Sometimes it is useful to have a variable resistor that can be controlled via a microcontroller, even if the adjustment resolution is not very fine. Often, as few as 16 steps are adequate (e.g., for volume control or tone adjustment). For this, searching in the component drawer, we might find some unused 4016 or 4066 CMOS chips. Inside these are four analog switches that can be controlled with as many microcontroller outputs. Using just one chip and five resistors, you can construct a 16-step variable resistor.