A simple circuit that demonstrates the usage of a single MOSFET to bi-directionally translate the voltage from a higher voltage source (12V in this example) to a lower voltage source (3.3v in this example. e.g. an Arduino). This circuit includes a 100 Ohm resistor to ground on the high-voltage side that serves as a pull-down resistor for a sensor that may leave it's output floating. You can also change the voltage to any voltage you like that may suit your application. Just remember to keep the voltage on the low-side (the gate and source voltage) lower than the voltage on the high-side (the voltage on the drain).
