According to the spec it uses the touchscreen, or at least some touchscreens:

>On-screen detection: Touch digitizer reports the onscreen location through a capacitive pattern (Studio only)

https://www.microsoft.com/en-us/p/surface-dial/925r551sktgn?...

Right, to sense location, not rotation. Rotation goes through Bluetooth, as with any number of existing knob controllers.

Funny, I have a whole sketch for this. Well the cat is out of the bag, we might as well complete this to prevent any patents.

I envision using cam levered suction cups to hold on rotary and linear sliders that had touch screen sensitive rubber tips. One could go as far to 3d print arbitrary interaction devices that could get attached to the face of the touch screen. You can use the multitouch sensor w/o the screen but still be able to configure arbitrary devices to go on the front.

I even had a design for joystick. Lots of analog opportunities when you have something like a back illuminated camera or a touch controller that can sense areas. You could also serially transfer data from the device to the touch screen, either using physical touches or electrically simulated touches.

Yep, any number of other controls besides knobs would work under the same basic principle. A linear slider control would be an obvious one, as would calculator-style membrane buttons.

I'd be surprised if the concept weren't already patented, though, just because the idea of a generalized capacitive control surface seems fairly obvious, and the patent office doesn't really apply an "obviousness" test. What definitely surprises me is that, patented or not, I can't just go out and buy these sorts of controls.

These are great ideas! Tbh I think that much of the reason that these don't exist is the configurability of software UIs - these controls in Linux/ Windows/ OSX would need to be specifically programmed for by the programmer, rather than say in Squeak by the users. Breaking down that user/ programmer barrier is key I think.

What if the metal base of the rotatable knob has a certain rotationaly asymmetric pattern instead of being completely flat?

We would then be able to receive that pattern and understand how the knob is rotated.

What’s the resolution of todays touchscreen?

It's an interesting thought. You'd want to use a full bandwidth data channel (e.g. Bluetooth) for anything complicated.

But for simple things, if possible without affecting the other parts of the screen, it'd be amazing to have a broadly supported, low bandwidth standard.

I can't really make sense of the bandwidth (information rate) of a tactile interface. A measure in units of length would make more sense to me.

Any digital control signal effectively has a minimum bandwidth.

This might be as simple as "Here's my encoded position * frequency of sampling", but for a general interface you'd want something adaptable.

What if there were two dials on the control? Two dials and three buttons? One dial, four buttons, and a joystick?

It's enough for knobs of 1 inch spacing or wider, no easy support for fancy geared knobs that coaxially have a rough setting and a fine adjustment.