VFD interference problem

[eurikain]

This could be your problem. The BOB is tying PC ground thru the PP cable to GNd on the 5V supply. For test remove the 5V and power bob using USB.

Okay this one also is a great idea ! That would explain why the noise does not appear when the PP cable is not connected ! I add this as first entry of my checklist.

Regards Spare cheap BOB's that's like simple adding 2+2=4.???. . . Crap + Crap = Crap so why bother.!

Always knew you were good at math :D