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Topic: VIN + 5v pin + USB  (Read 95 times) previous topic - next topic

JPlanck

I have a project board which I'm planning to use an arduino micro for, and will socket the arduino into the board.

The board is powered by 12v for certain chips, 5v for other chips, and will at times also want to have the USB plugged in.

The arduino will not be able to provide enough current for all the chips on the board, so a regulator (LM7805) will be used.

For power I'd like to use the VIN pin to power the arduino from the 12v line and also have the USB plugged in, which works fine. However, during tracing it has proved difficult even after moving the chips around to get traces routed sensibly due to the board size and number of components, especially the 5v power trace because it goes everywhere on the board and the arduino takes up a lot of the space.

What I'd like to do here is run the LM7805 5v output into the arduino 5v pin, then run another trace out of the 5v pin on the other side of the arduino micro to bridge the 5v traces on both sides of the board while keeping signal traces under the arduino where they are.

So the question I have here is, will this cause power issues with the arduino micro and/or burn anything out? If I do this I will have 12v going into the VIN of the arduino, 5v going into the 5v of the arduino, and 5v coming out of the other arduino 5v pin, while also having the USB plugged in. Will this cause problems for the arduino specifically or will this work fine?

Gyro_Gearloose

According to the datasheet, your processor has an absolute maximum operating voltage of 6 volts. Giving it 12 volts will do it no favours.

How will you separate the USB power from your 12 volt power supply? Again, accidentally feeding 12 volts back up your USB cable will do your computer no favours.

DrAzzy

You can't power an Arduino Uno via the 5v pin when connected to USB, the 5v supply and the USB supply will fight, which can result in damage to the board.

If you have 12v on the VIN pin, the on-board regulator will be providing 5v to the Arduino (and the 5v pin), as well; You shouldn't try to power it via the 5v pin when you're also powering it via Vin. 
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JPlanck

Yeah I figured it might be a bad idea, thanks for the replies.

According to the datasheet, your processor has an absolute maximum operating voltage of 6 volts. Giving it 12 volts will do it no favours.

How will you separate the USB power from your 12 volt power supply? Again, accidentally feeding 12 volts back up your USB cable will do your computer no favours.
Applying 12v to the VIN pin has always worked before, is it not supposed to? I thought I read the VIN can accept anything up to like 14 or 20v somewhere. I've used 12v to power the arduino micros many times before without issues.

As far as separating the supplies, the traces for 12v and 5v don't run together obviously, they are routed separately.

Gyro_Gearloose

Yeah I figured it might be a bad idea, thanks for the replies.

Applying 12v to the VIN pin has always worked before, is it not supposed to? I thought I read the VIN can accept anything up to like 14 or 20v somewhere. I've used 12v to power the arduino micros many times before without issues.
Sorry. My mistake. For some reason I assumed that VIn fed the 5 volt power directly and didn't go through a regulator. 12 volts should be fine as its the recommended upper limit of the power supply. Anything higher should be avoided.


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