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I am trying to make a copper pipe which is placed in a natural park capacitive. It is placed in the soil meaning that it is already grounded. I am using a basic arduino and their capacitive sensing library to quickly experiment with, but the issue I am having is that the arduino itself needs to be grounded in order to have a decent value output. But grounding the arduino to the copper pipe (or anywhere) doesn't work. Because than the ground and the capacitive sensor are directly connected.

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tl;dr: How can I make a grounded object capacitive?

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If it's actually grounded, then it can't easily be used for capsense; you need to insulate it at some point. – pjc50 Mar 25 '14 at 12:47
up vote 6 down vote accepted

Your basic problem is that you have a relatively small resistance accross your capacitor. This resstance is dominating when you try to measure the capacitance.

You are trying to measure something that doesn't make much sense. You have to decide what exactly you are really trying to measure. If you want to measure capacitance between two conductors, then the resistance between them should be quite high. Otherwise, the capacitance will be hard to measure and it is unlikely a usefull metric even if you could measure it.

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thank you for your answer and you are absolutely correct. The reason why I had to ask was because a capacitive sensor guarentees a specific interaction that I desire. I want to have an output that increases the closer I get to the sensor. So that when a user is sliding his hands over the copper the value is different at each location. – rfs Mar 25 '14 at 14:36

You have answered your own question. You have grounded the capacitive sense object (pipe) and thus the value of the reading will be near zero or at least not have much of a change range. In order to sense people approaching the pipe you need to have it isolated from the ground.

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