Re: [CAD_CAM_EDM_DRO] Parallel Port Interface

In a message dated 03-Nov-01 09:15:53 Central Standard Time,
fenerty@... writes:

> Check your controllers. Many already have opto's on their inputs. (gecko's
> for example). If your controller does not have opto's, I defnitely
> recommmend them. Nuthin worse than a blown computer!
>

I didn't read Gary's original inquiry that elicited this response, but I can
add MY 2¢ worth: I use 74HCT541's (octal buffer) (with 10K pull-up resistors
on all-8 input-lines to the 8 buffers, which otherwise go to the
parallel-port's pins 2-9). Then, as some computer-op-sys might "OUTput" a
too-short pulse to "fire" these optos, I use two 74HC4538 dual-monostables,
to "pulse-stretch" bits 0-3 (for my esoteric use) to, say, 100 µS. This is
usually enough to adequately "fire" a good opto. (If not, simply change the
R/C combinations on the '4538's!)

Then, for "output" of this interface, I have used (with great success)
ULN2003 darlington DIP's, but I got summarily scolded by one of Mariss'
employees for doing that, as the ULN' is not "ideal" for that application. I
suppose such as the 75477 (is that the right number?) "periferal driver" may
be a better choice. Some might properly argue that an ordinary 'HC IC can
drive an opto's input-LED adequately, and I guess this is so, if those gates
are not used to input to "logic", as well. Requires some breadboarding!
(AND experience with such!)

Hope this helps! It works for me, earning money every day (when I'm not
loafing, that is!)

Jan Rowland, Troll


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