Single switch controls digital potentiometer

Texas Instruments SN74HC132


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.

A single switch is all you need to control a digitally programmable potentiometer.
Figure 1. A single switch is all you need to control a digitally programmable potentiometer.

IC1A and IC1B, 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 /INC input of the DPP. The clock output of IC1D drives /INC. The clock becomes enabled when you depress the rocker switch either up or down. The RC networks at the inputs of IC1C 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.

Materials on the topic

  1. Datasheet ON Semiconductor CAT5114
  2. Datasheet Texas Instruments SN74HC132


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