250 K ohm pots

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stickMaker
Posts: 55
Joined: Thu Dec 01, 2005 7:44 pm
Location: NYC

250 K ohm pots

Post by stickMaker »

Can the modules be made to work with a 250K ohm pot? I know as they are now they won't, but can you do something on your end to widen the range? This way smaller degrees of mechanical movement can cover the 0 > 100K ohm electrical range, beats using gears!
TY
Guido Körber
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Post by Guido Körber »

The modules could be modified to work with 250K pots, but not to use only a part of the resistance range.

You should look for pots with a smaller electrical angle. Typical pots for joystick applications have 50-65 degree electrical angle. Even though the pot can mechanically travel 270 degrees, the change of resistance is happening in the smaller range.
stickMaker
Posts: 55
Joined: Thu Dec 01, 2005 7:44 pm
Location: NYC

Post by stickMaker »

Guido my friend,
I did that very thing, surfed like a mad man. 270 degree ( single turn )was all I could find. Its like thier not available unless you order specific like, could find nothing off the shelf. Even my rudder pedal does not use 60% of the pot, I added a switch at the jumper 1 port, lifted one side of the auto centering and it works great. It does not have to be as subtle as the stick. My P 51 stick uses slide pots, 90% of range is used and it works nice with your usb mod. One of the pots in the spitfire stick is also a slider. I had to use a rotary in that upper pivot point tho, maybe using 80 degrees of range only. Gearing would have made it to bulky. Can they be made as a two wire system. The computer wants a 5 volt signal attenuated between the 0 > 100K Ohm range. Just asking. lol
Guido Körber
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Post by Guido Körber »

OK, first to answer your questions about alternatives: We chose the ratiometric method to measure the pot position, which means we are taking a reading of the resistance between the wiper and each of the ends. This allows us to compensate for tolerances in the absolute value of the pot and get a pretty good center value as well as a quite stable reading considering the simple conversion method.

The game port method uses only two of the pot connectors but has the problem that it does not get a good center value if there are tolerances in the pots. This is a totally different approach and not compatible with JW25A8-x.

Using pots with significantly different values does not work because the JoyWarrior expects a certain range for the charge time of the measuring capacitor.

Trying to use only a part of the pot does reduce the effective resolution since you still measure the full resistance range with the 8 bits but you use only part of that.

Agilent (HP) used to make the right kind of pots. But since HP has done yet another reorg (Agilent is only measurement now, components is Avagotech) these products have been moved elsewhere. Avagotech seems to have only the optical stuff from Agilent and I have not yet found out where the passive parts have gone.
stickMaker
Posts: 55
Joined: Thu Dec 01, 2005 7:44 pm
Location: NYC

Pots

Post by stickMaker »

:)
Did you ever find where to get pots that use smaller elec angles? I did not.
Still useing the spitfire style stick, but I got a gameport to USB adapter, which did improve the performance a little. Still useing a 250 k ohm pot on the X-axis.
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