On Wednesday 17 May 2017 01:47:17 Bertho Stultiens wrote: > On 05/17/2017 04:24 AM, Gene Heskett wrote: > [snip] > > > The ideal situation in this instance would be to mirror the design > > of the 7i90 so as to rotate the 26 pin header 180 degrees, which > > would allow the cable to be only an inch long. Or mount the pi > > upside down, which would have the same effect. Humm, why not, I > > have some looong standoffs? While I'm waiting on 7i42TA's, why not > > try it? More than one way to skin this scrawny cat. > > Reducing the cable's length to an inch would help. Then the > transmission line characteristics would be much less a problem at > 50MHz. > > > Why is it I think best while writing > > about a problem? Can't be the age of the wet ram. Or is it... :( > > It is called reflection of your own thoughts ;-) It works very well > while doing something completely different (like taking some time on > the toilet). > > >> BTW, I think that not only the probe tip has influence, but also > >> where your probe's ground-lead is placed (and not that fluffy long > >> aligator-clip lead). > > > > Chuckle, guilty yur honor, but its only a 4" lead. :) In this case > > clipped onto a corner of a usb sockets frame. > > Well, using the default ground-lead on the probe at high frequency > makes anything you see on the scope suspect. You do still have those > springy clips that come with the probes, which clip onto the tip's > ground-ring?
Someplace, but to use them I'd need three things. 1. A ground it could reach. 2. jigs to hold the probes in constant contact since there are no gripping hooks. 3. 6 arms & hands. I can't hold the probe in contact, retrigger the scope to capture the next snapshot, and hit the up-arrow then a return to initiate the next signals existence as linuxcnc starts up. Birth defect I guess, I'd need 6 arms, all steadier than the 2 I do have. Or 3 of me in telepathic contact. :) > With your confession, I'd be expecting ringing on the signals you > measured. That makes me wonder if your probe is properly impedance > matched to your scope... Maybe time to test and recalibrate the probes > on the 1kHz scope reference? BTDT, many times. For this sort of thing, the scopes need a 100khz test signal, and an isolated ground immediately adjacent, but this one has neither, dammit. The scope itself is running on a ground isolation adapter, so I'm not getting the ground loop noises from that in my displays, nor is power applied to the motors as I have that tied to the motion enable gui button. So yes, I do understand that the scope pix I posted links to yesterday are showing the effects of that 4" long ground lead. 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
