Can a Eurorack analog-sounding audio volt per octave VCO be built using an RP2040 MCU and AD9833 breakout board?

Yep....see the blog post:

https://audiodiwhy.blogspot.com/2023/03/ad9833-voltoctave-vco-new-jacks-n-pots.html

it's a somewhat complex project: a standard volt per octave control signal (0-10V) sets the pitch of the VCO (tested accurate from LFO frequencies to at least 7 octaves).

The digitized version of this CV is sent to a lookup table in an RP2040 MCU, which in turn sends the appropriate frequency, accurate to 3 cents, to an AD9833 function generator IC.

Finally the AD9833's audio output is buffered and converted via analog circuitry to the standard waveforms found an an analog audio VCO.

It provides standard ramp, triangle, and pulse; the pulse output has pulse width modulation; there is also an input for frequency modulation.

The project uses embedded C, not Arduino sketch, but fortunately uploading the firmware to the MCU is easy. You can copy the uf2 firmware found on github to the RP2040 processor--that means no toolchain or embedded C knowledge needed--the file is good to go, drag and drop it to a SEEED XAIO 2040 mcu.

You can get Embedded C code, gerbers, pcbs and pdf using the links in the repos mentioned below.

Note: the project requires 4 PCBs: a front panel (fabricate this PCB with black soldermask and white silk), a board for the jacks and pots, a waveform conversion board, and a buffer board for the MCU and A/D conversion. You will need all 4 to make the VCO work.

Overall i compared this digital VCO against several analog audio volt per octave oscillators I have in my rack (13700 based; 3340 based; discreet triangle core based), for a digital VCO it sounds to my ears "analog"; accurately tracking the volt per octave control signal over a very wide range.