USB Problem with Arduino Nano 3.0 With External Power Applied

I am unable to get a Nano 3.0 to be recognized by Windows USB port when I apply 5v to the regulated input or 12v to the VCC input. All my Nanos behave this way. I've seen this problem described in other posts. Apparently, this issue may be specific to the Nano. I disabled the 5v power line on a USB cable, but the Nano received no USB power when itis powered by my circuit board. So it seems like Nano can get power from its USB, but USB can't get power from Nano. I haven't reviewed the schematic, but I'm guessing there's a diabolical diode in there somewhere.

I have two Nanos on this board.

Even more curiously, I can't get the USB working when the Arduinos are seated in the board and there is no power applied.

I do have the serial ports connected together so the Arduinos can talk, but I don't think this is the problem, because it happens when they are not mounted, or when only one is mounted.

My board is too complicated to breadboard this test, but what do you gurus think about putting a jumper switch that will disable the 5v input trace to the Nanos when connecting to USB and uploading sketches?

Has anyone dealt with this?

Thanks, Rennie

Hi I have two NANOs myself and I'm dealing with same issue. I'm guessing that the problem is in 5V auto selector. In Other arduinos there's some sort of transistor to deal with that. But since NANO is so small thing used to select voltage between USB and Input is Schottky diode.

There is a diode in there, but according to the schematic, it should not prevent the USB chip from getting power from either the 5v or the Vin (you said VCC, but you must have meant Vin).

Are these genuine Nanos or clones?

BTW, if you connect the serial ports together, it may interfere with downloading sketches.

Thanks for your replies:

Yes, I'm using cheap Chinese clones, $14 and free shipping on Ebay. That's what a cheap a middle-aged wimp I am, as I'm only charging $100K for my machine (which goes quickly when you have a teenage daughter and a Starbucks habit). I had assumes that these suckers would follow the same schematic as American (or in this case, Italian) superiority. If anyone uses certified authentic double-secret probation Nano 3.0 Arduinos that don't exhibit this problem, I'd glady pony up the extra $20 to get rid of this headache (That means no Starbucks on weekends).

Otherwise, has anyone solved this problem?

What do you think of my jumper solution?

Hmmm,

How can anyone tell if your jumper idea will work until we've determined how the power is connect to the ICs on the board? According the the schematic, it should not be required and would not make a difference. So, the fact that things do not work as expected leads me to believe that your boards do not follow the schematic, so I can't imagine what will happen with your jumper idea.

Why don't you try it.

BTW, I'm not saying there is anything 'wrong' with you using a clone, just that there may be a little investigation required first.

In any case, your attitude sucks, so I'll leave this one alone.

In any case, your attitude sucks, so I'll leave this one alone.

Sorry,I was trying to be witty. I'll put in for an attitude adjustment. As far as the board goes, it is very possible there is a problem with the board, but I think there is also something up with the Nano, as I get this problem even when the Nano is not mounted in the board.

Thanks for your thoughtful reply.

this is originally written about NANO on this site

Power: The Arduino Nano can be powered via the Mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source.

The FTDI FT232RL chip on the Nano is only powered if the board is being powered over USB. As a result, when running on external (non-USB) power, the 3.3V output (which is supplied by the FTDI chip) is not available and the RX and TX LEDs will flicker if digital pins 0 or 1 are high.

legwinskij: The FTDI FT232RL chip on the Nano is only powered if the board is being powered over USB.-

This is not consistent with the schematic. Has it been officially recognized that the schematic is wrong? Has there been a correction published? Does anyone know? Or care?

when running on external (non-USB) power, the 3.3V output (which is supplied by the FTDI chip) is not available and the RX and TX LEDs will flicker if digital pins 0 or 1 are high

This is even more screwy. I think my Nanos put out 3.3v when powered from my board 5v. I can't verify that because I accidentally fried them both by putting 24v into the 5v board connector! (More import Nanos are on the way). But I'm pretty sure I have been able to power the Wiznet Daughter board from the Nano 3.3v output. Again, I'm using an import Nano 3.0 clone.

I'm ordering proto boards from ExpressPCB on Friday, so I'll find out if USB will work with the jumper disabling the 5v board power to Nano.

I guess should buy a genuine Nano and try it it too.

I'll post again when I get the boards back and tested.