The rotor of this electromechanical rotary encoder is composed of three resistors having 560, 1000 and 2200 Ohms soldered on a washer. One wiper makes steady contact with the washer, pulling the potential to ground while the second contact is connected to the +5V pin of an Arduino through a 1 kiloohms resistor. We get a reading of 5000mV, thus 5V whenever the switch is open. If the switch gets closed through the 560 Ohms resistor, a voltage divider composed of a 1 kiloohm and a 560 ohms resistor at 5V input voltage is formed. In theory we get a voltage drop of 1.79V across the 560 ohms resistor.”