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). 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. -- Greetings Bertho (disclaimers are disclaimed) ------------------------------------------------------------------------------ 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
