Touch sensing

[Anon_LG]

I was playing with some aluminium foil and copper tape (as most people do), and noticed a voltage effect. Below is a layering diagram of my setup. The copper is on top with a piece of sellotape preventing it from touching the aluminium.

=========== copper tape
:::::::::::::::::::::::::::::: sellotape
------------------------------- aluminium foil

When I touched both the copper and aluminium foil at the same with my finger, a voltage was measured between the copper and aluminium of 0.1 to 0.2 volts! There is no connection to ground, the sellotape is completely insulating and the effect does not occur when the surface are homogenous, eg aluminium +aluminium or copper+copper. The effect occurs whether the finger is dry or wet. The voltage is continuous and appears to be proportional to the surface area contacted.

What is this caused by? Is it capacitive touch sensing? I am sure it is not static as a grounded myself then tried and it still occurred.

Can anybody give me an idea of how I can amplify this? FETs are sensitive to ESD, is there any way to overcome this? I would use bipolars but I doubt the current produced is anything to be spoken of, and FETs are voltage controlled, so they would be optimal.

I am interested in your ideas, thanks,

 

[dorke]

Chemistry is to blame.
I think you have created a battery,
your conductive finger is replacing the liquid.
see here.

 

[Anon_LG]

OK, it is of little use then. Thank you for informing me. Aluminium and copper are two of the materials I have been using when playing with electrochemistry, I did not expect that my dry finger would be sufficient to cause an electochemical reaction though!

I could test with a graphite rod and copper to ensure it is electrochemical, as both are sufficiently unreactive enough.

Thanks,