user65894: I understand that some arduinos are capable of presenting themselves as a USB HID device to a PC.
I would like to use one to build a custom input controller that lets me read maybe 8 or so turn knobs that can infinitely turn left and right.
I am new to Arduino, but have cross-compiled avr binaries before.
Which arduino would be a good choice for this? And any additional parts that would help?
The end product would look like a MIDI mix panel, but it shouldn’t talk MIDI, just USB HID (to a linux PC.)
Note: there is an expensive, and out of stock, device that is similar to what I have in mind called MIDI Fighter Twister, pictured below, to get an idea.
 

user64075: Options for the Arduino you have:

Get an Arduino supporting HID drivers (e.g. 32u4 based boards, Due /Zero/ Arduino Leonardo/ Micro or Pro Micro/ M0)
You use this library it supports UNO/MEGA/Leonardo/(Pro)Micro/ any 8u2/16u2/at90usb8/162/32u2/32u4 compatible boards and some more

Then you have to "just" code the communication between your programm and the HID driver -> pretty standard serial/usb stuff.
The parts (knobs) you seek could be rotary encoders, which have no fixed zero point, endless rotation and need 2 input pins per encoder (except GND or optional push function). The signals a rotary encoder produces (and what can be handled by libraries) are based on a 2-bit gray code available on 2 digital data signal lines. 
So when choosing whatever Arduino make sure you have enough (usable) I/O ports for the number of encoders and possible additional parts (status led/s or similar, I2C LCD display)

65894: <p>I understand that some arduinos are capable of presenting themselves as a <a href="https://en.wikipedia.org/wiki/USB_human_interface_device_class" rel="nofollow noreferrer">USB HID</a> device to a PC.</p>

<p>I would like to use one to build a custom input controller that lets me read maybe 8 or so turn knobs that can infinitely turn left and right.</p>

<p>I am new to Arduino, but have cross-compiled avr binaries before.</p>

<p>Which arduino would be a good choice for this? And any additional parts that would help?</p>

<p>The end product would look like a MIDI mix panel, but it shouldn’t talk MIDI, just USB HID (to a linux PC.)</p>

<p>Note: there is an expensive, and out of stock, device that is similar to what I have in mind called MIDI Fighter Twister, pictured below, to get an idea.</p>

<p><a href="https://i.stack.imgur.com/3O1Wl.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3O1Wl.jpg" alt="Twister"></a> </p>
 64075: <p>Options for the Arduino you have:</p>

<ul>
<li>Get an Arduino supporting HID drivers (e.g. 32u4 based boards, Due /Zero/ Arduino Leonardo/ Micro or Pro Micro/ M0)</li>
<li>You use <a href="https://github.com/NicoHood/HID" rel="nofollow noreferrer">this library</a> it supports UNO/MEGA/Leonardo/(Pro)Micro/ any 8u2/16u2/at90usb8/162/32u2/32u4 compatible boards and some more</li>
</ul>

<p>Then you have to "just" code the communication between your programm and the HID driver -> pretty standard serial/usb stuff.<br>
The parts (knobs) you seek could be rotary encoders, which have no fixed zero point, endless rotation and need 2 input pins per encoder (except GND or optional push function). The signals a rotary encoder produces (and what can be handled by libraries) are based on a <a href="https://en.wikipedia.org/wiki/Gray_code" rel="nofollow noreferrer">2-bit gray code</a> available on 2 digital data signal lines. 
So when choosing whatever Arduino make sure you have enough (usable) I/O ports for the number of encoders and possible additional parts (status led/s or similar, I2C LCD display)</p>
