A capacitive mutibutton configuration application note from Microchip describing how to scan and detect button presses on more than 4 capacitive buttons.
This application note will discuss three different
approaches to implementing multiple touch buttons
using Microchip microcontrollers. The first approach
creates a simple 4 sensor system using the on-chip
4-to-1 analog multiplexers tied to the inputs of the
comparator module. The second approach expands
the 4 sensor system of the first approach, into a 10
sensor system by combining pairs of the original 4
inputs. The third approach creates an expandable
system, which relies on multiplexing additional
sensors through an external analog multiplexer.