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Re: A2 Joystick Maintenance

Paul Schlyter wrote:

In article <H5mdnWUhguVQk77YnZ2dnUVZ_tednZ2d@comcast.com>,
Michael J. Mahon <mjmahon@aol.com> wrote:



Linards Ticmanis wrote:


Michael J. Mahon wrote:




A typical pot will require about 270 degrees of rotation for full
resistance, but a joystick usually provides only about 30-40 degrees,
necessitating use of a higher value pot.


It's also often helpful to connect a second, physically small, higher
valued pot in parallel to the main pot, to fine-tune things. Combined
with the usual sliders in the stick, this makes it easier to get the
stick into a state where the reading is really 0 at one end, 128 in the
middle and 255 at the other end of the scale.


To actually "fit" those two points (128 and 255) would require
*two* adjustments, not one--but one will help get to a better
compromise.



....and to "fit" all three points (0, 128 and 255) would require
*three* adjustments....


True, but one of the adjustments is mechanical.  I was talking
about the two electrical adjustments.


The 0 and 255 points are fairly easy to adjust though, by just choosing
appropriate values of the other resistors around it.  The purpose of
that pot in parallell is to get the 128 (or 127?) point right.


Actually, the most likely connection of a pot would adjust for a
0-255 range.  Working on the midpoint is a little trickier,
particularly since it's just a rheostat connection.


Correcting a pot for linearity is, in general, quite hard.



Indeed - and even getting all three of the 0, 128 and 255 points right
is no guarantee that the pot then is linear.  Otoh it won't mnatter
that much, since it's just about playing games anyway - right?


I hope I didn't suggest that hitting three points fixes a straight
line through 256 points!  That's why I said it was hard.  ;-)

It's a good thing that none of this really matters, since good
joysticks all have a mechanical centering adjustment that fixes
the midpoint (128), which is the appropriate calibration point for
most joystick uses.

-michael

New, faster SUDOKU v2.0 solver for Apple II's!
Home page:  http://members.aol.com/MJMahon/

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