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am wondering if it's safe to send 12V to the Ground Pin on the arduino which I think is connected somehow to the usb port. Am afraid that it might burn something up. I found this sketch online -> enter image description here

Am a total newbie is this circuit safe?

The Little Cousin
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    Your question needs clarification. You certainly cannot send 12V directly to ground without issue. – Bort Mar 08 '17 at 15:33
  • RGB I take to be LED (returns) being fed with the +12V from power so you are not taking 12V to ground but the current from the 12V source through the LEDs (and their resistors) switched by the BJTs (c-e) to ground. – JIm Dearden Mar 08 '17 at 15:33
  • What are you trying to accomplish? You don't have to plug the +12 into anything. If you insist, you can plug in a dummy resistor but all that will do is create a small heater. – BB ON Mar 08 '17 at 15:34
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    What you did here is similar to showing us a car seat and asking us if that would make for a safe car when used. You need to show the whole car or in this case the whole circuit. Depending on what you connect to this circuit it will work and not destroy itself or it will blow up. Either is possible. – Bimpelrekkie Mar 08 '17 at 15:39

2 Answers2

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here's the picture

enter image description here

Putting a short circuit from a 12V source to ground (0V) is liable to result in the release of the magic blue smoke.

However, limiting the current through a resistor, led and BJT (aka an electronic circuit) to a safe value will not.

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JIm Dearden
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I understand your confusion but like Jim Dearden says in the comments:
"you are not taking 12V to ground but the current from the 12V source through the LEDs (and their resistors) switched by the BJTs (c-e) to ground"

I think this particular section here is what's causing your confusion (correct me if I'm wrong)

enter image description here

Linking the grounds together like this is the correct thing to do, even if they are the ground points for different voltage sources.
There are multiple questions here that cover the topic of connecting grounds together I'll link a couple for you to do some extra bedtime reading:
Why connect two power supply grounds?
Connecting two grounds together
Connecting grounds together.... why? (Arduino forum)

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