Hello
I want to measure the battery voltage (ballpark measurement) in a car so I thought I do that with a voltage divider connected to a msp430 ADC pin, but I wanted to add overvoltage protection with a zener as in the schematics in the link below. I am using 100k / 10k in the voltage divider and a BZX79C2V7 zener. If I leave the zener disconnected I get the divider to work as expected in a linear fashion, but when I connect the zener I get the correct reading when the input voltage is 10V but if for example I double the input voltage to 20V I get a lower reading compared to when the zener