Variable Capacitance Testing

[Aztecphoenix]

I think you may be going about it the wrong way. The water itself should act as one electrode. I think a fairly usable capacitor could be made using a strip of copper foil, as one capacitor plate, along the inside wall of your build container, insulated from the water, perhaps with some kapton tape, or laquer, making sure to get a good seal around it. For the other "plate", place an electrode that won't corrode, close alongside it in direct electrical contact to the water all the way to the bottom. The water would be salinated, which of course it needs to be for the peachy anyway.

I don't beleive the salt level will matter much as you'd be relying on the capacitance, which is based on the thickness, and dielectric constant of what you use to insulate the strip. It should be unaffected by temperature, or resistance of the water. You could simply use this as the capacitor in a 555 timer based oscillator (astable multivibrator) if you keep it in the audio range you can read it on the mic input of a sound card. Sound cards are very good with frequency accuracy.

I could whip something up. I've been thinking about it a while, I've just been lazy and unmotivated :-P

the problem with what you're suggesting is the chance of electrolysis, in other words, the disolved metals electroplating themselves onto the contacts obscuring the readings, this is why both the anode and cathode are isolated from the water

[jsondag]

Other that the possibility of it becoming a galvanic cell if you use dissimilar metals both contacting the water, which would be minimal, and could be eliminated by using similar metals between the build mesh, and the contact, you won't have any electrolysis if only one contact is in the water. There won't be any actual current flow, just an electrostatic charge building up in the insulator between the water and the strip. It's a not uncommon type of homemade capacitor, and it's capacitance varies with the water level.