I have designed a PC board to have a socket for a Nano and have a question of design.
I see that on Nano board, pin 27 (+5V) is listed as an input/output pin. My design has a +12V input for running stand-alone (with an external +12 power brick) and an on-board 7805 +5V regulator for powering the board and all components. The +12V is also used for motor control as well if needed.
Now the problem. When I have my board populated with the Nano and connected to my computer to verify functionality, I didn't have the power brick plugged in since the USB connector was powering the Nano and board, but after initial testing, I wanted to test stepper motor control and plugged in the +12V power as well. Didn't take long for the +5V regulator on the Nano to get hot and smoke!! Nano still works OK as long as it is just powered by the USB cable, but won't work stand-alone with the +12V brick.
It seems that while pin 27 is listed as input/output, it can't have a computer USB cable plugged at the same time as +5V feeding pin 27. Do I have this correct?
I guess I need to modify my design with a 3 position jumper to make pin 27 an output (when the +12V power from my board is not connected (allowing the Nano to drive the +5V to the rest of my board iuf needed), and then change the jumper to allow my on-board regulator to drive pin 27 as an input when the Nano is not connected to the USB cable. Do I even need to drive pin 27 with +5 V?
Anyone see a better solution? What do other designs that have a socket for a Nano implement?
Thanks for responding!