How to use capacitor to stabilize capacitve sensor

Using Arduino Sensors
1

My goal is to use a plant as a capacitive sensor.
I have accomplished this using the CapSence library and following this topic:
http://playground.arduino.cc/Main/CapacitiveSensor?from=Main.CapSense

What I would like to do is to make the sensor more stable. One of the methods I'm trying is connecting a 100 pF capacitor from the sensor pin to ground.
this method is mentioned in the link above - "Research has shown that a small capacitor (100 pF) or so from sensor pin to ground improves stability and repeatability."

I have a very basic knowledge of circuits and the method seemed pretty straightforward forward but it is not working for me. (the serial port shows -2)

Can someone please help me? maybe by uploading a diagram or something?

(this is my first arduino project and first time uploading a Topic so please be patient with me)

2

Meaning: the plant influence is effectively suppressed.

I suspect that many effects like soil moisture affect the sensor readings. You also should place the Arduino as close as possible to the plant so that no long wire can act as an antenna for environmental noise.

Eventually a Gnd wire into the soil will help?

3

by Gnd wire into the soil do you mean from the soil to Arduino's ground or to actual ground?
I was planning to eventually ground the plant to the earth somehow but for now, my laptop charger is plugged in which should be enough.

4

Reliable capacitive sensors use 2 plates where one can be connected to Arduino Gnd. A capacitor may be added in series to prevent current flowing through conductive material between both plates.

5

Hi, thanks for replying. Could you maybe send a diagram of how to add the capacitor to the circuit? I have tried to simply add a capacitor between the receive pin to the Arduino's ground but the program just returned -2 (time out)

6

Do not add a capacitor unless you connect Gnd to the soil. Then put a capacitor between the Uno pin and sensor.

7

Thanks for replying.
Could you please explain your suggestion?
According to the document the capacitor is supposed to be connected to ground and sensor pin and not between Arduino pin and sensor

8

That arrangement removes not only noise but also the sensor signal. You already found out yourself that it's a very stupid idea to do so.

The capacitor in series with the sensor (capacitive coupling) is well known practice from audio circuits to suppress unwanted DC currents.

9

Pretty interesting. I will definitely try this and learn more about capacitive coupling.
Thanks for your help!

10

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