[Coco] Wico Trackball?

[Torsten Dittel]

> 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
> compression.

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.

Up---------Up--------Up---------Up
(if you move the trackball slowly upwards)

Up---Up---Up---Up---Up---Up---Up
(if you move the trackball medium speed upwards)

UpUpUpUpUpUpUpUpUpUpUpUpUpUpUpUp
(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

Yep.

> 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).

Regards,
Torsten