ESD safe resistance measurement with ESP32

[chromo23]

Hi,

for a little side project i need to measure the resistance of two or three people holding hands. The experimental setup works fine.
As this will be a permanent installation I am wondering about the ESP protection. I think I read somewhere that all ESP32's have some form of protection.
But just in case, I thought about adding an external TVS diode. What do you think? (I am a little worried because a lot of people are walking across a carpet, holding hands and touching metal.)
Does anyone have any suggestions on how to make this as reliable as possible? Any help is welcome

Here is the basic schematic:

resisance.png (77.85 KiB) Viewed 1598 times

[TD-er]

I would also add an 1M (or 10M) resistor between GPIO-33 and GND. Or maybe parallel to D1.

When possible you could try to make the ESP's GND completely floating from anything else and then add some 10M resistor from the pads to earth.
This way the static discharge itself also isn't that painful.
Those RJ45 sockets with a shield often also use some high voltage 1nF/2kV capacitor between their common pins and the shield. (via 75 Ohm resistors)

So it would then be something like this:

pad --- TVS --- GND --- 1nF/2kV + 10M (parallel) --- earth.

Not sure if adding a second TVS between 3V3 and GND would be useful. It just feels a bit like some spark may jump over the potentiometer.
Maybe adding some fast diode between 3V3 and GND to prevent too high negative input when the ESD discharge happens via the right pad? The negative voltage will be more than the break voltage of the TVS.

Also the long cable will for sure act as an antenna and picking up all kinds of noise.
I would add a small capacitor between GPIO-33 and GND close to the ESP itself.
Just experiment with the capacitance as without it your measured signal will be quite noisy. But you also would like to get a rather quick update.

[chromo23]

I would add a small capacitor between GPIO-33 and GND close to the ESP itself.

Small capacitor big impact. This helped a lot against the noise.
Thanks's for your input