I'm tinkering on my garage project, standard vehicle stuff - 12 V lead acid battery, 3-phase stator, reg/rec. I would like to put few additions to its circuit. Being a rookie, I'm not sure how to approach this correctly in terms of providing safe 5 V for the Arduinos (I need few of them). I've read a lot of articles on transients and noises in vehicle environment - load dumps, over and undervoltages, spikes...and also proper grounding, ground loops, it just seems overwhelming - hence this thread.
I've sketched up (sorry for any drawing mistakes) the circuit I plan to make, there's two of the sketches actually - the difference being grounding of the Arduinos, since I don't know which method is actually correct, grounding them to chassis or grounding them to the buck converter that will be providing the 5 V. I have a Traco Power TMDC 20 unit for this job - if you have the time you can look up its specs, from my limited knowledge that converter should be good for my use case but do let me know if its not.
Also another issue I'm worried about is grounding Arduino's buttons for logic level signals - I presume they all should be grounded on the Arduino GND pin - but then there's a issue of physical distance. The buttons themselves will be at least 2 meters away from the Arduino, if not more - so this makes me think about interferences, noises on the wire, etc. - how do I approach that issue? Here's the schematic and thanks for any help.