I am trying to measure voltage with PIC18F1320 microcontroller. Power supply to MCU is 5V. Measured voltage will be applied to analog microcontroller input (ADC) and in normal case will not exceed 5V. But in sometimes it can rise to 10V. I think it can be dangerous to my MCU. So i want to limit input voltage to, say 5V maximum. So i want to do voltage limiter with zener diode. What zener should i choose, and how choose series resistance? Zener must do no influence to my measurement results, while input voltage will not reach 4 or 4,5V.