Duet on board power supply testing

Andy has done an in depth investigation of the FET switching spikes, and their effects on the Duet, which I have written up in a blog post.

http://blog.think3dprint3d.com/2014/01/duet-on-board-power-supply-testing.html

In summary we have done a lot of bed switching and can't trace any freezing/hanging to the 12V spike on bed switch off. Not saying it can't happen, just that it appears to be more complicated than this issue in isolation. On the other hand Radian has reported his fixes improved his board's reliability
http://forums.reprap.org/read.php?340,285306,285324#msg-285324
There is clearly more going on.

Our next area of investigation is the repeatable issues that appear to be due to ground loops and USB noise (thanks markbee):
http://forums.reprap.org/read.php?340,291241,292310#msg-292310

Firmware fixes have also improved reliability and I am currently digging through a repeatable bug that causes indefinite pause when absolute extrusion is selected.

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DuetWifi.: advanced 3d printing electronics

Hi Tony

Here's another good couple of posts regarding the USB ground loop: [forums.reprap.org] and [forums.reprap.org]

Ian
RepRapPro tech support

Thank you for posting this.
I have replied to bump it up the list again!
Thanks

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Ormerod #007 (shaken but not stirred!)

Hi T3P3, In your blog post it says of the transient: "This noise is relatively local to the MOSFET though, at the 12V input connector it is down to 750mV pp."

While it's true that there's only a small transient on the 12V rail probably due to parasitics and the recover of the PSU, a transient of 50V wrt ground is still present throughout the Bed and connecting ribbon cable at a high dV/dt. Given the "open" nature of the Duet enclosure and connected looms, and the large electrical area described by the heater, I would be concerned about inductive and capacitive coupling, paricularly into CMOS inputs for the latter. Has any examination of coupling into signals other than the power rails been made?

EMI from external equipment is undoubtedly causing problems that have a clearer "cause and effect" but, in the case of switching off the mains to a soldering iron, this is also a case of interrupting the current in an inductive load. So, somewhere in the Duet circuit there would appear to be a susceptibility to this kind if event.

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RS Components Reprap Ormerod No. 481