On Dec 16, 9:37*pm, Ignoramus6780
wrote:
...
What I would ilke to do is, somehow, make sure that encoder counts are
not missed due to some mistake of mine such as bad wiring,
misalignment, etc. I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

i

Consider the possible and likely failure mechanisms, and balance the
consequences against the added expense of monitoring.

Initially if the encoder sensor output looks clean on a scope you
probably aren't dropping counts.
http://club.myce.com/f61/eye-pattern-195197/
http://i.cmpnet.com/digitaltvdesignl.../Monster3C.jpg
As it ages and collects dirt or shifts out of alignment you could lose
either signal. Can EMC2 compare the commanded and measured speeds and
trip an error if the difference exceeds limits?

If you want a simple hardware monitor you could divide the encoder
counts by 4096 with one of these:
http://www.fairchildsemi.com/ds/CD%2FCD4060BC.pdf
and clock a bidirectional counter down from the divider output and up
from the index.
http://www.intersil.com/products/dev...?pn=CD40193BMS
Display the count output with LEDs and occasionally check to see if it
has drifted off 0000 (all 4 off), or really that its normal pattern is
changing.

Also you could trigger one-shots with the encoder pulses and light
green LEDs with the outputs. This would detect a complete failure of
either encoder.

These could be connected to the controller to give error inputs that
it can poll occasionally instead of wasting its time looking for pulse
edge transitions.

jsw