I'm looking for ideas on how to protect A/D inputs from disaster. My current application is automotive, but I seem to be blowing up the AD ports pretty regularly.
Zeners are not ideal (they don't always trigger at a voltage low enough to protect the port).
My understanding is that the port is good to Vcc + 0.3V; after that you can blow the port or the whole chip.
If I use voltage dividers and set VREF lower (say 2.56V) using analogReference(INTERNAL2V56) does that give me room between 2.56V and Vcc+0.3 for over-voltages? Then I could use a 4.5V zener without any trouble.