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.

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 ...

Capacitive touch sensors are entirely in the domain of DIY, requiring little more than a carefully-chosen conductive surface ...

The discrete prototype demonstration functions to transmit the touch sensor data over the DisplayPort AUX channel while driving the digital and analog needs of the LCD panel.