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Planetarium program can't sense direction of encoders

equipment dob mount planetarium software
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#1 Chris Westland

Chris Westland

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Posted 06 February 2021 - 02:45 PM

I thought I'd start this topic because I ran into a problem using SkiSafari Pro that I've seen on several forums (including Simulation Curriculum's own) without a resolution.  (but I have one here).

 

My problem was that the direction of the Alt/Az axis on my dob (HO14") using the SkyHub-B box, and Basic Encoder setting on SS6, were moving the cursor the wrong direction on SkySafariPro 6 (SS6), no matter whether I specified +8192 or -8192 ticks on either axis.  So everyone is blaming SS6 for not fixing the problem, right.  

 

It turns out I have a bad cable, and changing the cable rectified the problem.  

 

Here is my explanation of what happens.   When you lose one of the two channels from a quadrature encoder (what is used on most amateur scopes) the scope knows 'how much' to move, but not which direction.  The code disk inside a quadrature encoder contains two tracks usually denoted Channel A and Channel B. These tracks or channels are coded ninety electrical degrees out of phase, and this is the key design element that will provide the quadrature encoder its functionality. In applications where direction sensing is required, a controller can determine direction of movement based on the phase relationship between Channels A and B. When the encoder is rotating in a clockwise direction its signal will show Channel A leading Channel B, and the reverse will happen when the quadrature encoder rotates counterclockwise.  Apart from direction, position can also be monitored with a quadrature encoder by producing another signal known as the “marker”, “index” or “Z channel”. This Z signal, produced once per complete revolution of the quadrature encoder, is often used to locate a specific position during a 360° revolution.

 

Anyway, the cable was old and both axes had problems (not always at the same time) so the problem was sporadic.  

 

Moral:  before blaming the software, check your cables and encoders.

Attached Thumbnails

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Edited by Chris Westland, 06 February 2021 - 02:50 PM.

  • btschumy, Xeroid and Adun like this

#2 StarryNightGuy

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Posted 08 February 2021 - 09:11 AM

Chris,

 

Amazing sleuthing! Thanks for the detailed report. I'll disseminate this wherever appropriate.

 

- Dave




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