I am making a Project with an Arduino driving a stepper motor with a driver board. USB will still be connected to send commands over serial. EDIT: I am building an EggBot driver board for my Arduino Uno which needs to be connected to my pc by USB for sending commands with the eggbot-software. Here is my schematic https://i.stack.imgur.com/WmLw4.jpg)
Will I destroy my Laptops USB by having another power source connected to the same ground?
(I felt that I lacked general knowledge about DC power supplies and the resulting potentials. Therefore I tried to ask a more general question about AC to DC PSUs)
1. How different are the potentials between the neutral wire, the GND USB** and the GND PSU?
2. The power supply is a cheap one from amazon. So I assume there is no transformer and the 12V are not "floating". Is this safe to assume?
3. If both supplies are not floating, can there be a difference in potential between the GNDs?
4. If not, is there any workaround besides opto-isolation of logic?)