I was going to tag this onto the end of another thread but I think it's actually a bit of a different question. I started by reading this document: https://www.digikey.com/en/articles/protecting-inputs-in-digital-electronics
I understand what's going on, and it seems that voltage spikes can come from long wires, particularly in an Automotive environment. I have one instance on a board design, where I want to read several switches from an indicator and wiper stalk in a car, and they all switch to ground. The switches will only be a few cm from the Teensy Arduino I intend to read them with, but the ground path to the battery will obviously be much longer, so I guess any voltage spikes are likely to come from further down the path. Since I have 13 input, I want to try to avoid placing 13 optocouplers and resistors on my small PCB, so I was wondering whether I could be a bit smart and put the spike protection on the ground side, like I show below and thereby using just the one schottky diode. Could this work? I guess I may still need to add a small cap on each input, perhaps 100nF?