Eurorack Knob Idea

Tangential idea, but I've wondered if it would be possible to make synthesizers a lot cheaper by only having a couple rotary encoders. You could have hundreds of parameters on the panel, but each parameter would just be a neopixel LED and button. You could link the rotary encoder with a parameter by pressing it and the parameters' button at the same time. Certainly not as nice as a dedicated knob for each, but you'd also get an interface that is ~$40 instead of ~$600...

There are loads of systems where every button and encoder has many functions, with modal or paged interfaces. But I'm trying to stick to a model of no hidden or ephemeral state with my modular, just for fun, I guess. Mostly analogue, so no non-volatile memory to store settings, the positions of the patches and knobs set everything, and the test is that if I power it down and back up it must come back doing what it was doing when the power went out (very long cycle lfos notwithstanding!)

When a laptop can simulate anything, the physicality of the interface is most of the attraction, so might as well go all the way...

The physical interface is an intrinsic part of the design of any eurorack module, including artistic elements. If you actually use these, then you quickly tire of menu diving for simple options, and only modules that do very particular things make it worth the bother. For everything else, the layout must be accessible, memorable, understandable, and not too crowded. And it helps if the visual of the thing conjures up memories of how it sounds or what it does.

For sure! The interface is the most important part these days when practically everything can be emulated.

In my design, I wouldn't say the state is hidden though—that's the point of having an indicator light with every parameter. The LED becomes the state visualization. So, write-wise, yes, it's overloaded, but read-wise it's not.

I'm just now realizing I didn't explain that well in the OP, lol. And really this is more of a budget-friendly approach, rather than a user-friendly approach. I'm trying to meet those half way...

There was a trend in 80s synthesizers along these lines: Yamaha DX7, Ensoniq Mirage, etc.

They were famously hard to program. The DX7 in particular is known for basically being a preset machine because almost no one could figure out how to build patches with it.

Muscle memory is really important and it's hard for users to build a mental model of the internal architecture if the external architecture doesn't reflect it at all.

If you had a little silkscreened circle around each parameter's LED, and a Hall effect sensor underneath, you could even make a passive magnetic knob that you could use to adjust parameters by simply placing it on top of them and twisting. It wouldn't feel great due to the complete lack of resistance but it's a fun idea :)