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  1. #16
    Prolific Poster hadv215's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    Actually the digipot will be used as a source for a control voltage for a monophonic synth.
    The idea is based on an aritcle I read in Nuts and Volts, the author uses a R/2R DAC but I am not happy with the quality (even using matched 1% resistors).
    The source of all this is a MIDI keyboard I had lying around.
    The uc picks up the note information and converts it to a digital value to be fed into the digipot.
    The synth by the way is the ominous Gakken SX150 Mark II.
    I would love to see you build a synth from a PIC24.

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  3. #17
    Prolific Poster charliecoultas's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    Hadv: have you seen any references to building a Theremin using a PIC (preferably a PIC24)?

    I built a true analogue Theremin using un-locked oscillators but I am sure there is a modern shortcut around somewhere.

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  5. #18
    Prolific Poster hadv215's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    No, I have only seen analogue versions. But I would not be surprised if someone came up with something.
    After all, you only need 2 ADC's and some oscillating software.
    By the way, the author of the Nuts and Volts article describes the possibilities of the Gakken synth as mostly theremin. I don't really agree because it has no volume control, but the sound is definitely weird.

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  7. #19
    Prolific Poster charliecoultas's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    Just looked it up online and it's a pretty basic tone generator with bells and whistles. It's the hand-proximity that gives the Theremin its appeal for me. If I get time, I'll look into capacitive sensing of the human hand and generating an audio tone (logarithmic or whatever) using a P24. Plus volume of course, from the other hand.

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  9. #20
    Prolific Poster hadv215's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    The biggest problem for a theremin is, as far as I can see, the sensitivity of the antennas.
    I've been experimenting with cap sense in Pic devices, but I don't think they are sensitive enough.
    Maybe abusing an anolog input can do the trick, I will do some experiments in the near future.

    Oscillating should pose no problem, I've been searching the web and there is a plethora of vco circuits, including the famous cem3340 that is used by a number of commercial synths. This chip is still for sale! https://www.thonk.co.uk/shop/curtis-...0-ic-vco-chip/

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  11. #21
    Prolific Poster charliecoultas's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    Hmm, that chip looks like a good starting point. I am currently doing a project for the National Museum of Computing at Bletchley Park, and I can't allow myself to be distracted. But a digital Theremin is so tempting.....

    I did wonder about the "gesture sensing" chips that are around; they can track hand movements in excess of the range of a conventional Theremin.
    Last edited by charliecoultas; 8th March 2019 at 17:52.

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  13. #22
    Prolific Poster hadv215's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    Your remark about gesture sensing made me search for them.
    I found the ADPS-9960 and ordered 2 of them.
    Will start experimenting as soon as they are here & will keep you informed.

    Regards
    Harm

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  15. #23
    Prolific Poster charliecoultas's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    Now that sounds very interesting! You might be on the verge of inventing the Harmomin.

    Please keep me informed. Trouble is I'm travelling abroad from the end of March for two months but my wife
    is taking her mini-iPad so I should be able to stay in touch.

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  17. #24
    Prolific Poster John Drew's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    Is this when you are visiting Oz, Charlie?
    John

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  19. #25
    Prolific Poster charliecoultas's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    It is John. We fly to Perth on 7 April, India Pacific Railway from Perth to Adelaide on 14/15/16 April, Adelaide to Melbourne 17 April, Melbourne to Sydney 21 April, Sydney to Cook Islands 26 April.

    When I suggested we have a beer together I hadn't realised what vast distances were involved. I'd love to meet up but I will take advice from you.

    Charlie

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  21. #26
    Prolific Poster hadv215's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    Dropped the APDS for the moment (pretty complex and I get the impression that the distance is too short) and picked up a HC-SR04 sensor. This works easy up to 60 cm (and more, but that would be not very useful for a theremin-like instrument).
    The reading is lineair, so conversion to a pitch and a volume should not be that hard.

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  23. #27
    Prolific Poster charliecoultas's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    60cm is about two feet in old money. I would be happy with that range on a theremin-type device.
    Why do you think otherwise?

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  25. #28
    Prolific Poster hadv215's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    I don't think otherwise (though the HCSR04 goes up to 4m = 13 feet but my arms are not that long).

    I have developed the circuit. It contains a 16F88, 16F689 (both selected for no other reason than that I have both), two MCP41010 (1 for the VCO, 1 for the output volume) a and 4046-based VCO that will run from approx 50 Hz to 16 kHz.

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  27. #29
    Fanatical Contributor top204's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    Did you ever see my article I wrote, far too long ago? It was creating an ultrasonic range finder with a few components. I then went on to the commercially available units back then, which is now the HCSR04.

    http://www.protonbasic.co.uk/content...-Range-Finding

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  29. #30
    Prolific Poster hadv215's Avatar
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    Default Re: mcp41*** Microchip Digital Pot

    No, I never read that article. Nice to see it though. Basically the underlying principle is the same.
    Thanks
    Harm

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