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

Is it reasonable to wait for the next step the usage of neural network with feedback ("learning")?

We are all waiting for great sounds!

"Is it reasonable to wait for the next step the usage of neural network with feedback ("learning")?"  - ILYA

Probably not on my watch.  And I don't think there are enough presets, statistically speaking, to have a NN generalize about what's going on in them.  Though one user ran the preset screens by ChatGPT to see what it thought of them, and it started hallucinating knobs.

Light Fixture

Back down in the lead mines, soldering away, 12 main boards are complete but untested.  Finally broke down and made a fixture for the tuner, just a handful of 470 Ohm resistors and a connector on a small proto-board:

This lets me check the LEDs for even brightness and blemishes and stuff before soldering.  No problem this time with the blue ones, but 24 out of 144 of the white ones had either casting voids or deep leads marks from jumbling around in the bag together during shipment, which is a 1/7 reject ratio.

With it I was able to finish 12 display boards.  I did the driver boards yesterday, here they are assembled together:

Also almost got through 24 AFEs today, but had to make a Digi-Key order for more 3.3V regulators and 4.7uF tantalums.

Nice looking tech porn. 

Light FixtureBack down in the lead mines, soldering away, 12 main boards are complete but untested.  Finally broke down and made a fixture for the tuner, just a handful of 470 Ohm resistors and a connector on a small proto-board:This lets me check the LEDs for even brightness and blemishes and stuff before soldering.  No problem this time with the blue ones, but 24 out of 144 of the white ones had either casting voids or deep leads marks from jumbling around in the bag together during shipment, which is a 1/7 reject ratio.With it I was able to finish 12 display boards.  I did the driver boards yesterday, here they are assembled together:Also almost got through 24 AFEs today, but had to make a Digi-Key order for more 3.3V regulators and 4.7uF tantalums.

Super excited to see more DLevs in production!

Coil Dope

Yesterday I wound 10x 1mH pitch coils but ran out of 30AWG so ordered some more.  Then wound 12x 2 mH volume coils with plenty of 32AWG to spare.  Put the wire-wrap leads and heatshrink tubing on today:

For larger orders from China I'm having to pay customs import duties now, which is new, and DHL's automated system is a pain (refused two different credit cards, no reason given, finally got a call-back from a human).  For the parts I buy there's no way to tell ahead of time how much the tax will be, or even the threshold at which it may or may not kick in, so it's a bit of a nail-biter.  I'm starting to wonder if the recent bout of inflation is just trade wars and profit taking.

Yesterday I wound 10x 1mH pitch coils but ran out of 30AWG so ordered some more.  Then wound 12x 2 mH volume coils with plenty of 32AWG to spare.  Put the wire-wrap leads and heatshrink tubing on today:

Looking very nice.
Eric, are you using some winding device? Could you please share a photo / link here?

What is used for the coil frame?

For larger orders from China I'm having to pay customs import duties now, which is new, and DHL's automated system is a pain (refused two different credit cards, no reason given, finally got a call-back from a human).  For the parts I buy there's no way to tell ahead of time how much the tax will be, or even the threshold at which it may or may not kick in, so it's a bit of a nail-biter.  I'm starting to wonder if the recent bout of inflation is just trade wars and profit taking.

I've faced the same issues after moving to Portugal. Everything above EUR 20 is a subject for VAT. If price is more than 100 of 200 EUR may be taxed additionally.

"Eric, are you using some winding device? Could you please share a photo / link here?"  - Buggins

It's the same simple winder I've been using since the beginning of the project.  Here it is winding a dual coil, which I thought was a good idea at the time:

The wire comes off the spool in the background, under the coil, under the copper pipe in the front, then up to the coil.  This way I can use my left index finger to keep the turns tight as I turn the crank with my right hand.  There's no way I'd want to motorize this without somehow automating the wire guiding too, just too finicky.

"What is used for the coil frame?"

It's "1-1/2 in. x 12 in. White Plastic Flanged Strainer Sink Drain Tailpiece Extension Tube":

The above is polypropylene, which is all the local hardware store stocks lately.  It's 300mm long, if it were just a few mm longer I'd be able to get more parts out of it and generate less waste.

The above is a "solvent weld" type made of ABS, which is more rigid and much smoother, and so makes for better coil winding, but I can't get them anymore.  They were less expensive as well.  ABS has a bit higher dielectric constant than polypropylene (1.9 vs. 1.6) but the thin wall in both cases here likely makes that rather moot, structural integrity is perhaps more important to control drift.

BTW, what is better for coil frame, higher dielectric constant or lower?
How does it affect coil Q?

"BTW, what is better for coil frame, higher dielectric constant or lower?"  - Buggins

Lower is better, though once you pick a plastic or phenolic or cardboard or something, I believe much of this is in diminishing returns territory.

"How does it affect coil Q?"

It's a self capacitance thing - which appears in parallel with the winding so it lowers SRF.

"I've faced the same issues after moving to Portugal. Everything above EUR 20 is a subject for VAT. If price is more than 100 of 200 EUR may be taxed additionally."

Yeah, I probably shouldn't complain, most of the world's borders are pretty crazy for importing.  It seems they just keep getting crazier though, and it's a small world.