Let's Design and Build a (mostly) Digital Theremin!

DIY Capacitor

Len Sherman cleverly used a twisted pair of wires for the series capacitor in the AFE C divider in his D-Lev build: https://lensprojects.com/2024/11/20/building-a-d-lev-digital-theremin/.  This was in parallel with the jumpered PCB pads, which total 2pF.  Len just trimmed the length until the sense voltage was within bounds of the AFE supply voltage of 3.3V and ground, minus some margin.

I was curious as to the approximate value of this capacitor, so I got some solid Radio Shack wire and twisted my own.  Len's cap looks to have 16 or so turns, and I have no idea of the wire gauge he used, just eyeballing things here.

Above: Measuring the twisted wire cap with my handy dandy LCR meter.

So, 5.7pF or so, in parallel with 2pF gives 7.7pF.  The bottom end of the C divider is 100pF.  Coil drive is 2.5Vpp, and the C divider voltage is similarly around 2.5Vpp, so the Q works out to 107.7pF / 7.7pF = 14, which seems kinda low.  The kits ship with the ratio set to 101.5pF / 1.5pF = 67, which also seems on the low side for a coil Q of over 100 when presented with typical antenna C.  The divider isn't perfect, and there's lots of stray field and stray C stuff going on, so these aren't definitive calculations by any means, though they probably suffice for rough comparison purposes.

Hey folks
Sorry for this OT, ...about winding coils, have you ever thought to make HoneyComb coils instead air coils? those are not available anymore by JW miller, but i wonder to myself if it works for this kind od theremin...thank you.
In web there are some projects to make the tiny machine to make the coils

"...about winding coils, have you ever thought to make HoneyComb coils instead air coils? those are not available anymore by JW miller, but i wonder to myself if it works for this kind od theremin...thank you."  - robonil

They do indeed work for this kind of Theremin.  Pi-wound on powdered iron or ferrite can have good Q.  But miniaturization unfortunately brings with it temperature dependence and drift.  There may be a way to make OK pi-wound air core inductors, but I don't know how and can't find any equations to help.  My own experiments in this direction yielded coils with lower Q than equivalent single layer solenoids.  Litz wire would probably help, but that's expensive and fiddly.

But miniaturization unfortunately brings with it temperature dependence and drift. - dewster

This may be right für the ferrit or iron core? But I suppose that the competition between the larger selenoid air coils and the air-core pi-wound coils has not yet been won.
It's a good task to figure out what's really relevant for the theremin construction. 

- Cross windings causes lower proximity effect and make the geometry more stable.
- A selenoid can inflate slightly or become more oval in diameter - the forces to avoid this are weaker. 
I have not found any scientific or technical results on this. We should continue to test it in practice.   

Volumetric Constrained Printing

I ran across this video in my YouTube "feed": https://www.youtube.com/watch?v=WgXM2zPusXo

Following its advice I switched from the stock 0.4mm nozzle to a 0.6mm nozzle, and am now using the Arachne perimeter generator in the Prusa slicer.

Also ran across this Reddit post: https://www.reddit.com/r/3Dprinting/comments/13ynxg0/finally_made_sense_of_the_prusa_slicer_autospeed/

Following its advice I set most speeds to their default settings (to be calculated by the slicer) and set "Max volumetric speed" to 8mm^3/sec.

With the 0.4mm nozzle I was printing 70mm diameter Theremin coils with 4 walls, or 1.6mm total, which required an internal stiffener.  Four walls with the 0.6mm nozzle gives 2.4mm total, which is considerably stiffer and may not need extra help in that department.  The volume coil takes about 2.5 hours to print now, which is totally acceptable IMO, particularly for this key operational component.

3D printing has too much art and insufficient science.

Site Maintenance

The D-Lev web site hosting was coming up for renewal in March.  The current host (iPage) wanted $615 for 3 years, plus $26 per year for the domain.  That's $693 for three years, or $231 per year, which struck me as outrageous for a simple static "presence" type web site.  

IONOS had a Black Friday sale of $174 for three years including domain fees, or $58 per year.  I signed up via their web page but hours later I got an email stating that the order was denied.  I spent hours on the phone with support, with them talking vaguely and alarmingly of fraud, and refusing to elaborate or escalate the issue.  Days later IONOS called and apologized about cancelling the order (it was overzealous security on their end) and offered me a discount to try again.  I told them I took the advice of two of their support staff (!) and looked elsewhere for hosting - that felt kinda good after what they put me through.

Hostinger also had a Black Friday sale, and I was able to score four years + 3 months of hosting for $85.  The domain is free for the first year, and $20 per year after that.  Switching the domain registration to Hostinger was an additional $10 (watch out for those hidden fees!).  So a total of $155 for over four years, or $39 per year.

I must say (for what it's worth) you can get someone on the blower pretty quickly at IONOS.  You really can't at Hostinger, though the AI assistant isn't terrible (as these things go) and my text chat with a human rep resolved a couple of small issues and answered some questions with the account.

Domain registration is transparent to you and those who visit your site, and your host probably doesn't care one way or the other, so it's less of a technical or aesthetic issue to bargain shop for.  Cloudflare Registrar has significantly better domain pricing, and I may switch to them once the free period on Hostinger runs out.

This blog post is rather relevant: https://den.dev/blog/be-a-property-owner-not-a-renter-on-the-internet/

Hey everybody! I've started work on collecting information and a parts list for making my own D-Lev, but the size of the task has started to become very daunting, especially considering my relative lack of electrical engineering experience.

Right now I have pretty exclusively used D-Lev.com has my primary resource, but as I have come to find out it seems to be more for kit-builders or existing owners. I'm aware this *very long* forum post likely has everything I would ever need and more, but 3486 posts over 13 years is a lot to go through. Is there any holy grail of resources I'm missing? I would really love to continue work on this project as it seems like it would be very fulfilling for me once I get a good start. 

Thanks to anyone who takes notice, and let me know if I should make a separate post for continuing this!

"Hey everybody! I've started work on collecting information and a parts list for making my own D-Lev, but the size of the task has started to become very daunting, especially considering my relative lack of electrical engineering experience." - Rocklost

What's you level of electronics experience?  The D-Lev isn't super complex in terms of external circuitry, but I wouldn't recommend it as a first project.

"Is there any holy grail of resources I'm missing?"

Well, I'd highly recommend you build something as close to the kit as possible for your first go.  It's not that there's anything super exotic to the design, but it's a known quantity, and there are a thousand ways to die in this biz.  Get some PCBs made from the gerbers in the KiCAD zip file, and there's also a file in there named "pcb_stuffing_instructions.pdf" which helps you stuff the PCBs with the components.

If you have any specific questions you can contact me via email, it's in my TW sig and also on the D-Lev web site.  And I'm always open to a Zoom or similar video chat session too with any folks who are interested in the project.

Where are you located?

Thanks for responding!

While I don't have much practical experience in circuitry I am very well versed in software/computers (and with it some basic circuitry know-how), so I feel I'll be able to get the hang of the circuitry considering the extensive documentation (thank you!). Of all the files I combed through I happened *not* to stumble across the PCB stuffing instructions, which was causing me much confusion trying to match links to parts on the parts list spreadsheet, so that will definitely help.

I'm not able to put my location and further info on my profile quite yet due to spam protection, but I'm located in Portland Oregon, USA, so shipping shouldn't be too different from NJ. I'm currently in the process of taking your parts list spreadsheet and converting them to 2025 prices and links (including tariffs), I would be delighted if you could take a look at it after I finish my first pass. 

I would love to schedule a video chat once I get my shopping list sorted before I start on the build, I really appreciate your willingness to help!