z axis feed back for under a dollar? - variable capactive-> freq-> mic

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Originally Posted by Spelljammer

Good stuff. Maybe use more aluminum. I know the salt water high voltage capacitor, aluminum foil wrapped around a plastic bottle, is 1800pF. http://www.instructables.com/id/Make...p10/Completed/

And a typical Leydon jar made of glass had about 1000pF capacitance. That is an easy value to work with. Something like 30 square inches of foil, minimum would be needed.

I like this whole idea as well. A sound card can pickup 20-20khz. A quart jar has about 1000 ml in it and 20 ml per drop, that is 20,000 drops per quart or liter. This might be accurate enough to distinguish a 1 drop height change. In real world, it would be less, but 1/10th of that is still accurate enough. For instance, 2000 steps (up to 20,000 possible) in about 4 inch (100 mm) height change in water, would be 0.05 mm Z axis accuracy. That is a 50 micron accuracy, with a possible 5 micron accuracy.

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What about a laminate of several layers of aluminium and kapton, would that work?

I had been thinking about this. So tried it out with a foil wrapped container:
Attachment 1453

With a 4.7 Meg Ohm resistor I can hear the tone - and here is what I could see:
Attachment 1456Attachment 1457

add some water (next post because of image issue.)....

So added water and got:

Attachment 1458Attachment 1459

And clearly the tone changes.

Video posted here of filling the container. http://youtu.be/YpQnxEugeLQ

So, there is a lot of noise. I might be able to lower the resistance value to see if the noise reduces. For some reason, the act of filling the container seems to change the tone, regardless of level. While water is pouring in, the tone changes, as the level goes up, that changed tone drops, then when the pouring stops the noise steps again. I don't know if the stirring of the water as the pour happens has anything to do with that.

If anyone can find me any good PC sound card signal analysis (e.g. frequency sampling tools) I can plot the changes against height of water.

The issue that I see here is that you wrapped the whole container with foil, and that creates a large surface area which can store charge (like those globes you put your hand on and your hair stands up). It might not be that much compared to the inside capacitance, but it could introduce some tone jitter.

Did you make sure to pour salt water in?? (or was is simply normal tap water?)

The act of pouring a lot water in might cause weird ionic effects within the water to throw things off. Also keep in mind when water is being poured in, it makes an electrical connection between you and the system via the water stream, and that will throw things off too.

This is why the inside salt water probe needs to be earth grounded (and you as well).

You should do it in shots.: Take a shot glass and transfer water a bit at a time, slowly, to compare the tone.

Also make sure you have enough salt in the water.


Awesome work!

- UD

Ya! Awesome Work! colehard
from what I saw this is still looking really promising