Microcontroller multiplexes six digital potentiometers

Ted Salazar, Maxim Integrated Products, Sunnyvale, CA -- EDN, 5/11/2000

In Figure 1's circuit, a µC lets you adjust as many as six digital potentiometers. Like mechanical potentiometers, digital potentiometers can adjust regulator outputs or speaker volumes and act as rheostats. Available in resistances of 50, 100, and 200 kV, they let you throw away your mechanical potentiometers and the little flat-headed screwdrivers that go with them.

A DIP switch, two pushbutton switches, and IC₆'s µC control the six digital potentiometers, IC₀ through IC₅ in the circuit. All of the potentiometers have a nominal end-to-end temperature coefficient of resistance of 50 ppm/°C. At power-up, each potentiometer assumes its midrange value of resistance. Each wiper connects to one of 32 equally spaced taps along the linear-taper resistance between the H and L terminals for that potentiometer.

Of the 13 I/O ports on IC₆, Port A (A₄ through A₀), comprises the inputs. Port B (B₇ through B₀) comprises the outputs. To operate this manually controlled digital system, you select the desired potentiometer by setting a code via the DIP switches (Table 1) and then increment or decrement the potentiometer via pushbutton switches that connect to A₁ and A₀ (Table 2). Click here to obtain the µC's assembly-language program. (DI #2529)