I am experimenting with a simple resistive touch sensor, made up by two thumbs tacks. One is connected to +5V and the other to a digital pin with a resistor in parallel to ground as a pull down. I activate the sensor by shortening the two tacks with my finger. I used a sketch for a Normally OFF momentary push switch. It took me a while to figure out that it was not working because I was using the recommend (for a switch) 10K pull down resistor (and the fact I am so proud that I figured it out all by myself gives a new meaning to the word "newbie"). I checked the resistance across the shortened tacks (my finger pad resistance) and got about 1.4M. I replaced the pull down resistor with 2.2M but it did not work too well. So I replaced with a 4.7M and now it works. Problem is that you have to cover the two tacks completely in order for it to work. It is not enough to touch them both (with the same finger). In other words, it is not sensitive enough. I tried to increase the resistance of the pull down resistor to 6.9M with two resistors in series (2.2 + 4.7) but it does not seem to change much.
Short of licking my fingers or wearing thimbles (one is gross, the other impractical) is there a simple way to increase sensitivity?