[Coco] Wico Trackball?
Torsten at Dittel.info
Sat Sep 8 13:51:53 EDT 2007
> Ok, so it has a microcontroller reading the opto-interrupter inputs and
> putting out an analog voltage for the CoCo's (6-bit) ADC to read. I
> sincerely hope that's not what was patented. So much for
> "non-obvious". In any case, any patent on the Wico Trackball should be
> about expired by now, along with the original Amiga chipset and LZW
The "big deal" of the patent was, that the custom chip has a selectable
mode: True "analog output" (e.g. for CoCo) or "digital output" (e.g. for
Atari). In the latter mode, the chip generates pulse width modulated
Atari type joystick output, e.g.
(if you move the trackball slowly upwards)
(if you move the trackball medium speed upwards)
(if you move the trackball fastly upwards)
and the same for all 3 other directions at the same time. That way you
could controll a mouse cursor on the Atari with the trackball, which
would normally (with an Atari type joystick) "go" only to 8 directions
with a constant speed (something like Uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuup
if you want).
> But I can see your point. The original CoCoMax 8-bit ADC might work,
> though there might be some quantization weirdness between the two
> The CoCoMax 3 ADC, and other stuff based on the Tandy Hi-Res interface
> wouldn't fare so well.
Yep, those don't do ADC by reading the joystick's divider voltage using
a DAC, a comparator and SW successive linear approximation. They use the
joystick's pot resistance as a sawtooth generators's timing constant,
mainly a capacitor loaded (or discharged? Don't remember...) lineary via
OpAmp => Integrator circuit. The time until the threshold is reached is
then measured by the CoCo using the cassette's 0-crossing detector.
Correct me if I'm wrong, I analyzed that one more than 20 years ago and
actually never used it because I didn't have a CoCo3 in those times
(just the interface).
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