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I'm slowly beginning to understand more about how these work thanks to answers I have received on this site. I believe one area of confusion for me has been I've looked at two differently designed Capacitance Sensors, and I believed they were basically the same, but now I've come to think that they are not.

Chirp!

http://wemakethings.net/chirp/

Other one

http://zerocharactersleft.blogspot.ca/2011/11/pcb-as-capacitive-soil-moisture-sensor.html

From my new understanding, Chirp! is only providing one "plate" and the other version is providing two. But hopefully someone can explain this more clearly.

Thanks very much in advance.

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  • \$\begingroup\$ More Chirp! info: github.com/Miceuz/PlantWateringAlarm and github.com/Miceuz/PlantWateringAlarm/blob/master/pics/… \$\endgroup\$
    – Dave
    Commented Jan 27, 2016 at 15:23
  • \$\begingroup\$ after reading what you posted, these two sensors are identicle. The chirp! uses the ground plane as the second plate. "The other one" does the exact same thing. \$\endgroup\$
    – R. Johnson
    Commented Jan 27, 2016 at 18:10
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    \$\begingroup\$ All capacitive soil sensors follow this theory. This exact question was asked and answered here: electronics.stackexchange.com/questions/184845/… \$\endgroup\$
    – R. Johnson
    Commented Jan 27, 2016 at 18:14
  • \$\begingroup\$ Thanks @R.Johnson but I'm still not sure about this. Just be looking at the pictures of the two boards, it looks to me that the Chirp! has one trace that is connected on both sides. Where as the "other one" has two separate traces leading into large pads that do not connect. That's why my understanding was that Chirp! was reading between that single trace and an 'outside plate' and the "other one" was reading between the two traces on the board. But I'm not sure of course, otherwise I wouldn't be asking. Thanks again! \$\endgroup\$
    – Dave
    Commented Jan 27, 2016 at 18:40
  • \$\begingroup\$ If you look under "Moisture sensing" in the chirp! documentation they specifically state that they use the ground plane as the second plate. If they did not use a second plate you would not be able to sense using capacitance. . . \$\endgroup\$
    – R. Johnson
    Commented Jan 27, 2016 at 18:43

1 Answer 1

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@R. Johnson pointed out that the two designs were the same in theory, and once they pointed out how to see this it made sense.

Thank you.

Dave.

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