You need same chart, like on page 2, accurately drawn for your sensor (each sensor is slightly different from others). So you taking arduino, flashing code from link in replay #4, than using voltage divider and buffer amplifier you connecting sensor to arduino analog input.
Next step, is a calibration, when you setting two sensors side by side on the same surface, and changing frequency you getting data for chart. Last step, would be create look-up table.