Adapting touch sensor to mechanical control system

[lkoren]

Hi. I've just started working with the MPR121 capacitive sensor (at the moment I'm working with the MPR121 breakout board sold by sparkfun) for an application that involves detecting a toolhead's distance above a work surface. It's not a problem to ground part of the tool head and some initial tests I've done with breadboard and tinfoil electrodes suggest this might be workable. Based on this we're ready to start doing some PCB prototyping.

Freescale has published a lot of material about this chip, including a design guideline discussing best practices for electrode design. However, all this material seems to be based on the assumption that what you are sensing is a person, specifically a finger attached to a person. We are trying to sense a chunk of metal attached to a machine, in a somewhat noisy electrical environment (steppers going on/off, uController doing all sorts of stuff, a few amps flowing through various parts of the tool head).

I was just curious if there are any tips or resources out there for deploying capacitive sensing in this sort of context.

L

 

[anorlunda]

I think the combination of very low capacitance, plus a noisy environment would make this approach troublesome.

Optical sensing would be my guess for the best approach. That eliminated the electrical noise.