Archive of the former Yahoo!Groups mailing list: MOTM

Anybody got their joystick circuit drawn up yet? Since I already have my
joysticks, I am just about ready to start mine. After some advice from
Paul and some great reading in "The Art of Electronics" I think I am ready.
It really seems simple.

My joystick pots are only 5 K. So, I am planning two resistors (12K or
larger) in series with each end to the -/+ supply to limit the current in
the joystick pot and reduce the voltage out from the joystick pot to about
0 to 5 VDC (maybe a little less). I plan to have a 100K pot for "offset"
and sum that voltage on the front end of an op amp motm style. The summing
resistors would set the range for the offset. Then I plan to attenuate the
whole thing at the front of the op amp and make that pot a "gain" pot to
control the total voltage range of the joystick. The first op amp will
have a gain of about 2 or 3 depending on the voltage I end up with out of
the joystick pot. I want that voltage out to be about 10 VDC with the gain
at maximum. That will provide the first output from that axis. That
voltage will also feed a no-gain op amp. Both op amps will be inverting.
So, the output of the second op amp will be just opposite of the first at
the same magnitude.

Multiply that whole thing times two for the other axis and I am done. So,
I end up with 4 buffered outputs (X+, X-, Y+, & Y-) and four pots -- offset
(or trim if you prefer) and gain for each axis.

The idea of the offset control lets you do two things:
1 - exactly zero the voltage when the spring return joystick is at center.
2.- set some voltage other than zero to the center point.

When I get the whole thing done I will share my results. This seems simple
enough that even a non-engineer stooge like me will not screw it up. If I
do, then someone with a little more skill in this area can correct me (if
that is possible <grin>).

Larry Hendry