A growing trend in the design of electronic equipment is to replace analog knobs used to increase or reduce a continuous signal (such as volume or brightness) with "up" and "down" keys. However, replacing a low-cost analog potentiometer with a digital potentiometer can be costly. The low-cost circuit in Figure 1 can eliminate the analog potentiometer in many applications. The circuit is based on a 16-channel CMOS multiplexer/demultiplexer and a string of resistors.

The circuit in Figure 1 can control such parameters as the view angle of an LCD screen or the volume in audio applications. One of the main advantages of this design is that a microcontroller and associated software can control it. The microcontroller system can, for example, adjust itself or calibrate peripherals depending on external conditions. With some extra logic (Figure 2), the digital potentiometer can work as a stand-alone system.

The range of the potentiometer depends on the values of the resistors. If you choose equal-value resistors, you obtain a linear potentiometer. (For example, 15 resistors of 330(ohm) produce a 5-k(ohm) potentiometer.) If you mix resistors of different values, you can configure a nonlinear potentiometer, such as one with a logarithmic or audio taper. (DI #1800)