On Tue, May 5, 2020 at 9:15 PM Nicklas Karlsson < [email protected]> wrote:
> > Do you have a dual trace 'scope? Spin the spindle and look at the input > > and output of the opto-isolator. See if there really is a lag. If you > > have a new scope would you have it capture the screen and post it. I'm > > really skeptical that those isolators are THAT bad. > > > > Here is the datasheet for the opto. > > https://www.mouser.com/datasheet/2/143/EL817-G-26528.pdf > > They claim an 18 uS rise and fall time. A 1KHz square wave will have a > > 1000 uS period and a 500 uS pulse width at 2 KHz the pulse width is still > > more than 10X the raise time of the opto. But maybe the opto is a fake > > counterfeit part with very poor performance. > > Opto couplers are rather slow. With a high resolution encoder frequency > could be maybe up to a few hundred kHz, > 2000*period/revolution*3600rpm=120000period/second=120kHz, 200PPR will be > 12kHz at 3600rpm, 1/(2*18µs) = about 27778Hz = about a little bit below > 28kHz if mad no misstake. > Yes, you can just barely get a 28 kHz signal through one of these isolators. But this case was 10X slower than that. But it hardly matters because the parallel port is even slower. I'm sure the BoB was designed for stepper motor pulses and limit and home switches. I think about the fastest signal you can push through one of those optos might be about 80 uS period or 12.5 kHz square wave. All optoisolators are not this bad. My leadshie staper motor driver has an opto chip in it. All the signals are isolated that way and you can put over 100 kHz through it. In theory, they can be very fast. After all what is a fiber optic cable but a kilometers long optical isolator? The one the comes into my house is sending data at gigahertz class speed. > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
