Control Shaft Encoders

Introduction:

I ordered a Grayhill control knob encoder for a lighting control project but found that the device was unsuited for the application (mostly it was noisy and it was a bit hard to turn). So I ordered a Panasonic one. It was unsuitable for a different reason. So I decided to investigate the market. The results became an article in Circuit Cellar issue #250 (May 2011) . A few interesting facts were uncovered and I found that data sheets for these devices were all over the place in their usefulness.

The line-up:

Here's a photo, similar to the one in the article, of all the devices I investigated. The table below the photo gives lots of detail. Note that the first 7 were obtained from Digi-Key and the last 7 from Mouser.

Findings:

• The most surprising finding was that most of the units did not provide one mechanical detent per code position. Ignoring the 4 that have no detent (at least that fact was always obvious from information avilable from the vendors), there are only 2 that have 1 code per detent. It turns out that there are some advantages: requiring a transition on both tracks before a change in position is declared will reduce the effect of contact bounce (at a transition) and sliding noise (when a contact is moving on a metal region but dirt. etc. cause it to momentarily open). I'm not sure that there is any advantage to requiring that both signals need to transition both directions, which is the case when there are 4 codes/detent, over the 2 codes/detent design, though.
• The contact design that was most common is one that is not even recognized in the Wikepedia article on rotary encoders , nor in any of its references (still, even in 2022, at least). It is a rather clever design which involves three wipers spaced at 120° on a single rotor: they make contact with three regions, each tied to a device pin. One region is solid, and the other two correspond to the A and B tracks spaced at a relative 90° from each other. See the photo below, which is #4 taken apart (the grid on the underlay is 0.2").