References:

(1)http://playground.arduino.cc/Main/CapacitiveSensor?from=Main.CapSense

(2)http://hyperphysics.phy-astr.gsu.edu/hbase/electric/pplate.html

(3)http://www.atmel.com/images/doc10752.pdf

A capacitive sensor utilizes two pins on an arduino. A DC pulse is emitted across a Resistor-Capacitor (RC) circuit. As the capacitance value of that circuit changes the frequency of the receive pin will change. The resistor as suggested in the arduino guide can be a value of 100 kilohm - 50 megohm. The capacitor as shown is a bit of conductive foil/wire that can be brought next to any other conductive material with a dielectric in between. As your finger/foot approaches the exposed wire the width of our dielectric (air) changes. The formula for a parallel capacitor is as follows.

Where k is the permittivity of dielectric ( Air = ~1 ) and Epsilon is the permittivity of free space constant 8.854*10^-12

This mean that sensing your foot on plexiglass on the surface of your plate is the same as sensing your foot from a distance that is effectively 3.4 times closer than if it were air.

We need to find the optimal point between a clean signal and a fast signal. "As a rule the RC time constant should be reduced as far as possible..."(3) There is a formula for the measured frequency of our sensor.

We know that we cant change our capacitor. A standard DDR pad is 11"x11" and you are stuck with whatever feet you were born with. The only hardware change we can make is to that of the resistor. The lower the resistance, the higher the frequency, the faster the signal. We want this resistance as low as possible while maintaining a clear and measurable result. The larger the resistor, the farther away from the sensor we can sense.

The first step was to upload the example code to our arduino to verify function. A 1 Mohm resistor was chosen to test the initial exposed wire circuit. Once the prototype was created, this was reduced to a 250kohm resistor. Your results may vary.