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Topic: Capacitive Sensor schematic question (Read 152 times) previous topic - next topic

saxdame

Hello,
I am utilizing the Cap sense library in a sound installation involving 32 sap sensors sending midi to sounds in Ableton. I followed the wiring scheme shown in the attached image per the tutorial found here.

https://playground.arduino.cc/Main/CapacitiveSensor?from=Main.CapSense
 
The project is working however it is rather unruly. After a lot of interaction it starts triggering itself...which can be really interesting, but in a gallery setting potentially annoying.
So, I'm looking at the illustration and suggestions in the tutorial to add two small capacitors to the circuit.

From the tutorial
"Research has shown that a small capacitor (100 pF) or so from sensor pin to ground improves stability and repeatability."

I understand where to place this cap in the circuit.

The second one however, I don't understand.

"Adding small capacitor (20 - 400 pF) in parallel with the body capacitance, is highly desirable too, as it stabilizes the sensed readings."

Can anyone help me understand "adding a small capacitor (20 - 400 pF) in parallel with the body capacitance"

I don't fully understand how and where would I wire this into the circuit. Any help greatly appreciated.
This is a link to a work in progress video of the project in action if you are interested.
https://vimeo.com/209081271
Thanks in advance.
td


Grumpy_Mike

Quote
Can anyone help me understand "adding a small capacitor (20 - 400 pF) in parallel with the body capacitance"
It is the capacitor, shown in the diagram you attached, as Csensed and drawn in dotted lines.

saxdame

Yes, I understand that it is the cap shown with dotted lines but I don't understand how to actually wire it into the circuit.
"In parallel" does that mean both legs of the cap inline between the sensor and receive pin?

bos1714

Yes, I understand that it is the cap shown with dotted lines but I don't understand how to actually wire it into the circuit.
"In parallel" does that mean both legs of the cap inline between the sensor and receive pin?
I believe it should be connected at the "foil" node and then to ground
Time line? Time isn't made out of lines. It is made out of circles. That is why clocks are round.

Grumpy_Mike

#4
Jul 14, 2018, 12:09 am Last Edit: Jul 14, 2018, 06:17 am by Grumpy_Mike
Quote
but I don't understand how to actually wire it into the circuit.
Wire it like the diagram you posted shows you where to wire it.
From the wire connected to the foil to ground.

Anyway these things are intrinsically unstable due to them having a very high input impedance which easily picks up interference. A much better soloution would be to use one of the many capacitive sense break out boards you can buy.

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