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View Full Version : Rotary Encoders (slightly) Demistified



Kennair
09-23-2007, 09:44 AM
I don't know about others but I have battled over the technical description for rotary encoders since I started in this business (hobby). 1/4, 1/2 wave, detents, clicks, pulses. Perhaps it's just me but I couldn't get the hang of what was actually needed for most cockpit interface cards. But I found a description that satisfies me so I thought I'd share with others who might be having a similar dilemma.

I found it trawling the Avsim forum and it's from long standing member Tuomas in response to a question from another contributor:

8565, RE: Dual and Triple Rotary Encoders
Posted by tigert, Thu Jan-01-70 07:00 AM

>I have 3 questions:
>
>First: "6 cycles 24 detents" Does this mean you can cycle only
>6 times 360 in one direction?

At least with iocards one bit change causes one event. The "cycle" is one "full cycle" of the encoder *waveform*, ie: 00->01->11->10 is one cycle, whichafter it repeats the signal pattern - and "1/4 cycle per detent" means each of those 4 steps has a "click". So 4 clicks to go through the full waveform. 6 x 4 cycles = 24 clicks = 24 events. So it works like you hope it does - one detent causes one event, even though the "pattern" is repeated only 6 times in a full circle of the knob. But the electronics usually work in the "24 events" -level.

>Second: What means detents? For example: if I use the switch
>to adjust a heading bug which is moving one degree per click,
>do I need to cycle the rotary 2,5 times 360 to move the
>heading bug 10

A detent is the "click". So yes, turning the knob a full circle gives you 24 events. But at least FSBUS and IOCards have a "acceleration" feature in the software that you can make to "kick in" when you rotate faster, thus making it more useful for things like heading or altitude preselect which you need to move quite big values, but still need rather fine grained precision once you get close to the desired value.

>Third: Has the triple rotary three rotary's or two rotary's
>and one push switch?

This is something I want to know better too. It would be best to list all the different options, and what the prices will be, to make it less confusing. Pictures would be nice to see also.

//Tuomas

Here is the full thread: http://forums.avsim.net/dcboard.php?az=printer_friendly&forum=142&topic_id=18538Based on this explanation I found a rotary encoder in Australia through Radio Spares that conforms to the required specs, however they are $12.70 each and don't come with a switch. Hence it's more cost effective to buy them online from overseas and get them with a switch!

Anyhoo! :?