I have a proto build which may be gearing up for production in the next 3-4 months. The prototype's user interface uses common ground for the LEDs and accompanying buttons. I use INPUT_PULLUP on my Arduino for the buttons and the LEDs are connected through resistors to GND. 4 buttons and 11 LEDs total.
Is there any reason for me to think that common +V might be 'a thing' and that a true commercial quality PCB (manufacturer) may instead want to use common +V instead of common ground? My first step beyond the proto build is to reach out to a manufacturer of membrane switches with the layout of the UI and the traces required.
P.S. All the buttons and LEDs in the proto build are using either the 5v onboard pin or 5v logic level from individual IO pins.
Consider the use of 3.3V and 5V sensors or controllers together. Then these work based on a common - GND, with individual + supply. This behaviour defeats the use of a common +V. Also GND indicates a connection to a common ground (earth).
Thanks for posting DD. Yes, I did consider the points you made here about varying voltage levels and then of course it would make sense to have common GND (and they all get 'tied in' together). My question originally came out of fear (mostly) in that I have to make some serious inquiries into PCBs and UI systems very soon...I didn't want to get caught blindsided by my lack of experience/knowledge on the matter or be pigeon holed into designing the PCBA a specific way (further down the road) due to bad decisions early on. I swear I had one (just one) proto build back 2-3 years ago where I did in fact use common +V. I can't for the life of me remember why I would have done it this way in the past (possibly using only a single voltage level for everything...idk) but it got me spooked that maybe I was forgetting something I once knew, to the point that I thought I better ask here in the forum. I'm pretty sure I still have that proto build at work still so that I could review and maybe figure out why I did that BUT I CAN'T GO THERE RIGHT NOW BECAUSE I/WE ARE CONSIDERED NONESSENTIAL!
Is there any reason for me to think that common +V might be 'a thing' and that a true commercial quality PCB (manufacturer) may instead want to use common +V instead of common ground?
Can you explain why you are asking, because I cannot see any reason for your question.
Some things that might help you:
The PCB manufacturer doesn't care, they will make whatever design you send them as long as the files you give them meet the design rules for their process, which they will if you have used one of the common PCB design packages.
You are, I think, confusing ground with the -ve supply from the power supply. Ground / earth / 0V is the common reference point in the circuit. It might be connected to the chassis of the equipment. It might be connected to the mains electrical earth on mains powered equipment. On many PCBs there is a 'ground plane', which is a big area of copper on on side forming the 0V connection. In many circuits ground / earth / 0V is connected to the -ve pole of the power supply, which is why they get confused. However, it does not have to be that way. In my industry, telecoms, equipment typically runs on -50VDC, so the +ve pole of the power supply is connected to the ground (physically connected, with a big electrode buried outside), and is the 0V connection. In analogue audio circuits there is typically a -15V, 0V, +15V supply, so the middle is ground, not -ve, not +ve.
It is common practice inside equipment to make connections off the circuit board common ground, for example maybe there's a circuit board buried deep inside a machine and a cable to a panel with buttons and lamps on it. The cable could get damaged and short to the chassis of the machine. If everything is common ground then the worst that happens is wires that were ground anyway get shorted to ground, so no power supply gets shorted out.
If none of that answers your question then please ask a clearer question.
Hi,
Common gnd is basically a standard, so any filtering and EMR problems can be easily addressed as well as making different power busses easier to handle as already discussed.
Tom... 
IF you are in the USA, are you also designing so your product will eventually pass the FCC tests?
Paul