Can Capacitive Touch Sensors Detect Submersion

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DCSConcepts
 
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Can Capacitive Touch Sensors Detect Submersion

Post by DCSConcepts »

Hi, I'm envisioning a wearable which activates upon submersion into water. I want to avoid anything exposed through the enclosure to keep it waterproof. Could an internal capacitive touch sensor mounted to the inner side of the enclosure's wall (say 1mm thick) be used for this purpose? Thanks for your help.

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dastels
 
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Re: Can Capacitive Touch Sensors Detect Submersion

Post by dastels »

Possibly. There's https://www.adafruit.com/product/4026 but I'm unsure whether it will work in water as opposed to wet soil. Maybe worth experimenting.

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Re: Can Capacitive Touch Sensors Detect Submersion

Post by T_Mo »

I'd call that "unlikely".

Capacitance depends on the dielectric value of whatever insulates the two plates of a capacitor.
If you want to protect the sensor from water, then whatever the protective enclosure is (i.e. plastic?) will be the primary dielectric that the capacitor plates see.

If you immerse the plastic enclosure in water, there might be some small difference in the effective dielectric, but I expect the difference would be subtle, and that could make the measurement unreliable.

Seems like a fun experiment, though. If you work on it, please report back your results.

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dastels
 
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Re: Can Capacitive Touch Sensors Detect Submersion

Post by dastels »

Right. A capacitive sensor inside the enclosure wouldn't be able to detect water outside the enclosure. I read the original post as wanting to detect leaks into the enclosure. I can see how I could have misread that.

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Re: Can Capacitive Touch Sensors Detect Submersion

Post by DCSConcepts »

Thanks for the feedback.

Just to clarify, I am referring to a plastic enclosure.

What I don't understand is that I've read that the sensor can detect a person's touch through different materials (including plastic) as long as they're thin enough (hence my proposed 1mm thick wall).

Adafruit's description of https://learn.adafruit.com/adafruit-cap ... -breakouts mentions "Custom sense-pads can be made from nearly any conductive material and these sensors can detect touch through thin layers of non-conductive materials such as glass, plastic, fabric or even wood."

So given the above why wouldn't the sensor detect being submerged? (Thanks again for your help.)

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dastels
 
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Re: Can Capacitive Touch Sensors Detect Submersion

Post by dastels »

The thing with a finger touch is that the body becomes part of the system. I'm not sure that being near water would do the same thing. It bears some experimentation IMO.

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Re: Can Capacitive Touch Sensors Detect Submersion

Post by T_Mo »

So given the above why wouldn't the sensor detect being submerged?
This is thoroughly in the realm of "Well, that depends". Dimensions, materials, sensor sensitivity, software processing, ambient temperature, all of that could impact how well this may (or may not) work.

Experimentation is required.

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Re: Can Capacitive Touch Sensors Detect Submersion

Post by DCSConcepts »

Thank you all for your replies. I'm not an engineer, just an idea guy ;)

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Timeline
 
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Re: Can Capacitive Touch Sensors Detect Submersion

Post by Timeline »

Your question was about capacitive touch sensing, but there are capacitive proximity sensors that can detect liquid through other materials. Unfortunately they tend to not be cheap, at least the ones I have worked with. Example...

https://www.pepperl-fuchs.com/usa/en/cl ... rodid=1884
pepperl-fuchs.PNG
pepperl-fuchs.PNG (27.04 KiB) Viewed 35 times

Of course this is a German company so you know they are expensive but also work well. There might be other companies that make something like this that are not as, ummmm, "German Engineered" ($$$).

But back to your original question, some of the MCUs like the ESP32-S2/S3 have capacitive touch. So it would be pretty simply to bring those pins out to a pad and try it out and see what happens when the area directly on the other side of the pad goes from air to water.

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