Variable current switch by human touch

Question

Two goals:

1. Make an LED turn on when a person touches two conductive pads (e.g. two square of aluminum foil)
2. Make the RGB LED change color depending on how hard the pads are squeezed. I will figure out the color algorithm later. For now I just need to be able to sense variable conductivity/capacitance/current (one of those?).

I have an Arduino LilyPad. I know this can be done because I've seen it before (just don't remember the code or circuit). Example image:

I know the human body is conductive, so I'm not quite sure why the LED won't go on when I contact the conductive pads. My only hypothesis is that the resistance is too high, but that must mean some current is going through, no?

Thanks.

Answer 1

I am going to make this answer as simple as I can, the body is not THAT conductive, you gotta use something like a touch sensor.

Answer 2

Okay; to start with, the Arduino Playground has a how-to guide, the components are commonplace - either recycle a high-resistance resistor from junk or buy one from eg Maplin at 38p.

This works as follows: You charge the capacitor with one output, through a resistor. This charges the capacitor in RxC seconds - C is very small, typically 10^-11 or so, so a decent sized resistor helps make it slow, in computer terms. Ensure this is held on for long enough to charge fully. You can use one charge pin for many touch sensors.

You then drop the charge pin to 0, and see how fast the sense voltage drops; this will be affected by fingers etc, giving a time value reflecting the degree of contact; normally this is used as a threshold on/off, but does allow for some pressure sensitivity. You need one R/C/sense-pin per switch.