I need to monitor the status of a wire in an automotive application that can have 10-40VDC on it at any time. What is a good approach to limit the voltage to a microcontroller input across such a wide range? I plan to use a 10nF cap and TVS for ESD and other transients but I'm not sure the best approach to limit the expected voltage. If I can reliably detect 10V, 40V may burn up the input resistors (or resistor and zener?) or I can limit for 40V and not sense 10V.
The signal is a simple on off status line that I'm tapping into. It won't be carrying any data or change state very often. I will be sampling it occasionally in the micro to determine if it's high (1V to 40V) or low (GND to under 1V).
Edited to add that my microcontroller will be running at 3.3V and a logic low needs to be under 1V. Any solution I use must include a low value cap between the input and GND and either diode clamps to Vdd and GND or a Transil.