I have all the information I need to build a Optical controller (wheel,
gas, brake, clutch) except for the resistance value range. Since I haven't
yet found a schematic for a USB port, I'll be building this for the Sound
card game port. I know I can run from 0 ohms to at least 250K ohms but what
is the sweat spot range for controller resistance?
I remember reading a site on the subject but I can't remember anything
about it. If you don't know the above answer and can't answer me directly,
Could someone point me to that site, assuming someone knows what site I'm
talking about?
--
Michael A. Barlow
FILSCA (www.filsca.com)
Michael Barlow <[email hidden]> wrote in message news:0SVJ7.75836$[email hidden]...
> I have all the information I need to build a Optical controller (wheel,
> gas, brake, clutch) except for the resistance value range. Since I haven't
> yet found a schematic for a USB port, I'll be building this for the Sound
> card game port. I know I can run from 0 ohms to at least 250K ohms but what
> is the sweat spot range for controller resistance?
I believe 0-100k is standard. Certainly my single-axis
pedals use two 50k pots wired in series...
HTH,
Jonny
I've used 100K and 50K pots in my old wheel, using full range. Both worked well
and didn't seem to make any difference in my lap times or car control, although
the 100k was a little more jittery (+/- 2) at the high end this was off-set by
the better resolution. IMHO I would think 250k would be too high (see below).
Don't remember the exact cal numbers I was getting, maybe 0-250 for the 50k and
0-500 for the 100k?, but the counts will depend on the speed of the computer
anyway (cel 600,->faster gives higher counts).
There used to be a site giving the workings of the standard gamecard and the
dedicated gamecards at http://www.gplonline.com/tech-talk/hardware-tech.htm but
the link is dead now.
From memory the jist of the site was that there is a trade off between
resolution and speed. The standard gameport times how long it takes a capacitor
to charge to give the count seen in the cal menus (one for each axis). The
higher the resistance the less current flowing, requiring more time for the
capacitor to charge giving a higher count. So using a higher resistance range
will give a bigger range during cal, giving better resolution. So larger ranges
sound good, but there is problem. Higher resistance (counts) requires more time
for the gameport to read the signal. If "poll with interrupts" is used then the
program must wait for the gameport to do the count causing drops in frame rates,
etc. If poll with interrupts is not used then the counting can be disrupted by
other devices giving spikes and excessive jitters (I may have this reversed?).
The other problem with using high resistance is that the currents in the wiring
are lower so that background noise now becomes more apparent causing more
jitters.
So what to do? Use the lowest resistance range (count) you can live with based
on resolution (i.e. do you need to steer in 1/1000 increments with some jitters,
1/100 without jitters, or maybe 1/500 with a few jitters) Also use the low end
of the pots, use shielded cables, and keep the cables as short a possible to
reduce noise. Or get a dedicated gamecard if you still have an isa slot and can
still find one. Don't know if a gameport to usb converter exists or not?
Ken
PS How do these optical controllers work... can you give a link or part #?
Michael Barlow wrote:
