I have an analogue system supplying 0-28V which I intend to reduce to 0-5V with a voltage divider (3.9K and 18K in this case).
Assuming an absolute maximum allowable input of 5.5V to an Uno pin, this means the supply is allowed to get to ~30.9V but "just in case" I want to put a bit of added protection in the circuit.
To me, the easiest way to do this would just be to put a 5.1V zener in parallel with the 3.9K resistor. That lets the input voltage drift a fair way with the 18K resistor still providing a limit on the current.
People on here seem to really be against doing this though and always suggest a crowbar circuit instead. So, please, I would like to learn why is the added complexity of the crowbar is so much more advantageous in a situation like this?