I've got a dashboard which I want to control from an Arduino. I've got the concept but I'm having issues with the power supply of the circuit. The Arduino is connected to my PC via USB (and it's supply is the USB).
To power these I've got a switch-mode power supply (24V DC).
My problem is whether I can safely connect the negative terminal of the supply to the ground of the Arduino (which is connected to the PC). I'd need this otherwise the circuits won't work properly, but I'm not sure it's alrigth to do so.
I tried to measure the voltage between my PC USB port (GND) and the negative terminal of the supply - I got a randomly changing voltage between about -0,15V and +0,15V. But there's a spike when I touch the multimeter to the cables, maximum of ~2,5V. Though I don't know this measurement is correct or not.
I'm afraid if the ground potentials are not the same, I'll destroy my PC motherboard via the USB.
So can I connect them safely or should I try to come up with something else?