Limited OI Range From Linear Slide Potentiometers

[Jake M]

Well, we're currently using a 20K ohm rotating pot and we can get values from 0 to 1024 without any other resistors. Don't ask me how, but that's what happens. Just to clarify, is your wiring something like this....

Potentiometer Diagram
------------------------
(1)________________(3)
(2)________|
------------------------
Pin 1 on pot to red +5V pin on analog input.
Pin 2 on pot to white signal pin on analog input.
Pin 3 on pot to black ground pin on analog input.

[Dave Flowerday]

Originally Posted by Jake M

Well, we're currently using a 20K ohm rotating pot and we can get values from 0 to 1024 without any other resistors. Don't ask me how, but that's what happens. Just to clarify, is your wiring something like this....

It looks like the pot you're talking about is connected to the Robot Controller (because the RC can measure 0 to 1023, the OI can only measure 0 to 254). The original poster is talking about a pot wired to the Operator Interface, which measures analog signals differently than the robot controller. It requires 100K ohm pots (or else some fancy trickery) to work correctly.

[Chaychay]

Thanks for the replies everyone!

Yeah, I was under the impression that the OI needed 100 K ohm resistors as per the manual, however I have 2 reasons to believe otherwise:

1. http://www.chiefdelphi.com/forums/sh...4&postcount=15

2. We have a 10 K potentiometer wired as well, and it works just fine, we get the whole 255-0 range corresponding to the whole range of the pot.

If anyone has any other suggestions, please let me know. Thanks a ton!

[Mark Pierce]

First, there are posts in this thread that are confusing the RC inputs with the OI. This thread is about the operator interface, not the Robot Controller, they are different designs.

The wiring is currently: Negative on pot to pin 4 on OI (ground). Positive on pot to pin 1 on OI (+5 V), & signal from pot

The Operator interface is designed to work nominally with a 100 K ohm variable resistance (potentiometer or switched resistors) with only two connections as shown in IF documentation and the 2007_Guidlines_Tips_Good_practices document. It probably will generate values throughout the range of a 120K pot due to various tolerances.

Disconnecting your ground should give you a range of values of around 128 values (I forget if it is 0-128 or 128-255).

By connecting the ground you are drawing more current than intended by IFI and thus messing up their current measuring circuit and software. Connecting a pot in this manner can also cause the OI input to look like a disconnected joystick which will generate a 127 as an output value at one end of the range.