Your support/donation is very important for the development of the project, besides, you can get more personalized technical support, advice, access the aircraft conversion file (see this list), get beta versions or modified firmware versions (if available or upon request).
The central control unit of the RealSimControl system is a single "master" controller board Mega2560 (Arduino2560) with RSC firmware uploaded to it only once (until next firmware update).
All pins that are available in the CONFIGURATOR can be assigned for inputs/outputs or extensions
These signal lines are reserved for outputs only - LCD, 7-segment displays and LED drivers, see more in the related sections:
Note: These 8 pins are configured as outputs, so you may think about common precautions not allowing outputs overload when you mistakenly short the pin to the GND. You can add serial safety resistors (30 - 100 ohm to each signal line) for current limiting, but in RealSimControl firmware these outputs are always in "low level" and for only a very short period of program time they can be in a high level state, so it's unlikely you will overload the address line.
NOTE: The +5V output pin can be used as a source for all multiplexers connected to RealSimControl bus and also it can be used to power some low-current output devices. See more detail about system powering here.
You can create a flexible modular system and have full set of input controls for any complex cockpit and easily expand it by adding more extension modules at any time.
You can use any of the Mega 2560 based controller boards available on the market. In the photo you can see three mini controller boards that are tested with RealSimControl / SimVimX, the firmware was uploaded to every of these boards from SimVimX plugin menu without any problems.
There are some other atmega2560 controller boards on the market like "Crumbuino-Mega", various "core" modules. You can find them yourself using such keywords as "2560 core", "atmega2560 mini", etc.