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dfro
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« on: July 04, 2006, 03:26:38 PM »

I would like to use Mach3 with a opto-isolated interface board.  However, the optoisolators slow down the speed that the pulse reaches the driver board by 10 or more usecs.  Is this a problem?

What is the pulse width of the step/direction pulses at different frequencies? Is it adjustable?  Is there some documentation where I can read about this spec and how to change it, if it can be changed?  I could not seem to find info in the Mach2/3 manuals, which by the way I think are very well written.

Thanks.
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Brian Barker
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« Reply #1 on: July 04, 2006, 04:49:28 PM »

The pulse width is about 3 usec.. you can make it greater by adding time to the step pulse under the motor tuning page Smiley If you are going to run slow opto's run in Sherline mode, this will give you a step pulse that is about 20 usec long

hope that helps
Brian
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dfro
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« Reply #2 on: July 04, 2006, 05:28:12 PM »

Thanks, Brian, for the info.  I finally found the screen shot on 5-12 of the Mach3 manual, which shows where you can choose a step or direction pulse width of 1-5 usec.  No discussion of this setting, though.  I cannot find anything about Sherline mode in the manual.  What is that?

I am planning to make a homebrewed opto-isolated interface board.
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Brian Barker
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« Reply #3 on: July 04, 2006, 05:35:00 PM »

Sherline mode is in Mach3 Smiley If you are just getting started you should run mach3 it is MUCH more stable...
Thanks
Brian
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dfro
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« Reply #4 on: September 27, 2007, 01:58:46 AM »

Brian,

I would like to request that an explanation of the step and direction pulse width settings be added to the manual.  I am going to use an opto-isolated bob and opto-isolated driver board in the setup I am constructing.  Tuning the step/dir pulse width accurately is important, since the signal will have to make it through two optos.  I imagine that a lot of novice cnc builders/operators are having problems with steps being lost, because they have optos on both their bobs and driver boards. I preface my comments and questions with the fact that I have not gotten any machine working, yet.  I also think your Mach 3 Mill and Turn manuals are excellent.  They have been the best primers on cnc machining I have found.  They video tutorials are great, too.

Questions/Comments:

In the "Port Setup & Axis Selection" window there is a box in the "Restart if changed" section that says "Sherline 1/2 pulse mode".  What does that mean?  What does "1/2 pulse" mean?  If checking this makes the pulse longer, why the "1/2 pulse" label?  If you check that box what happens?  I assume this makes the pulse width 20 usec, based on what you wrote earlier in this thread.  But, the label does not make this clear.  IMHO, this should be explained in the manual or the label to the check box should be clearer.

If I check "Sherline 1/2 pulse mode" and enter 5 in the "Step Pulse" and "Dir Pulse" boxes in the "Motor Tuning" section, will the pulse width now be 25 usec?  This is unclear.

Also, I read in another forum thread that the "Step Pulse" and "Dir Pulse" settings can be put as high as 15 usec.  To my knowledge, that is explained nowhere in the manual.

You said earlier in this thread that the base step/dir pulse is 3 usec.  The Gecko drive literature says that it needs a minimum 4 usec pulse width on one of the step pulse edges.  If people are putting opto-bobs with opto-Geckos, I imagine problems with pulses not making it to the driver chips (and a lot of hair being torn out of a lot of heads).  This could be clearly explained at 4.4.3 in the manual where you talk about opto-isolation or "5.2.3 Defining Special Features" (In fact this section defines nothing). 

I hope this might help you improve your product.

Thanks for the great software and the great manual.

Dave
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Brian Barker
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« Reply #5 on: September 27, 2007, 09:33:11 AM »

Sherline mode will make the pulse 20us long... There is going to be a rewrite for the manual in the next year. the Manual rewrite will cost about 10,000 minimum! So we are going to let mach3 finish growing and will start back on the manual.
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Whacko
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« Reply #6 on: September 27, 2007, 05:52:02 PM »

I have opto isolated step pulse and dir very succesfully with the fast schmidt trigger optocoupler from Fairchild. Part no H11L1 in dil06 package. You can buy online from Fairchild.

Whacko
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dfro
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« Reply #7 on: September 28, 2007, 12:16:11 AM »

Brian,
I look forward to the rewrite.  As it is, your Mach 3 manual is still one of the best primers on cnc machining out there.

Whacko,
The AVR-based driver board kit I am going to use for my machine, uses the H11L1M, like you suggest:

http://www.bright.net/%7Eagarb/STMD/AVR_STMD.html

A .1 usec rise and fall time is very good, I think.  I will be using these boards with the cnc4pc.com multi-function board.  It uses the HCPL2531 opto's, which are good - around .4 usec rise time and .3 usec fall time.  Still better is the HCPL2360 opto - 20 nsec rise and 30 ns fall time.

Dave
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