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

[Cris Harrison]

On 2/21/2012 3:28 AM, Roy Coates wrote:
>
> The signal you (and the boards) are interested in is between the wiper 
> and the ground pin. The voltage on the wiper will vary from the supply 
> voltage (on your + pin) and the ground pin.
>
> So, wire your supply voltage to the + pin.
> wire your - pin to the ground.
> Take a wire from the wiper to the input of your plasma board.
>
> Roy.
>
>
> On 21 February 2012 06:24, <dabigboy at cox.net 
> <mailto:dabigboy at cox.net>> wrote:
>
>     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
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Roy you are right that how a pot works but Mat is going down the wrong road.
1. Gables heads use ARINC410
2. They do not generate a voltage, frequency or anything else.
3. They are a 5 bit device not 8
4. They are LOW active.  I have not looked at yours but the resistors 
are pull up.
5. to show you self whats going on get 5 leds and wire them to the 
channel (one led per bit) the other end to power.  (check to see which 
way your led goes and remember to use a 220 ohm resister in series with 
the led to limit its current and not burn out)
6. Freq selector common to logic ground
7. now watch the leds as you rotate the knob..

also send me your pdf and I will look at it for you...
harrison at phoenixaerospace.us


Cris.



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