It seems ass-backwards to me, but it works.
A piece of foil in the base of the jar works.
A piece of foil stuck to the side of the jar works too, but not as well as a piece in the base.
Quote from: fungus on Apr 10, 2014, 10:28 pmA piece of foil in the base of the jar works.Insofar as it is actually (capacitively) coupling itself to the bench on which it is sitting which is itself well coupled to the "real" "ground"/ "earth"/ whatever. If on the other hand, the jar is picked up, it will lose this.
Quote from: fungus on Apr 10, 2014, 10:28 pmA piece of foil stuck to the side of the jar works too, but not as well as a piece in the base.Needs to be a ring of foil in the neck of the jar, not too close to the lid but so the hand approaches this as it approaches the lid. Whilst it may not be as sensitive, it will be much more reliable as it will not be affected by what the jar is - or is not - sitting upon.
I want a Tiny85 based device under the lid of a jam jar. I want it to turn on some LEDs when I touch the lid. It's powered by a coin cell.
But you don't -want- more capacitance between the sensor and the lid. ...
My lid is metal, not much chance of changing it.
How about get a cheap 'touch lamp.' Open it up and find out how they did it. They usually have metal base. Inside is doubtless a dielectric and another metal plate and a little circuit. You can recreate it or even easier pull the guts out and adapt it to your jar.
The "touch lamps" operate by sensing capacitance against the mains - 110 or 240V. The "ground" side of the detector is actually the full mains voltage so that the capacitance of a person touching it provides a capacitive coupling to the actual ground. I do not think he wishes to connect his bottle to the mains.