Sharing a power supply between arduino and led strip?

Sorry if this is a stupid question, but I notice that the wiring of my first proper project means that the arduino uno r3 and my 120 neopixel WS2812B LED strip share a common ground but not the +ve.

My power supply unit (psu) is 5v 10A for the LEDs and the board is USB powered.

My question is, why can’t they both share the external psu? It has ample power and 5v. Would it make any difference if the psu was, say, 7v since I read somewhere that the board prefers higher than 5v when not USB powered? Or is it just a no-no to share a psu for higher ampage projects?

Thanks for any insights you can provide.

RobertPN:
Sorry if this is a stupid question, but I notice that the wiring of my first proper project means that the arduino uno r3 and my 120 neopixel WS2812B LED strip share a common ground but not the +ve.

Cool, that is the correct arrangement.

My power supply unit (psu) is 5v 10A for the LEDs and the board is USB powered.

My question is, why can’t they both share the external psu? It has ample power and 5v. Would it make any difference if the psu was, say, 7v since I read somewhere that the board prefers higher than 5v when not USB powered? Or is it just a no-no to share a psu for higher ampage projects?

The barrel connector input to the Arduino goes through a 5V regulator, and then to the board. A regulator requires a slightly higher voltage than it’s intended to output. That’d be ~6.5 minimum, so 7V is typical.

I don’t know what the specs are for your LED strip but unless it says it can operate at 7V then it ‘shouldn’t.’

RobertPN:
My question is, why can't they both share the external psu?

They can both use the same PSU, no problem. If it's a 5V PSU then simply connect the 5V from the PSU to the Arduino 5V pin.

nb. Make sure it's a regulated (switching) supply with exactly 5V. Don't try to connect the USB cable at the same time or anything like that. Connecting two PSUs together is bad, mmmmkay...

thank you both for your help. Regards, Robert