FDC1004: Emulate Mechanical Rotary Encoder with Capacitive Sensing?

Hi John,

Typically, this is achieved with inductive sensing.  See the reference design below.  I would recommend this approach if it is possible in your design.  

https://www.ti.com/tool/TIDA-00828 

The same type of concept could be done with capacitive sensing as well, but we do not have a reference design available for this.  If your target(the "fingers") are ungrounded, you could use something like the parallel fingers approach shown below.  If your target is grounded, the isolated sensor approach could work.  

https://www.ti.com/lit/an/snoa927a/snoa927a.pdf 

Is there a specific reason you would want to use capacitive instead of inductive sensing?

Thanks. Inductive sensing is fine. The application would be consumer/home, which I assume is "ungrounded" (?)

TIDA-00828 is a turning knob. We don't want a "knob" that turns. We're looking for a finger movement that emulates a turning knob. The fingertip will sit inside a circular channel, and the finger will then move in a circular motion CW and CCW about that circular channel. It's like how a finger engages with a capcitive-sensor, but with a bunch of quadrature sensors placed in a circle.

Any ideas?

Thanks. That looks like a solution. What are the minimum Dev Kits I need to test the user interface of the capacitive touch wheel and slider functions? Ideally, we would be interfacing the dev kit with our existing product, which uses a Silicon Labs micro.

Which would be better for testing a touch-wheel?

CAPTIVATE-BSWP ?

or

CAPTIVATE-PHONE  ?

And which interface board(s) will allow us to talk with the quadrature inputs of a general microprocessor?

Thanks. It says the "wheel sensor" uses three elements. Does that mean that it offers a resolution of one "increment" for every 120 degrees of finger movement? We need far better resolution, similar to a rotary encoder -- something like 16 or 20 increments for 360 degrees. Possible?

Thanks. It claims up to 1000 increments. Is that per a single time-cycle? That's really good. Are your linear and rotational capacitive sensing solutions rock stable? This will be used as an audio level control. One stray glitch (static body discharge?) could cause havoc, and destroy speakers.