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Thread: VCA with offset circuit for x-y?

  1. #1
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    Default VCA with offset circuit for x-y?

    Hi, I'm currently working on adding more dmx control to my projector.

    I'm looking for a voltage controlled amplifier circuit with bias (offset) so i can use a propeller output to set size and position.

    BA6110 looks to be promising, but have anyone tried something like this?

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    Quote Originally Posted by Tormod View Post
    Hi, I'm currently working on adding more dmx control to my projector.

    I'm looking for a voltage controlled amplifier circuit with bias (offset) so i can use a propeller output to set size and position.

    BA6110 looks to be promising, but have anyone tried something like this?
    Back in the day we used AD532s, but boy they've gotten expensive...

  3. #3
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    Hmm, I would probably look to a digitally controlled potentiometer chip instead of a DAC.
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  4. #4
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    Quote Originally Posted by dave View Post
    Hmm, I would probably look to a digitally controlled potentiometer chip instead of a DAC.
    I'd avoid transconductance VCA circuits like the plague. LM13700, CA3880, all that stuff is obsolete, heck most makers of matched pairs and matched quads are dropping the products. Part of the problem is chip makers are dropping the old wafer sizes and analog processes used for the traditional transconductance circuits.

    Multiplying D to A converters and digital potentiometers are common and cheap these days. Since you are interfacing to DMX or MIDI, you might as well stay in the digital control domain. AD and TI make nice digital gain/loss chips, one email or live chat l to the duty application engineer will probably result in your finding a "jellybean" part that is easy to use, with a SPI, Microwire, or parallel interface.

    Two weeks ago I was looking at 1024 step digital potentiometers in both log and linear at Digikey for 2$, some of them had something like 64 steps of log and 256 steps of linear in series, giving you a huge possible range.

    Steve

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    I agree, if you are confortable with digital use that otherwise I recomend analog parts from THAT, they have the old DBX ICs and newer/improved more advanced stuff, all the matched transistors and VCA,s you can use!
    http://www.thatcorp.com/
    (you can even use their specialized IC fabrication processes for custom work if you have the $$$!)

  6. #6
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    Thanks :-)

    Digital potentiometers is the way I'm going for. Cheap and easy to use. And as DMX is my control source 256 steps linear is sufficient. Maxim DS1267 is added to my order list. All i need now is some analog multiplexers for inverting x/y and color mapping.

  7. #7
    mixedgas's Avatar
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    I forgot about THAT Corp, really good stuff.

    Steve

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    Quote Originally Posted by mixedgas View Post
    I forgot about THAT Corp, really good stuff.

    Steve
    My big beef with Maxim is that a lot of their useful parts (to me anyways) are DFNs/QFNs, not exactly the most hobbyist/breadboard friendly. They are really generous with samples though!

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