RE: [CAD_CAM_EDM_DRO] Re: Parallel Port Interface

In various rendition of my setup I have had the computer connected directly
to the drives without any problems ever and nothing blown-up. Opto isolation
sure sounds nice, but I have never added the extra complexity and don't miss
it. If I eventually fry a computer it will probably cost me considerably
less that the time and expense to put together a proper opto system that
does not introduce new problems.

Reading about the inverting problem mentioned below, I would have to think
it was real the interaction with the drives that was the problems?? EMC is
open loop and could care less how you handle the signals. It is the drives
that are picky about the direction of the signal.

Tim
[Denver, CO]

> -----Original Message-----
>
>
> 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
>
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