(published on 07/05/07)
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I don't think there's any way that the water connection between the shafts could be in series with the motor. The resistance is much too high. Instead, I bet there's a separate circuit including the water between the shafts through which a small current flows that controls some switch on the main motor circuit. Thus the shaft-to-shaft connection would be in series with the on-off switch, as you found, but not in series with the motor.
Presumably that's done for some sort of protective reason. Perhaps if the motor runs freely in air it overheats.
(published on 08/18/13)
Yes, I was also wondering if it relies more on resistance or capacitance. If it works with de-ionized water I bet it's capacitance, since the resistivity is so high. It doesn't really matter much for the safety switch circuit, which is unlikely to notice the phase of the current.
(published on 08/19/13)
The capacitative sensors on the Ipad screen will pick up the presence of any conductor or very high dielectric-constant material very close to the screen, since those increase the capacitance of the closest capacitors. You can get styli with conducting tips for the Ipad. You don't need the capacitance to ground provided by the body. The styli could be manipulated by anything.
(Most other touch screens use little resistive switches activated by mechanical pressure. Their styli usually aren't conductive, so they won't work with the Ipad. )
(published on 08/26/13)