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Absolute encoder for anemometer direction indicator?

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John Hill:
I need to make a direction sensor for a replica WWII airport control tower and all the synchros/selsyns I have are too big and clunky for the lightweight mast.

So, here is the idea.  Make a wind vane in the traditional pattern with a vertical shaft and a (slightly) off centre steel disk mounted on the end of the shaft.  A hall effect sensor is mounted close to the edge of the disk and sees a varying gap as the wind vane revolves with changes in wind direction.  A second hall effect sensor is mounted 90 degrees from the first.  The two sensors are connected to an Arduino.

Now the questions,  are two sensors enough to read absolute position of the disk and hence the wind direction?

John

philf:
Hi John,

I'd say no it wouldn't work - there would always be two possible positions up to 180 degrees apart giving the same result. Do Hall Effect sensors give an analogue output? I've only used them as a digital sensor for speed or position sensing.

Phil

Edit: Sorry - I was talking utter crap when I said there would be two positions giving the same result. I also found some analogue output Hall Effect sensors which I didn't know existed. However they are looking at a magnetic field and your off-centre disc would have to be magnetised axially so the polarity didn't change as it rotated. The maths involved are also quite complex. How did you propose calculating the angle from the two measurements in the Arduino?

awemawson:
What is wrong with a standard encoder based on a slotted (or reflective) disk. Quadrature output will give you up/down counts (CW and CCW in your case) to apply to a standard counter and a reference marker can zero your counters at (say) true north  :scratch:

John Rudd:
Gray encoding?
I think epe magazine did a weather station project that used Gray coding for the weather vane, but it was some years back.....

I came across this too.....might be food for thought...

http://sandaysoft.com/forum/viewtopic.php?t=4570

John Swift:
Hi John

EPE Dec04  wind indicator

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