breakout board with no opto's

[dolomitedave]

Hi,

I am slowly building a machine i have got 1 axis stepper working so far and want to test it with some software.

So i need to build a breakout board, am i right in saying that if i only have outputs from the PC then i don't really need opto's? i would only need them for inputs to the PC via the parallel port.

i have 2 supply's 1 for the steppers 1 for the driver. so i don't see how any large spike could cause any damage.

I guess it's best to be safe but i have also heard that opto's have a slight delay and can cause timing problems.

i am only looking to use just 3 pins/wires from the parallel port 1 for step 1 for Dir 1 ground

your thoughts please

[doorknob]

If you rephrase your question as, "if a high enough voltage gets applied to one of the parallel port output pins, could it damage the port?", I think that the answer would have to be "yes".

Having said that, though, it seems that plenty of people do indeed directly interface their parallel port output pins to their stepper driver input pins without benefit of isolation and without blowing anything up. You have to consider the possibility of running into things such as defective components, screwdrivers dropped in the wrong place, metal chips shorting out PCB traces, static electricity, and miswiring, as well as line and inductive surges. In a commercial or industrial setting, it's a good idea. In a hobby setting, well, people cut corners all the time.

So what it comes down to is you have to ask yourself the Dirty Harry question: "Do you feel lucky?"

Well, do ya?

Yes, some optos can have significant propagation delay, and they can turn once-sharp signal transitions into mush. You can get fast optos if you wish. Also there have been various circuits posted on this forum that claim to address that issue. So YMMV...

[dolomitedave]

Thanks for your thoughts,

I don't think i do feel lucky, you just never know. depending on your PC motherboard manufacture the parallel port should also be opto isolated there anyway buy if you do manage to pass incorrect voltage back to the PC in theory all your going to blow is the optos there, but then you have no parallel port. so you either have to buy a new motherboard or buy an PC IO card that has a parallel port on it.

my point being like you were getting at, for the sake of doing it right in the first place can save you in expense the future

i will take a look around on here regarding the propagation delay i am thinking for what i am doing it wont be a problem for me.

Dave

[Al_The_Man]

The PC parallel port is not commonly isolated, the PC. P.S. common and MB common is at earth ground, and so is the PP 5v common.
I have used non-isolated darlington IC's as buffers for the PP, this allows the driving direct of 24vdc devices relays or Optos.
So far I have not lost a PC.
Al.

[Mariss Freimanis]

I would avoid opto-isolating the Step and Direction outputs on a breakout board if you plan to use drives that have opto-isolated Step and Direction inputs.

Mariss