The sensor forms an image and OpenCV detects the actual touch configuration. It appears you can use the raw data from the Arduino, too, but it might be a little harder.

[mircemk] shows how to create a simple non-contact proximity sensor using little more than an Arduino Nano board, and a convenient software library intended to measure the value of capacitors. The … ...

At the heart is an Arduino compatible microcontroller (based on the Leonardo) with a few extras baked in, including a Freescale touch sensor connected to 12 electrodes and an audio processor for ...