Hi All,

Need some quick assistance for a project I'm taking to the Orlando Maker=20
Faire this coming weekend... I'd like to add seat vibration to a race=20
car simulator, which is essentially a PC-based race car game, race seat,=20
force-feedback steering wheel, pedals and gear-shift, but with real=20
gauges instead of the usual on-screen ones.  For the curious, gauge data=20
gets dumped out of the game (LFS) to UDP, Python takes that and spits it=20
out the serial port, a PIC18F takes the serial data and converts it into=20
a digital stream with 6 parameters, and each of the 6 gauges on the dash=20
will grab whichever piece of data they need from the bus stream.

This is what I have for the seat vibration...=20
http://www.thebuttkicker.com/gamer2 . It's essentially a subwoofer=20
that's bolted under the seat, but there's an issue in that it uses line=20
level audio for it's input so connected to a speaker output, it rumbles=20
more (due to wind, engine and some road noise) as the car goes faster,=20
and that's out of sync with what's expected... ie: rumbling/jolting when=20
the car goes off-road.  The force-feedback signal that goes to the=20
steering wheel has the rumbles/jolts correct.

I've connected the buttkicker input to a function generator and a=20
low-frequency (~30 Hz) signal produces a nice rumble... even a square=20
wave works well.  But now I need to get the force-feedback signal to=20
modify the amplitude of a square-wave signal I generate. There are two=20
options I can think of...
(a) Grab/convert the motor signal (from inside the force-feedback=20
steering wheel) and have that modulate the square wave.
(b) Use acceleration/velocity data from the game (which I can get and=20
also dump out the serial port) to modulate the square wave.

Any of you know about these force feedback wheels and can tell me if (a)=20
will be relatively simple?  IE: can I just isolate and filter the motor=20
signal to get a signal whose amplitude varies with the force that the=20
game is applying to the wheel?  That would then go into an op-amp=20
voltage-controlled amplifier to drive the butt-kicker.

If I use the data from (b), I can have the same PIC generate an analog=20
output (proportional to how much rumble is required) and a separate=20
30-Hz square wave.  Both of those would go into a VCA also as in (a).

I have only a couple days to do this, so any help in figuring out the=20
easiest path here or any other options would be appreciated.

Cheers,
-Neil.


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