Uno to NodeMCU Serial Connection Problem

Question

This is my first project with any sort of development board and it has been a blast so far.

I am running into some issues, however, while trying to send serial data from my Uno to a NodeMCU board.

I have the following connections:

Uno Rx to NMcu Tx

Uno Tx to NMcu Rx

Uno GND to NMcu GND

microUSB from computer to power NMcu

usb from computer to power Uno

EDIT: after some suggestions, I have also tried the following.

Uno DigitalPin 5 to NMcu D6

Uno DigitalPin 6 to NMcu D5

Uno GND to NMcu GND

microUSB from computer to power NMcu

usb from computer to power Uno

With the following code:

// UNO sender Code
#include <SoftwareSerial.h>
SoftwareSerial toESP(0, 1); //Rx, Tx (also tried 5,6)
void setup()
{
 Serial.begin(115200);
 toESP.begin(9600);
}
void loop()
{
 Serial.println("sending");
 toESP.println("message from Nano");
 delay(1000);
}

---

// NodeMCU receiver code
#include <SoftwareSerial.h>
SoftwareSerial fromNano(3, 2); //Rx, Tx (also tried D5, D6)
void setup()
{
 Serial.begin(115200);
 fromNano.begin(9600);
}
void loop()
{
 if (fromNano.available())
 {
 char inChar = fromNano.read();
 Serial.print(inChar);
 }
 else {
 Serial.println("not available");
 }
 delay(2000);
}

I can pull up a serial monitor from both and see the UNO sending data (the TX led also blinks on the uno).

The NodeMCU code never satisfies the fromNano.available condition.

Is there anything I am overlooking that is causing this not to work? I've attached a picture of my connections as well.

enter image description here

Any help is much appreciated.

• Juraj: 0 and 1 are hardware Serial pins in Uno and 3 is a hardware Serial pin on NodeMcu so you should not use it for SoftwareSerial. and the wires are on pins 1 and 3 on NodeMcu (hardware Serial pins)
• Lamar: Hmm, thanks for the response. I tried using other digital pins on the arduino and nodemcu (and made sure to update the corresponding code) the other night, but didn't have any luck. I tried something like SoftwareSerial(5,6) for the sender (arduino) and SoftwareSerial(D5,D6) for the receiver (nodeMCU). Making sure that arduino digital pin 5 is connected to nodemcu D6, and vice versa. I'll try again later tonight.
• Lamar: @Juraj - After trying on digital pins 5,6 on the arduino, and D5,D6 on the nodemcu, I still cannot receive serial data. fromNano.available() is always false. I've set both to 9600 baud rate. imgur.com/a/gfVo2nt

Answer 1

Arduino UNO is using pin 0 and pin 1 to have serial with USB serial Communication. You can not use them to softserial. Change softserial to other pins. /Mikael

• Lamar: Thanks for the comment. Is it fine to just use any other digital pins to initialize the SoftwareSerial?
• Lamar: I tried digital pins 2 and 3 (and also 5,6) for RX,TX respectively and it didn't seem to solve the issue. Thank you for the suggestion though.
• Carlmikael: Why do use 2 serial conections, you only need one.
• Lamar: I'm only using one serial connection between the boards from my understanding. I just tried on pairs (2,3) and (5,6) independently for troubleshooting.
• Carlmikael: In the code you are using two.

Answer 2

@Carlmikael is definitely correct in his answer, I should not have been using hardware pins with softwareserial.

Besides that problem, my issue was resolved ultimately when I noticed that if I powered up the NodeMCU before powering up the Arduino, everything worked as expected.

Maybe someone can elaborate as to why this caused an issue?