Confused about potentiometer values

[Kirk]

We're trying to solve a problem using a steering wheel. We tried using a joystick potentiometer hooked up to the operator interface but, when we spun it to the 270 degrees that we needed, it only gave us the values from 127 till 170 while turning 45 degrees left and right of center. What kind of potentiometer should we use to correct this. We want it to read from 0 to 254 for the full 270 degrees.

[Joe Ross]

On the OI, you need 100 kohm linear taper pots. Do you know what value you were using?

You can get one that works for about $3 at Radioshack.

[steven114]

You can get them much cheaper from places online, such as Jameco or Digikey...

[Travis Covington]

We were using one pulled out of a joystick. Could the problem have been those potentiometers really only move 45 degrees, and as such, only effectively work through that range?

I am off to buy a radio shack 100k ohm pot and see if that fixes the problem.

Thanks!

[DonRotolo]

Originally Posted by Travis Covington

We were using one pulled out of a joystick. Could the problem have been those potentiometers really only move 45 degrees, and as such, only effectively work through that range?

Joystick potentiometers have a total of 90 degrees of rotation, and the full zero-to-100k Ohm range is limited to that 90 degree movement. A standard pot has around 300 degree rotation for the 100k range. Make SURE you use a LINEAR (also called B-Taper) potentiometer, NOT an A-Taper (Audio) pot!

Umm, how exactly do you have the pot connected? 127 to 170 is not a good thing, but maybe it's not connected right. There are three terminals on a pot, you need only two, the center and one end. (Your choice of end depends on whether you want the value to increase or decrease when you turn it clockwise). The one end goes to Pin 1 of the 15-pin OI port, the other end goes to Pin 3, 6 or 13 (depends on whether you want it to be read as X, Y or Thumbwheel axis, respectively). See the schematic. Any other connection would bring problems.

Good luck,
Don