Re: Parallel Port Interface

Gary:

For what it is worth, here's what I've done.

When I figured out my parallel port connection I decided to put in
opto-isolation. This is going from the parallel port to Camtronic 5A
drivers using EMC. I wanted this to protect the computer. I also
purchased an ISA parallel port board. The reasoning here is a fault
would fry the add on board but hopefully not the motherboard.

I designed and built the opto-isolation circuit (quite an accomplishment
for my) and this worked well. However, it inverted the signals and EMC
did not like this. EMC would lose one step when it reversed directions
at one end of its travel. i.e. it would lose a step going from + to -
but not - to +. It thus drifted slightly as the program progressed in
both X and Y. I removed the opto-isolators and the problem went away.

So I am now running without opto-isolation. So far I haven't had any
problem and will no doubt continue this way until I do fry something.
So, you might consider in designing the opto-isolation, if you use it,
to not invert the signals. This particularly if using EMC.

Hugh Currin
Klamath Falls, OR

On 3 Nov, Gary.Rose@... wrote:
> Hi,
>
> I'm putting together a small cnc system (Sherline based) and am at
> the point where I'm thinking about how to connect the parallel port
> to the stepper drivers, limit switches, manual jog controls, etc.
>
> Some schematics that I've found on the web show the step and
> direction and other lines directly connected to the parallel port,
> others use optoisolators (4N33 for example), others just have pull up
> resistors, still others use buffer gates.
>
> Any thoughts? I'm leaning toward optos, because that's what I know,
> but what do you guys think? Is it worth the trouble or not?
>
> Thanks
>
> Gary