Ok, then it would be simpler to use a buck converter module. You would simply represent this on the schematic as a box, labelled to indicate it's purpose, and showing and labelling the terminals it has.
By the same principal, it would be easier to use a module containing an atmega328, such as an Arduino Nano. Such a module would contain it's own voltage regulator and could be powered by 12V, removing the need for a separate 12V to 5V converter circuit.