Opto-isolating HobbyCNC board

[nickswimsfast]

Hello, I'm trying to figure out a simple method for opto-isolating my computer.

I've successfully built and used a hobbycnc board for a homebuild cnc machine...

I was hoping to find a fairly straight forward solution to opto-isolating my computer such as buying a PCI card like this one:

http://www.newegg.com/Product/Produc...82E16815166007

Problem is I don't know if this would protect my computer, rather than simply adding another part to fry....

Thoughts? Is there another aftermarket part I could buy to protect my computer? Or perhaps a fairly straight forward kit/circuit with corresponding components to do this task? If I wasn't on a budget as much I probably would have gone with gecko drives...

Just can't afford to lose the computer that this will be hooked up to.

Any help is appreciated!

-Nick

[jalessi]

Nick,

You could add a breakout board with opto isolation between the HobbyCNC driver board and your P.C..

After working on tens of thousands of personal computers and experiencing zero parallel port failures the odds are very small you will have a problem.

As you mentioned in your post a replacement parallel port card is less than $20.00

If you check in with the guys at the HobbyCNC Yahoo Forum, you will find no mention of a damaged parallel port ever.

The HobbyCNC board operates at a relatively low d.c. voltage, that in itself makes damaging the parallel port difficult.

Keling sells a KL-DB25 breakout board for $25.00 however you would still need to make a adapter to connect it to your HobbyCNC board.

http://www.kelinginc.net/BreakoutBoards.html

I do not think its worth the additional cost or time wasted.

Jeff...

[ger21]

In the 7 or 8 years I've been reading about CNC through the parallel port, I've seen 1, maybe 2 at the most cases where the parallel port was damaged. And in order to do that, you need to wire either the AC or the motor power supply directly to the parallel port pins.

And you can buy a complete PC on Ebay to run a machine for under $50, if your that concerned.

[nickswimsfast]

Thanks for the helpful responses fellas. You have alleviated a lot of my fears concerning frying my computer.

I may be mis-interpreting, but it sounds as though the parallel port is the only component that would fry if something bad happened... Is this a correct assumption?

I'm also not entirely clear whether installing a PCI parallel port card would provide protection to the computer itself. I'm ok with losing a 20$ PCI card if it provides a protection to the computer. The problem is the card does not specifically say "opto-isolation" on it, from a google search i found some cards with opto-isolation integrated, but they cost 300$ - obviously not a feasible solution.

Thanks again!
-Nick

[ger21]

Originally Posted by nickswimsfast I may be mis-interpreting, but it sounds as though the parallel port is the only component that would fry if something bad happened... Is this a correct assumption?

Depends on how bad you mis-wire it. If you run 110V AC into the parallel port, you'll probably do a lot more damage.

[Al_The_Man]

Isolation and common grounding etc is one of the most misunderstood concepts in putting together a system.
If you have a PC that is anything other than a Laptop, there is 99.9% chance your parallel port common is connected to 120vac common (neutral) by virtue of the fact that the PC power supply is at ground (Earth) potential as is the AC Neutral.
In the final analysis, any amount of isolation external to the port is not going to prevent this.
This leads to another subject, which is bonding, and this refers to ensuring that all earth grounded parts of the systems are at the same potential, when this is achieved, this helps ensure that noise related problems, premature input triggering etc, will be minimized
Al.

[nickswimsfast]

Al, thanks for the information.

So does this mean by connecting both power supply grounds(stepper power supply + computer power supply) together I can help minimize these noise related issues?

-Nick

[Al_The_Man]

As far as isolating any other parts of a system from the common earth ground, there is two basic philosophy's, one is to attempt to isolate all other systems from this common completely, the other to ensure a common bond so that zero potential exists.
I have always followed the latter method and have yet to experience any detectable noise problems in the systems I have installed.
It is your choice as to what you decide to follow.
There have been a few past posters here that have had ongoing random triggering problems that have succeeded in eliminating them once the common bonding was done.
Al.