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Topic: Wheel Potentiometer (Read 3 times) previous topic - next topic

andyopayne

I'm thinking about making a forward kinematic arm (sort of like a microscribe - http://microscribe.ghost3d.com/gt_microscribe.htm) and I need to find a way to determine the angle between each leg.  My thought had been to use a potentiometer at each joint, and just convert the analog value into rotational degrees using a little math.  I found these really small wheel potentiometers at radio shack (http://www.radioshack.com/product/index.jsp?productId=3064080) that look like they could do the trick, but they have 5 pins instead of the typical 3 that I'm used to (Gnd, 5V, and pin).  I believe these wheel pots are generally used for audio control, but I'm wondering if you guys can help me figure out how to wire it up (ultimately, I'm hoping it works just like a standard pot in that it returns a value between 0-1023).  In the comments section, I noticed one poster states:

Place it with the pins pointing down and the 5-pin edge facing toward you. From left to right, the pins are:

1) Common (GND for audio use)
2) R1 Wiper (Out 1 for audio)
3) R2 Wiper (Out 2 for audio)
4) R2 End (In 2 for audio)
5) R1 End (In 1 for audio)

The only thing is that I'm not using it for audio.  Is there a way I can wire this to just return a single value?  Thanks in advance for the help.

AWOL

Common to ground, R1 wiper to analogue input, R1 end to 5V.

I think I saw a comment it's a log device.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
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andyopayne

That's perfect.  Thanks for the advice.  You mentioned that you thought it was a log device... I'm guessing this will make it more difficult to find the exact angle (or position) of the pot because I can't use a linear correlation... hmm. I'll have to think about that one.  Thanks for the hookup suggestion.
Cheers,
Andy

zoomkat

You might try the below trim pot.  

http://www.radioshack.com/product/index.jsp?productId=2062301
Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

RuggedCircuits

Potentiometers will be OK for prototypes, but long term reliability and accuracy is not good. If you want a demo project they'll be fine; if you're actually trying to make accurate measurements....you're going to get some pretty noisy data as the pots degrade.

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andyopayne

Thanks for the help.  The device I'm making doesn't have to be all that precise (I'm thinking more in the line of an instructable).  It's definitely in prototype phase.  I think I'll try the trim pot suggested above, but if those fail, I'll try an optical shaft position encoder.  Anyone know where to get one of those?

RuggedCircuits

Avago makes some optical encoders:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=516-2018-ND

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