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More accurate potentiometer?

Discussion in 'Electronic Basics' started by themadscientist, Apr 19, 2004.

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  1. I'm using the linear pot here:

    http://tinyurl.com/3ctuf

    interfaced into the joystick port of a PC. The problem is that it's not
    very accurate. For instance, during the first and last 30 degrees of turn,
    the pot doesn't register any change. I've also just noticed that a
    position on the pot changes depending on which direction I'm turning. If I
    change my code to do something when the pot hits 180 degrees, it may work
    correctly if I turn clockwise, but when I turn counter clockwise, that 180
    position is closer to 145 degrees.

    I'm trying to simulate a radio dial, so the positioning needs to be pretty
    accurate. Any thoughts on other options? I tried Beau's suggestion of
    using a 74HC14, but Linux seems to have a hard time getting an accurate
    timing.

    Thanks
     
  2. Rich Webb

    Rich Webb Guest

    FYI, many people *never* follow tinyurl links.
    See "The Secret Life of Pots"
    http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

    If you really need a precision pot, they're available but are priced
    accordingly. Something like this http://www.bourns.com/pdf/3590.pdf will
    run you about $10 qty one.
     
  3. dB

    dB Guest

    The basic problem is that you are using a crappy pot.

    There is lost motion, sometimes referred to as backlash, between the
    shaft and the moving contact.

    You will also notice on the spec. sheet for that pot that they state
    the (mechanical) rotation but coyly avoid mentioning the electrical
    rotation. As you have discovered the latter is quite a bit less than
    the former. A decent pot. manufacturer will tell you both figures.


    The answer to your problem lies in using a better made product, i.e.
    one with zero backlash. Or you could, perhaps, open up a pot and
    eliminate the lost motion with an application of epoxy glue.
     
  4. Thanks for the explanation on backlash. I've never heard that term before,
    but I'll definitely keep an eye out for it.


    (dB) wrote in @posting.google.com:
     
  5. FYI, many people *never* follow tinyurl links.

    I know, but the mouser link took three lines and I figured people would be
    even less inclined to use that one.


    That link is great, thanks! I knew in the back of my mind that $1.50
    wasn't buying quality, but I didn't think they would be as crappy as they
    are. Thanks for taking the time to help out.
     
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