1.It can process digital and analogue signals (the voltage must not be as VCC), and can be connected in the direction. To control it, connect the 4 digital outputs with the address selection pins (S0S3) of the chip and send it the bin address of the desired channel (details can be found in the data sheet). This allows you to connect up to 16 sensors to your system via 5 pins! 2.Since the Mux/Demux can also process digital signals, you can use it to transmit serial data at TTL level to multiple devices. For example, you can connect the Tx pins of 16 devices to an Rx pin of a microcontroller. Then you can select one of the 16 devices to listen to. 3.This is a very convenient 16 channel analog/digital multiplex/demultiplex breakout board CD74HC4067. This chip works like a rotary switch it internally routes a common pin (Com in the wiring diagram, on the board) to one of 16 channel pins (Chanxx). 4.If you want bidirectional communication, you can add a second board to direct the Tx line of the microcontroller to the Rx line of the 16 devices. By using multiple boards, you can create similar arrangements for I2c, SPI etc.