Serial communication with arduino supplied through VIN

Other Hardware General Electronics
1

Thanks for reading.

I have three arduino’s brand new rev3, two mega and one uno, supplied 8V through the VIN pin. I want to do serial communication with the arduinos with my computer. I have cut the red wire if the usb cable, but I can’t find the port on my computer. When the VIN is supllied with 5V, there is no problem finding the port, but not 8 and 12V. An older arduino I have have no problems establishing communication in all these voltages using the same setup. I have just been using a usb with the power wire not cut, and I have assumed that it uses the VIN power and ignores the usb power :laughing:

I would love to hear from anyone knowing whats happening. When reading the arduino documentation, my understanding is that the cut red wire shouldnt be any issue, like im used to from previous projects.

Thank you.

2

Higher voltages on Vin separate the 5V from USB (to the USB chip) from the MCU 5V, turning off the USB chip. Variations depending on the actual PCB version are possible, though.

3

?? Never mind, found it in the schematic. Learned something new.

I power my (original) Mega with 9V on Vin (actually 5V through a boost converter to 9V) and use a normal A/B USB cable without a problem.

4

You can of course power the Arduino directly onto the 5v port IF it’s a stable 5v.

5

Only if it doesn't conflict with the USB 5V.

6

Problem is that the 5V can flow back into your PC.

7

Yea that looks like I got it wrong, I thought it was ok - sorry guys.

(I run back through a powered usb hub and that doesn’t seem to mind )

8

It depends on the board; for a classic Nano it's OK as there is a protection diode.