Endless potentiometer decoding

Hi there,

I wrote a C++ class to decode an “endless potentiometer” and would like to share it here, in the case it could be useful to someone.

An endless potentiometer is a kind of crossing between a regular potentiometer and a rotary encoder. It can rotate 360° without stop and has two outputs in phase quadrature, as shown on the picture below:


The only parts I could find so far are the Alpha RV112FF series. If someone finds other endless potentiometer parts, please tell us.

It is possible to retrieve the absolute angular position of the shaft, or a relative angular movement. They work similarly to rotary encoders, but the latter are very coarse, making them unsuitable to audio FX parameter adjustment (contrary to standard analog pots). These endless pot give you the best of both worlds, although they are a bit expensive (~4 €/part when writing these lines) and each unit uses 2 ADC channels from the microcontroller.

It’s a good solution to switch between different parameters on the same physical control, thus saving space. Or retrieve saved presets without having the current pot position altering the freshly restored settings.

The decoding is not very challenging but there are several pitfalls related to the taper imperfection if we want the angular position to be as continuous and monotonic as possible. The PotEndless class takes measured voltages as input (output of the ADCs) and outputs two angular positions: one physical, and one counting the total number of turns from an initial physical position. A model with graphs and formulas is shown here, for the math interested people.

If a rotary encoder behavior is desired, it is recommended to filter out the noise from the result before trying to get relative movements (delta between two positions). Otherwise small variations will be completely buried into the noise. Filtering could be a low-pass filter, an adaptive band-pass filter (like the excellent smoother from Cytomic) completed by an hysteresis. But this is not the scope of this class.

The use is quite simple with the following methods:

  • set_safety_margin() tells the object the extent of the “unsafe” values at the end of the taper range. Default should be O.K., and you can set it to 0 to bypass this processing if the result is good enough.
  • set_dualpot_val() feeds the object with a new measurement (2 × 16 bits from the ADCs).
  • get_pos_phys() retrieves the physical position of the shaft.
  • get_pos() retrieves the current logical position (number of integer turns + fractional position).
  • set_pos() resets the logical position.

Example of decoded position vs. ADC outputs:

There is another approach by Bjørn Brandal, but it focuses mainly on relative decoding.

I hope this will be helpful!


Woah, this sounds wild! I didn’t know endless turn potentiometer was a thing until today. It seems like it’s pretty rare to see in the market.

I would absolutely love to give this a try. I think it’ll open up new possibilities with instrument design :slight_smile:

Thank you so much for writing and sharing the class + documentation, Firesledge!

P/N AL0-09-0044

Found In the AKAI APC 40 mk II (17pcs)

Don’t know if it’s made by Alpha originally for inMusic brands (ALesis and more)

Microchip makes an interesting chip that lets you build-sense the position of a metal object. They have examples and eval boards for linear and rotary versions:

Here is what looks to be the same part but cheaper. May be worth testing a couple of these. :wink:


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From what I can tell there is no agreed upon terminology for “endless potentiometers” or am I confused

For example mouser calls them “no detent encoders”, “magnetic encoders”
It looks like any company that makes regular encoders also makes these but they have different names.

Magnetic encoders go from the same cost as a normal pot, to really expensive.

The OP asked for any other version, here are a few I found that I am pretty sure are the same technology.
AlpsAlpine No Detent Encoders

Other names for similar technology that could replace pots include “No Contact Potentiometers” and “Magnetic Angle Sensors”

Magnetic Angle Sensors are the same things Tunages mentioned above, I think you could do some really cool things with these but it would be a lot of work, fun work

This is damn cool - didn’t know Rotary Pots existed!

I’m currently looking for a Pot solution for my project. Was gonna use a rotary encoder - but the angle resolution is so low - they feel HORRIBLE . Rotary pots could be that answer for me - thanks for posting. I also looked at T.E. OB-4 - I have one and it has motorized encoders= - and they are superb - don’t think they are Rotary encoder - waaay too smooth. Thinking about taking my OB-4 apart to see what the hell they’ve used - 3 phase dc motor and shunt checking any pulses e.t.c.?

Unless I’m missing something, the Alps Alpine products you linked look like regular rotary encoder, that’s not what I was writing about.

The Infineon magnetic angle sensors look much more similar to the endless pots I mentioned. They are a bit more complex (some chips do only the sensing, others do the decoding too). They also don’t include the mechanical part that would be interesting here (a shaft with a magnet). But that’s an interesting alternative.

No it was me who missed something, so the RV112FF actually functions as a variable resistor?!

Or does it output a voltage?

I’m trying to wrap my head around how this hardware is possible without a sudden jump in the output, thank you for sharing, that is indeed one strange device.

Yes, it’s a dual variable resistor.


There is a continuous circular track with two cursors shifted from 90° [edit: clarified]

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Wow, I was just about to write decoding SW for a bunch on these pots that I have on a project, thanks for sharing!! It’s a really cool part, used on a bunch of Akai and Novation gear. Props for the link to RK11 part on aliexpress, these pots are pricey and hard to find