USB max current?

[Brenck]

Is USB max current really 500ma?

Do you guys think its ok to use USB power supply to run opto iso's in a 4 axis opto isolated parallel por break out board? Or it will deppend on the optoisolator?

Thank You

[pminmo]

A typical high speed discrete opto driver input will run 15 or so ma. Considering 2 per axis at 4 axis is roughly 120ma and that would bee if they were all on at the same time. Step/dir signals pulse and depending on active low or hi there is some duty cycle. Other signals that are more steady state and have lower bandwidths can use opto's that have a higher transfer current ratio and get by with a few ma per discrete. So yes, a usb 5V should be more than plenty to support the requirement.

[Brenck]

Is it really necessary to use highspeed couplers? I was wondering on using the cheapest optos ever 4N35. A high speed one like HCPLS are expansive.

Why they have to be high speed?

[pminmo]

depends on software, emc2 allows you to set pulse widths. the downside is you limit your pulse frequency.

[Brenck]

On your website there is a 4 Axis Opto iso interface. Have you tried it?

The only problem I see there is the price of that opto...

[pminmo]

Yes, I've built it as have others.