The CD74HC4067 High-Speed CMOS 16-Channel Analog/Digital Multiplexer Breakout Module is a board for a very handy 16-Channel Analog/Digital Multiplexer/Demultiplexer. This chip is like a rotary switch that can internally route the common pin (COM in the schematic, SIG on the board) to one of the 16 channel pins (CHANxx). It works with both digital and analog signals (the voltage can’t be higher than VCC), and its connections function in either direction. To control it, connect 4 digital outputs to the chip’s address select pins (S0-S3), send it the binary address of the channel you want (for more see the datasheet for details). This allows you to connect up to 16 sensors to your system using only 5 pins!