Arduino Nano. Is vin also vout?


I have a project where I power the Arduino with 6V on the vin pin. When I connect to a computer by usb, the computer crashes when I unplug it. I suspected the vin pin was passing current the wrong way and added a 1N4007 diode now the computer acts normally.

Can anybody confirm that the vin pin outputs voltage when the Ardiuno is powered by USB. Or is the problem caused elsewhere?


Have a look at this:,d.ZWU

In particular look at the "5V REG" and "5V AUTO SELECTOR" bits. I can't see how current could be flowing back to the PC. I suspect your PC crash must be due to something else, but I can't explain why the problem stopped when you added that diode.


Just had chance to put a multi metre on it and it is outputing 3,8v on the vin pin when connected by USB.

Odd, that. It's coming out of the input of the voltage regulator. How much does that voltage drop if you put a low value resistor (~100R)?

Added a 100ohm resistor between vin and GND. Measuring either side of the resistor I have 3.27 volts.
Measuring between vin and GND without the resistor is still 3.8 volts.

So drawing about 30mA from it is causing a voltage drop of 0.5V. Not a very stable voltage source then! But no surprise, voltage regulators are not meant to be used that way. I would not use/rely on it at all. Stick to the using 5V output to power other circuits, or if you need to draw > 0.5A, add your own regulator direct to the 6V source. Use a "low voltage dropout" type, because an ordinary 78(L)05 really needs at least 7V input to give a reliable 5V output.

But we are still no closer to an answer as to why your PC crashes when you unplug the Arduino from USB, or why your diode stopped this from happening. I have no ideas.


Hi Paul,

thanks for your comments.

The vin (vout) is not used as a supply it is connected to the out pin on a LM7806 though.
In stand-alone mode the Arduino is powered from a 12V supply which is reduced to 6V by a LM7806. The power supply circuit is based on Derek Molloy’s video from Youtube. In stand-alone mode the Arduino works fine.
Before adding the power supply circuit the Arduino was always powered from the USB and I never had an issues with the host computer. It started crashing after adding the circuit which is why I suspected the vin pin. The vin pin was not used prior to adding the new circuit.

Not clear from the above but the crash happened when I unplugged from the USB. While plugged in it seemed to work OK.