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Support Forum » Resistance Capacitance Help

March 20, 2011
by missle3944
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Hi all,

I am working on a project that involves resistance capacitance. I am able to get it to work (sort of). The signal between the 2 sheets of aluminum foil seems to be very finicky and sometimes wants to work and not work. Also I am using 2 of the same size sheets of aluminum foil and I was wondering why you guys use such a large sheet on the bottom of the bowl? I will probably get some 680 ohm resistors this week but I knew that it was picking up the hand and the capacitance because the LED would go on an off. Also for some strange reason on the code it says that the LED will blink twice to show that it is ready but sometimes it doesnt and also sometimes nothing is displayed to the serial port when I know the LED is going on and off. I am Veryyy confused on this... -missle3944

March 21, 2011
by mongo
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Foil? sounds like a foil condenser. Usually, they are several alternating layers sandwiched between panes of glass. If you are not using a fixed dielectric like glass, (air) it becomes very unstable. Humidity, temperature and air density all change throughout the day and they will play havoc on it.

March 21, 2011
by missle3944
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How would I make a dielectric? Would it be much more reliable?

March 22, 2011
by mongo
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A simple way is to layer foil and paper. Two of each. Roll them in a spiral and set in a non conductive container filled with mineral oil. Tha is essentially a non polarized electrolytic capacitor. If the layers are wound up evenly, they should be pretty stable.

March 22, 2011
by missle3944
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Would this create a plate so I would have to touch it for it to get a signal. Becuase I want it to be more of the proximity sensor idea in their Halloween '09 tutorial. What do you mean by rolling them into a spiral? -missle3944

March 22, 2011
by Ralphxyz
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"What do you mean by rolling them into a spiral? "

I believe that is literally what he means!

Lay a piece of foil down on the table then lay a piece of paper on top and then roll them, if you loosen your brain you can see why mongo said "rolling them into a spiral" i.e. roll them up. The number of "rolls" will determine the capacitance.

Works for me, at least in my thoughts I have not tried it literally.

Ralph

March 22, 2011
by missle3944
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Ok thanks, just came back from a day of school work so my brain is still in "work mode".

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