An unbuttoned circuit for setting digital pots
This Design Idea enables you to program digital potentiometers with inexpensive rotary incremental encoders.
Recent Design Ideas for circuits that manually control digital potentiometers have mostly “revolved” around UP/DOWN pushbutton switches. I’ve certainly resorted to that same “reciprocating” recipe myself.
But the fact remains that after a lifetime of dialing in analog parameters like audio volume and tone adjustments, lamp dimmers, water faucets, etc., with rotatable knobs and levers, UP/DOWN buttons just don’t, and probably never will, really feel natural.
Wow the engineering world with your unique design: Design Ideas Submission Guide
So I was pleasantly surprised to recently come across a series of inexpensive (~$2 apiece in single units and, of course, cheaper in quantity) rotary bidirectional incremental encoders offered by Bourns (with whom I have no personal affiliation aside from from-afar product line admiration). That’s cheap enough to compete head-to-head with push buttons.
And they’re just as simple (or even moreso) to interface to an increment/decrement DPOT! Figure 1 shows how it works.
Figure 1 This 24 pulse-per-rev quadrature encoder can run the 128 position DPOT U2 from limit to limit with just 5 + 1/3 quick rotations, easily completed in about as many seconds.
The contact-type rotary encoder generates 24 quadrature pulses per turn, as shown in Figure 2.
Figure 2 The quadrature phase relationship between encoder A and B contacts causes clockwise rotation to increment the DPOT setting, and counterclockwise rotation to decrement it.
Contact A provides clock pulses that are signal conditioned (debounced by R3C1) and sharpened (by Schmidt trigger U1) for presentation to U2’s edge-triggered Clock pin 1 input, causing U2 to execute an increment/decrement operation when A goes from ON to OFF.
Quadrature contact B is time-delay matched (by R4C2) and connected to U2’s Up/-Down pin 2 input. Figure 2 shows how the quadrature phase relationship between A and B causes U2 to count UP on each clock pulse when rotated clockwise, and DOWN when rotated counterclockwise.
Tastes will obviously differ, but for mine, when compared to button pushing, this method definitely offers a turn for the better.
Stephen Woodward‘s relationship with EDN’s DI column goes back quite a long way. Over 200 submissions have been accepted since his first contribution back in 1974. They have included best Design Idea of the year in 1974 and 2001.
Related Content
- DPOT push up/down
- Finger-friendly DPOT pushbuttons do ups, downs, and dittos
- Push to increase, decrease a digital potentiometer
- Digital potentiometer simulates log taper to accurately set gain
- Synthesize precision bipolar Dpot rheostats
The post An unbuttoned circuit for setting digital pots appeared first on EDN.
