[sdiy] sin/cos pot

[rsdio at audiobanshee.com]

On Jul 10, 2017, at 3:29 AM, Ove Ridé <nitro2k01 at gmail.com> wrote:
> On Monday, 10 July 2017, Michael Zacherl <sdiy-mz01 at blauwurf.info> wrote:
>> How would you tell the direction of the movement?
> 
> There are two tracks shaped as cos and sin. If you graph one rotation, you would get cos and sin, aka sin and 90 degree out of phase sin. Another (in this case helful) representation is the unit circle, where the x and y axis are repreented by cos and sin. Since every position on the pot is indexed uniquely by an angle (that is, each pair of values is unique to a single angle) everything else follows naturally. It's a quadrature source and you could also draw direct a comparison to a rotary encoder, which essentially does thesame thing, but per step instead of full cycle, and discrete instead of continuous.

Does anyone know why these pots are cosine and sine instead of two linear ramps that are offset by 90 degrees or 180 degrees?

I searched the Taiwan Alpha company web site, but they don't seem to have a straightforward search by part number. Instead, their products are broken down in tables, and I couldn't find the RV112 line.

The reason I ask is that log pots are only approximations of log using piecewise linear segments. I'm assuming that sine response would require more complex piecewise linear approximations, and certainly more expensive than simple linear.

Someone on these lists described dual pots with standard linear response, but without end stops. They have dead zones at the end where the normal resistive material ends, but these dead zones are offset by 180 degrees between the two tracks, so it's possible to track continuous rotation by reading both and using the track that's not reading 0 Ohms to get a reading from the dead zones.

Brian