On 01/01/2017 04:33 PM, Gene Heskett wrote: > Well, in my case, the cable might be 8" long. The power to the pi and the > power to the 7i90, originate from the output terminals of a separate 5v > supply. But the pi has a ferrite choke on its power lead that the 7i90 > lacks. The 5v supply's ground terminal is taken back to the common point > bolt with a heavy braid.
Are /both/ 5V power supplies' GND connected to the common point? If yes, then you have a ground-loop. The signal's GND and the PSU's GND have two ways of interconnecting, through the PSU/common point and through the signal GND. > The noise at the 50 pin ground connection is easily 10x that on the - > power terminal of the 7i90, which tells be that ground at the i/o > connectors gets there by a rather circuitous route, so when I have the > supplies up and running, if the noise persists, I will move the shield > of that cable to the common bolt. That is a good indication of a ground-loop. You are obviously receiving a lot through an antenna function in the wiring. > The idea Bertho is to see if there is a bulletproof method that will > get rid of the noise. Ha, bulletproof, that'll be the day. It often turns out that there is a brainfart in the design or implementation somewhere (and I too generate plenty of brainfarts). However, going as far as saying "there is a bulletproof method" would be stretching it. You probably have to rethink your assumptions more than once and go very very small step-by-step in the buildup and assembly. Each addition can then be seen in the context of the whole and see if and where it breaks down. Then, at least, you know where to look. Applying the bulletproof vest may still be hard work. -- 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
