Bus

RS485 will be used as the principal bus.

Hardware

IO Controller

Sensor Nodes

Software

In order to communicate between the nodes, the MODBUS RTU protocol will probably be used.

Addressing

If possible, the addresses could be dinamically addressed using some discovery protocol. This seems really to realize on modbus and thus, some DIP switch could allow the user to set nodes addresses. Since the modbus adressing can go up to 255, a 8 input DIP switch will use 8 GPIOs.