Drop in Capacitive Sensor

Other Hardware Sensors
1

Hi,

I have a simple Capacitive Sensor I have built and using the CapacitiveSensor library.

This all works great but only when I used the Serial plotter to see what was happening I noticed that every 30-40 seconds the capacitance drops. I have attached a screenshot to show.

I have tried search the many posts and articles on the internet (eg youtube, instrucables and this forum etc) but I can't see if this drop in capacitance is normal or not.

In the image, there are 2 data sets (Red and Blue) and these are the same sensor but through 2 different smoothing formulas. The red trace just has an additional 10 added to the value JUST TO DIFFERENTIATE between the 2 formulas for my own testing etc.

My current guess is that the antenna builds up a charge and some how dissipates the charge and this cycle is approx 30-40s long.

This screenshot is just the Capacitive Sensor Antenna left by itself without myself or anyone else near it, ie at rest.

Does anyone with knowledge of capacitance know why this happens. Thanks

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2

That doesn't sound normal to me - do post some images of your setup and your code.

There seems to be something else at every 10 seconds or so (I see two minor changes twice between the big changes). Is there some climate control device nearby device switching? Such as A/C, fan, dehumidifier. A change in humidity, temperature or other air flow may be the cause. Or some other device that switches at this interval.

This kind of drastic change in capacitance is what you're looking for to detect a touch or proximity. However, having no idea what the units at the axis mean (or even what zero means in this case!) it's even impossible to say whether these changes are indeed significant. Can you post a graph which has this effect plus one or two points where you actually touch it? That would give a perspective of scale, and whether this is something to worry about.

At the moment I'm also in the guessing stage, the more info you provide the more chance you have for someone to see the cause!