I am trying to make a design with a driven shield ring on the bottom layer and a capacitive electrode plate in the middle with two solder mask covered single pin footprints and drawing the fills or planes for it to fill in those can you use two on one layer?
see image
This looks very familiar to:
https://forum.kicad.info/t/4layer-pcb-need-via-to-connect-2nd-layer-only/10497
If you put the opamp just next to your sensor, or make some small cutouts in your “guard ring layer” then you can very likely simply use a 2 layer PCB instead of 4.
The bigger distance between the “Detection disk” and the “Guard Ring Layer” will decrease the capacitance between them, but I think that is an advantage here. It means that the realative change in capactiance between the sensor and an approaching object will be bigger.
At what kind of frequencies is this capacitive sensor supposed to operate?
As an alternative you can also make a relatively big hole in the PCB, and solder a wire to a coin for your sensor. Then you can experiment with distances and such.
Hi the other post is mine and the opamp and adc are all on top of the capacitive active electrode so the 4 layers allows for the opamps and adc to bring digital signals mostly and the common mode signal for the driver right leg. It’s for a EMG system for keyboard and mouse. The sensor plate is covered in solder mask so it does not make contact with the body and the shield is a layer above the sensor plate and around it would be great like in the posts reference pic.
You can use as much planes on a Layer as you wish. Just select in the “right” “prioritylayer” (something like that, my GUI language is non English).
So I’m guessing priority means I can draw a larger than one inch if I want a capacitive electrode plane one inch then draw over it a box marked shield plane for the outside and the shield will stay away from the electrode by the clearance if the electodes a higher priority. Then it could all be covered in soldermask.
You could test it, and let the rest of us know.
Or, maybe out of curiosity I might test this out for myself; although at the moment I’m not seeing the need in my current designs.
Hint: If you need circular zones KiCAD doesn’t have the ability yet - only straight lines, but you can edit the pcb file and modify the coordinates of that poly-string.
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