The recent thread about Holtek decoders vs. PICs brought back to mind some
questions I was tossings around a while ago. I want to build a 3-axis
quadrature decoder for an NC milling machine, with high resolution optical
encoders. The positioner, which I have, is a 12" by 18" X-Y rig, with full
length optical encoders good to around 0.0001" resolution. I will add a
third axis for a mill head, obviously much less travel, and not requiring
quite as much resolution...

I looked at the Holtek docs when the HT12D was mentioned here yesterday.
This clearly isn't the sort of decoder I need, but just *maybe* a 3D mouse
controller might be! Any idea what the maximum count rate (with the stock
2MHz clock) might be, per axis? I could possibly use a fairly standard PS2
mouse interface on the MC control PC, to read the encoders, accumulating
counts to handle the full travel. No complex hardware, encoder interface
boards, etc., and (almost) direct BIOS support for the counters. Does this
make any sense? Would I be better off with a PIC, re-inventing this kind
of "wheel"? I'd still need to dump the counts from a PIC back to the PC,
and I'm not sure I'd be ahead of the development curve doing it that way,
if a mouse controller is already most of the job!

Dave Bell

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