Limited OI Range From Linear Slide Potentiometers

[Chaychay]

Mr. Pierce, we tried disconnecting the ground as well, and got the exact same range of data from the OI. (0-255, but from 80% motion of pot)

Mr. Anderson, what is the "low end" of the pot?, what is the "wiper"?, sorry about my lack of terminology. Why a 22K resistor, why not say, a 50K?

Thanks for your help!

[Alan Anderson]

When I said "low end", I meant the end of the pot that you had connected to ground (as opposed to the "high end" which you had connected to +5).

The "wiper" is the traveling contact inside the pot that sees a different resistance to the ends of the pot based on its position. I think you called its pin the "signal".

I suggested 22k ohms because that way your total resistance will change between about 22k and 72k, with center being approximately 50k. The standard 100k joystick pot also has the center being approximately 50k. You will seea limited range of values being read by the OI, from about 60-190 instead of 0-254, but you should get usable values from the full range of travel on the slider.

[Chaychay]

Mr. Anderson, Thanks very much for the explanation, it makes things a lot clearer . We will definitely try this out tonight.

[Dave K.]

Originally Posted by Alan Anderson

When I said "low end", I meant the end of the pot that you had connected to ground (as opposed to the "high end" which you had connected to +5).

The "wiper" is the traveling contact inside the pot that sees a different resistance to the ends of the pot based on its position. I think you called its pin the "signal".

I suggested 22k ohms because that way your total resistance will change between about 22k and 72k, with center being approximately 50k. The standard 100k joystick pot also has the center being approximately 50k. You will seea limited range of values being read by the OI, from about 60-190 instead of 0-254, but you should get usable values from the full range of travel on the slider.

Alan,

Of course this will approximately center the pot's range in the reported A/D value range, it does so at the expense of cutting the resolution in half.

I'm not certain that this was clear in your origional post.

I do agree that it is an entirely practical and workable solution, but if one is concerned with being able to generate a full range of values, then one end of the pot needs to be lifted with a series resistor to accomplish that goal.

Thanks,

[Chaychay]

Dave,

Thank you very much for your insight! We added a ~1.5K resistor to our 10K pots, and they work a lot better now. (full range of motion w/ full range of values).

We discovered yesterday that our slider was actually not linear, it was logarithmic. (WARING: If your buying from a "surplus" store, make sure you are buying a linear one (you can check with a multimeter)).

We found another one @ mouser, so that should be ok.

Thanks for all the help from everyone!

[Mike Betts]

Originally Posted by Chaychay

Mr. Pierce, we tried disconnecting the ground as well, and got the exact same range of data from the OI. (0-255, but from 80% motion of pot)

Mr. Anderson, what is the "low end" of the pot?, what is the "wiper"?, sorry about my lack of terminology. Why a 22K resistor, why not say, a 50K?

Thanks for your help!

Jay,

Read paragraph 3 of page 5 of this document to understand what is happening.

Regards,

Mike

[Dave K.]

Originally Posted by Mike Betts

Jay,

Read paragraph 3 of page 5 of this document to understand what is happening.

Regards,

Mike

I'm glad to see that they've finally posted an updated version of the OI document with some additional explanation, but my measurements here indicate that the "cable off" threshold is higher than the 50mV they state. On one unit here, where the +5V Aux voltage was running about 100mV high, the end of travel was reached at 632mV and the cable disconnect voltage was right around 500mV.