USB Powered Arduino and Floating Power Supply

[Charles Creations]

Hi,

I am working with an arduino uno that I have hooked up to an analog amplifier that I feed with a 15V supply from by bench supply. I attach the ground lead of the bench supply to the ground of the USB on the arduino uno, and the 15V positive lead to the amplifier voltage rail. The arduino runs perfectly while the 15V supply is off, but when I turn the 15V supply on, the arduino slowly browns out over about 3 seconds (LED grow dimmer, and it reenters setup in the program). It goes into an infinite loop through its setup, so I see the serial terminal sending "Starting up" repeatedly.

Anyone have any advice on using a bench supply to supplement a USB supply when you must keep USB intact for serial com?

Oddly enough, if I am measuring the voltage of the USB 5V rail with my multimeter or oscilloscope, then the brownout does not occur... I cannot explain it. Strangely reminds me of Heisenberg uncertainty principle because every attempt to measure it causes something else.


Thanks,
Charlie

[Fraggie]

Are both power supplies switching power supplies ?
Had a weird thing myself , powering a odroid board from a switching laptop supply , no probblems, using a dc-dc converter from 24 to 12v , and the powerled on the odroid starts lighting up and dimming in sequence.. weird. (dc-dc rated 5A)

I power a arduino from the pc(usb) and a steppermotor from a 12v laptop psu.. no problems.

You do need to tie both the negative wires together from the arduino and the other board.. (even is one is 5v and the other 12v)
That might be it.

[alimirjamali]

...I attach the ground lead of the bench supply to the ground of the USB on the arduino uno, and the 15V positive lead to the amplifier voltage rail...
Anyone have any advice on using a bench supply to supplement a USB supply when you must keep USB intact for serial com?

Connect Ground of your bench supply to one of two ground pins and the +15V to VIN. I emphasize again: VIN. There is a NCP1117 regulator and a bunch of diodes and MOSFETs that will take care of both bench supply and USB power.

See picture below (1st and 2nd PINs from right; Power header):