I'm using Arduino UNO R3 with NodeMCU and SIM800L module. I have to connect these two devices to UNO and make a serial communication between them: UNO<>SIM800L and UNO<>NodeMCU.

Can I use GPIO0 and GPIO1 of UNO (RX, TX) to communicate with one of above devices?

Thanks in advance.

  • RX/TX is used to communicate with the computer over USB
    – Juraj
    Dec 2, 2019 at 17:11
  • Okey, but if I do it this way: 1. Upload program first. 2. Power off uno, disconnect from PC and then power ON. 3. Then connect for example SIM800L to GPIO0 and GPIO1. ?
    – kslevel11
    Dec 2, 2019 at 17:26
  • yes. do you know that you can use the NodeMcu as Arduino?
    – Juraj
    Dec 2, 2019 at 17:50
  • Why both Uno and NodeMCU? For wifi?
    – chrisl
    Dec 2, 2019 at 18:24
  • 1
    NodeMCU for using it as Web Server.
    – kslevel11
    Dec 2, 2019 at 19:13

1 Answer 1


If all you need to do is communicate between the NodeMCU and the SIM800L, what do you need the Arduino for?

Connect the SIM800L directly to the NodeMCU and program the NodeMCU to do whatever communication is needed for the SIM800L.

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