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

If only one switch out of the 8x3=24 is closed, you can manipulate the bottom 8 open drain/collector leads to find out which one it is, and then use an inactivity timer to know when to do another search.  So turning an encoder quickly would retain the focus on it (with velocity calcs and such), turning it very slowly might trigger a search at each detent (where you don't care about velocity), and with no activity there would be no active searching going on to cause noise.

Ok. If no encoder wheel switches are ON in neutral wheel position (corresponding to one of 12 or 24 ticks) then of course it should work w/o diodes.

For the techno-curious, I finally got around to updating the design document for my Hive processor

Thank you! I'm techno-curious. Very interesting reading.

"Thank you! I'm techno-curious. Very interesting reading."  - Buggins

Great!  I gave it final comb-thorough edit this morning: https://d-lev.com/support/Hive_Design_2022-10-24.pdf

I need to write a few more papers:
1. Creating an assembly language, assembler, and simulator.
2. Creating int and float math packages.
3. Designing a digital Theremin.

FPGA Boards (aye, there's the rub)

Still poking around, looking for FPGA boards / replacements.

This is the FPGA board the first 20 kits used: https://smile.amazon.com/gp/product/B08BLFK7C2
You can still find them here and there, most want like $250USD which is like 10x what they cost a year ago.  I found some for around $90, not sure if they're real or not.

I could probably use this: https://www.amazon.com/dp/B09FY2QBXX
But no 3.3V at the headers, and it looks like those headers can't utilize a single female socket per side due to the weird spacing between them.  Odd configurator too.

This one is amazing: https://www.aliexpress.us/item/2251832762966437.html
Inexpensive, large FPGA, nice memory, sane pin breakout.  But all three voltage regulators are of the switching variety (which might interfere with the fields?), the configurator seems non-standard (non-Altera), and only qty 15 are available.

This one is similar: https://www.aliexpress.us/item/2251832626667349.html
Same pros and cons as above, but the breakout headers are soldered to the wrong side, which makes it unusable.  190 pcs available though.

This one has the smaller D-Lev FPGA: https://www.aliexpress.us/item/2251832626066661.html
Pins on wrong side, and I don't think I could utilize the DRAM.

A more compact offering: https://www.aliexpress.us/item/3256803924610412.html
But the D-Lev sized FPGA can't use the DRAM.

This one is the closest I've found to the D-Lev board: https://www.aliexpress.us/item/3256804512902832.html
Pictures show pins both on the top and on the bottom, which is scary (what if they ship the wrong ones?).  Plenty of inventory though, and I think I could buy it for less.

This one is very close too: https://www.ebay.com/itm/133952851480
But only qty 2 available.

There are a million of these: https://www.ebay.com/itm/123896865981
But pins are on the wrong side, and the square grouping could be problematic.

These are pretty and many offer it: https://www.ebay.com/itm/125040684205
A little pricey though, and it doesn't look like 3.3V is available at the headers.

Interesting Xilinx offering: https://www.aliexpress.us/item/3256802705341392.html
But again with the switching regulators.

I've been between two worlds on this issue for way too long.  On one hand I'd like to make more of the original design, on the other I'd like to have more resources for development.  But larger FPGAs draw more power, and the original design is right at the official USB limit.  And supply chains aren't helping, though perhaps they're easing up a bit.

Very sad list. I want back in the past by 2-3 years, with everything in stock, 2-3 times cheaper than current out of stock.

Are you sure on-boards regulators may cause issues with theremin sensors?
Is there some kind of regulators which does not introduce noise?

Do you really consider switching to Xilinx world from Altera?

"Are you sure on-boards regulators may cause issues with theremin sensors?"  - Buggins

I really don't have a clue, but it's hard to check this sort of stuff out in a rigorous manner, and it seems a little like asking for trouble.

"Is there some kind of regulators which does not introduce noise?"

I feel safer with the linear ones.  And an emissions guy who contacted me said switching regulators were tough to pass compliance testing.

"Do you really consider switching to Xilinx world from Altera?"

No, not quite yet.  Though kinda hard to know where anything is going.  I don't have anything against Xilinx.

And an emissions guy who contacted me said switching regulators were tough to pass compliance testing.

Did someone measure emission from Theremin?
Isn't theremin with 1000Vpp on antenna a good transmitter which will never pass compliance testing?

"Did someone measure emission from Theremin?"  - Buggins

Yes, he somewhat informally tested his Claravox, though an anechoic chamber and other professional instrumentation was involved.

"Isn't theremin with 1000Vpp on antenna a good transmitter which will never pass compliance testing?"

The gist of it is radiated emissions testing starts at 30MHz, so if the antenna waveforms are sinusoid, and if the field is electrostatic, very little energy will be radiated.  The Cvox passed with flying colors here.  He also told me that Theremins are in the unintentional radiator category, something that was confusing me. 

Evidently compliance testing can be something you do and certify all by yourself, though if called on it by regulatory authorities you have to show your work, and it better be good.  He said that keeping things on one PCB is best because interconnect radiates, and that the PCB be at least 4 layers with an internal ground plane, preferably a sandwich of ground planes.  ESD diodes on all I/O, capacitors too if possible.  Common mode chokes on power leads.  All of these things are good electrical practice anyway.  He really de-mystified a lot of stuff for me, and I really appreciated it!

Trumpet Mute 2

I'm re-reading a university course PDF that I snagged from somewhere: "The Physics of Music: Brass Instruments" by James Bernhard.  In it he states: "Harmon mutes have open pipes in the center with resonances at around 1500 Hz, 3000 Hz, and 4500 Hz."  The hot linked samples in the paper track back to Joe Wolfe's UNSW web page: http://www.phys.unsw.edu.au/jw/ which, among other things, is a goldmine of music physics, and related in a highly approachable way.  Here is his page for brass "lip reed" instruments: http://www.phys.unsw.edu.au/jw/brassacoustics.html - a triumph of substance over style (give me the old web back!).

Anyway, I took my old muted trumpet preset and changed the mute formants to those listed in the paper.  Previously there were 6 located at 1244, 1760, 2489, 3520, 4978, and 7040 Hz.  So it was just a matter of zeroing out three of them and adjusting the remaining ones.  Increasing the resonance of the 1108 Hz oscillator 2nd order high-pass filter also seemed to help the realism.  Finally, I boosted the velocity sense a bit to make it easier to play staccato.

I think it's an improvement: https://d-lev.com/audio/2022-10-27_sweet_mute.mp3

Booyah!

For Halloween, a spooky mix of D-Lev presets exclusively, plus a healthy dose of outboard reverb: https://d-lev.com/audio/2022-10-28_booyah.mp3

Booyah!For Halloween, a spooky mix of D-Lev presets exclusively, plus a healthy dose of outboard reverb: https://d-lev.com/audio/2022-10-28_booyah.mp3

Trumpet sounds nice.

Halloween D-Lev mix is awesome!

P.S: Found EP4CE22 board with interesting form factor on aliexpress. Linear regulators. But this is noname chinese manufacturer (unlike QMTECH which is almost brand).