# More accurate potentiometer?

T

Jan 1, 1970
0
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

R

#### Rich Webb

Jan 1, 1970
0
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.

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. D #### dB Jan 1, 1970 0 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. T #### themadscientist Jan 1, 1970 0 Thanks for the explanation on backlash. I've never heard that term before, but I'll definitely keep an eye out for it. [email protected] (dB) wrote in @posting.google.com: T #### themadscientist Jan 1, 1970 0 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. 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.

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.

D
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