[simpits-tech] Simple (?) electronics question - potentiometers

[dabigboy at cox.net]

Alright, got a little dilemma here, hoping someone can help. I am wiring up this Gables nav head for my sim, and the left side of the frequency selector (the 108-117) uses a bunch of resistors to determine frequency....basically, there are two signal pins. Resistance between those pins is varied depending on frequency selection. "Great!" methinks, "I can just wire this into a joystick axis and voila!" Old gameport joysticks just use two wires, so it should be OK, right? Well, apparently my controller (a Beta Innovations Plasma V2) REQUIRES the ground terminal of the pot to be connected.

It appears to me that all the ground pot does is provide a "reference" voltage, ergo, the max resistance of the pot. The Plasma manual says you hook the wiper terminal of the pot to any analog input, then hook the other two terminals (+ and -) to any common voltage and common ground terminal, respectively. A pot measures its max resistance between the + and - terminals, all the time....so, I tried using resistors to equal the max resistance of the resistor pack on the Gables unit, and wire that to a common negative and common positive terminal on the Plasma. It did not work.

How would I go about wiring this up? I don't really understand why the Plasma (and Bodnar board, for that matter) "need" the pots grounded to even just have the axis show up and move a little. Or is it that the Plasma needs to see the resistance between the wiper and ground be the INVERSE of the resistance going to the analog input? If that is the case, I'm not sure how I can make this work........

Matt