com/index.php...enLaserShowDAC

    Not only is it a USB DAC but it also can function as a standalone test device. It features built in test frames (Quadrature, Laser Media, ILDA, and a few others) that can be displayed at different speeds and in greyscale or full color. The board includes a button to switch the unit into test frame mode. Since an Arduino can be run on batteries it can do this independently of a host computer.

    No finished boards or kits are available at this time, however I do have some V3 bare boards if anyone is interested. Price for the bare boards are $5 plus whatever shipping is.

    --- Happy New Year! ---

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    Very nice. I know a large group of people who I think will be very interested in this.

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    Why the low colour resolution? As far as I know the AVR (Arduino) is fast enough to send data to more DAC chips than just for the X/Y scanners. Never had a problem with that on my laser harp.

    If the SPI bus happens to be too slow, you can always sacrifice a full 8-bit port along with a few latches and R/2R ladder networks for the DAC, since you're not going to need the pins for something else anyway.

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    Cost and time. V4 implements 5 bits per color. 32k is quite a few colors. For V3 512 colors is enough to be useful. How many colors in the ILDA palette?

    A handful of resistors is quite inexpensive and gets the job done. Also it takes a bit of time to write to 3 SPI DACs (3 x 16 bit SPI writes) vs. 2 parallel writes for V3 or 1 x 16 bit SPI transfer for V4. This leaves a lot more cycles for doing other stuff.

    Keep in mind this DAC costs < $20 in parts + PCB Board + Arduino which equates to about $45 in parts (including arduino + some assembly required). The goal was to cost a bit less than the iShow while providing more functionality.

  5. #5
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    Quote Originally Posted by cfavreau View Post
    Keep in mind this DAC costs < $20 in parts + PCB Board + Arduino which equates to about $45 in parts (including arduino + some assembly required). The goal was to cost a bit less than the iShow while providing more functionality.
    If you get rid of the Arduino and just program a bare AVR chip using ISP and the V-USB library for communicating to the host directly, there's plenty of processing power left to do other stuff. The Arduino board is quite costly for what it actually does, a bare ATMEGA8 or even ATMEGA16 chip is only a few bucks.

    Arduino's are great for quick and dirty prototyping but not so great for production-level boards that are built in higher volumes.

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    While leaving the Arduino out and just putting an AVR on board will make the board less expensive and a better candidate for mass production, it does take away from the other qualities that being an Arduino shield has. For most of us it really doesn't matter however for those of us that are tinkerers here is what you can do. You can use any of the other Arduino compatible development boards that use more powerful micros such as the ones that use the PIC32 or ARM processors and also feature other interfaces such as Ethernet and SD cards. Thanks for you input.

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    Quote Originally Posted by cfavreau View Post
    Cost and time. V4 implements 5 bits per color. 32k is quite a few colors. For V3 512 colors is enough to be useful. How many colors in the ILDA palette?

    A handful of resistors is quite inexpensive and gets the job done. Also it takes a bit of time to write to 3 SPI DACs (3 x 16 bit SPI writes) vs. 2 parallel writes for V3 or 1 x 16 bit SPI transfer for V4. This leaves a lot more cycles for doing other stuff.

    Keep in mind this DAC costs < $20 in parts + PCB Board + Arduino which equates to about $45 in parts (including arduino + some assembly required). The goal was to cost a bit less than the iShow while providing more functionality.
    On one hand, I do think that 512 or 32K colors is more than enough to make a nice show. On the other hand, I wonder about mapping from the 8 bit output of laser show software to 3 or 4 bits on your DAC. It's easy enough to shift right to go from 8 to 3 but I am not sure if that is going to produce the desired effect. The default ILDA palette that most use contains 63 colors. You certainly support more than that. But, does your arrangement of bits support the specified 63 colors? In other words, do the bit combinations that your DAC will produce map directly to the values in the default table? If not, that's a bit of a problem but it can be overcome by "close to" mapping which is what most applications do when saving full color images to the default palette. More work than just shifting right is required, though. I am curious to hear your thoughts on this.

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    The 3 bit RGB can do colors in steps of 32 in reference to 256 being the brightest color. So... 0, 32, 64, 128, 160, 192, 224, 256. I believe this covers all of the 63 color ILDA palette. The larger ILDA palette it does not quite cover (like the one here http://paulbourke.net/dataformats/ilda/).

    The 5 bit RGB can do colors in steps of 8. So for the larger palette it does not quite do it either... closer but no cigar. It uses numbers like 12 which is not quite divisible by 8 evenly.

    Now this all assumes that your diodes are linear and all that jazz.

    My opinion is that it works just as well as my other 8 bit RGB DACs with no color remapping on my projector. The biggest advantage that I have seen so far of the 5 bit vs. the 3 bit is the ability to fade in and out. It is a bit quick with 3 bits.

  9. #9
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    Hi guys, hi cfavreau!

    Yesterday I decided to play with this device. I didn`t assemble the hardware, only programming aspect. I'm at an impasse and I need your help . Now a bit more details:
    To begin with, that is in my possession-
    Arduino clone from China w/ATMEGA328P and FT232RL USB interface
    LDS Pro w/license, LSX 2011 Demo from DrLawa (thanks to him)
    OS, where I experimented: Win7x32, Win7x64, WinXPx32

    What I did- i installed CDM drivers, uploaded this firmware to the arduino board via avrdude.
    After rebooting, I found signal at pin#2 (LED1 DAC board) and LED (pin#13) is turn on (dimly). After that I decided to start the OLSDTest utility. It froze with the message "Initialized OLSD", and no any response from the board ("RX" "TX" LEDs are sleeping)
    Click image for larger version. 

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    If I run this utility without the arduino, a message appears "failed to initialize the OLSD"

    LSX detects this DAC (somehow 2 pieces) if i connect arduino to PC, but there is no reaction to this.
    Click image for larger version. 

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    That the same story with the LDS software.
    Probably, I'm on the wrong path

    P.S. My english is not very well, sorry

  10. #10
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    Ah, but you need possibly another wire connected in the hardware. Look at the schematics, there is a feedback wire from the FT232 chip to one of the arduino pins. I think if you hook that up, the serial handshaking will work. I don't have my schematic with me right now, but that is what I would check first, based on what you have said.

    Steve

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