RE: Spinner Replacement for Omega Race

From: Clay Cowgill <>
Date: Fri Aug 01 2008 - 17:49:30 EDT

> [...] I'm never going to sell thousands of these
> little things anyway so I don't need to worry very much about
> the relatively minor cost difference between the two parts.

If you ever pack it down into a 9536 let me know, I think I have a bunch of
5V parts in PLCC you can have. (They have the numbers sanded off, but
otherwise should be fine.)

> I don't think that a CPLD is available that has a built-in
> analog output peripheral but just as with microcontrollers, a
> CPLD could easily generate a fast PWM output signal (i.e. 20
> kHz or even faster) that can be RC-filtered and op-amp
> buffered into a true analog signal.

I think that's basically what Ed's saying. Just a one-bit sigma delta DAC
output. Takes an opamp or two (depending on how steep you want the filter)
to integrate/filte to 'analog', but should work good. You'd probably want
mid-high 100's of KHz for good audio resolution.
> I have never seen the inside of the Star Wars flight yoke but
> I've read about the problems with the gears, springs, and
> calibration. [...] However, there remains the problem that the
> Bourns quadrature encoder is an incremental position sensor
> and a pot is an absolute position sensor.

Star Wars is very forgiving of "changes" to the absolute position values.
It's actually calibrating all the time. (originally they used the POKEY pot
inputs which yielded the occasional bad conversion, so the code is sort-of
expecting poorly behaved pots as a result. Hence the "laggy/swimmy" feel of
the targeting retical. It's doing a bunch of software filtering.)

On easy thing would be to just use the encoder to output an 8 bit digital
code and spit it out SPI-style to a Maxim digital pot. ;-) On powerup the
yoke is probably mostly centered, so it might "just work" anyway. Probably
even a little R2R DAC would work as a current/voltage source.

(With a little micro it would be easy just to adjust the range of the
pot/current output to center based on maximum number of pulses counted on
each axis in either direction, but I bet Star Wars would do that
automatically for you... It'll take the min and max values seen on the "pot"
and scale it to 'center' mid-range no matter what the absolute scale is.)

> What would you say is I suggested using a completely
> different type of sensor? There are certain programmable
> magnetic-resistor-bridge based intelligent sensor chips that
> are available these days that can read the angle of the field
> of a magnet (that's the angle of flux lines, not the field
> intensity). In other words, throw out the gears and the
> pots, glue in two magnets, install a couple of these tiny
> sensor chips and out comes your absolute analog position.
> The sampling rate is 4 kHz, linearity is excellent, output is
> 0 to 5V with 10-bit accuracy, and the maximum range of travel
> is 180 degrees.

Those sound very cool! Part number? Price?

I got a kick out of a Sega Masters Golf control panel I looked at a while
ago. There's a little spring-loaded lever that simulates the motion range
of a golf club being swung... On the back of the control panel is a PCB
loaded with (lots of) reed switches. There's a magnet on the back of the
shaft of the 'club' which closes the reeds sequencially giving an indication
of magnitude and speed of the swing. ;-)


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Received on Fri Aug 1 17:51:35 2008

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