On Wed, Dec 01, 2010 at 10:22:27AM -0800, Kirk Wallace wrote: > On Wed, 2010-12-01 at 12:59 -0500, Stephen Wille Padnos wrote: > ... snip > > What you really want is an edge detector that's controlled by the home > > switch. When the switch output is 0, the output of the detector is 0. > > When the home switch is 1, the next rising edge of the encoder will set > > the detector output high until the home switch goes back to 0. This > > would effectively delay the switch output until an index is seen, but > > would leave the home switch output high until the switch is no longer > > active, which is a requirement of a home switch. > > > > I haven't written out the actual logic, but I could sure do it with an > > AVR :) > > > > - Steve > > I think there is another problem if the home switch edge "fuzzy" zone > can have more than one index pulse in it. Each home and index system > needs to take into account how wide the home pulse is, how wide the > worst-case home fuzzy zones are, and how close are the index pulses. > Having a 180 degree lead screw flag is looking attractive. So, home AND > flag AND index?
Kirk, Stephen has perfectly described what percolated into my mind,
reading this thread. Here's a picture.[1] Using the home signal to
reset the JK provides our ANDing. If a microswitch has 20 mS contact
bounce, it's time to fit a new one, I think.
AIUI, we must always detect the first index after home switch closure?
(Otherwise home is out by an entire leadscrew pitch.)
I must admit that doing this in an ATtiny means it can be tweaked after
wiring up.
Erik
[1] In case the "values" don't show well, it's a 74HC14 and a 74HC109.
(The latter is good in the parts box, because it makes D latches
just by connecting J and /K together.)
R3 is there just to protect the input against transients. (Used that
in a digital clock design for the Ford XD Falcon. There were
negative several hundred volt spikes on the Accessories line when it
was switched off, due to a relay coil. The CMOS didn't like it.)
Home_Switch_Filter.pdf
Description: Adobe PDF document
------------------------------------------------------------------------------ Increase Visibility of Your 3D Game App & Earn a Chance To Win $500! Tap into the largest installed PC base & get more eyes on your game by optimizing for Intel(R) Graphics Technology. Get started today with the Intel(R) Software Partner Program. Five $500 cash prizes are up for grabs. http://p.sf.net/sfu/intelisp-dev2dev
_______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
