On Saturday 31 December 2016 12:16:50 Bertho Stultiens wrote: > On 12/31/2016 05:54 PM, Gene Heskett wrote: > > While I like the SPI interface as its faster that even a parport, I > > am finding it quite susceptible to mistakes cause by emi from a > > switching psu's typical of stepper motor psu's. These things it > > seems can radiate back out the line input connections, while > > switching at 17 kilohertz, is making the whole system bounce around > > with high frequency switching noises of 5 or more volts with rise > > times in the sub 5ns range, 2 feet of ground braid away from the > > common bolt, totally tearing up the data integrity of the spi bus. > > The real question is whether you are seeing common-mode noise (EMI > induced junk on all signal and ground lines) or you have a (DC+AC) > current-carrying GND vs GND reference in a combined setup (inducing a > loop). > > The common-mode noise is well dampended using good cable design with > proper layout and using filters plus ferrite beads at the right > places. > > However, if the reference ground is not equal at both ends of the > signal line, then you are in trouble. This is why you would use a > balanced line (differential), which is not absolutely referenced to > ground, but switches on the differential (and you can clamp the > lines). > Do you know of a 4 wire to 8 wire and back interface that can function at 32 megabaud and doesn't cost 5 grand+? Neither do I. :) Laser diodes and detectors that could handle 2x the video speed needed to hit an HDTV transmitter would be required, times 4 to do it optically.
There are capacitatively coupled chips I have seen the announcements for, intended to steal some of the jobs the MOC chips are doing, but no clue as to their useable bandwidth. I'll see what google says. A paper by Silabs <https://www.silabs.com/Support%20Documents/TechnicalDocs/CMOS-Digital-Isolators-WP.pdf> says the are using a nominally 10 megahertz carrier in a cmos circuit, about 30x too slow for this. Searching further, TI has a family of them, 3 channels one way, 1 the other, would only need one, at 3.49 in 1k lots, claims 100 megahertz bandwidth. I'll see how much power it needs, and what the small qty price might be. Not available, so I've ordered samples of 2 variations, one of which is inverting but I don't see which is which. Its an SOIC package, dunno if I could hack a pcb for that. Perhaps this might be the better method? Jeff Epler, can you chime in here with your 2 cents? > You will need to measure which effects are causing trouble to choose > the best way to solve it. > > BTW, the common bolt should not carry current. That would make EMI > radiation just too bad. That common bolt is connected only to the house static ground, I have been careful not to mix-n-match as I spent 18 years at the tv station fighting with that because the now deceased jerk that wired the place originally had them cross connected at a few places. I would have had to shut it down for a couple days and change $2000 worth of boxes in the entrance lashup to fix it. Verified isolated again just yesterday. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
