ModernWires
Posts: 7
Joined: Mon Jul 29, 2019 11:23 am

Is it safe to connect the GND pin to the GND of an external USB psu?

Sun Aug 11, 2019 9:57 am

Is it safe to connect the GND pin of the raspberry pi (I'm using the new pi 4b specifically) to the GND of another USB power supply like shown below? I want to turn on and off a mosfet based on the output of a gpio pin. I don't want to use the on board USB or the 5V pin to power the load because I'm afraid of destroying the USB controller or even the entire raspberry pi if I accidentally do something stupid.
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pcmanbob
Posts: 7306
Joined: Fri May 31, 2013 9:28 pm
Location: Mansfield UK

Re: Is it safe to connect the GND pin to the GND of an external USB psu?

Sun Aug 11, 2019 10:00 am

Simple answer YES.

You will need both grounds connected together as you will need both grounds for your circuits to be complete or it wont work.
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boyoh
Posts: 1353
Joined: Fri Nov 23, 2012 3:30 pm
Location: Selby. North Yorkshire .UK

Re: Is it safe to connect the GND pin to the GND of an external USB psu?

Wed Aug 14, 2019 8:38 am

Yes the , communing the ground connections is ok
But if you want to keep Bothe power supplies
Isolated you could use a Opto Isolator to switch
The signal, this will give total physical isolation
Between power supplies and noise isolation
No need to common the grounds

Regards BoyOh
BoyOh ( Selby, North Yorkshire.UK)
Some Times Right Some Times Wrong

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