Re: [CAD_CAM_EDM_DRO] Re: USB or Ethernet machine control

Jerry and others who "do their own electronics": I now know it is "industry
standard" to have STEP and DIRECTION lines ("Logic Levels") to
stepper-drivers, whereas SOME folk used, instead, CW and CCW lines, before.
In fact, Superior Electric makes ITS drivers with an input that allows one to
CHANGE the meaning of the two input-lines to be one or the other pair.

HOWEVER (and potentially important to this hobby-group, I suspect), I built
MY first CAM Lathe based on CW and CCW inputs, NOT STEP/DIR. Thus, lotsa
software is written that way, and, being old and very, very lazy, I will NOT
change-back! (Would be a NIGHTMARE!). So, as I have recently gotten a pair
of Gecko G210 drives and new Superior Electric KML062 motors for a planned
plotter, and prepared for breadboarding, I inquired, and Mariss sent me
details how to make a one-IC (quad CMOS NOR) circuit which will convert
CW/CCW to STEP/DIR. Simple. So, I made a little PC with sockets (ALWAYS use
sockets for IC's!!!), and hooked all up to an old laptop, to test/check-out.
WOW! Stepper-motors were going NUTS! One would step kinda OK in ONE
direction, only, and both would SKIP many steps of an even-multiple of 100
sent to them, etc., etc. I was about to begin using untoward language when a
VISION came to my feeble mind! I had 74HCT02 IC's for both pairs of inputs,
and, as my laptop was putting-out a good 4+ volts for logic-HI, I pulled
those and put in 74HC02 (no T), and all was GOOD, again! Oh, and I taken NO
particular care with the "dress" of the LPT-1 cable and "logic-IN" wires for
this temporary lashup, as I realized it wasn't permanent, anyway, and that
often, as in this case, helps "find" sensitivities to such nastiness. (Yep!
That EMI will GETCHA!)

To recap: Use 'HC' (not 'HCT') logic between your PC and stepper-drives! Do
the wiring sensibly, and SHIELD your LPT-1 cable (many (most?) store-bought
LPT-1 cables ARE shielded, anyway) to stepper-drive inputs.

On my successful PC-controlled machines, I have always put a 74HC541 (octal
buffer) between the PC printer-port and "next", and then that "next" is a
couple of 74HC4538 monostables set for 4 uS, each, and, for driving the
opto-isolator inputs of most stepper-drivers, I use a GOOD O.C. "sink" driver
IC, last. The opto-isolators work WONDERS! I know, as I had built a
still-working home-brew lathe (run by a long-defunct CBM "PET"!!!) where the
parallel port is directly connected to the "TTL inputs" of my stepper drivers
(the old unipolar L/R kind), and "where did THAT come from?" steps show up
now and then. But NEVER once, since I have been using opto-isolator input
drivers. At least the Superior Electric "black boxes". Remains to be seen
how the G210's will fare, but I suspect JUST FINE! (Knock on wood!)

Jan Rowland


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