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

Data Logging

I expanded the D-Lev librarian "stats" command to do automated data analysis and logging to screen and file.  The raw unfiltered 32 bit pitch and volume operating points are read and processed once per second.  The data is filtered via a boxcar moving average of width equal to the logging period, and 2nd order low pass filtered with user selectable cutoff for some extra smoothing.  Running statistics are done on the unfiltered samples: average, standard deviation, and kurtosis.  There is a user selectable start delay so one can move far away from the measurement area and things can calm down physically and capacitively before data collection starts.

Above is my lab unit from cold start to 10 minutes.  Graphing it too much longer would probably just show variation with room temperature and such, I was mainly interested in the start-up drift.

With a sample rate this low, the possibility of serious aliasing rears its ugly head.  But I'll mainly be using this to test the stability of units before they are shipped, and perhaps to help diagnose any field issues.

This was an interesting exercise, I learned a fair amount about statistics, and now have an additional testing tool.

[EDIT] Kurtosis turned out to be rather useless, so it's been replaced by max - min.

[EDIT2] A video showing the logging function in action (skip to 10:00): https://www.youtube.com/watch?v=brEq_eKuyLk

dewster, thank you for all the details, for all the detailed information. For all this unique work.

excellent demonstration of timbres, presets

"dewster, thank you for all the details, for all the detailed information. For all this unique work."  - Martel

You're welcome Martel!  Glad you're finding something of use in all my ramblings.

You create truly high-quality timbres for the theremin. They sound musical, wide, rich.
Your tenacity and enthusiasm are impressive.

(only I don’t understand much about digital devices, I’m more of a musician, not an electronics engineer).

Thank you Martel!  What really helps is the project embraces many of my interests: music, controller ergonomics, processor design, synth design, DSP, capacitance sensing, vocal synthesis, basic physics, etc.  It's really stretched me as an EE and as a lay musician.

"Data logging"

Very interesting. I've been exploring the spot where my right hand is flat and touching the pitch plate and the left hand is away from the volume plate, where the frequencies cross (Octave 7, volume max).

There is a small spot where volume drops of a few dB and frequency is sticky. Nothing of any concern, this point is not easy to reach. I am just wondering if switching AFE boxes to have Pitch Frequency < Volume Frequency should be the default setup for "farther = louder" operation mode. (it would put the cross point in the silent area but could make some noise artefacts appear from silence)

Dewster,
Is the D-Lev kit available for purchase at this time? Sorry if the question is redundant. I'm sure you have been asked many times somewhere in the last 315 pages

"There is a small spot where volume drops of a few dB and frequency is sticky. Nothing of any concern, this point is not easy to reach. I am just wondering if switching AFE boxes to have Pitch Frequency < Volume Frequency should be the default setup for "farther = louder" operation mode. (it would put the cross point in the silent area but could make some noise artefacts appear from silence)"  - Mr_Dham

Yes, swapping the boxes may be best for traditional farther = louder playing.  The DPLL parameters are the same for both so it should work.  If you want to experiment along these lines I'd be interested in your results!

I just posted an improved version of the librarian: https://d-lev.com/support/d-lib_2024-02-16.zip

The initialization now samples at 1Hz which gives a better baseline, all readings go through the boxcar and LPF, the LPF is now single pole, HPF is also displayed, and you can pick which axes to log via the -p and -v flags (the default is both).

"Is the D-Lev kit available for purchase at this time?"  - bisem

I'm finishing up the last 6 kits for a while, and they're pretty much spoken for.  I need to spend more time on R&D, applying the things we've learned from the kits, trying a few new things, redesigning for manufacturability, etc.

"Is the D-Lev kit available for purchase at this time?"  - bisemI'm finishing up the last 6 kits for a while, and they're pretty much spoken for.  I need to spend more time on R&D, applying the things we've learned from the kits, trying a few new things, redesigning for manufacturability, etc.

Thanks for the reply. Can you keep me in mind for a time when they will be available again?