Yep - Bela is specifically designed for this (it’s come out of a music+technology research programme); it has lots more ADCs/DACs built-in than the Teensys (which are just exposing the ones built into the MCUs), and most importantly they’re higher resolution - sixteen bits rather than twelve. What I can’t remember off the top of my head is the voltage range on them - I’d imagine it’s 0-3.3V, and possibly 0-5V, but no more. As ever: offset/scaling is possible with extra components.
I assume that Monome will give some specific Norns-Crow interface that does the I2C talking for you?
Yeah - given it’s an official solution, and the things we’ve seen about Norns’ design and assumptions I’d imagine there will be a wrapper API inside Norns that means you just write crow-specific commands - I2C is lower level than a lot of the (Lua-side) scripting in Norns exposes.
how hard is it to just have a eurorack module just sitting on a desktop? It seems like even the standalone power supplies for eurorack gear are kind of expensive ($80 range)?
It’s not impossible. There are cheaper PSUs available, that don’t spit out much current, but might be enough. The only reason people leap to Eurorack is that it’s where a lot of the digital->CV work is going on right now owing to the increasing popularity of the format. (Eg: RT just making Salt a product). I think you’re right that it’s probably not worth it for just a CV solution.
Although Bela doesn’t have a screen - it really is just a development board - it’s possible to add one. Because the Beaglebone Black it sits atop is running Linux, you’re effectively just SSHing into it to write or upload code in your format of choice - Puredata is popular, as well as Supercollider or lower-level code. I guess it depends what you want a screen for - as an interface to the finished thing, or a developer tool. The Beaglebone Black almost certainly supports SPI or I2C, making many of the popular OLED screens that firms like Adafruit can sell viable, providing you can just write an interface to them. (Norns uses an I2C screen that it addresses as a Linux screenbuffer, I believe).
Each of the off-the-shelf solutions is taking a different perspective: despite the technologies involved, Norns’ main designed focus is the higher-level end - scripting and interacting with existing engines. Bela is focusing on being a dev board or engine for other instruments, in particular things with low latency and lots of ADC/DAC requirements; PiSound is emphasising the openness/scope of the Raspberry Pi platform; Expert Sleepers are focusing on the Eurorack community; each of them is a different set of assumptions and, of course, compromises. If you’re working on a lower level solution, at some point you probably end up doing more outboard electronics: either to amplify, or scale/offset, or to add controller inputs or, say, DACs to a chip that doesn’t have enough, or enough at high enough resolution.
I’m also aware - though haven’t said it explicitly yet - that when I say “you could just whack an SPI screen on a Bela and some knobs and off you go!” I’m assuming a variety of things around electronic competency and/or enthusiasm - or desires to spend time plumbing rather than programming, or available time, and those are all actually factors that inform decisions, and the compromises we choose to make.