Re: Stepper controllers

>
> From: "Ian W. Wright" <Ian@...>
>
> Hi,
>
> Having just started to play with my home-brew stepper controllers on a
> Pentium machine and realised that the 486 I was trying to use is just
> not man enough for the job, it has occurred to me that, rather than
> risking just one output card as on the 486, I am now putting my whole
> motherboard at risk of destruction by feedback spikes. Even though the
> motors are protected by diodes I was wondering if I should try to fit
> opto isolators on the input lines to the controller cards. In looking at
> published circuits, I couldn't find one which uses opto isolators
> (although I did see one which seemed to use them only on the limit
> switch inputs for some inexplicable reason ) so, is it usual to use
> optos, is it necessary and do you know of available designs which do use
> them? Thanks,
>

In the FWIW department, more years ago than I care to remember, I worked
for a company that was building computer controlled machine tools using
the (then) revolutionary 8080. Some of the stuff was pretty neat - they
had a gear cutter that was set up through the console. After the setup,
just toss a blank in and cut.

Anyway, their equipment was not, shall we say, extremely robust and we
were always getting stuff back for rework. I do recall that all of the
control lines from the processor used opto isoloators and they still
managed to fry the motherboards.

In the home shop environment, this is not quite so critical, but to be
safe, I'd use them. Motherboards are pretty cheap these days, but it's
still a headache to swap them out.

For a TTL output, or anything capable of sinking the optoisolator drive
current, you can use something like this for a signal line:

+----\ |
Sig in | )----|<------\/\/\/\-- +
+----/ |
\_

------
/ \
\/ \-------+--\/\/\-- +
| |
Gnd +--- Sig out

300 - 500 ohm resistors would work for a 5V supply. You can use a non
inverting gate as a driver or just use the signal line if there's
nothing else attached (and it can sink 10 ma). Or you can use an
inverting gate (7404) and put one on each side to buffer the isolator
and increase fanout.

I suppose if you're really picky, you'd put a schmidt trigger buffer
on the output.

And you really want separate power supplies (otherwise, what's the point? you'd
just couple the noise, spikes, etc through a couple of resistors)

--
Paul Amaranth | Rochester MI, USA
Aurora Group, Inc. | Software Development
paul@... | Unix / C / Tcl-Tk