I am working on connecting two Arduino boards (Arduino Uno & Arduino Nano). I am trying to run a stepper motor connected to Arduino Nano with two digital Pins on Arduino Uno to alter the direction of the stepper motor(BYJ48) connected to the arduino Nano. While making connections I attached the pins as:

1] 5V (UNO) -> 5V (NANO) & GND (UNO) -> GND (NANO)

2] 5V (UNO) -> 5in (NANO) & GND (UNO) -> GND (NANO)

Both [1] & [2] worked fine initially but I kept the arduino powered and tried toggling the Vin with 5v. Nothing went wrong in the beginning but later fumes started coming out and I dont know the reason why? Was that because I kept the power on while toggling between Vin & 5v ?
NOTE: besides the code and success in running the possible reason of fumes is much important here.

  • Why did you connect arduino's 5V and GND at all? What was the reason? And why did you use two arduinos to drive stepper motor?
    – Divisadero
    Jul 25 '17 at 11:24
  • task for me was to connect the two arduinos with just any two pins and try to communicate between two with the digital pins on ARDUINO UNO. I was trying to gather the ways how i can do that and i thought let just try with simply 5v->5v & GND -> GND like the way we do for I2C. I was just checking if that can be done or not.
    – Sonali_B
    Jul 25 '17 at 11:29
  • 1
    Ah so, this is not the case at all... If you want to use I2C you need to use digital pins, not 5V or GND! You can read more there instructables.com/id/I2C-between-Arduinos
    – Divisadero
    Jul 25 '17 at 11:32
  • 1
    GND is connected to keep the relative zero the same, but 5V is not used for sure.
    – Divisadero
    Jul 25 '17 at 11:32
  • 1
    Yes, you can write your own protocol, but it is not an easy task and except of learning, no real reason to do that.
    – Divisadero
    Jul 25 '17 at 11:37

You can try software serial communication between the two boards. Any two digital pins of one board can be used as Rx and Tx, and make sure the roles of Rx and Tx are reversed on the other board. See the Software Serial library: https://www.arduino.cc/en/Reference/SoftwareSerial

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