Re: [CAD_CAM_EDM_DRO] Re: Capicitor tuning VCO/DRO

On Wed May 12 16:03:50 2004 caudlet wrote:

>Bill there are going to be several issues. 1.) the amount of
>capacitance change is going to be relatively small (although you can
>work within a narrow range of the VCO). One interesting circuit is a
>one that would "read" the value of a capacitor. I have seen various
>circuits that use cheap parts and output a DC voltage porportional to
>the capacitor value. Google for "capacitance meter circuits"
>or "measuring capacitance". Find ones that will read small values of
>capacitors down into the mmfd ranges.

Most of the few I've seen, amount to small frequency range RC oscilators
feeding a counter, and the cap under test being the C part of the RC value.
I'll look, at google, but suspect the range factor to be too small.

>2.)A added issue will be the possible non-linearity of the wire in
>the tube configuration. Honestly I don't know if the surface area of
>the two plates of a capacitor and the distance apart are a linear
>function. Surrounding masses of capacitance (people, machinery, etc)
>could have effects. I once built a circuit that would sense the
>capacitance of a human body at about 6'. It was notoriously unstable
>because things change with different ground moisture and air humidity
>conditions. RF worked a lot better.

Another fudge factor woulld be the amount of clearence between the insulated
wire, and the tube. Sag in the wire might add non-linearity, too.

>I am sure there are measuring instruments out there that use
>capacitance to measure distance.
>
>You might be able to make a really neat random frequency transmitter
>or an interesting theremin (audio frequency changes with capacitance)
>project! Your neighbors will love you!

Oh, joy! :-)

Bill

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