re: Limit Switch wiring for UNO

I didn't want to muddy the water by hijacking this thread .

I get that using NO and NC switches both have their place depending on the system. And I don't know enough to argue one over the other for any certain application.

But recently, I ran across information where it was said that using opto-isolators (optocoupler, photocoupler) was the best way to prevent noise in wiring for a CNC.

What's your thoughts on using opto-isolators for this purpose?

Link to where I read about using opto-isolators

There's nothing to argue.
Isolation is just that.
What you are rssentially saying is:
"To isolate, or not to isolate, that is the question ?
Is it better to suffer the slings an arrows of outrageous noise or is it better to hide behind
a 5000V isolation barrier ? Shall I live in a clean
world or a dirty world, where micro arc-flashing
generates noise comes back to haunt me ?"

They make opto isolated relays but some people
defeat the purpose by not using separate
supplies for the two sides of the isolation barrier.

There's a couple of different kinds of electrical noise you might be dealing with here:

  1. Unwanted switching - that is, the noise is causing your Arduino to think the limit is hit when it isn't.

  2. Static electricity, usually picked up from humans, usually the humans don't even notice small sparks of static up to 10,000 volts.

  3. Wiring errors and accidents like a power wire disconnected from somewhere else coming in contact with an exposed metal part of your input wiring. Could be 110V or 240V at very low impedance, meaning that enough current flows to heat up your wiring and make it burst into flame.

An optoisolator (so long as it's not horribly engineered like Rash suggests) will protect against 2 and 3.

Designing a circuit to protect against 1 does not require an optoisolator.

MorganS:
Static electricity, usually picked up from humans, usually the humans don't even notice small sparks of static up to 10,000 volts.

Don't know about that!

I certainly notice it when I get out of the car. :astonished:

When you notice it, it's probably more than 10,000 volts.

If it sparks, I notice it! :astonished:

Appreciate the insight fellas!