Arduino UNO power

Hi,

So, for quite some time I've been powering my Arduino Diecimila with a 328 chip on 3.3v. I recently realized that the way I'm doing it is not considered correct and I'm quite impressed/surprised that it actually works.

I'm feeding 3.3v to the 3.3v voltage regulated output with the EXT power selector and the board runs fine on it.

Reading about others trying 3.3v for the Arduino, I see they have been given all sorts of advice about how to do it/not to do it and I don't see my 'solution' mentioned at all.

Now here is the question. Is the Arduino designed to run like this or is it just a bug that became a feature? I can find no mentioning of it anywhere. I'm about to purchase a bunch of UNOs and I need those boards to be powered the exact same way. Can I expect it to work the same way on the UNO?

Cheers

I don't see my 'solution' mentioned at all.

No because it is the most stupid thing I have ever heard of. Back feeding a regulator in the USB chip to bleed power through to the main processor is not a good idea. Although you say it works you are probably damaging your components and giving them a very short time to live.

That I do understand. If I could power it directly with 3.3v on Vin I'd be glad but that doesn't work, by design.

For what I'm doing it's ok that the components take a hit. What I really need to know is if I can expect this stupid solution to work the same way in the UNO?

What I really need to know is if I can expect this stupid solution to work the same way in the UNO?

1st, I wouldn't expect this to work with any solution. So factor that into your question. 2nd, the UNO uses a "auto-switch" design to determine how it gets powered. There isn't a jumper. This is going to be added complexity (and likely a failure point in your setup.)

Well, as I said I was surprised that it worked. :slight_smile:

Thank you James, this is very good to know. I believe you just saved me some $$$ and also saved a few UNOs from abusive treatment. :wink:

In the Diecimila the 3v3 regulator is inside the FTDI chip where as in the Uno there is a separate 3v3 regulator. It is such a different setup that there is no telling if it will function. I don't say work because this is abuse of the highest order.

For what I'm doing it's ok that the components take a hit

So you won't mind when it stops working then.

If it would stop functioning it would definitely disturb my work so Yes, I do mind and now that I can’t just buy another device (since it’s pretty much deprecated) I’m currently redesigning my future proof-of-concept prototypes to work in the correct way.

It takes some 7-8 extra components but I’ll take that hit. :slight_smile:

Thank you all for your input.

sending power “backwards” through a regulator is usually really bad for them. Many sample circuits for simple regulators include a suggestion of additional diodes connected to protect the regulator from such problems.

If I could power it directly with 3.3v on Vin I’d be glad

It should work to feed 3.3V into the 5V power pins; the 5V pin is connected to the main power bus that powers all the chips, rather than just the output from a regulator.

Keep in mind that running a 328 processor at 3.3vdc @ 16Mhz if not within the speed/voltage specification per the AVR datasheet specs.

Lefty

because i have a usb power issue with my arduino uno board ( and a shield proto kit ) i try to follow this discussion, what i not understand is, why there is a on board 3v3 regulator, LP2985, is it used only for LM358 OP input? ( the OP is powered with 5V)
and its job is to detect external Vin ( and switch of USBVCC ? in that case ?)

What i see from arduino-uno-schematic.pdf the rest only use 5V. ( the Volt from USB normally ) right?