Single switch controls digital potentiometer

Edited by Bill Travis

Chuck Wojslaw and Gary M Craig, Catalyst Semiconductor, Sunnyvale, CA -- EDN, 2/7/2002

The control of electronic potentiometers in most today's applications comes from controller-generated signals. However, a significant number of applications exist that require adjustments using manual, front-panel controls. The circuit in Figure 1 uses one IC, one switch, and 10 discrete components. It implements the interface of a single DPDT, momentary-contact rocker switch to a DPP (digitally programmable potentiometer). The Catalyst DPP has a three-wire increment/decrement interface. The traditional way to implement the front-panel controls for potentiometers with this type of interface is to use two single-pole, single-throw switches. Switch S₁ reduces the front-panel hardware by half. The action of the switch is natural for the control of increment-up/increment-down potentiometers.

IC_1A and IC_1B, which implement an R-S flip-flop, control the potentiometer's wiper direction—up or down. The output of the flip-flop reflects the up/down position of S₁. The potentiometer's wiper advances on the falling edge of the signal driving the input of the DPP. The clock output of IC_1D drives . The clock becomes enabled when you depress the rocker switch either up or down. The RC networks at the inputs of IC_1C debounce the switches. If you momentarily depress the rocker switch, the clock generates one pulse. If you continuously depress the rocker switch, the clock free-runs at a frequency of approximately 1/R₁C₁.

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