I do have an Arduino Nano (v3.0) board and to my surprise the USB (and communication with board) is disabled after I restart the PC.

If I do unplug and plug the USB cable the USB port becomes available.

Is this an Arduino Nano "feature"? (As I see that my other Arduino UNO board works fine after a reboot)

  • \$\begingroup\$ This is a user-level question having nothing to do with electrical engineering. \$\endgroup\$ – Olin Lathrop Jun 26 '13 at 14:53
  • 2
    \$\begingroup\$ @olin-lathrop That is why I asked if it's something specific to Nano architecture \$\endgroup\$ – Gheorghiu Alex Jun 26 '13 at 16:05
  • \$\begingroup\$ Maybe you can delay the reset line on the Arduino with a capacitor long enough for the PC to have initialized the USB bus? For starters you could try to manually pull the reset line low and see if the device registers with the PC as you expect. \$\endgroup\$ – jippie Jun 26 '13 at 17:53
  • \$\begingroup\$ I'd be tempted to ask if you could tell us about how it behaves in the case of power-on while connected vs a warm restart while connected, but I don't know if what passes for bios these days would initialize the USB bus before the ultimate operating system re-initializes it, and that might destroy any difference. \$\endgroup\$ – Chris Stratton Jun 26 '13 at 20:24
  • \$\begingroup\$ @jippie I connected the reset to the ground of board and indeed the board reset and then appeared in the Device Manager. The 3rd time I tried that I think I did something wrong as I burned the board :D I will get a some extra boards and I hope I will not do the same mistake. \$\endgroup\$ – Gheorghiu Alex Jun 27 '13 at 7:04

Pin 19 (RESET) of the FT232RL (USB driver) seems to be unconnected according to Nano's circuit diagram.

Double check if this is indeed the case. If so, try connecting a 100nF capacitor from that pin to ground and a 10k resistor to +5V. This may reset the device long enough for the USB host (PC) to initialize.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Can you check this diagram and let me know if that is what you meant? \$\endgroup\$ – Gheorghiu Alex Jun 27 '13 at 7:05
  • \$\begingroup\$ This link FTDI USB locks up on power up seems very similar to my problem. Could it be the same? \$\endgroup\$ – Gheorghiu Alex Jun 27 '13 at 17:30
  • \$\begingroup\$ Not sure if it is the same issue, it seems similar indeed. I updated my answer with a circuit diagram, does that clarify thing? \$\endgroup\$ – jippie Jun 27 '13 at 19:12
  • \$\begingroup\$ Does the down arrow (with empty triangle) has to be connected to another GROUND (from Arduino board for example) or is just a convention? \$\endgroup\$ – Gheorghiu Alex Jun 29 '13 at 9:16
  • \$\begingroup\$ It is common ground on the Arduino. \$\endgroup\$ – jippie Jun 29 '13 at 11:00

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