Driven shield for touch sensors

[colinives]

I'm working on a product development using a touch wheel based on the ESP32 touch sensors. The ESP32 is very close behind the touch wheel and the grounded meta cover is messing with the sensitivity. I could design in a driven shield plane between the touch sensors and the ESP32 metal case but don't know where I can take an active signal from to use as the shield. I'm assuming a copy of the touch waveform would limit the effects of parasitic capacitance.

Does anyone have an idea where I can pick up a isolated waveform from the ESP32 matching the touch sensing waveform to uncouple the sensors from the ESP32 ground plane.

Thank you.

[colinives]

By the way - I have previously used touch sensors which used a static DC voltage to read the touch sensor - in this situation I drove a plane behind the sensor using a DAC with the average analog sense voltage on the touch pin - this worked very well. The trouble I have with the ESP32 is that it drives a saw-tooth waveform which I can't easily replicate. I thought about using another touch sensor to drive the shield plane but the ESP32 uses time-multiplexing for driving each touch pin.

So, still looking if there is an answer to shielding the touch wheel from the ground of the ESP32.

[s-ol.nu]

I'm also curious about this - as per the ESP32-S3 technical reference manual the RTC_CNTL_TOUCH_SCAN_CTRL_REG has a bit for

RTC_CNTL_TOUCH_SHIELD_PAD_EN - Touch pin 14 will be used as shield_pin. (R/W)

From this brief description it sounds like setting this bit may turn touch14 into an active driven shield. I can't find any other details however, it's only mentioned once in relation to moisture tolerance:

39.2.10.1 Moisture Tolerance
The presence of water droplets on the touch pads can cause adjacent touch pads to be electrically coupled
(if the water droplets are large enough to physically bridge two more adjacent touch pads). Coupled touch
pads will lead to the false detection of touches due to the capacitance caused by the coupling.
To configure moisture tolerance:

• Set the drive strength of touch sensor 14 by RTC_CNTL_TOUCH_BUFDRV.
• Enable touch sensor 14 to be used for moisture tolerance feature by setting RTC_CNTL_TOUCH_SHIELD_PAD_EN