Encoders can be added to the Raspberry Pi to provide zynthian with an interface designed to drive the Graphical User Interface, and act as parameter controllers for any device managed by the zynthian. This is one of the zynthians key features and allows control of almost any parameter of the Audio engines that it manages.
There are a number of ways of implementing the basic zynthian encoder interface, and these have developed alongside the project. The techniques used in the early Version One days have been supplanted by more recent design and a software environment has been constructed that allows these differing approaches to be integrated with no difference between the implementations.
1 Encoders directly connected to GPIO Pins
This is the original approach used from the start the Encoder were connected directly to GPIO pins on the Raspberry Pi.
2 Encoders connected using a MCP23017 chip
As an interface grows ( when 4 user definable switches were added to V3 (?) we had already moved away from the direct encoder route in favour of a much more efficient way of reading encoders and switches, which passed off some of the effort to another piece of silicon. The MCP23017 16 port I2C multiplexer. This board meant the communication between the Raspberry Pi and this 20 pinned chip could be handled by only a few wires at the Pi end, and a standard form of communication called I2C.
3 Other nefarious methods
Other methods can be accomodated using the zynthian's inbuilt Control Device interface.