Original Circuit Diagram: Arduino UNO R3. Now, have a look at our favorite Arduino UNO to find out the AVR chip inside. It is ATMega328P-PU, a low-power version of the traditional ATMega328-PU. The P ...

As a industrial controls engineer that has worked globally, keep the arduino in hobby zone where it belongs. There are machines running with 20, or 30 year old control systems that are PLC controlled.

The resistor values (R1&R2) in the circuit diagram provide some over-voltage protection then measuring low voltages. Keep it in mind that any input voltage higher than about 55V could fry the Arduino.