On Dec 18, 10:34*pm, Ignoramus7337
wrote:
...
2. I use Jon's Pico Systems hardware based encoder counter.

* *http://pico-systems.com/encd.html

It can count even more counts per second. I have a recollection of
what Jon was saying, but will not repeat since I am afraid I may
misremember.

3. My main concern is, what if due to whatever screwup of my adaptor
manufacturing process, the optical disc is more misaligned than the
specification permits, and thus would not count as well.

i

In my experience building prototype ink jet printers with encoders if
you can't see radial or axial wobble it won't be a problem. The eye
pattern test should show you how good your mechanical alignment is.
Connect right at the analog output of the photodetector, not a
buffered logic signal.

Beyond that the encoder will probably pick up speed variations from
motor cogging that would be measurable as harmonics on a spectrum
analyzer, or as timing jitter in the eye pattern. I doubt you care,
but we did since the encoder drove a phase locked loop to clock the
ink jet firing, and speed variations became stripes on the page. I
mention it because a sensitive instrument detects all sorts of
unexpected phenomena.

That board is similar to the atomic clock control interface I designed
and should be more than enough to measure spindle speed and
position,if you have enough I/O lines. You do have a possible timing
uncertainty which translates to position or speed error when you read
it unless you can afford to disable interrupts while you capture the
count and its timestamp.

jsw