Page 10 of 12 FirstFirst ... 6789101112 LastLast
Results 91 to 100 of 116

Thread: CYGN-A

  1. #91
    Join Date
    Jun 2009
    Location
    St. Louis, MO
    Posts
    896

    Default

    I used encoders in the field, but by the time I was in LA I was wearing too many hats. Choreographer was a full time job.

    One way to do real time editing is to use a computer. Maybe a midi control surface for input. A time code on the sound track.

    One approach to color mod: Start with 5 comparators and build a ladder circuit to convert a discrete analog color mod signal to ILDA RGB converter. Build a ladder voltage divider with -15V 13K - 1k 1k 1k - 1k 13k - +15V.
    Connect the nodes of the 1k resistors to the inputs of the comparators so they trigger on -2V, -1V, 0V, 1V, and 2V. This allows the signal in the -2 to -1V range to be defined as red, -1V to 0 as yellow, 0 to 1 as green, 1 to 2 as blue and >2 as black. Put an inverter on each output and connect the output of the inverter to one input of a NOR gate. Connect the other input of the NOR gate to the next higher voltage (non-inverted!) comparator output. This shuts off the red signal when the yellow triggers etc. The black comparator shuts off the Blue when the signal goes above 2 volts. Black is an important part of the color modulation effect. Then take the red, yellow, green, & blue signals from the outputs of the NOR gates to build your RGB output signals.
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

  2. #92
    Join Date
    Mar 2010
    Posts
    246

    Default

    What a great idea. The graphic shows what I think has been described, but a recommended approach to the NOR gates would be helpful. I have HD74LS02 NOR gates which operate 0 to +5V. The square waves from the comparators are +-15V. Should I:

    1) use voltage dividers and summing amps to scale and offset the comparator and inverter outputs for the NOR gates

    2) build +-15V NOR gates using op amps (search didn't provide much info on this)

    3) try to get NOR gates that work at +-15V
    Attached Thumbnails Attached Thumbnails colormod_to_RGB.png  


  3. #93
    Join Date
    Jun 2009
    Location
    St. Louis, MO
    Posts
    896

    Default

    The LM339 comparators have open collector outputs. You choose a pull up resistor appropriate to the logic family you use. I'm sorry, the inverters I mentioned, sometimes called NOT gates. Example 74LS04 hex inverter.
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

  4. #94
    Join Date
    Mar 2010
    Posts
    246

    Default

    I do have 74LS04 hex inverters and LM339 comparators. I'm afraid I'm still a bit confused though. The configuration in the graphic doesn't seem right, with the negative voltages on the inputs of the comparators. Not sure I've understood correctly.
    Attached Thumbnails Attached Thumbnails colormod_to_RGB_2.png  


  5. #95
    Join Date
    Jun 2009
    Location
    St. Louis, MO
    Posts
    896

    Default

    Sorry, you want to run the comparators at +/-15 volts, and pull their outputs up to +5 volts to match your 5V 74LS logic down stream. What we're going for is a whole lot of headroom on the analog input. +/- 2 volts will cover the RYGB output giving RYGBBGYR with no black at all. When you turn the gain up getting +/-10 volts input to the comparators you get a lot of black and small patches of color. B--------L--------A--------C--------K-RYGB-B--------L--------A--------C--------K-BGYR.
    Last edited by laserist; 04-21-2021 at 11:54.
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

  6. #96
    Join Date
    Jun 2009
    Location
    St. Louis, MO
    Posts
    896

    Default

    Sorry I'm stupid. We'll have to run the comparators +15 and ground, or do something clever that I haven't thought of yet. Common cathode doesn't accomplish what I wanted when the "cathode" is at -15V Oh well, we needed to be able to offset the input signal in any case.
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

  7. #97
    Join Date
    Jun 2009
    Location
    St. Louis, MO
    Posts
    896

    Default

    I think a opto-isolator per comparator would salvage the bipolar design.
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

  8. #98
    Join Date
    Mar 2010
    Posts
    246

    Default

    Not a good solution, but the resistor network shown in the graphic is triggering the inverter. Unfortunately I only have 4 opto-isolators, and nothing much else I need to order at present, but that should be enough to see it working soon.
    Attached Thumbnails Attached Thumbnails colormod_inverter_demo.jpg  

    colormod_to_RGB_3.png  


  9. #99
    Join Date
    Mar 2010
    Posts
    246

    Default

    Maybe I could do something with a germanium diode to limit negative excursion and a 5.1V Zener for the other limit.

  10. #100
    Join Date
    Jun 2009
    Location
    St. Louis, MO
    Posts
    896

    Default

    Just connect a 30K resistor between the output of the comparator and the 10K pull up resistor. The 30K resistor will act with the 10K as a voltage divider and give you a virtual ground when the comparator is low.
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •