I've currently got my eye on the earthing: the supplied ATX PSU ties the mains earth to the 0V on one edge of the Duet PCB and the USB lead can connect to another mains earth (via connected PC) creating a potentially large enclosed loop. In the middle of this ring is the ground plane upon which the microcontroller sits. Ormorod is too power-hungry to connect to my PC supply which is derived from a UPS so it's on a differnet mains outlet to the PC therefore I'm unable to bring the two earths together as close as I would like to.
I was wondering if potential grounding issues had been taken into consideration when I found that the USB shell had been left unsoldered (I have yet to solder mine to the PCB). It might have been better practice to connect the USB shell directly to the 0V PSU connection using star grounding technique. But as supplied, any 'earth currents times cable resistance' Voltages superimposed on the USB 0v line appear as a direct input to the Duet's 3.3V regulator among other things.
Connecting the outer screen of the USB cable via the USB socket shell should reduce any volt-drops in the inner 0v wire but such currents will still be flowing along the full length of the PCB. That's why I'm considering isolating the USB shell and connecting it via a beefy wire directly to the PSU 0V input terminal
I've been trying to figure out if this might br what causes crashes when soldering irons and other mains items are switched off. It only takes -0.5V to cause a CMOS latch-up.
I was wondering if potential grounding issues had been taken into consideration when I found that the USB shell had been left unsoldered (I have yet to solder mine to the PCB). It might have been better practice to connect the USB shell directly to the 0V PSU connection using star grounding technique. But as supplied, any 'earth currents times cable resistance' Voltages superimposed on the USB 0v line appear as a direct input to the Duet's 3.3V regulator among other things.
Connecting the outer screen of the USB cable via the USB socket shell should reduce any volt-drops in the inner 0v wire but such currents will still be flowing along the full length of the PCB. That's why I'm considering isolating the USB shell and connecting it via a beefy wire directly to the PSU 0V input terminal
I've been trying to figure out if this might br what causes crashes when soldering irons and other mains items are switched off. It only takes -0.5V to cause a CMOS latch-up.