How to use Opto-isolators?

[Plecc]

Hi all,
I would like to try and build a simple opto-isolated parallel port breakout board, for convenience i would like to use this opto (4N25) available from maplin.co.uk if this is a poor choice i would be happy to go with anything available from :-
Rapid Electronics - Electronic Components > Optoelectronics (LEDs)

My electronics knowledge is novice at best, i have played around with basic components and ic programing but never used optos.
If anyone can recommend a good open-source schematic, or has any experience working with optocouplers it would be great to hear from you!
I'm not sure of the best way to integrate optos into a breakout board or which channels require isolating to fully protect my PC, when connected to a 3 axis machine?

[Bubba]

Plecc,
I also am "playing" around with optos. The 4N25 is a good basic one, but there are some out there that are faster! You just have to get the data sheets and figure out which is best for you.
Now, to protect your PC, you will want to have separate power supplies for each side. NOTHING will be common between them. If you use Gecko drives or equivalent, the step direction connections have their own optio isolation so you only need to buffer those connections. Any other I/O should be isolated.
The input to the isolator is simply a led so you need to treat it as such. I usually set things up such that my control "sinks" the load on the cathode end of the led. So the anode end is tied to the appropriate voltage and current limit resistor. The output of many of these isolators is simply a transistor. So depending on you you want to treat it, you will connect the collector the the appropriate supply rail and the emitter to the other with the necessary resistance.

PIMO has some excellent example of how to do this.

[Al_The_Man]

I would like to point out that there is two methods of interfacing different systems, either make all commons equal to earth ground or attempt to isolate them all.
I favour the first method and have used this extensively.
I only use opto devices to transition between one supply or system and another.
Keep in mind that if you have the usual desk top or tower PC, the PC power supply common is at earth ground potential, as well as any mains driven devices such as 120v/240vac spindles etc, so in effect you do not have isolation anyway between these two, however much isolation you attempt.
Al.

[Plecc]

Bubba and Al,
thanks for the feed back,
sry such a slow response from me!
I ended up purchasing some motors and microstepping drivers, fortunately these are already isolated, so for the moment i will knock up a simple direct breakout board for testing and build a separate opto board to isolate the coolant and spindle relays.

Bubba,
i did a bit more research and i quite like the look of the Fairchild 6N139 connected to a 74HC14 Schmitt trigger using usb to power the parallel port half of the board, this looks like a better alternative.
what do u think?

Al,
That is a very good point!
When you say "I only use opto devices to transition between one supply or system and another.
" do you mean power supplies and systems as (computer - drivers - spindle - coolant pump)?
sry for my stupidity.

These are the motors and drivers i went for-
Zapp Automation
Zapp Automation
But I could do with some help choosing a suitable power supply, i was told it was best to power all your drivers form the same power supply to help keep them all in phase?
Would a transformer like this be suitable?
P Sup Rec Non Fil 24v 360w 15a - Legrand - Edmundson Electrical
for a 3-4 axis machine using 20-50v drivers and the stepper motors wired Bipolar Parallel so 2.73V and 4.2A?

Thanks for your help.

[Al_The_Man]

Al,
That is a very good point!
When you say "I only use opto devices to transition between one supply or system and another.
" do you mean power supplies and systems as (computer - drivers - spindle - coolant pump)?
sry for my stupidity.

Yes I bond all my supply commons to a star point at Earth Ground reference.
Never had a noise issue!.
Al.

[Bubba]

Yep, another good way to skin the cat! Should do a good job for you.